WO2025199584A1 - Nanosheet-based proton conducting nanochannel membranes for electrochemical device applications - Google Patents

Abstract

The disclosure of the application provides a membrane design encompassing three main considerations; (1) employing 2D nanosheets as proton-permeable building blocks to facilitate through-membrane proton transport; (2) assembling 2D nanosheets to form 2D channels, capable of confining the proton conductor to thereby prevent loss of the proton conductor, or to prevent physical or chemical degradation of the proton conductor under the conditions in which the membrane may be exposed in its application(s); and (3) incorporating proton conductors to occupy the intersheet spaces forming the 2D channels, and/or incorporating proton conductors to form at least part of the inner surfaces of the 2D channels, enabling intersheet proton transport while blocking hydrogen gas molecules, thereby providing membranes with ultrafast proton conducting pathways due to synergistic proton transport, with high retention of the proton conductor achieved through nanoconfinement in 2D channels.

Description

NANOSHEET-BASED PROTON CONDUCTING NANOCHANNEL MEMBRANES FOR ELECTROCHEMICAL DEVICE APPLICATIONS

TECHNICAL FIELD

[0001] The present invention relates to proton conducting membranes suitable for applications in a range of electrochemical devices.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority to Australian Provisional Application No. AU 2024900829, filed 27 March 2024, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND ART

[0002] Proton-conducting membranes (also known as Protonic membranes), play a vital role in renewable energy technologies based on electrochemical devices, including H2/O2 fuel cells, water electrolysis, CO₂ reduction, ammonia synthesis, and hydrogen purification. In these electrochemical processes, proton-conducting membranes serve as separators, dividing the reaction into two half-cells, and as electrolytes, enabling rapid proton transport pathways.

[0003] High-temperature operation is crucial for proton-conducting membranes to achieve enhanced proton conductivity, to facilitate electrochemical reaction kinetics, and to improve compatibility with certain catalysts. High-temperature proton exchange membrane fuel cells (HT- PEMFCs) operating above 100°C offer numerous benefits, including a broad range of fuel options, easy water management, the resistance to catalytic poisoning by impurities like carbon monoxide and the possibility of using non-noble metal catalysts, which reduces costs for large-scale implementation. However, further advancements in proton exchange membranes are needed to enhance proton conductivity and long-term stability at elevated temperatures, in order to facilitate improvements to the overall performance and practicality of HT-PEMFCs.

[0004] Protonic membranes can be classified into two main categories: polymer membranes such as Nation, operating below 100°C; and inorganic membranes such as solid oxides, suitable for temperatures above 400°C. However, the temperature range between 100°C and 400°C poses a significant challenge in developing protonic membranes with high conductivity and stability to bridge the performance gap between existing polymer and inorganic membranes.

[0005] To extend the temperature limit, inorganic proton conductors such as phosphoric acid and solid acids have been employed. Phosphoric acid, typically in a liquid state, requires a matrix to retain the acid, leading to the construction of hybrid membranes like polybenzimidazole (PBI) doped with phosphoric acid. Although the operating temperature can be extended to 200°C with this approach, they encounter challenges related to low proton conductivity, acid loss at high temperatures, and limited long-term stability. [0006] Solid acids such as CsHSC exhibit good anhydrous proton conductivity up to 200°C but face difficulties in producing dense membranes with high mechanical strength, making them prone to fuel cross-over. Addressing these challenges is essential for the practical application of these protonic membranes in high-temperature electrochemical devices.

[0007] One approach to achieving sufficient mechanical strength involves assembling membranes from nanosheet materials. However, while nanosheets can be readily stacked to form membranes with favourable mechanical properties, they suffer from the problems of substantial increase in resistance to proton transport between the nanosheets and the leaking of gas through the 2D nanochannels that form within the membranes.

[0008] Hydrogen plays a central role in decarbonizing the global economy as it offers a clean and versatile solution to reduce greenhouse gas emissions and transition towards a more sustainable and environmentally friendly energy future. It is not only essential for creating methanol, ammonia, and a variety of petroleum products, but also represents a clean energy source for the power generators and vehicles of the future. The most common way to produce hydrogen from natural gas is through the steam reforming of methane, followed by a water-gas shift reaction. This process results in a gas mixture that can reach temperatures up to 1000 °C and is primarily composed of carbon dioxide (CO₂). To obtain pure hydrogen, it is crucial to separate CO₂ and other impurities from the mixture. If this separation can be achieved at temperatures above 300°C without cooling the mixture to room temperature or below, it could largely reduce the energy required for hydrogen production. While the industry often uses energy-intensive and expensive methods like cryogenic distillation or pressure swing adsorption for gas separation, membrane technology presents a more efficient and scalable alternative. However, the effectiveness of this technology depends on the availability of cost-effective membrane materials with high selectivity and permeability for specific gas components.

[0009] Membranes suitable for hydrogen purification can be fabricated from a diverse range of materials, including inorganic substances, polymers, and their hybrids. The category of inorganic materials is broad, including ceramics, metals, graphene oxides (GOs), molybdenum disulfide (MOS₂), MXenes, zeolites, silica, and metal-organic frameworks (MOFs). Ceramic membranes, such as perovskite oxides-based membranes, rely on a mixed protonic-electronic conducting (MPEC) mechanism for their transport and selectivity, requiring an operational temperature exceeding 700°C. While MPEC ceramic membranes typically provide 100% selectivity for hydrogen separation, they often exhibit low permeabilities. Conversely, metallic membranes, such as palladium (Pd) and alloy membranes, employ a solution-diffusion mechanism to separate hydrogen. They can dissociate hydrogen molecules into hydrogen atoms at the surface of the Pd membrane. Subsequently, hydrogen atoms diffuse through the metal lattice, driven by the partial pressure gradient, to reach the opposite side of the membrane. These membranes exhibit a remarkable combination of high permeability and selectivity. However, their broader application is restricted by the high cost of materials.

[0010] Other types of inorganic membranes like microporous zeolite and MOF membranes can isolate specific gases from others using a molecular sieving mechanism and preferential adsorption of gas components on their surface. However, the fabrication process for these membranes is time-consuming. Therefore, the industrial-scale application of these inorganic membranes remains a significant challenge. Recently, two-dimensional (2D) membranes such as GO, MoS₂, and MXene membranes have gained attention. These are typically created by layering 2D nanosheets into a laminar structure to form sub-nanometer channels that function as molecular sieves to separate small gas molecules from larger ones. However, these 2D membranes can only operate up to 150°C before they start to degrade and lose their selectivity.

[0011] Polymeric membranes present a potential solution for hydrogen production via steam reforming of methane, primarily due to their good processability and low cost. However, achieving a balance between permeability and selectivity continues to be a hurdle in the field of polymeric membranes. Polybenzimidazole (PBI) membranes are notable for their structural stability at high temperatures, ranging from 150 to 300°C. While the diffusion-based selectivity favours hydrogen transport due to its smaller kinetic diameter (2.89 A) compared to CO₂ (3.3 A), the solubility-based selectivity aids carbon dioxide transport, making it difficult to attain high H2/CO2 selectivity. To tackle this challenge, phosphoric acid (PA) has been incorporated into PBI membranes. This integration enhances the efficiency of polymer chain packing by crosslinking PBI chains with the acid, reducing the fractional free volume (FFV). However, prolonged operation at temperatures above 150°C may lead to PA loss, with concomitant reduction in hydrogen permeability and selectivity due to an increased FFV.

[0012] On the other hand, the PA-doped PBI membranes enable the creation of an efficient proton transport pathway within the membrane, which can be used for electrochemical hydrogen separation. In a system resembling a fuel cell, a gas mixture is introduced at the anode, leading to the oxidation of hydrogen molecules into protons and electrons. While protons pass through the proton conducting membrane, electrons traverse an external circuit to reach the cathode, where they combine with protons to generate hydrogen molecules. Due to the limited electrical conductivity of the PA-doped PBI membrane, an external circuit is required to transfer electrons between the two electrodes, introducing complexity and constraining scalability.

[0013] There is a need to develop low cost, easily manufactured proton transport membranes with high proton conductivity, high thermal stability, and high mechanical strength; or at least to provide viable alternatives to the prior art proton transport membranes, that address one or more of the challenges or limitations discussed in the preceding paragraphs. [0014] It is against this background that the present invention has been developed.

[0015] The previous discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date ofthe application.

SUMMARY OF INVENTION

[0016] The present invention provides a facile process for preparing proton exchange membranes high proton conductivity, high thermal stability, and high mechanical strength, suitable for use in a broad range of electrochemical applications.

[0017] In one aspect the disclosure herein provides a proton conducting membrane comprising nanosheets, and 2D-nanochannels formed between the nanosheets, wherein the 2D- nanochannels comprise a proton conductor confined within the 2D-nanochannels, and wherein the proton conductor is physically and chemically stable at temperatures of 150°C and above.

[0018] In one aspect the disclosure herein provides a proton conducting membrane comprising nanosheets, and 2D-nanochannels formed between the nanosheets, wherein the 2D- nanochannels comprise an inorganic proton conductor confined within the 2D-nanochannels.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Further features of the present invention are more fully described in the following description of several non-limiting embodiments thereof. This description is included solely for the purposes of exemplifying the present invention. It should not be understood as a restriction on the broad summary, disclosure or description of the invention as set out above. The description will be made with reference to the accompanying drawings in which:

Figure 1 is a series of plots showing the analysis of thickness and lateral size distribution of the as-prepared monolayer Graphene (A, B) and BN (C, D) nanosheets based on AFM results (Data obtained from 100 pieces of graphene and BN nanosheets respectively).

Figure 2 provides; selected low (A) and high-resolution (B) TEM images of a single-layer graphene nanosheet with corresponding selected area electron diffraction (SAED) pattern inserted; (C) Diffraction intensity analysis along the white line in (A); Selected low (D) and high- resolution (E) TEM images of a single-layer BN nanosheet with corresponding SAED pattern inserted; and (F) Diffraction intensity profile along the white line in (D). Figure 3 provides; (A) FTIR spectra of polyethylenimine (PEI), PEI-modified monolayer graphene nanosheet (PEI-Graphene), and PEI-modified monolayer BN nanosheet (PEI-BN); and (B) TGA results of PEI, PEI-Graphene, and PEI-BN.

Figure 4 provides; (F) Photograph of a free-standing Graphene/BN/Phosphoric acid (GBP) membrane; (G) Schematic illustration showing the bi-layer structure of the GBP membrane with possible transport pathways for electron, proton and hydrogen; (H) SEM cross-sectional image of the produced GBP membrane; and (l-L) EDX maps showing the distribution of boron (I), nitrogen (J), carbon (K), and phosphor (L) within the outlined column in figure 4H respectively.

Figure 5 are; Local magnified SEM cross-sectional images of the top BN layer (A) and bottom graphene layer (B), respectively, within the GBP membrane.

Figure 6 is a plot of the elemental composition analysis of the marked area in figure 7B using EDX spectroscopy with relative composition table inserted.

Figure 7 are; (A) TGA curves of phosphoric acid (PA), Graphene-BN (GB) membrane, and GBP membrane in air; (B) Recorded weight loss of GBP membrane kept at 250°C in the air for 24 hours; and (C) XPS P 2p spectra of GB membrane, PA, GBP membrane, and GBP membrane after treatment at 250°C in air for 24 hours.

Figure 8 are; (A) XPS survey spectra; (B) C 1s; and (C) N 1s XPS spectra of; Graphene-BN membrane (GB), Graphene/BN/PA membrane (GBP), and GBP membrane after treatment at 250°C for 24 h (GBP 250°C) - Examination was conducted on the graphene side of the membranes.

Figure 9 provides; (A) Temperature-dependent through-plane proton conductivity of Graphene/BN (GB) membrane without phosphoric acid (PA), and Graphene/BN/Phosphoric acid (GBP) membranes with 25, 43, 60, 67 and 78 wt% PA incorporated and 50 pm thickness; (B) XRD curves of GB membranes with different amount of PA incorporated; (C) Solid ³¹P NMR spectra of PA-doped PBI membrane and GBP membranes with varied PA loading; (D) Intersheet spacing of nanosheets and energy barrier for proton transport of GBP membranes with varied PA loading; (E) Electrical conductivity and energy barrier for proton transport of GBP membranes with different BN layer thickness; and (F) Proton conductivity comparison of the 60 wt% PA-doped and 50 pm-thick GBP membrane with the state-of-the-art membranes at various temperatures.

Figure 10 are plots of Temperature-dependent through-plane proton conductivity of 60 wt% PA- doped GBP membranes with 3, 9, 36 and 80 pm-thick BN layer above a constant 41 pm-thick graphene layer (A); and with 15, 41 and 93 pm-thick graphene layer under a constant 9 pm-thick BN layer (B). Figure 11 is the XRD spectrum of the Graphene and BN nanosheet membrane of one aspect of the invention.

Figure 12 are Solid ³¹P NMR spectra of; (A) PA-doped polybenzimidazole membrane (PBI/PA); and (B-F) Graphene/BN/PA membranes with 25, 43, 60, 67 and 78 wt% PA incorporated. Each spectrum is fitted with Gaussian function, where the as obtained spectrum is shown in solid line, the fitted peaks are shown in dotted line, and the total fitted curve is shown in dashed line.

For the spectra of the GBP membranes, the left peak represents the weakly absorbed PA molecules in the 2D nanochannels and the right peak relates to the strongly absorbed PA.

Figure 13 provides (A) Normalized peak area; and (B) Chemical shifts (ppm) relating to strongly and weakly absorbed PA molecules in the GBP membranes with different PA loadings.

Figure 14 are Arrhenius plots and related linear fitting curves of the proton conductivity of; (A) Graphene/BN (GB) membrane and Graphene/BN/PA (GBP) membrane with different PA loadings; (B) GBP membranes with various graphene-layer thicknesses; and (C) GBP membranes with different BN-layer thicknesses.

Figure 15 are plots of proton conductivity at 250°C varying with BN-layer thickness (A); and Graphene-layer thickness (B). The intercepts at the Y axis estimated from the matched linear fitting curves are 171.8 and 186.4 mS/cm for (A) and (B) respectively.

Figure 16 is a plot of the recorded proton conductivity change at 250°C as a function of time for the Graphene/BN/PA membranes with 60 wt% PA and 50-pm thickness.

Figure 17 provides; (A) Diagrams showing the in-/through-plane proton transport pathways within the GBP membrane; Proton conductivity (B); and Arrhenius plots with related linear fitting curves (C) of the in-/through-plane proton conductivity of Graphene/BN/PA (GBP) membranes with 60 wt% PA and 50-pm thickness. The corresponding activation energies are estimated from the slopes as 5.6 and 7.7 kJ/mol for the in-plane and through-plane proton transport respectively.

Figure 18 provides; (A) A schematic illustrating an H₂/O₂ fuel cell assembled with the GBP membrane, and proton transport across the membrane; (B-C) l-V polarization and power density plots (B), and Electrochemical impedance spectra (C) of the cell assembled with 60 wt% PA- doped and 50 pm-thick GBP membrane measured at 160°C, 200°C and 250°C; (D) Operating stability of the cell based on 60 wt% PA-doped and 50 pm-thick GBP membrane at a current density of 400 mA/cm² and 250°C; and (E) Comparison of maximum power density of the cell assembled with 60 wt% PA-doped and 50 pm-thick GBP membrane with other advanced membrane-based cells under H₂/O₂ conditions.

Figure 19 provides; a comparison of H₂/O₂ fuel cell performance at 250°C (A); and proton conductivity as a function of temperature (B); between a Graphene/BN/PA membrane (GBP) in accordance with the present invention and a conventional m-PBI/PA membrane with 60 wt% PA and 50-um thickness.

Figure 20 provides; a comparison of H2/O2 fuel cell performance at 250°C between H2 flowing on the graphene side and BN side for the Graphene/BN/PA membranes with 60 wt% PA and 50-pm thickness.

Figure 21 provides; (A) A schematic illustrating a direct methanol fuel cell (DMFC) assembled with the GBP membrane, and proton conduction through the membrane; (B-C) l-V polarization and power density plots (B), and Electrochemical impedance spectra (C) of the DMFC assembled with 60 wt% PA-doped and 50 pm-thick GBP membrane measured at different temperatures and supplied with 16 M methanol and oxygen; (D) Methanol crossover current density of GBP and PBI/PA based MEAs measured at different temperatures; (E-F) l-V polarization and power density plots (E), and Electrochemical impedance spectra (F) of the DMFC assembled with the GBP membrane measured at different temperatures and fed with 16 M methanol and air; (G) Operating stability of the GBP membrane-based DMFC supplied with 16 M methanol and oxygen at a current density of 400 mA/cm² and 250°C; and (H) Comparison of peak power density of the GBP membrane-based DMFC with other advanced membranes-based DMFCs fed with oxygen.

Figure 22 provides; Temperature-dependent performance of the GBP membrane-based DMFC supplied with 16 M methanol and oxygen, in terms of; (A) Variation of ohmic and polarization resistance with operating temperature; and (B) Changes in open circuit voltage and peak power density as a function of operating temperature.

Figure 23 provides; Variation of methanol crossover current density with applied voltage measured at different temperatures and with the supply of 16 M methanol and dry N2 for; (A) GBP; and (B) PBI/PA membrane-based MEAs. Under an applied external potential, methanol is transported from the anode to the cathode, where it undergoes oxidation. The methanol crossover current density is limited by the methanol permeability of the membrane, which was be represented by the current density at the plateau of the IV curves around 0.8 V.

Figure 24 provides l-V polarization and power density plots of the PBI/PA membrane-based DMFC measured at different temperatures and supplied with 16 M methanol and oxygen.

Figure 25 provides l-V polarization and power density plots of the GBP membrane-based DMFC measured at 250 °C and supplied with oxygen and methanol at various concentrations.

Figure 26 provides; (A) SEM cross-sectional images of the catalyst-coated graphene nanosheet/phosphoric acid (CGP) membrane; (B-C) Local magnification of the catalyst layer (B) and GP membrane (C); and (D-E) EDX mapping results of the CGB membrane showing the distribution of platinum (D) and phosphor (E). Figure 27 provides; (A) XRD results of graphite, the graphene nanosheets membrane (Graphene) and the graphene nanosheets/phosphoric acid-based membrane (Graphene/PA); and (B) FTIR curves of the polyethylenimine (PEI), phosphoric acid (PA) and Graphene/PA.

Figure 28 provides; (A) TGA results of the polyethylenimine (PEI), phosphoric acid (PA), graphene nanosheets membrane (Graphene), and graphene nanosheets/phosphoric acid-based membrane (Graphene/PA); and (B) Weight change of the Graphene/PA membrane recorded in air at 250°C.

Figure 29 provides; (A) Temperature-dependent conductivity; and (B) Arrhenius plot of the graphene nanosheets/phosphoric acid-based membrane with equivalent circuit inserted.

Figure 30 provides single-gas permeation test results of the GPC membrane as a function of operating temperature.

Figure 31 provides an AFM image of the synthesized PWA nanosheet and its corresponding height profile along the highlighted line.

Figure 32 provides; (A) SEM cross-sectional image of the PWA/BN nanosheet membrane with corresponding EDX maps for (B) boron, (C) nitrogen, (D) oxygen, (E) tungsten, and (F) phosphorus; (G) TGA curves of the PWA nanosheet, BN nanosheet, and 5wt% PWA/BN nanosheet membrane; and (H) Nitrogen adsorption-desorption isotherms and pore size distribution curves of the PWA/BN nanosheet membrane.

Figure 33 provides; (A) Temperature-dependent proton conductivity of the PWA/BN nanosheet membrane at 3% RH; and (B) Time-dependent proton conductivity of the PWA/BN nanosheet membrane at 250 °C and 3% RH.

Figure 34 provides; Electrolysis performance of the GBP membrane-based electrolyzer with lrO₂ and 10 RH% on the anode; (A) l-V curves and (B) Nyquist plots at 160, 200, and 250 °C; (C) Cell voltage and efficiency change with time when operating at 250 °C and 200 mA cm'²; and (D) Electrolysis comparison of with other advanced membranes (CsH2PO4/SiP₂O7⁶⁰, Nafion/SiO ⁴, Aquivion/PA⁴¹, Nation 117⁶¹, Nafion/SiO?⁵) at elevated temperatures.

Figure 35 provides; (A) TEM image and (B) XRD of the produced Fe-NSC catalyst; (C) Normalized linear sweep voltammetry in 1 M H₂SO₄ at room temperature for Fe-NSC and lrO₂; Electrolysis performance of the GBP membrane-based electrolyzer with Fe-NSC and 10 RH% on the anode: (D) l-V curves and (E) Nyquist plots at 160, 200, and 250 °C; and (F) Cell voltage and efficiency change with time when operating at 250 °C and 200 mA cm'².

DETAILED DESCRIPTION OF THE INVENTION

Proton Conducting Membranes [0020] The present invention employs a membrane design encompassing three main considerations: (1) employing 2D nanosheets as proton-permeable building blocks to facilitate through-membrane proton transport; (2) assembling 2D nanosheets to form 2D channels, capable of confining the proton conductor to thereby prevent loss of the proton conductor, or to prevent physical or chemical degradation of the proton conductor under the conditions in which the membrane may be exposed in its application(s); (3) incorporating proton conductors to occupy the intersheet spaces forming the 2D channels, and/or incorporating proton conductors to form at least part of the inner surfaces of the 2D channels, enabling intersheet proton transport while blocking hydrogen gas molecules. The membranes of the present invention offer ultrafast proton conducting pathways due to synergistic proton transport, with high retention of the proton conductor achieved through nanoconfinement in 2D channels.

[0021] In one aspect the disclosure herein provides a proton conducting membrane comprising nanosheets, and 2D-nanochannels formed between the nanosheets, wherein the 2D- nanochannels comprise a proton conductor confined within the 2D-nanochannels, and wherein the proton conductor is physically and chemically stable at temperatures of 150°C and above.

[0022] In some embodiments, the stability of the proton conductor at temperatures of 150°C and above is surprisingly and unexpectedly facilitated for proton conductors that would not otherwise be physically and chemically stable at temperatures of 150°C and above (such as, but not limited to, phosphoric acid, for example), by virtue of the nanoconfinement of the proton conductor within the 2D-nanochannels formed between the nanosheets of the proton conducting membrane.

[0023] In one aspect, the disclosure herein provides a proton conducting membrane comprising nanosheets, and 2D-nanochannels formed between the nanosheets, wherein the 2D- nanochannels comprise an inorganic proton conductor confined within the 2D-nanochannels.

[0024] As used herein, the term “2D-nanochannels” is to be understood to refer to the channels formed by the stacking of the nanosheets during production of the proton conducting membranes of the present invention, in accordance with the processes of the present invention. These channels form a 2-dimensional network through the proton conducting membranes of the present invention. Accordingly, the term “2D-nanochannels” is to be understood as not including 3- dimensional networks of interconnected pores such as, for example, the 3-dimensional networks of interconnected pores observed in mesoporous silica and analogous materials. Within the intersheet spaces between stacked nanosheets, 2D-nanochannels form. Furthermore, throughout the entire membrane, these 2D-nanochannels are interconnected by gaps among the nanosheets, creating through-membrane proton transport pathways. In addition, another feature of the 2D nanochannels includes the ability to arrange confined molecules along the longitudinal direction of the nanosheets, thereby restricting their motion perpendicular to the nanosheets. In some aspects and embodiments, the 2D-nanochannels are formed, at least in part, by nanosheets of a proton conducting material, such that at least part of the inner surfaces of the 2D channels comprise the proton conducting material, resulting in the proton conducting material being confined within the 2D-nanochannels. In this sense, the phrase “wherein the 2D- nanochannels comprise a proton conductor confined within the 2D-nanochannels”, and similar phrases such as “wherein the 2D-nanochannels comprise an inorganic proton conductor confined within the 2D-nanochannels” should be understood to mean, throughout the present specification and claims, that the proton conductor is physically and chemically accessible within the 2D- nanochannels, and that it is prevented from moving from within the 2D-nanochannels.

[0025] In some embodiments, the proton conducting membranes of the present invention comprise a plurality of microlayers, wherein at least one microlayer comprises a plurality of nanosheets.

[0026] As used herein, the term “nanosheet” is to be understood to refer to a sheet of material having a thickness in the scale of nanometres (nm). The term “nanosheet” includes monolayer nanosheets as well as multilayer nanosheets. Thus, the term “nanosheet” shall be understood to refer to a sheet of material having a thickness in the order of 0.1 nm to 10 nm. Preferably, the thickness of the nanosheets is in the order of 0.3 nm to 10 nm.

[0027] In some embodiments, the proton conducting membranes of the present invention comprise boron nitride nanosheets.

[0028] In some embodiments, the proton conducting membranes of the present invention comprise graphene nanosheets.

[0029] In some embodiments, the proton conducting membranes of the present invention comprise boron nitride nanosheets and graphene nanosheets.

[0030] In some embodiments, the proton conducting membranes of the present invention comprise nanosheets of materials other than boron nitride nanosheets and/or graphene nanosheets. For example, without departing from the scope of the present invention, nanosheets of other materials may be employed such as, but not limited to nanosheets of mica, nanosheets of covalent organic framework TAPB-PDA, nanosheets of solid proton conductor, nanosheets of inorganic proton conductor, nanosheets of heteropolymetalates, nanosheets of silicotungstic acid, nanosheets of phosphomolybdic acid, nanosheets of phosphotungstic acid (PWA), nanosheets of zirconium phosphate, nanosheets of titanium phosphate, nanosheets of zeolitic imidazolate framework, nanosheets of porous graphitic carbon nitride (g-CsI^ ), nanosheets of graphene oxide, nanosheets of metal organic frameworks, and nanosheets of transition-metal phosphorus trichalcogenides. [0031] As used herein, the term “microlayer” is to be understood to refer to a layer of material having a thickness in the scale of micrometres (pm). That is to say, the term “microlayer” is to be understood to refer to a layer of material having a thickness of at least 1 pm. Preferably, the microlayers have a thickness falling within the range of 3 pm to tens of pm.

[0032] In some preferred embodiments, the proton conducting membranes of the present invention comprise;

(i) a first microlayer and a second microlayer, wherein the first microlayer is nonconductive to electrons, and the second microlayer is conductive to electrons; preferably wherein the first microlayer comprises a plurality of boron nitride nanosheets, and the second microlayer comprises a plurality of graphene nanosheets; or

(ii) a first microlayer, a second microlayer and a third microlayer, wherein the first microlayer comprises a plurality of nanosheets of a first substance, the second microlayer comprises a plurality of nanosheets of a second substance which is different to the first substance, and the third microlayer comprises a plurality of nanosheets of a third substance which is different to the second substance; optionally wherein the substance of the first microlayer and the substance of the third microlayer are the same; preferably wherein the second microlayer comprises a plurality of boron nitride nanosheets; most preferably wherein the first microlayer and/or the third microlayer each comprise a plurality of graphene nanosheets; or

(iii) a first microlayer and a second microlayer, wherein the first microlayer is nonconductive to electrons, and the second microlayer is conductive to protons; preferably wherein the first microlayer comprises a plurality of boron nitride nanosheets, and the second microlayer comprises a plurality of phosphotungstic acid (PWA) nanosheets; or

(iv) a first microlayer, a second microlayer and a third microlayer, wherein the first microlayer comprises a plurality of nanosheets of a first substance, the second microlayer comprises a plurality of nanosheets of a second substance which is different to the first substance, and the third microlayer comprises a plurality of nanosheets of a third substance which is different to the second substance; optionally wherein the substance of the first microlayer and the substance of the third microlayer are the same; preferably wherein the second microlayer comprises a plurality of phosphotungstic acid (PWA) nanosheets; most preferably wherein the first microlayer and/or the third microlayer each comprise a plurality of boron nitride nanosheets nanosheets.

[0033] In some embodiments, the proton conductor of the proton conducting membranes of the present invention is selected from the group(s) consisting of; solid acids, inorganic acids, protonic ceramics, protic inorganic polymers, protic ionic plastic crystals, protic organic ionic plastic crystals (POIPCs), zirconate based perovskites, rare-earth ortho-n iobates, rare-earth ortho- tantalates, rare-earth tungstates, heteropolyoxometallates, silico-aluminates, transition metal oxides, zeolites, and protonic Metal-Organic Frameworks (MOFs), including nanosheets comprising any of the aforementioned proton conductors.

[0034] In some embodiments, the proton conductor of the proton conducting membranes of the present invention is selected from the group consisting of; phosphoric acid, sulfuric acid, boric acid, perchloric acid, phosphotungstic acid (PWA), cesium hydrogen sulfate, aluminium phosphate, silico-aluminophosphate, sulphated zirconia, titanium phosphate, zirconia, niobium phosphate, niobic acid, 1 ,2,4-triazolium perfluorobutanesulfonate, imidazolium methanesulfonate, acceptor doped SrCeOs, acceptor doped BaCeOs, and acceptor doped BaZrO₃, including nanosheets comprising any of the aforementioned proton conductors.

[0035] In some preferred embodiments, the proton conducting membranes of the present invention further comprise a residual exfoliating agent.

[0036] As used herein, the term “exfoliating agent” is to be understood to refer to any substance used in the preparation, via exfoliation, of the nanosheets employed in constructing the membranes of the present invention, that facilitates said exfoliation. The term “residual exfoliating agent” thus refers to any residues of such exfoliating agent substances left behind in the nanosheet starting materials, as a consequence of the exfoliation process used to prepare said nanosheet starting materials.

[0037] In some embodiments, the proton conducting membranes of the present invention further comprise a residual exfoliating agent selected from the group consisting of high-viscosity amine- functionalized polymers, high-viscosity polyamines, high-viscosity polyesteramides, high- viscosity polyimides, high-viscosity polyesters, high-viscosity polyepoxides, high-viscosity polyethers, high-viscosity polyvinylamines, high-viscosity polyallylamines and high-viscosity polyamidoamines; preferably wherein the residual exfoliating agent is a high-viscosity polyethylenimine or a high-viscosity polyacrylamide.

[0038] As used herein, the term “high viscosity” is to be understood to refer to a viscosity that is sufficiently high enough to facilitate exfoliation in the preparation, via exfoliation, of the nanosheets employed in constructing the membranes of the present invention. Preferably, the term “high viscosity” refers to a minimum viscosity of 7.5 Pa«s.

[0039] In some embodiments, of the proton conducting membranes of the present invention the intersheet spacing between adjacent nanosheets falls within the range of 1-20 nm or 1-10 nm, or 0.5-5 nm, or 0.5-4 nm, or 0.5-3 nm, or 0.5-2 nm. In some embodiments, the intersheet spacing between adjacent nanosheets is independently selected in each instance from the group consisting of; 0.1 nm, 0.2 nm, 0.3 nm, 0.4 nm, 0.5 nm, 0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm, 1 nm, 1.1 nm, 1.2 nm, 1.3 nm, 1.4 nm, 1.5 nm, 1.6 nm, 1.7 nm, 1.8 nm, 1.9 nm, 2 nm, 2.1 nm, 2.2 nm, 2.3 nm, 2.4 nm, 2.5 nm, 2.6 nm, 2.7 nm, 2.8 nm, 2.9 nm, 3 nm, 3.1 nm, 3.2 nm, 3.3 nm, 3.4 nm, 3.5 nm, 3.6 nm, 3.7 nm, 3.8 nm, 3.9 nm, 4 nm, 4.1 nm, 4.2 nm, 4.3 nm, 4.4 nm, 4.5 nm, 4.6 nm, 4.7 nm, 4.8 nm, 4.9 nm, 5 nm, 5.1 nm, 5.2 nm, 5.3 nm, 5.4 nm, 5.5 nm, 5.6 nm, 5.7 nm, 5.8 nm, 5.9 nm, 6 nm, 6.1 nm, 6.2 nm, 6.3 nm, 6.4 nm, 6.5 nm, 6.6 nm, 6.7 nm, 6.8 nm, 6.9 nm, 7 nm, 7.1 nm, 7.2 nm, 7.3 nm, 7.4 nm, 7.5 nm, 7.6 nm, 7.7 nm, 7.8 nm, 7.9 nm, 8 nm, 8.1 nm, 8.2 nm, 8.3 nm, 8.4 nm, 8.5 nm, 8.6 nm, 8.7 nm, 8.8 nm, 8.9 nm, 9 nm, 9.1 nm, 9.2 nm, 9.3 nm, 9.4 nm, 9.5 nm, 9.6 nm, 9.7 nm, 9.8 nm, 9.9 nm, 10 nm, 10.1 nm, 10.2 nm, 10.3 nm, 10.4 nm, 10.5 nm, 10.6 nm, 10.7 nm, 10.8 nm, 10.9 nm, 11 nm, 11.1 nm, 11.2 nm, 11.3 nm, 11.4 nm, 11.5 nm, 11.6 nm,

11.7 nm, 11.8 nm, 11.9 nm, 12 nm, 12.1 nm, 12.2 nm, 12.3 nm, 12.4 nm, 12.5 nm, 12.6 nm, 12.7 nm, 12.8 nm, 12.9 nm, 13 nm, 13.1 nm, 13.2 nm, 13.3 nm, 13.4 nm, 13.5 nm, 13.6 nm, 13.7 nm,

13.8 nm, 13.9 nm, 14 nm, 14.1 nm, 14.2 nm, 14.3 nm, 14.4 nm, 14.5 nm, 14.6 nm, 14.7 nm, 14.8 nm, 14.9 nm, 15 nm, 15.1 nm, 15.2 nm, 15.3 nm, 15.4 nm, 15.5 nm, 15.6 nm, 15.7 nm, 15.8 nm,

15.9 nm, 16 nm, 16.1 nm, 16.2 nm, 16.3 nm, 16.4 nm, 16.5 nm, 16.6 nm, 16.7 nm, 16.8 nm, 16.9 nm, 17 nm, 17.1 nm, 17.2 nm, 17.3 nm, 17.4 nm, 17.5 nm, 17.6 nm, 17.7 nm, 17.8 nm, 17.9 nm, 18 nm, 18.1 nm, 18.2 nm, 18.3 nm, 18.4 nm, 18.5 nm, 18.6 nm, 18.7 nm, 18.8 nm, 18.9 nm, 19 nm, 19.1 nm, 19.2 nm, 19.3 nm, 19.4 nm, 19.5 nm, 19.6 nm, 19.7 nm, 19.8 nm, 19.9 nm, and 20 nm.

[0040] In some embodiments, of the proton conducting membranes of the present invention the thickness of the membrane falls within the range of 10-1000 pm. In some embodiments, the thickness of the membrane is selected from the group consisting of; 10 pm, 11 pm, 12 pm, 13 pm, 14 pm, 15 pm, 16 pm, 17 pm, 18 pm, 19 pm, 20 pm, 21 pm, 22 pm, 23 pm, 24 pm, 25 pm, 26 pm, 27 pm, 28 pm, 29 pm, 30 pm, 31 pm, 32 pm, 33 pm, 34 pm, 35 pm, 36 pm, 37 pm, 38 pm, 39 pm, 40 pm, 41 pm, 42 pm, 43 pm, 44 pm, 45 pm, 46 pm, 47 pm, 48 pm, 49 pm, 50 pm, 51 pm, 52 pm, 53 pm, 54 pm, 55 pm, 56 pm, 57 pm, 58 pm, 59 pm, 60 pm, 61 pm, 62 pm, 63 pm, 64 pm, 65 pm, 66 pm, 67 pm, 68 pm, 69 pm, 70 pm, 71 pm, 72 pm, 73 pm, 74 pm, 75 pm, 76 pm, 77 pm, 78 pm, 79 pm, 80 pm, 81 pm, 82 pm, 83 pm, 84 pm, 85 pm, 86 pm, 87 pm, 88 pm, 89 pm, 90 pm, 91 pm, 92 pm, 93 pm, 94 pm, 95 pm, 96 pm, 97 pm, 98 pm, 99 pm, 100 pm, 101 pm, 102 pm, 103 pm, 104 pm, 105 pm, 106 pm, 107 pm, 108 pm, 109 pm, 110 pm, 111 pm,

112 pm, 113 pm, 114 pm, 115 pm, 116 pm, 117 pm, 118 pm, 119 pm, 120 pm, 121 pm, 122 pm,

123 pm, 124 pm, 125 pm, 126 pm, 127 pm, 128 pm, 129 pm, 130 pm, 131 pm, 132 pm, 133 pm,

134 pm, 135 pm, 136 pm, 137 pm, 138 pm, 139 pm, 140 pm, 141 pm, 142 pm, 143 pm, 144 pm,

145 pm, 146 pm, 147 pm, 148 pm, 149 pm, 150 pm, 151 pm, 152 pm, 153 pm, 154 pm, 155 pm,

156 pm, 157 pm, 158 pm, 159 pm, 160 pm, 161 pm, 162 pm, 163 pm, 164 pm, 165 pm, 166 pm,

167 pm, 168 pm, 169 pm, 170 pm, 171 pm, 172 pm, 173 pm, 174 pm, 175 pm, 176 pm, 177 pm, pm, 179 pm, 180 pm, 181 pm, 182 pm, 183 pm, 184 pm, 185 pm, 186 pm, 187 pm, 188 pm, pm, 190 pm, 191 pm, 192 pm, 193 pm, 194 pm, 195 pm, 196 pm, 197 pm, 198 pm, 199 pm, pm, 201 pm, 202 pm, 203 pm, 204 pm, 205 pm, 206 pm, 207 pm, 208 pm, 209 pm, 210 pm, pm, 212 pm, 213 pm, 214 pm, 215 pm, 216 pm, 217 pm, 218 pm, 219 pm, 220 pm, 221 pm, pm, 223 pm, 224 pm, 225 pm, 226 pm, 227 pm, 228 pm, 229 pm, 230 pm, 231 pm, 232 pm, pm, 234 pm, 235 pm, 236 pm, 237 pm, 238 pm, 239 pm, 240 pm, 241 pm, 242 pm, 243 pm, pm, 245 pm, 246 pm, 247 pm, 248 pm, 249 pm, 250 pm, 251 pm, 252 pm, 253 pm, 254 pm, pm, 256 pm, 257 pm, 258 pm, 259 pm, 260 pm, 261 pm, 262 pm, 263 pm, 264 pm, 265 pm, pm, 267 pm, 268 pm, 269 pm, 270 pm, 271 pm, 272 pm, 273 pm, 274 pm, 275 pm, 276 pm, pm, 278 pm, 279 pm, 280 pm, 281 pm, 282 pm, 283 pm, 284 pm, 285 pm, 286 pm, 287 pm, pm, 289 pm, 290 pm, 291 pm, 292 pm, 293 pm, 294 pm, 295 pm, 296 pm, 297 pm, 298 pm, pm, 300 pm, 301 pm, 302 pm, 303 pm, 304 pm, 305 pm, 306 pm, 307 pm, 308 pm, 309 pm, pm, 311 pm, 312 pm, 313 pm, 314 pm, 315 pm, 316 pm, 317 pm, 318 pm, 319 pm, 320 pm, pm, 322 pm, 323 pm, 324 pm, 325 pm, 326 pm, 327 pm, 328 pm, 329 pm, 330 pm, 331 pm, pm, 333 pm, 334 pm, 335 pm, 336 pm, 337 pm, 338 pm, 339 pm, 340 pm, 341 pm, 342 pm, pm, 344 pm, 345 pm, 346 pm, 347 pm, 348 pm, 349 pm, 350 pm, 351 pm, 352 pm, 353 pm, pm, 355 pm, 356 pm, 357 pm, 358 pm, 359 pm, 360 pm, 361 pm, 362 pm, 363 pm, 364 pm, pm, 366 pm, 367 pm, 368 pm, 369 pm, 370 pm, 371 pm, 372 pm, 373 pm, 374 pm, 375 pm, pm, 377 pm, 378 pm, 379 pm, 380 pm, 381 pm, 382 pm, 383 pm, 384 pm, 385 pm, 386 pm, pm, 388 pm, 389 pm, 390 pm, 391 pm, 392 pm, 393 pm, 394 pm, 395 pm, 396 pm, 397 pm, pm, 399 pm, 400 pm, 401 pm, 402 pm, 403 pm, 404 pm, 405 pm, 406 pm, 407 pm, 408 pm, pm, 410 pm, 411 pm, 412 pm, 413 pm, 414 pm, 415 pm, 416 pm, 417 pm, 418 pm, 419 pm, pm, 421 pm, 422 pm, 423 pm, 424 pm, 425 pm, 426 pm, 427 pm, 428 pm, 429 pm, 430 pm, pm, 432 pm, 433 pm, 434 pm, 435 pm, 436 pm, 437 pm, 438 pm, 439 pm, 440 pm, 441 pm, pm, 443 pm, 444 pm, 445 pm, 446 pm, 447 pm, 448 pm, 449 pm, 450 pm, 451 pm, 452 pm, pm, 454 pm, 455 pm, 456 pm, 457 pm, 458 pm, 459 pm, 460 pm, 461 pm, 462 pm, 463 pm, pm, 465 pm, 466 pm, 467 pm, 468 pm, 469 pm, 470 pm, 471 pm, 472 pm, 473 pm, 474 pm, pm, 476 pm, 477 pm, 478 pm, 479 pm, 480 pm, 481 pm, 482 pm, 483 pm, 484 pm, 485 pm, pm, 487 pm, 488 pm, 489 pm, 490 pm, 491 pm, 492 pm, 493 pm, 494 pm, 495 pm, 496 pm, pm, 498 pm, 499 pm, 500 pm, 501 pm, 502 pm, 503 pm, 504 pm, 505 pm, 506 pm, 507 pm, pm, 509 pm, 510 pm, 511 pm, 512 pm, 513 pm, 514 pm, 515 pm, 516 pm, 517 pm, 518 pm, pm, 520 pm, 521 pm, 522 pm, 523 pm, 524 pm, 525 pm, 526 pm, 527 pm, 528 pm, 529 pm, pm, 531 pm, 532 pm, 533 pm, 534 pm, 535 pm, 536 pm, 537 pm, 538 pm, 539 pm, 540 pm, pm, 542 pm, 543 pm, 544 pm, 545 pm, 546 pm, 547 pm, 548 pm, 549 pm, 550 pm, 551 pm, pm, 553 pm, 554 pm, 555 pm, 556 pm, 557 pm, 558 pm, 559 pm, 560 pm, 561 pm, 562 pm, pm, 564 pm, 565 pm, 566 pm, 567 pm, 568 pm, 569 pm, 570 pm, 571 pm, 572 pm, 573 pm, pm, 575 pm, 576 pm, 577 pm, 578 pm, 579 pm, 580 pm, 581 pm, 582 pm, 583 pm, 584 pm, pm, 586 pm, 587 pm, 588 pm, 589 pm, 590 pm, 591 pm, 592 pm, 593 pm, 594 pm, 595 pm, pm, 597 pm, 598 pm, 599 pm, 600 pm, 601 pm, 602 pm, 603 pm, 604 pm, 605 pm, 606 pm, pm, 608 pm, 609 pm, 610 pm, 611 pm, 612 pm, 613 pm, 614 pm, 615 pm, 616 pm, 617 pm, pm, 619 pm, 620 pm, 621 pm, 622 pm, 623 pm, 624 pm, 625 pm, 626 pm, 627 pm, 628 pm, pm, 630 pm, 631 pm, 632 pm, 633 pm, 634 pm, 635 pm, 636 pm, 637 pm, 638 pm, 639 pm, pm, 641 pm, 642 pm, 643 pm, 644 pm, 645 pm, 646 pm, 647 pm, 648 pm, 649 pm, 650 pm, pm, 652 pm, 653 pm, 654 pm, 655 pm, 656 pm, 657 pm, 658 pm, 659 pm, 660 pm, 661 pm, pm, 663 pm, 664 pm, 665 pm, 666 pm, 667 pm, 668 pm, 669 pm, 670 pm, 671 pm, 672 pm, pm, 674 pm, 675 pm, 676 pm, 677 pm, 678 pm, 679 pm, 680 pm, 681 pm, 682 pm, 683 pm, pm, 685 pm, 686 pm, 687 pm, 688 pm, 689 pm, 690 pm, 691 pm, 692 pm, 693 pm, 694 pm, pm, 696 pm, 697 pm, 698 pm, 699 pm, 700 pm, 701 pm, 702 pm, 703 pm, 704 pm, 705 pm, pm, 707 pm, 708 pm, 709 pm, 710 pm, 711 pm, 712 pm, 713 pm, 714 pm, 715 pm, 716 pm, pm, 718 pm, 719 pm, 720 pm, 721 pm, 722 pm, 723 pm, 724 pm, 725 pm, 726 pm, 727 pm, pm, 729 pm, 730 pm, 731 pm, 732 pm, 733 pm, 734 pm, 735 pm, 736 pm, 737 pm, 738 pm, pm, 740 pm, 741 pm, 742 pm, 743 pm, 744 pm, 745 pm, 746 pm, 747 pm, 748 pm, 749 pm, pm, 751 pm, 752 pm, 753 pm, 754 pm, 755 pm, 756 pm, 757 pm, 758 pm, 759 pm, 760 pm, pm, 762 pm, 763 pm, 764 pm, 765 pm, 766 pm, 767 pm, 768 pm, 769 pm, 770 pm, 771 pm, pm, 773 pm, 774 pm, 775 pm, 776 pm, 777 pm, 778 pm, 779 pm, 780 pm, 781 pm, 782 pm, pm, 784 pm, 785 pm, 786 pm, 787 pm, 788 pm, 789 pm, 790 pm, 791 pm, 792 pm, 793 pm, pm, 795 pm, 796 pm, 797 pm, 798 pm, 799 pm, 800 pm, 801 pm, 802 pm, 803 pm, 804 pm, pm, 806 pm, 807 pm, 808 pm, 809 pm, 810 pm, 811 pm, 812 pm, 813 pm, 814 pm, 815 pm, pm, 817 pm, 818 pm, 819 pm, 820 pm, 821 pm, 822 pm, 823 pm, 824 pm, 825 pm, 826 pm, pm, 828 pm, 829 pm, 830 pm, 831 pm, 832 pm, 833 pm, 834 pm, 835 pm, 836 pm, 837 pm, pm, 839 pm, 840 pm, 841 pm, 842 pm, 843 pm, 844 pm, 845 pm, 846 pm, 847 pm, 848 pm, pm, 850 pm, 851 pm, 852 pm, 853 pm, 854 pm, 855 pm, 856 pm, 857 pm, 858 pm, 859 pm, pm, 861 pm, 862 pm, 863 pm, 864 pm, 865 pm, 866 pm, 867 pm, 868 pm, 869 pm, 870 pm, pm, 872 pm, 873 pm, 874 pm, 875 pm, 876 pm, 877 pm, 878 pm, 879 pm, 880 pm, 881 pm, pm, 883 pm, 884 pm, 885 pm, 886 pm, 887 pm, 888 pm, 889 pm, 890 pm, 891 pm, 892 pm, pm, 894 pm, 895 pm, 896 pm, 897 pm, 898 pm, 899 pm, 900 pm, 901 pm, 902 pm, 903 pm, pm, 905 pm, 906 pm, 907 pm, 908 pm, 909 pm, 910 pm, 911 pm, 912 pm, 913 pm, 914 pm, pm, 916 pm, 917 pm, 918 pm, 919 pm, 920 pm, 921 pm, 922 pm, 923 pm, 924 pm, 925 pm, pm, 927 pm, 928 pm, 929 pm, 930 pm, 931 pm, 932 pm, 933 pm, 934 pm, 935 pm, 936 pm, pm, 938 pm, 939 pm, 940 pm, 941 pm, 942 pm, 943 pm, 944 pm, 945 pm, 946 pm, 947 pm, pm, 949 pm, 950 pm, 951 pm, 952 pm, 953 pm, 954 pm, 955 pm, 956 pm, 957 pm, 958 pm, pm, 960 pm, 961 pm, 962 pm, 963 pm, 964 pm, 965 pm, 966 pm, 967 pm, 968 pm, 969 pm, pm, 971 pm, 972 pm, 973 pm, 974 pm, 975 pm, 976 pm, 977 pm, 978 pm, 979 pm, 980 pm, pm, 982 pm, 983 pm, 984 pm, 985 pm, 986 pm, 987 pm, 988 pm, 989 pm, 990 pm, 991 pm, pm, 993 pm, 994 pm, 995 pm, 996 pm, 997 pm, 998 pm, 999 pm, and 1000 pm. [0041] In some embodiments, of the proton conducting membranes of the present invention the amount of proton conductor as a percentage of the overall weight of the membrane falls within the range of 10-90 wt%, or 10-80 wt%, or 10-70 wt%, or 10-60 wt%. In some embodiments, the amount of proton conductor as a percentage of the overall weight of the membrane is selected from the group consisting of; 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%,

29 wt%, 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, 35 wt%, 36 wt%, 37 wt%, 38 wt%, 39 wt%,

40 wt%, 41 wt%, 42 wt%, 43 wt%, 44 wt%, 45 wt%, 46 wt%, 47 wt%, 48 wt%, 49 wt%, 50 wt%,

51 wt%, 52 wt%, 53 wt%, 54 wt%, 55 wt%, 56 wt%, 57 wt%, 58 wt%, 59 wt%, 60 wt%, 61 wt%,

62 wt%, 63 wt%, 64 wt%, 65 wt%, 66 wt%, 67 wt%, 68 wt%, 69 wt%, 70 wt%, 71 wt%, 72 wt%,

73 wt%, 74 wt%, 75 wt%, 76 wt%, 77 wt%, 78 wt%, 79 wt%, 80 wt%, 81 wt%, 82 wt%, 83 wt%,

84 wt%, 85 wt%, 86 wt%, 87 wt%, 88 wt%, 89 wt%, 90 and wt%.

[0042] In some embodiments, of the proton conducting membranes of the present invention the proton conductivity of the membrane at 250°C falls within the range of 50-250 mS cm'¹; preferably 105-170 mS cm'¹. In some embodiments, the proton conductivity of the membrane at 250°C is selected from the group consisting of; 50 mS cm'¹, 51 mS cm'¹, 52 mS cm'¹, 53 mS cm’¹, 54 mS cm ¹, 55 mS cm'¹, 56 mS cm'¹, 57 mS cm ¹, 58 mS cm ¹, 59 mS cm'¹, 60 mS cm'¹, 61 mS cm ¹, 62 mS cm'¹, 63 mS cm ¹, 64 mS cm^-1, 65 mS cm ¹, 66 mS cm'¹, 67 mS cm'¹, 68 mS cm ¹, 69 mS cm' ¹, 70 mS cm'¹, 71 mS cm'¹, 72 mS cm'¹, 73 mS cm'¹, 74 mS cm^-1, 75 mS cm ¹, 76 mS cm'¹, 77 mS cm'¹, 78 mS cm ¹, 79 mS cm^-1, 80 mS cm ¹, 81 mS cm'¹, 82 mS cm'¹, 83 mS cm ¹, 84 mS cm' ¹, 85 mS cm'¹, 86 mS cm'¹, 87 mS cm'¹, 88 mS cm'¹, 89 mS cm^-1, 90 mS cm ¹, 91 mS cm'¹, 92 mS cm'¹, 93 mS cm ¹, 94 mS cm^-1, 95 mS cm ¹, 96 mS cm'¹, 97 mS cm'¹, 98 mS cm ¹, 99 mS cm' ¹, 100 mS cm^-1, 101 mS cm'¹, 102 mS cm ¹, 103 mS cm ¹, 104 mS cm'¹, 105 mS cm'¹, 106 mS cm'¹ , 107 mS cm'¹ , 108 mS cm'¹ , 109 mS cm^-1 , 110 mS cm^-1 , 111 mS cm'¹ , 112 mS cm^-1 , 1 13 mS cm'¹ , 1 14 mS cm'¹ , 115 mS cm'¹ , 116 mS cm^-1 , 117 mS cm^-1 , 118 mS cm'¹ , 119 mS cm^-1 , 120 mS cm ¹, 121 mS cm ¹, 122 mS cm ¹, 123 mS cm ¹, 124 mS cm ¹, 125 mS cm ¹, 126 mS cm ¹, 127 mS cm ¹, 128 mS cm ¹, 129 mS cm'¹, 130 mS cm^-1, 131 mS cm^-1, 132 mS cm ¹, 133 mS cm^-1, 134 mS cm'¹ , 135 mS cm'¹ , 136 mS cm'¹ , 137 mS cm^-1 , 138 mS cm^-1 , 139 mS cm'¹ , 140 mS cm^-1 , 141 mS cm ¹, 142 mS cm ¹, 143 mS cm'¹, 144 mS cm^-1, 145 mS cm^-1, 146 mS cm ¹, 147 mS cm^-1, 148 mS cm'¹ , 149 mS cm'¹ , 150 mS cm'¹ , 151 mS cm^-1 , 152 mS cm^-1 , 153 mS cm'¹ , 154 mS cm^-1 , 155 mS cm'¹ , 156 mS cm'¹ , 157 mS cm'¹ , 158 mS cm^-1 , 159 mS cm^-1 , 160 mS cm'¹ , 161 mS cm^-1 , 162 mS cm ¹, 163 mS cm ¹, 164 mS cm'¹, 165 mS cm^-1, 166 mS cm^-1, 167 mS cm ¹, 168 mS cm^-1, 169 mS cm'¹ , 170 mS cm'¹ , 171 mS cm'¹ , 172 mS cm^-1 , 173 mS cm^-1 , 174 mS cm'¹ , 175 mS cm^-1 , 176 mS cm'¹ , 177 mS cm'¹ , 178 mS cm'¹ , 179 mS cm^-1 , 180 mS cm^-1 , 181 mS cm'¹ , 182 mS cm^-1 , 183 mS cm'¹ , 184 mS cm'¹ , 185 mS cm'¹ , 186 mS cm^-1 , 187 mS cm^-1 , 188 mS cm'¹ , 189 mS cm^-1 , 190 mS cm'¹ , 191 mS cm'¹ , 192 mS cm'¹ , 193 mS cm^-1 , 194 mS cm^-1 , 195 mS cm'¹ , 196 mS cm^-1 , 197 mS cm ¹, 198 mS cm ¹, 199 mS cm'¹, 200 mS cm^-1, 201 mS cm^-1, 202 mS cm ¹, 203 mS cm^-1, 204 mS cm^-1 , 205 mS cm'¹ , 206 mS cm'¹ , 207 mS cm^-1 , 208 mS cm^-1 , 209 mS cm'¹ , 210 mS cm^-1 , 211 mS cm ¹, 212 mS cm ¹, 213 mS cm ¹, 214 mS cm ¹, 215 mS cm ¹, 216 mS cm ¹, 217 mS cm ¹, 218 mS cm ¹, 219 mS cm ¹, 220 mS cm ¹, 221 mS cm ¹, 222 mS cm ¹, 223 mS cm ¹, 224 mS cm ¹, 225 mS cm ¹, 226 mS cm ¹, 227 mS cm'¹, 228 mS cm^-1, 229 mS cm^-1, 230 mS cm ¹, 231 mS cm^-1, 232 mS cm ¹, 233 mS cm ¹, 234 mS cm'¹, 235 mS cm^-1, 236 mS cm^-1, 237 mS cm ¹, 238 mS cm^-1, 239 mS cm ¹, 240 mS cm ¹, 241 mS cm'¹, 242 mS cm^-1, 243 mS cm^-1, 244 mS cm ¹, 245 mS cm^-1, 246 mS cm'¹, 247 mS cm'¹, 248 mS cm'¹, 249 mS cm'¹, and 250 mS cm'¹.

[0043] In some embodiments, the proton conducting membranes of the present invention are thermally stable when exposed to air at 250°C. In some embodiments, the proton conducting membranes of the present invention are thermally stable when exposed to air at a temperature selected from the croup consisting of; 200°C, 201 °C, 202°C, 203°C, 204°C, 205°C, 206°C, 207°C, 208°C, 209°C, 210°C, 211 °C, 212°C, 213°C, 214°C, 215°C, 216°C, 217°C, 218°C, 219°C, 220°C, 221 °C, 222°C, 223°C, 224°C, 225°C, 226°C, 227°C, 228°C, 229°C, 230°C, 231 °C, 232°C, 233°C, 234°C, 235°C, 236°C, 237°C, 238°C, 239°C, 240°C, 241 °C, 242°C, 243°C, 244°C, 245°C, 246°C,

247°C, 248°C, 249°C, 250°C, 251 °C, 252°C, 253°C, 254°C, 255°C, 256°C, 257°C, 258°C, 259°C,

260°C, 261 °C, 262°C, 263°C, 264°C, 265°C, 266°C, 267°C, 268°C, 269°C, 270°C, 271 °C, 272°C,

273°C, 274°C, 275°C, 276°C, 277°C, 278°C, 279°C, 280°C, 281 °C, 282°C, 283°C, 284°C, 285°C,

286°C, 287°C, 288°C, 289°C, 290°C, 291 °C, 292°C, 293°C, 294°C, 295°C, 296°C, 297°C, 298°C,

299°C, 300°C, 301 °C, 302°C, 303°C, 304°C, 305°C, 306°C, 307°C, 308°C, 309°C, 310°C, 31 1 °C,

312°C, 313°C, 314°C, 315°C, 316°C, 317°C, 318°C, 319°C, 320°C, 321 °C, 322°C, 323°C, 324°C,

325°C, 326°C, 327°C, 328°C, 329°C, 330°C, 331 °C, 332°C, 333°C, 334°C, 335°C, 336°C, 337°C,

338°C, 339°C, 340°C, 341 °C, 342°C, 343°C, 344°C, 345°C, 346°C, 347°C, 348°C, 349°C, and 350°C.

Electrochemical Devices

[0044] Atomically thin crystals with rapid proton transport capability have emerged as promising candidates for electrolyte membranes in electrochemical devices, while their practical application faces significant challenges due to a propensity of nanosheets readily stack, causing a considerable reduction in proton conductivity. Herein is provided a new approach for building membranes using proton conductors such as but not limited to phosphoric acid to separate individual nanosheets. The present inventors have discovered that the stacking of nanosheets creates two-dimensional nanochannels, which facilitates the formation of an ordered proton conductor structure. This unique configuration not only enables high proton conductivity through the synergistic effect of proton transport between the nanosheets and the proton conductor phase, but also protects the loss of thermally sensitive proton conductors to result in enhanced stability at high temperatures. The membranes of the present invention exhibit a remarkable proton conductivity at 250°C, and the corresponding fuel cells reach unprecedented peak power densities of up to three times higher than that of traditional phosphoric acid-doped polybenzimidazole membranes. Such unique membrane structures and proton conducting mechanisms also endow the electrolyte with superior resistance towards methanol crossover, enabling fuel cells operatable with high concentration methanol solutions at high power densities under both oxygen and air atmospheres. The present invention provides a completely new strategy for the development of ultrafast proton conducting membranes with applicability to a broad range of applications.

[0045] The separation of hydrogen from CO₂ represents a critical barrier to conventional hydrogen production processes, particularly in steam methane reforming, with selectivity often limited due to the competitive transport of these gas species. The present invention leverages the mixed proton and electron conductivity (MPEC) of Graphene/Proton conductor membranes for application to hydrogen purification. Separation of hydrogen with nearly 100% H₂/CO₂ selectivity is enabled by the membranes of the present invention. Proton conducting membranes coated with catalysts on both sides, similar to the membrane electrode assembly in fuel cells, allow only hydrogen to permeate through the membrane. This selective transport occurs via the hydrogenproton conversion at the membrane-electrode interface and the associated proton transport across the membrane. The resulting membrane reactors display remarkable mixed conductivity over wide temperature ranges, resulting in surprising and unexpected hydrogen permeances of, for example, 61 GPU at 250°C. This exceptional mixed conductivity primarily arises from the high electron conductivity of graphene nanosheets and the rapid proton-transport pathways formed by proton-permeable graphene nanosheets comprising nanoconfined proton conductors. Moreover, the membranes of the present invention exhibit exceptional thermal stability, positioning them as promising candidates for hydrogen separation at elevated temperatures. The present invention enables, among myriad other electrochemical applications, the development of advanced 2D materials-based composite membranes geared towards the production of ultra-high-purity hydrogen, offering new possibilities in hydrogen energy technology.

[0046] In one aspect, the disclosure herein provides for the use of the proton conducting membranes of the present invention, for hydrogen purification, or for hydrogen production, or for water electrolysis, or for carbon dioxide conversion, or for carbon dioxide reduction, or for ammonia synthesis, or in a fuel cell, or in energy storage applications.

[0047] In one aspect, the disclosure herein provides an electrochemical device comprising one or more proton conducting membranes of the present invention.

[0048] In some embodiments, the electrochemical device of the present invention comprises one or more catalysts; preferably wherein the one or more catalysts are applied as one or more additional microlayers, to one or more microlayers of the proton exchange membranes of the present invention.

[0049] In some embodiments, the electrochemical device of the present invention comprises one or more electrodes, preferably wherein the one or more electrodes are applied as one or more additional microlayers, to one or more microlayers of the proton exchange membrane.

[0050] In some embodiments, of the electrochemical device of the present invention comprising one or more catalysts, or one or more electrodes, the one or more catalysts, or the one or more electrodes, are independently selected in each instance from the group consisting of; heterogeneous catalysts, noble metal catalysts, transition metal catalysts, alkali metal catalysts, alkaline earth metal catalysts, noble metals, transition metals, alkali metals, alkaline earth metals, main group metals, metallic lanthanides and metallic actinides; preferably wherein the one or more catalysts, or the one or more electrodes, are independently selected in each instance from the group consisting of; Pt/C, PtRu/C, RuO₂, lrO₂, Cu, Ag, Fe, Co, Ni, Mn, and Pd.

[0051] In some embodiments, the electrochemical device of the present invention is an electrolyzer for gas purification or for gas production, or for gas conversion, or for water electrolysis, or for ammonia production, or the electrochemical device is a fuel cell, or a proton battery, or a redox flow battery.

[0052] In one embodiment, the electrochemical device is a fuel cell, having a power density falling within the range of 0.5 to 1 .5 W cm^-2, preferably having a power density falling within the range of 0.8 to 1 .2 W cm ². In some embodiments, the electrochemical device is a fuel cell, having a power density selected from the group consisting of; 0.2 W cm'², 0.3 W cm'², 0.4 W cm'², 0.5 W cm^-2, 0.6 W cm'², 0.7 W cm ², 0.8 W cm ², 0.9 W cm ², 1 W cm ², 1 .1 W cm ², 1 .2 W cm ², 1 .3 W cm ², 1 .4 W cm'², 1 .5 W cm'², 1 .6 W cm'², 1 .7 W cm'², 1 .8 W cm^-2, 1 .9 W cm'², 2 W cm'², 2.1 W cm^-2, 2.2 W cm ², 2.3 W cm ², 2.4 W cm ², and 2.5 W cm ².

[0053] In preferred embodiment, the electrochemical device is a fuel cell, wherein the fuel cell possesses long term operational stability; preferably wherein long term operational stability is indicated by a voltage decay rate of not more than 0.5 mV h^-1 at 400 mA cm ² at 250 °C over a period of 150 hours or more. In some embodiments, the voltage decay rate of the fuel cell of the present invention at 400 mA cm^-2 and 250 °C over a period of 150 hours or more is selected from the group consisting of; 0.01 mV h’¹, 0.02 mV h’¹, 0.03 mV h’¹, 0.04 mV h’¹, 0.05 mV h’¹, 0.06 mV h ¹, 0.07 mV IT¹, 0.08 mV IT¹, 0.09 mV IT¹ , 0.1 mV IT¹, 0.11 mV IT¹ , 0.12 mV IT¹, 0.13 mV IT¹, 0.14 mV IT¹ , 0.15 mV IT¹, 0.16 mV IT¹ , 0.17 mV IT¹ , 0.18 mV IT¹ , 0.19 mV IT¹ , 0.2 mV IT¹ , 0.21 mV IT¹ , 0.22 mV IT¹ , 0.23 mV IT¹ , 0.24 mV IT¹ , 0.25 mV IT¹ , 0.26 mV IT¹ , 0.27 mV IT¹ , 0.28 mV IT¹ , 0.29 mV IT¹ , 0.3 mV IT¹, 0.31 mV IT¹, 0.32 mV IT¹ , 0.33 mV IT¹ , 0.34 mV IT¹, 0.35 mV IT¹ , 0.36 mV IT¹ , 0.37 mV IT¹ , 0.38 mV IT¹ , 0.39 mV IT¹, 0.4 mV IT¹ , 0.41 mV IT¹, 0.42 mV IT¹ , 0.43 mV IT¹ , 0.44 mV IT¹, 0.45 mV IT¹, 0.46 mV IT¹ , 0.47 mV IT¹ , 0.48 mV IT¹, 0.49 mV IT¹, and 0.5 mV IT¹.

[0054] In particularly preferred embodiment, the electrochemical device is a fuel cell, wherein the fuel cell is a direct methanol fuel cell, capable of operating at high power densities when fed with high concentration methanol solutions; preferably wherein a high power densitiy is defined as a power density of not less than 0.2 W cm'²; preferably wherein a high concentration methanol solution is defined as a methanol solution wherein the concentration of the methanol is not less than 5 M. In some embodiments, the direct methanol fuel cell is capable of operating at a power density selected from the group consisting of; 0.1 W cm^-2, 0.11 W cm'², 0.12 W cm^-2, 0.13 W cm' ², 0.14 W cm ², 0.15 W cm'², 0.16 W cm ², 0.17 W cm ², 0.18 W cm'², 0.19 W cm ², 0.2 W cm'², 0.21 W cm ², 0.22 W cm ², 0.23 W cm ², 0.24 W cm ², 0.25 W cm ², 0.26 W cm ², 0.27 W cm ², 0.28 W cm'², 0.29 W cm'², 0.3 W cm ², 0.31 W cm ², 0.32 W cm ², 0.33 W cm ², 0.34 W cm ², 0.35 W cm'², 0.36 W cm'², 0.37 W cm ², 0.38 W cm ², 0.39 W cm ², 0.4 W cm ², 0.41 W cm ², 0.42 W cm' ², 0.43 W cm'², 0.44 W cm ², 0.45 W cm ², 0.46 W cm ², 0.47 W cm ², 0.48 W cm ², 0.49 W cm ², 0.5 W cm'², 0.51 W cm ², 0.52 W cm ², 0.53 W cm ², 0.54 W cm ², 0.55 W cm ², 0.56 W cm ², 0.57 W cm'², 0.58 W cm'², 0.59 W cm'², 0.6 W cm'², 0.61 W cm ², 0.62 W cm ², 0.63 W cm'², 0.64 W cm'², 0.65 W cm'², 0.66 W cm ², 0.67 W cm ², 0.68 W cm ², 0.69 W cm ², 0.7 W cm ², 0.71 W cnr ², 0.72 W cm'², 0.73 W cm ², 0.74 W cm ², 0.75 W cm ², 0.76 W cm ², 0.77 W cm ², 0.78 W cm ², 0.79 W cm'², 0.8 W cm ², 0.81 W cm ², 0.82 W cm ², 0.83 W cm ², 0.84 W cm ², 0.85 W cm ², 0.86 W cm'², 0.87 W cm'², 0.88 W cm ², 0.89 W cm ², 0.9 W cm ², 0.91 W cm ², 0.92 W cm ², 0.93 W cm'², 0.94 W cm'², 0.95 W cm ², 0.96 W cm ², 0.97 W cm ², 0.98 W cm ², 0.99 W cm ², 1 W cm ², 1 .01 W cm'², 1 .02 W cm ², 1.03 W cm ², 1.04 W cm ², 1.05 W cm ², 1.06 W cm ², 1.07 W cm ², 1.08 W cm ², 1.09 W cm'², 1.1 W cm ², 1.11 W cm ², 1.12 W cm ², 1.13 W cm ², 1.14 W cm ², 1.15 W cm'², 1.16 W cm ², 1.17 W cm ², 1.18 W cm ², 1.19 W cm ², 1 .2 W cm ², 1.21 W cm ², 1 .22 W cm' ², 1 .23 W cm'², 1 .24 W cm ², 1 .25 W cm ², 1 .26 W cm ², 1 .27 W cm ², 1 .28 W cm ², 1 .29 W cm ², 1 .3 W cm'², 1 .31 W cm'², 1 .32 W cm ², 1 .33 W cm ², 1 .34 W cm ², 1 .35 W cm ², 1 .36 W cm ², 1 .37 W cm'², 1 .38 W cm'², 1 .39 W cm ², 1 .4 W cm ², 1 .41 W cm ², 1 .42 W cm ², 1 .43 W cm ², 1 .44 W cm'², 1 .45 W cm'², 1 .46 W cm^-2, 1 .47 W cm'², 1 .48 W cm'², 1 .49 W cm'², 1 .5 W cm'², 1 .51 W cm- ², 1 .52 W cm'², 1 .53 W cm ², 1 .54 W cm ², 1 .55 W cm ², 1 .56 W cm ², 1 .57 W cm ², 1 .58 W cm ², 1 .59 W cm'², 1 .6 W cm ², 1 .61 W cm ², 1 .62 W cm ², 1 .63 W cm ², 1 .64 W cm ², 1 .65 W cm ², 1 .66 W cm'², 1 .67 W cm'², 1 .68 W cm ², 1 .69 W cm ², 1 .7 W cm ², 1 .71 W cm ², 1 .72 W cm ², 1 .73 W cm'², 1 .74 W cm'², 1 .75 W cm ², 1 .76 W cm ², 1 .77 W cm ², 1 .78 W cm ², 1 .79 W cm ², 1 .8 W cnr ², 1 .81 W cm'², 1 .82 W cm'², 1 .83 W cm'², 1 .84 W cm'², 1 .85 W cm'², 1 .86 W cm'², 1 .87 W cm'², 1 .88 W cm'², 1 .89 W cm ², 1 .9 W cm ², 1 .91 W cm ², 1 .92 W cm ², 1 .93 W cm ², 1 .94 W cm ², 1 .95 W cm'², 1 .96 W cm'², 1 .97 W cm'², 1 .98 W cm'², 1 .99 W cm'², and 2 W cm'²; when fed with a methanol solution having a concentration selected from the group consisting of; 3 M, 3.5 M, 4 M, 4.5 M, 5 M, 5.5 M, 6 M, 6.5 M, 7 M, 7.5 M, 8 M, 8.5 M, 9 M, 9.5 M, 10 M, 10.5 M, 1 1 M, 11 .5 M, 12 M, 12.5 M, 13 M, 13.5 M, 14 M, 14.5 M, 15 M, 15.5 M, 16 M, 16.5 M, 17 M, 17.5 M, 18 M, 18.5 M, 19 M, 19.5 M, 20 M, 20.5 M, 21 M, 21.5 M, 22 M, 22.5 M, 23 M, 23.5 M, 24 M, 24.5 M, 25 M,

25.5 M, 26 M, 26.5 M, 27 M, 27.5 M, 28 M, 28.5 M, 29 M, 29.5 M, 30 M, 30.5 M, 31 M, 31 .5 M, 32 M, 32.5 M, 33 M, 33.5 M, 34 M, 34.5 M, 35 M, 35.5 M, 36 M, 36.5 M, 37 M, 37.5 M, 38 M, 38.5 M, 39 M, 39.5 M, 40 M, 40.5 M, 41 M, 41.5 M, 42 M, 42.5 M, 43 M, 43.5 M, 44 M, 44.5 M, 45 M,

45.5 M, 46 M, 46.5 M, 47 M, 47.5 M, 48 M, 48.5 M, 49 M, 49.5 M, and 50 M.

Processes For the Manufacture of Proton Conducting Membranes

[0055] In one aspect, the disclosure herein provides a process for manufacturing the proton conducting membrane of the present invention, wherein the process comprises the steps of; a. obtaining a dispersion of first nanosheets in a liquid; and b. filtering or tape casting the dispersion from step a. onto a substrate, to form a first microlayer comprising a plurality of first nanosheets, situated on the substrate; c. optionally obtaining a dispersion of second nanosheets in a liquid, and filtering or tape casting the dispersion of second nanosheets in a liquid, onto the first microlayer comprising a plurality of first nanosheets, situated on the substrate from step b., to form a second microlayer comprising a plurality of second nanosheets, adjacent to the first microlayer comprising a plurality of first nanosheets, situated on the substrate; d. optionally repeating step c. one or more times with one or more further dispersions of further nanosheets in a liquid, to thereby sequentially build up additional laminarly arranged stacked microlayers each comprising a plurality of further nanosheets, situated on the substrate; e. drying the product of step b. or step c. or step d., to form a membrane comprising nanosheets, and having 2D-nanochannels formed between the nanosheets; f. removing the membrane produced in step e. from the substrate; and g. incorporating a proton conductor into the 2D-nanochannels of the membrane.

[0056] In some embodiments of the process of the present invention, the, or each, dispersion of nanosheets in a liquid, is a mixed dispersion of nanosheets in a liquid, wherein the mixed dispersion of nanosheets in a liquid comprises nanosheets of more than one substance. In some embodiments, the mixed dispersion of nanosheets in a liquid comprises nanosheets of a substance which is nonconductive to electrons, and nanosheets of a substance which is conductive to protons. In some embodiments, the mixed dispersion of nanosheets in a liquid comprises nanosheets of a substance which is nonconductive to electrons, and nanosheets of a substance which is conductive to electrons. In a preferred embodiment, the mixed dispersion of nanosheets in a liquid comprises nanosheets of boron nitride (BN), and nanosheets of phosphotungstic acid (PWA).

[0057] In some embodiments of the process of the present invention, the, or each, dispersion of nanosheets in a liquid, is obtained by a process of exfoliation, facilitated by milling in the presence of an exfoliating agent selected from the group consisting of high-viscosity amine-functionalized polymers, high-viscosity polyamines, high-viscosity polyesteramides, high-viscosity polyimides, high-viscosity polyesters, high-viscosity polyepoxides, high-viscosity polyethers, high-viscosity polyvinylamines, high-viscosity polyallylamines and high-viscosity polyamidoamines; preferably wherein the exfoliating agent is a high-viscosity polyethylenimine or a high-viscosity polyacrylamide; preferably wherein the milling is facilitated by ball milling.

[0058] In some embodiments of the process of the present invention, the filtering is vacuum assisted filtration.

[0059] In some embodiments of the process of the present invention, the substrate is a polymer substrate.

[0060] In some embodiments of the process of the present invention, step f. of removing the membrane produced in step e. from the substrate is performed by peeling the membrane off the substrate.

[0061] In some embodiments of the process of the present invention, step g. of incorporating a proton conductor into the 2D-nanochannels of the membrane comprises immersing the membrane into a solution of the proton conductor for a period of time sufficient to incorporate the proton conductor into the 2D-nanochannels of the membrane, followed by removing the membrane from the solution and drying the membrane; or, step g. of incorporating a proton conductor into the 2D-nanochannels of the membrane comprises incorporating a proton conductor into the dispersion of first nanosheets in a liquid at step a., prior to filtration or tape casting (step b.), and/or incorporating a proton conductor into the dispersion of second nanosheets in a liquid at step c., prior to filtration or tape casting; and/or incorporating a proton conductor into the one or more further dispersions of further nanosheets in a liquid at step d., prior to filtration or tape casting.

[0062] In some embodiments of the process of the present invention, the process further comprises applying one or more catalysts, to one or more of the microlayers; preferably wherein the one or more catalysts is applied to one or more of the microlayers, via spray coating. [0063] In some embodiments of the process of the present invention, the process further comprises applying one or more electrodes, to one or more of the microlayers; preferably wherein the one or more electrodes is applied to one or more of the microlayers, via spray coating.

[0064] In some preferred embodiments of the process of the present invention, the one or more catalysts, or the one or more electrodes, are independently selected in each instance from the group consisting of; heterogeneous catalysts, noble metal catalysts, transition metal catalysts, alkali metal catalysts, alkaline earth metal catalysts, noble metals, transition metals, alkali metals, alkaline earth metals, main group metals, metallic lanthanides and metallic actinides; preferably wherein the one or more catalysts, or the one or more electrodes, are independently selected in each instance from the group consisting of; Pt/C, PtRu/C, RuC>2, lrC>2, Cu, Ag, Fe, Co, Ni, Mn, and Pd.

General

[0065] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. The invention includes all such variation and modifications. The invention also includes all of the steps, features, formulations and compounds referred to or indicated in the specification, individually or collectively and any and all combinations or any two or more of the steps or features.

[0066] Each document, reference, patent application or patent cited in this text is expressly incorporated herein in their entirety by reference, which means that it should be read and considered by the reader as part of this text. That the document, reference, patent application or patent cited in this text is not repeated in this text is merely for reasons of conciseness.

[0067] Any manufacturer’s instructions, descriptions, product specifications, and product sheets for any products mentioned herein or in any document incorporated by reference herein, are hereby incorporated herein by reference, and may be employed in the practice of the invention.

[0068] The present invention is not to be limited in scope by any of the specific embodiments described herein. These embodiments are intended for the purpose of exemplification only. Functionally equivalent membranes, electrochemical devices and processes are clearly within the scope of the invention as described herein.

[0069] The invention described herein may include one or more ranges of values (eg. Size, volume, concentration, etc). A range of values will be understood to include all values within the range, including the values defining the range, and values adjacent to the range which lead to the same or substantially the same outcome as the values immediately adjacent to that value which defines the boundary to the range. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. Hence “about 80 %” means “about 80 %” and also “80 %”. At the very least, each numerical parameter should be construed in light of the number of significant digits and ordinary rounding approaches.

[0070] Throughout this specification, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. It is also noted that in this disclosure and particularly in the claims and/or paragraphs, terms such as “comprises”, “comprised”, “comprising” and the like can have the meaning attributed to it in U.S. Patent law; e.g., they can mean “includes”, “included”, “including”, and the like; and that terms such as “consisting essentially of’ and “consists essentially of’ have the meaning ascribed to them in U.S. Patent law, e.g., they allow for elements not explicitly recited, but exclude elements that are found in the prior art or that affect a basic or novel characteristic of the invention.

[0071] Other definitions for selected terms used herein may be found within the detailed description of the invention and apply throughout. Unless otherwise defined, all other scientific and technical terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the invention belongs.

[0072] The following examples serve to more fully describe the manner of using the abovedescribed invention, as well as to set forth the best modes contemplated for carrying out various aspects of the invention. It is understood that these methods in no way serve to limit the true scope of this invention, but rather are presented for illustrative purposes.

EXAMPLES

[0073] Further features of the present invention are more fully described in the following nonlimiting Examples. This description is included solely for the purposes of exemplifying the present invention. It should not be understood as a restriction on the broad description of the invention as set out above.

Characterization of materials and membranes

[0074] Transmission electron microscopy (TEM), selected area electron diffraction (SAED), and high-resolution TEM were obtained using an FEI Tecnai G2 T20 operating at an accelerating voltage of 200 kV. Atomic force microscopy (AFM) was performed in tapping mode using a Bruker Dimension Icon with samples deposited on a cleaned mica or silicon substrate. For the AFM sample preparation, a crucial step involved dispersing the nanosheets in ethanol to ensure a uniform suspension, facilitated by ultrasonication. The prepared dispersion was then deposited onto a flat substrate (a silicon wafer or mica disc). During the AFM analysis, imaging was performed in tapping mode. Through scanning a sharp cantilever tip across the sample surface, AFM precisely measures the interaction forces between the tip and the sample, enabling an accurate determination of the nanosheet thickness. Fourier transform infrared spectroscopy (FTIR) was conducted from 4000 to 400 cm'¹ at a resolution of 2 cm'¹ using a PerkinElmer Spectrum 2 FTIR. Thermogravimetric analysis (TGA) was carried out on a TA Instruments SDT 650 with a heating rate of 10°C/min in air. All samples were pre-heated at 100°C for 3 hours to remove moisture. Weight loss under isothermal condition was recorded at 250°C in air following a pre-heating process with a heating rate of 1 °C/min. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were performed using an FEI Quanta 3D with an operating voltage of 10 kV and a spot size of 3, or 5. To prepare the samples for SEM analysis, the membrane samples were fractured in liquid nitrogen and securely mounted onto the sample holder using carbon tape, followed by sputter coating with iridium. The secondary electron image obtained from the Everhart-Thornley detector provides insights into the surface morphology of the sample. Additionally, the integration of an energy-dispersive X-ray spectroscopy (EDS) detector allows for the analysis of the elemental composition on the sample surface. X-ray photoelectron spectroscopy (XPS) was acquired using a Thermo Scientific Nexsa Surface Analysis System with an Al Ka incident radiation and a hemispherical analyzer. X-ray diffraction (XRD) was performed using a Bruker D2 Phaser with a Cu Ka radiation source (30 kV and 10 mA) and a 0.1 mm divergence slit at a step size of 0.02°; or a Rigaku MiniFlex600 diffractometer with Cu Ka radiation (40 kV, 15 mA), employing a step size of 0.02 degrees and a scanning speed of 2 degrees/min. Solid-state ³¹P nuclear magnetic resonance (NMR) spectra of the PA-incorporated membranes were obtained on a Bruker Avance 300 MHz wide-bore spectrometer with 4 mm cross-polarization magic angle spinning (CPMAS) probe using a ZrO2 rotor. The spinning rate was 2 kHz and chemical shifts were referenced relative to 85% H3PO4 at 0 ppm.

Example 1

Synthesis of Graphene Nanosheets

[0075] The graphene nanosheets were prepared by a sticky milling method in accordance with Wang et al (Z. Wang, X. Yan, Q. Hou, et al., Scalable high yield exfoliation for monolayer nanosheets. Nat Commun. 14, 236, 2023), the contents of which are hereby incorporated herein in their entirety. A high viscosity polyethylenimine was used as an exfoliating agent to aid the exfoliation process. In this method, 0.2 g graphite powder was mixed with 0.8 g polyethylenimine in a 100 mL ZrO₂ jar, along with three different sizes of ZrO₂ balls including 40 g <t> 10 mm, 80 g <t> 5 mm, and 8 g <t> 0.1 mm. The exfoliation was performed using a planetary ball mill (ZQM-0.4L, Changsha Mitr Instrument Equipment Co., Ltd) with a rotation speed of 500 rpm for 10 h. To disperse the exfoliated nanosheets in water, 40 mL DI water was loaded into the jar and the mixture was milled at 300 rpm for 30 min. The resulting nanosheets were then washed with a large amount of DI water by vacuum filtration on a Nylon membrane filter (with 0.45 pm pore size and 47 mm diameter) to remove excess polyethylenimine (PEI). The washed monolayer graphene nanosheets were redispersed in water through a 30-min ultrasonication. The final product was obtained from the supernatant after a 30-min centrifugation at 3000 rpm to remove unexfoliated thick graphene plates.

Example 2

Synthesis of Hexaqonal-Boron Nitride Nanosheets

[0076] The production of boron nitride (BN) nanosheets followed a similar method as that used for the monolayer graphene nanosheets, with a few differences in the processing parameters. In this case, a weight ratio of 1 :2 of the pristine BN powder to polyethylenimine was applied, and the main exfoliation process was conducted at a rotation speed of 600 rpm for 15 h. The subsequent purification process was the same as that used for the fabrication of monolayer graphene nanosheets.

Example 3

Characterisation of Nanosheets

[0077] During the ball milling process, micrometer-sized ridges on the surface of the grinding balls initially break down the raw materials into smaller pieces. The PEI molecules absorbed on the ball surface function as a buffer layer, reducing the compression forces and preventing excessive breaking. Then, the layered materials undergo delamination due to the strong shear forces generated from the relative sliding of neighboring milling balls with the aid of the sticky polymer. The as-prepared graphene nanosheets have a lateral size of around 0.76 pm and a thickness of about 0.68 nm, as determined by AFM (figure 1 , A and B). The ultrathin thickness of the graphene nanosheets obtained via the sticky ball milling process suggests that single-layer (monolayer) graphene nanosheets have been successfully produced.

[0078] The atomic-resolution TEM image presents a typical honeycomb arrangement of the carbon atoms in the graphene nanosheet with a minimum atomic distance of around 1 .44 A (figure 2B), which is correlated with the {2110} facets (outer spots) in the selected area electron diffraction (SAED) pattern. The higher diffraction intensity of the inner spots (related to {1 100} facets) compared with that of the outer dots in the SAED pattern reflects that the area belongs to a single-layer graphene nanosheet, which further confirms the successful preparation of monolayer graphene nanosheets (figure 2C).

[0079] The monolayer boron nitride (BN) nanosheets were also synthesized to have an average thickness of approximately 0.82 nm and lateral size of about 0.25 pm (figure 1 , C and D). The atomically thin property of the BN nanosheets is confirmed by the more intensive inner peaks of the corresponding SAED pattern (figure 2D) and the height profile in figure 2F. The high- resolution TEM image in figure 2E shows a minimum boron to nitrogen atomic distance of around 1 .45 A in a hexagonal lattice. The monolayer percentages of the as-produced graphene and BN nanosheets are estimated to be 95% and 85% respectively (figure 1 A, C), confirming the suitability of using them as proton-permeable building blocks for the fabrication of proton exchange membranes.

[0080] The suitability of the prepared nanosheets as materials for high temperature applications was evaluated by investigating their physical and chemical properties. The peaks at around 1600 cm^-1 on the FTIR curves correspond to the N-H bending of polyethylenimine (PEI), indicating the remaining PEI molecules (residual exfoliating agent) attached to the nanosheet surface (figure 3A). The TGA results reveal that the decomposition of PEI starts from 300°C, and the estimated graft amount of PEI on graphene and BN nanosheets is about 7.2 and 5.5 wt% respectively (figure 3B). Moreover, the graphene and BN nanosheets are thermally stable at temperatures up to 630°C and 1000°C, respectively, thereby suggesting their suitability for high temperature applications, such as for High Temperature Proton Exchange Fuel Cells (HT- PEMFCs) and High Temperature Hydrogen Purification membranes such as mixed protonic- electronic conducting (MPEC) membranes.

Example 3

Fabrication and Characterisation of 2D Protonic Multilayer Graphene / Boron Nitride / Phosphoric Acid (GBP) Nanosheet Membranes

[0081] The Graphene/BN (GB) membrane was produced through a two-step vacuum filtration process, followed by immersion in phosphoric acid (PA), as proton conductor as depicted in Scheme 1 , to provide PA doped GB membranes (GBP membranes): Scheme 1 : Fabrication process of the GB membrane via two-step vacuum filtration followed by immersion in PA to produce PA doped GB membranes (GBP membranes).

[0082] Graphene (G) and Hexagonal Boron Nitride (BN) nanosheet powders were separately dispersed in DI waterto produce 0.5 mg/mL nanosheet dispersions respectively. Specific volumes of each dispersion were filtered onto a Nylon membrane filter (with 0.2 pm pore size and 25 mm diameter) successively to fabricate the bilayer GB membranes with different layer thicknesses. The BN-layer thickness was altered from 3 to 80 pm while keeping a constant 41 pm-thick graphene layer. Additionally, the graphene layer thickness was tuned from 15 to 93 pm with a constant 9 um-thick BN layer. After fully drying under ambient conditions, the resulting membranes were peeled off from the polymer substrate.

[0083] The bilayer GB membranes and an m-PBI (poly[2,2’-(m-phenylen)-5,5 - bisbenzimidazole]) membrane, as a comparative example, were immersed in phosphoric acid (PA), as proton conductor, for a specific duration ranging from 0.5 to 24 h, leading to varying levels of acid incorporation. After being taken out from the acid, excess PA was gently wiped away with filter paper. After drying overnight at 80°C, the weight of the PA-doped membrane was measured and recorded as 1/14. The loading of PA was herein calculated using the formula:

PA loading (wt%) = [(W, - W_o)/W] x 100% [Eq uation 1 ]

Where l/l/₀ is the original weight of the membrane.

[0084] The Graphene/BN/Phosphoric acid (GBP) membrane (figure 4F) has a typical bi-layer structure, that comprises, in one of the examples produced, a 9-pm top BN layer to impede electron transport through the membrane and a 41 -pm bottom graphene layer to enhance mechanical strength (figure 4G, 4H). Comparing the cross-sectional morphology of the top (figure 5A) and bottom layers (figure 5B), the bottom graphene layer has a better- aligned laminal structure and a higher packing density due to the larger aspect ratio of the graphene nanosheets (around 1120 compared to 300 for the BN nanosheets). The ordered stacking of the nanosheets benefits the formation of a dense membrane that is suitable for fuel cell applications requiring a low gas crossover and high mechanical strength. The energy-dispersive X-ray (EDX) maps reveal the bi-layer structure with different element compositions, where boron (B) and nitrogen (N) concentrate on the top BN layer and carbon (C) mainly appears on the bottom graphene layer (figure 4I-L). The uniform distribution of phosphor (P) indicates that the phosphoric acid has been evenly incorporated into the membrane (figure 4L). The relative amount of phosphoric acid can be estimated as around 59 wt% from the EDX spectrum (figure 6), which is consistent with the phosphoric acid loading of about 61 wt% obtained from TGA results (figure 7A). [0085] The thermal degradation of phosphoric acid starts at about 165°C in air, which relates to the loss of water and formation of metaphosphoric acid. The following weight loss takes place between 351 °C and 583°C, where the metaphosphoric acid decomposes into polyphosphoric acid. The decomposition accelerates above 583°C owing to the breaking-down of phosphoric acid into phosphoric anhydride. Due to the strong interactions of phosphoric acid and polyethylenimine (PEI) molecules confined in the 2D nanochannels of the GBP membrane, the thermal stabilities of the phosphoric acid, PEI molecules, and graphene were improved with higher main decomposition onset temperatures of 225°C, 437°C, and 802°C respectively. Besides, the GBP membrane exhibits excellent thermal stability when exposed to air at 250°C, with only around 2.1 wt% PA decomposed, being surprisingly lower than that of conventional PBI-PA membranes having 10.3 wt% PA decomposition (figure 7B). The XPS analysis indicates the presence of carbon, nitrogen, phosphor, and oxygen on the graphene side of the membrane (figure 8A). The high-resolution C1s spectra present two distinct peaks at 284.6 and 286.5 eV, relating to the sp²- hybridized carbon of graphene and the C-N-H group of PEI (figure 8B). In the N 1s XPS spectra (figure 8C), compared with the peak at 399.8 eV related to the original amine group (-NH2) of PEI, the peak with a higher binding energy of 401 .9 eV corresponds to the protonated amine group (- NH³⁺) of PEI, which is surrounded by PA within the GBP membrane. This indicates the grafted PEI molecules on graphene nanosheets can assist the adsorption of phosphoric acid via electrostatic interaction and hydrogen bonding. In the P 2p XPS spectra (figure 7C), the peak at around 134.2 eV related to the P-O group of PA shifted towards lower binding energy when the PA was incorporated into the PEI-modified graphene nanosheet membrane, due to the ionic bonds formed between PA and PEI. The minimal difference observed among the peak ratios on the XPS spectra of the GBP membrane before and after heat treatment at 250°C confirms the surprisingly high thermal stability of the GBP membrane (table 1).

Table 1 : weight ratios of different peaks on the XPS spectra for Graphene/BN (GB) membrane, Grahene/BN/Phosphoric acid (GBP) membrane and GBP membrane after treatment at 250 °C in air for 24 hours. (All XPS results are obtained from the graphene-layer side.)

XPS peak GB membrane GBP membrane GBP membrane 250 °C

C1s (sp² carbon) 87.54 31.24 30.44

C1s (C-N-H) 8.77 10.66 10.46

N1 S (-NH₂) 3.70 0.48 0.51

N1s (-NH³⁺) - 2.27 3.22

P2p (P-O) - 48.37 48.34

O1 s (P-O) - 6.98 7.03 [0086] The through-plane proton conductivity of the GBP membranes was determined by a two-probe alternating current (AC) impedance method. The membrane was placed between two carbon papers and clamped with two polar plates. The electrochemical impedance spectroscopy (EIS) was measured at 0.4 V with a frequency range from 1 MHz to 0.1 Hz using a Gamry Interface 5000E potentiostat without humidification. The through-plane proton conductivity (a, mS/cm) was then calculated using the following equation: o = L /RA [Equation 2] where L is the membrane thickness, R is the ohmic resistance obtained from the Nyquist plot, and A is the effective membrane area.

[0087] The in-plane proton conductivity was measured via a four-probe AC impedance method (Scheme 2). The membrane was cut into a size of 30 mm x 5 mm and placed in contact with 4 silver electrodes. The in-plane proton conductivity was similarly calculated using Equation 2, where L represents the fixed distance between four probes, R is the measured membrane resistance, and A is the cross-sectional area of the membrane.

Scheme 2: Illustration showing the set-up for measuring in-plane proton conductivity of the Graphene/BN/PA membrane with a four-probe AC impedance method (W-Working electrode, WS-Working sense, R-Reference electrode, and C-Counter electrode).

[0088] The through-plane proton conductivities of the GBP membrane were measured from 100 to 260°C with various PA loading, BN-layer thickness, and graphene-layer thickness (figure 9A; figure 10A and 10B). Compared with the GB membrane without PA introduced, the GBP membranes present significantly higher proton conductivity (figure 9A), due to the largely reduced resistance for the proton transport in the intersheet spacing. The steep reduction of the energy barrier for proton transport through the membrane after PA incorporation proves fast proton conduction within the PA-filled 2D nanochannel membranes (figure 9D). The intersheet spacing of the GBP membranes increases with higher PA loading, as observed from the peak shifting towards a smaller diffraction angle on the XRD curves (figure 9B, figure 11 and table 2). Table 2: Phosphoric acid (PA) loading, 20 measured from XRD results (figure 9B), and estimated intersheet spacing of nanosheets of Graphene/BN membranes immersed in PA for different periods of time.

■ i Intersheet

Immersion PA loading 20 from time (h) (wt%) XRD (») ^m) ⁹

0 0 26.5 0.34

0.5 25 11.4 0.78

1 43 9.39 0.94

3 60 6.61 1.34

12 67 4.05 2.18

24 78 2.91 3.03

[0089] The proton conductivity first increases with rising acid loading from 25 to 60 wt%, achieving the highest proton conductivity of around 166 mS cm^-1 at 250°C. When the PA loading further increased to 67 wt%, the slightly decreased proton conductivity and higher energy barrier are attributed to the expanded 2D nanochannel size of 3.03 nm. This suggests a 60 wt% PA loading may be approaching optimal to effectively achieve fast nanoconfined proton conduction. The solid ³¹P NMR spectra of PBI/PA exhibit a single resonance at 0.04 ppm, indicating PA in a free state (figure 9C and figure 12A). In the case of GBP membranes, two distinct ³¹P resonance peaks can be observed (figure 12B-F). The left peak corresponds to weakly absorbed PA within the 2D nanochannels, resembling the bulk state. The right peak represents strong absorbed PA, influenced by the ring-current effects of the nanosheets and the interactions between PA and PEI molecules. Increasing PA loading leads to an increase in the normalized peak area of weakly absorbed PA owing to expanded channel size and excessive PA incorporation (figure 13A). Furthermore, the chemical shifts of both peaks increase with higher PA loading, attributable to the diminished shielding effects in larger channels (figure 13B).

[0090] The BN layer of the bilayer membrane blocks electron conduction through the membrane, whilst achieving nanoconfined proton transport. With a 9 pm-thick BN layer, the cross-membrane electron transport was effectively blocked to have an extremely low electrical conductivity of around 1.25 x w⁷ mS cm^-1 (figure 9E). The proton conductivities of the GBP membranes decreased when the BN layer increased in thickness (figure 10A), which corresponds to an increase of energy barrier. Additionally, a linear correlation between the proton conductivity at 250°C and BN-layer thickness was observed. The proton conductivity of the pure 41 pm-thick graphene/PA membrane is estimated to be around 171.8 mS cm^-1 (figure 15A), which is close to that of the GBP membrane with 3 or 9 pm-thick BN layers. These results show that 9 pm may be approaching an optimized BN layer thickness for the GBP membranes. Similarly, the proton conductivities of the GBP membranes also present a decreasing trend with the increased graphene-layer thickness (figure 15B). And the proton conductivity of the pure 9 pm-thick BN/PA membrane can be extrapolated as 186.4 mS cm^-1 (figure 15B), approaching that of the GBP membrane with 15 or 41 pm-thick graphene layer. Considering its high mechanical strength and proton conductivity, the GBP membrane with a 41 pm-thick graphene layer represents a desirable membrane for fuel cell applications. Within the membrane with 50-pm overall thickness, the top 9 um-thick BN layer has slightly smaller resistance to the proton transport than that of the bottom 41 um-thick graphene layer. Compared with other advanced membranes, the 60 wt% PA-doped and 50 pm-thick GBP membrane have outstanding proton conductivity over the temperature range from 100°C to 250°C. Meanwhile, the proton conductivity of the GBP membrane also exhibits excellent long-term stability at 250°C (figure 16), which may be attributed to its high thermal stability.

[0091] The proton conduction through the GBP membrane was further investigated regarding the proton transport mechanisms. Considering the monolayer properties of the graphene and BN nanosheets, the dissociated proton can penetrate the monolayer nanosheets through the vacancies of the electron cloud to realize near-straight transport. Meanwhile, protons can also bypass the nanosheets through the slits of the nanosheet assembly and transport within the 2D nanochannels via hopping along the hydrogen-bond network formed by the confined PA molecules. The through-/in-plane proton conductivities of the GBP membrane were then compared as a function of temperature. The higher in-plane proton conductivity is attributed to the continuous proton transport pathway with less tortuosity (figure 17, A and B). The faster proton conduction along the nanosheet direction of the membrane reveals the proton prefers to transport along the 2D nanochannels, which is proven by the smaller energy barrier relating to the in-plane proton conduction (figure 17C).

[0092] High Temperature Proton Exchange Fuel Cells (HT-PEMFCs) and High Temperature Hydrogen Purification membranes such as mixed protonic-electronic conducting (MPEC) membranes.

Example 4

Assessment of Fuel Cell Performance of Graphene/BN/Phosphoric acid (GBP) Membranes and Their Application to High Temperature Proton Exchange Fuel Cells (HT-PEMFCs)

[0093] A GBP membrane in accordance with the present invention, comprising 60 wt% PA loading and 50-pm thickness was made into membrane electrolyte assembly (MEA) to test its hydrogen fuel cell performance by using Pt/C as electrocatalysts for both electrodes (figure 18A). The maximum power density increases as the operating temperature increases from 160°C to 250°C, due to the reduced cell resistance caused by enhanced proton conductivity at elevated temperatures and improved electrocatalytic activity for both electrodes (figure 18, B and C). The cell can achieve an outstanding peak power density of around 101 1 mW cm^-2 at 250°C (table 3), which is three times higher than that of a commercial PBI/PA membrane, attributable to the higher proton conductivity of membranes of the present invention (figure 19, A and B).

Table 3: Summary of proton conductivity and H₂/O₂ fuel cell performance for the Graphene/BN/PA (GBP) membrane in accordance with the present invention compared to other advanced membranes. Test Proton Power

Membranes Binder . . temperature conductivity density

(mg cm ) (°c) (mS/cm) (mW/cm²)

Polyether/PA/PBI PBI 0.6-0.7 170 120 320

PDA-PA/PBI PDA-PBI 0.6 160 83 460

SnAIP₂O₇/PA/PBI BASF GDE 1 200 32 440

QAPOH/PA QASOH 0.6 160 155 738

PA/PIM PTFE 0.5 160 143 815

PA/PIM PTFE 0.5 200 133 647

BPO PA/PTFE PTFE 0.6 250 30 290

SiO₂/PA/PBI PTFE 1 250 29 289

HPW/PA/PES/PVP PVP 0.35 160 144 416

HPW/MCM-41 Nation 0.5 150 45 90

PA-TPP/Nafion QASOH 0.5-0.6 240 79 868

GBP PTFE 0.7 160 125 821

GBP PTFE 0.7 200 145 919

GBP PTFE 0.7 250 166 101 1

[0094] Additionally, the GBP membrane of the present invention also presents excellent long-term operating stability at 250°C, maintaining stable power output at a constant 400 mA/cm² current density for around 150 hours with a low voltage decay rate of 0.19 mV/h (figure 18D). The high stability over an extended period demonstrates the robustness and durability of the GBP membrane under high-temperature conditions. The ability to sustain high current density with minimal degradation is crucial for the practical implementation of fuel cells and other electrochemical devices. The long-term stability of the GBP membrane further solidifies its potential as a reliable and efficient solution for high-temperature applications, confirming its suitability for long-term operation in demanding and high temperature environments.

[0095] Considering the asymmetry of the GBP membrane, the fuel cell performance with H₂ flowing on the graphene and BN sides were also tested respectively (figure 20). The relatively small difference in peak power density indicates the asymmetric structure has negligible effect on the cell performance. Despite the different electronic conductivity and proton affinity of graphene and BN, they can create similar 2D channels that confine phosphoric acid, facilitating effective proton transport and gas blocking. Besides, the reactions primarily take place at the three-phase interphase involving catalysts, phosphoric acid, and reacting gases. The GBP membrane with the asymmetric structure still offers a sufficient surface area for these reactions, resulting in comparable performance when switching the reacting gases on both sides of the cell. These factors could explain the minimal difference in polarization plots and highlight the robustness of the GBP membrane design. Compared with the cells using conventional polymer and ceramicbased PEMs, the fuel cell constructed with the GBP membrane exhibits significantly higher power density, particularly at elevated temperatures (figure 18E). The superior performance observed in GBP membrane-assembled cell is attributable to the efficient proton conduction and high- temperature stability enabled by nanoconfinement.

[0096] The application of GBP membranes in direct methanol fuel cells (DMFCs) was also explored (figure 21 A). DMFCs using methanol from biomass, syngas, or renewables are gaining popularity in clean shipping due to their advantages in transport and storage compared to hydrogen. DMFCs also show great application potential in portable devices due to the high energy density of methanol. Unfortunately, due to the methanol crossover issues of conventional Nation membranes, only highly diluted methanol is applicable to conventional DMFCs, leading to poor practical energy density. In addition, the conventional DMFCs suffer from low power density and CO electrode poisoning issues. Due to the permeability of BN, graphene and H3PO4 only to protons, in principle methanol crossover is fully avoided in GBP membranes with nanoconfined proton conductors in 2D nanochannels. Indeed, the GBP membrane-based DMFC exhibits an impressive peak power density of 502 mW cm^-2 at 250°C when supplied with a high concentration of 16 M methanol as fuel and oxygen for the cathode (figure 21 B, table 4).

Table 4: Summary of direct methanol fuel cell performance for the Graphene/BN/PA membrane and other advanced membranes.

Anode Methanol _T .

.. . C _at ..hode ' concent .ra . „ Test . P . ower

Membranes . . . .. . temperature d .. cata yst tion and . e ..n..sity

■ loading f.low rate ( ' C) ' ( 'mW/cm²) ' „ Anode Methan .o _T .

.. . Catho Test Power

Membranes . . de . c .o. ncentr .a t . „ . . .. cata yst tion and emperature . de ..n..sity

1 loading c filow ra *te ( ' C) ' ( 'mW/cm²) '

2 mg/cm² 40

Graphene/Na wt% PtRu/C | 2 M, 2 _7n fion 2 mg/cm² 40 mL/min wt% Pt/C

2 mg/cm² 60

Fullerene/Naf wt% PtRu/C | 2 M, 2 ion 2 mg/cm² 40 mL/min

Zeolite wt% PtRu/C | 2 M, 2 _7n . ,._q

4A/SPEEK 2 mg/cm² 40 mL/min ^{ZU 1 by} wt% Pt/C

4 mg/cm² 50 110 39

HPW/MCM- wt% PtRu/C | 2 M, 1 _{130 65}

41 1 mg/cm² 50 mL/min wt% Pt/C ^{150 90}

4 mg/cm² 50 80 43

HPW/meso- wt% PtRu/C | 2 M, 0.5 120 91 silica 2 mg/cm² 50 mL/min 150 113 wt% Pt/C 160 134

3 mg/cm² 50 170 167

PA/meso- wt% PtRu/C | 2 M, 2 200 200 silica 2 mg/cm² 50 mL/min wt% Pt/C ^{220 193}

160 108

200 114 220 140

PA/PBI/SiO2 230 162 ^{240 185}

250 212

260 237

160 173

1 mg/cm² 50 ₂00 231

Graphene/BN wt% PtRu/C | 16 M 1

/PA

250 502

[0097] With rising temperature, the increase in peak power density can be attributed to the concurrent reduction in both ohmic and polarization resistance, coupled with an increase in open circuit potential (figure 21 C and figure 22). A significant temperature transition point occurs at approximately 200°C, leading to a remarkable increase in peak power density (figure 21 H). This improvement can be ascribed to greatly enhanced kinetics for methanol oxidation at the anode, as evidenced by a substantial increase in open circuit potential and a reduction in polarization resistance. Methanol crossover is indicated by the limit current density resulting from methanol permeating from the anode to the cathode under an applied voltage. As expected, owing to the well-aligned 2D nanochannels and dimension stability, the GBP membrane displays significantly lower methanol crossover current density (3.1 - 8.4 mA/cm²) compared to the PBI/PA membrane (47 - 102 mA/cm²) in the temperature range from 160°C to 250°C (figure 21 D and figure 23). In addition to its high proton conductivity, the GBP membrane’s exceptional resistance to methanol crossover preserves a high open circuit potential, resulting in superior DMFC performance compared to the PBI/PA membrane at elevated temperatures (figure 24). Due to the strong methanol impermeability of the membrane, raising the methanol concentration from 5 M to 20 M has minimal impact on its open circuit voltage. The optimal observed performance was at 16 M (with a methanol molar ratio of 0.45), which can be attributed to the 1 :1 reaction of methanol and water catalyzed by PtRu/C at the anode. The operational capability of the cells on high concentration methanol solutions brings a great advantage for portable applications, such as power sources for drones due to obviously increased energy density.

[0098] Air-breathing DMFCs show great potential in compact systems such as drones and motorcycles, streamlining design and eliminating the need for oxygen purification and storage components. The performance of the GBP membrane-based DMFC supplied with air was also investigated. The highest power density observed was 310 mW/cm² at 250°C due to a slight increase in polarization resistance as compared to that with pure oxygen as the cathode atmosphere (figure 21 , E and F). Additionally, the GBP membrane based DMFC, operated with 16 M methanol and oxygen, demonstrated favorable operating stability with a low voltage decay rate of around 0.42 mV/h at 250°C and 400 mA/cm², owing to the membrane’s excellent thermal and dimensional stability (figure 21 G). Comparing its performance with other advanced protonexchange membrane-based DMFCs, the GBP membrane-based DMFC in accordance with the present invention stands out with the highest reported power density. This exceptional performance can be attributed to the combined advantages of significantly reduced methanol crossover and improved proton conductivity at elevated temperatures. These findings highlight the potential of the GBP membranes as a promising alternative for high-temperature applications, surpassing the performance limitations of conventional proton-conducting membranes. More broadly, they open pathways for developing proton conducting membranes with high proton conductivity and thermal stability, suitable for use in high-temperature electrochemical devices.

Example 5

Fabrication and Characterisation of MPEC Hydrogen Permeation Membranes [0099] The graphene nanosheets / phosphoric acid (GP) membranes were fabricated through vacuum filtration and subsequent immersion using the same general process as that described in Scheme 1 . Graphene nanosheet powders were dispersed in DI water to create nanosheet dispersions with a concentration of 0.5 mg/mL. Controlled volumes of these dispersions were sequentially filtered onto a 0.2 pm pore size, 25 mm diameter Nylon membrane filter to create graphene membranes with varying layer thicknesses. After complete drying under ambient conditions, the resulting membranes were peeled from the polymer substrate. Subsequently, the graphene membranes were immersed in phosphoric acid, as proton conductor, for specific durations ranging from 0.5 to 24 hours, leading to varying levels of acid incorporation. Any excess phosphoric acid was gently removed with filter paper post-acid treatment. Following overnight drying at 80°C, the weight of the PA-doped membrane was measured, enabling the calculation of loaded phosphoric acid by comparing the weight before and after acid incorporation. Finally, both sides of the GP membrane were spray coated with a specific quantity of Pt/C catalyst on a hotplate at 100°C.

[00100] The combined electron and proton transport resistance in the GP membranes was determined using electrochemical impedance spectroscopy (EIS). The membrane was placed between two conductive carbon papers (AvCarb MGL 190) and held together by bipolar plates similar to the set-up for the fuel cell tests. The EIS was measured using a Gamry Interface 5000E potentiostat at 10 mV with a frequency range from 1 MHz to 1 Hz across a temperature range spanning from 20°C to 250°C. The conductivity (a) is calculated via Equation 3; o = L /SR [Equation 3] where L is the membrane thickness (cm), S is the effective membrane area (cm²) and R is the measured resistance from EIS. Besides, considering the temperature-dependence of the conductivity, the corresponding activation energy (E_a) is estimated from the slope of the curve on the Arrhenius plot according to Equation 4; o = A exp(E_a /RT) [Equation 4] where A is a pre-exponential factor, R is the gas constant (8.314 J mol^-1 K^-1) and T is the testing temperature (K).

[00101 ] The single gas permeance of the GP membranes was assessed using a custom-built permeation apparatus employing the constant-volume/variable-pressure method. The flat membrane was affixed to a porous stainless-steel sample holder with epoxy resin (Supreme 17HTND-2, MasterBond). The serving temperature of the epoxy is up to 288°C. This holder was placed inside a Pyrex tube with the feed gas flowing, while the opposite end was connected to a pressure transducer (MKS 628B Baratron) and a vacuum pump (Scheme 3). Tube fumace

Scheme 3: Gas permeation test set-up.

[00102] Individual permeance measurements for gases such as He, H2, and CO2 were conducted across a temperature range of 20 to 250°C, maintaining a feed gas pressure of 1 bar. To establish a stable permeation state, the permeate side was subjected to vacuum conditions for approximately 30 minutes for each gas.

[00103] The microstructure of the catalyst-coated graphene nanosheet/phosphoric acid (CGP) membrane was thoroughly examined using SEM and EDX. In figure 26A, the CGP membrane displays an 8 pm-thick graphene nanosheet (GP) layer in the middle, flanked by two 4 pm-thick catalyst layers on both sides. Notably, the catalyst layers exhibit a relatively high degree of porosity, as depicted in figure 26B, which enhances gas transport to the membrane's surface, facilitating subsequent conversion processes. In contrast, due to their high aspect ratio, monolayer graphene nanosheets tend to form well-aligned laminates when incorporated with phosphoric acid, effectively impeding gas transport through the composite membrane, as illustrated in figure 26C. Additionally, figure 26E demonstrates the uniform distribution of phosphoric acid within the GP membrane. Based on the EDX spectrum, the estimated acid loading is approximately 59 wt% within the GP membrane. These findings confirm that the microstructure of the CGP membrane is well-suited for application as a membrane reactor for hydrogen purification.

[00104] The physicochemical properties of the GP membrane were comprehensively characterized through XRD and FTIR analyses. In Figure 27A, both pristine graphite and the graphene membrane exhibited a distinctive peak at 26.7°, corresponding to an interlayer distance of 3.33 A. However, with the incorporation of phosphoric acid (PA), the interlayer spacing in the graphene expanded to 1 .33 nm, as indicated by the prominent peak at 6.6°. This shift in the XRD peak on the GP membrane indicates the creation of an ordered structure during the infusion of PA. In Figure 27B, the FTIR curve of PEI and GP membrane displayed a peak at 1640 cm^-1, associated with the N-H bond stretch, signifying the functionalization of graphene nanosheets with PEI through sticky ball milling. Additional peaks at 1454 and 1275 cm^-1 on the FTIR curves of PA and GP membrane indicated the stretching of the P-OH and P=O bonds of PA molecules. Consequently, within the GP membrane, PA molecules could have strong interactions with the PEI molecules, driven by electrostatic forces and hydrogen bonding. Without wishing to be bound by theory, the present inventors believe this interaction contributed to the immobilization of PA within the 2D nanochannels formed by the stacking of the graphene nanosheets.

[00105] The thermal characteristics of the materials and membranes were assessed through TGA in air. As depicted in Figure 28A, the graphene nanosheets and PEI demonstrate considerable thermal stability, remaining intact at temperatures up to 300°C and 630°C, respectively. In contrast, the decomposition of phosphoric acid initiates at 165°C, resulting in the formation of metaphosphoric acid. The confinement of phosphoric acid and PEI molecules within the 2D nanochannels of the GP membranes exhibits a substantial improvement in thermal stability. This is evident in the higher decomposition onset temperatures of phosphoric acid (225°C), PEI molecules (437°C), and graphene (802°C). Besides, the amount of PEI remaining on the prepared graphene nanosheets is estimated at approximately 7.2 wt%. The loading of phosphoric acid in the fabricated GP membrane is evaluated to be roughly 56 wt%, which closely aligns with the values derived from EDX analysis. The thermal stability of the GP membrane, as illustrated in Figure 28B, was further validated by observing a minimal mass reduction of approximately 0.94 wt% during a 25-hour test at 250°C in an air atmosphere. This surprising, unexpected and outstanding thermal stability can be attributed to the strong nanoconfinement effect of phosphoric acid within the 2D nanochannels and the robust interactions between phosphoric acid and PEI molecules. These findings confirm the suitability of the GP membrane for high-temperature hydrogen separation applications.

[00106] The mixed proton electron conductivity (MPEC) test of the GP membrane was performed across a temperature range spanning from 20°C to 250°C. As depicted in figure 29A, the conductivity exhibited a substantial increase with the elevation of temperature, attributable to the rising mobility of protons and electrons at highertemperatures. The peak conductivity of about 308 mS/cm was achieved at 250°C. The overall resistance during the MPEC process through the GP membrane can be represented as the electron-transport and proton-transport resistances in parallel. Notably, the electrical resistance of the graphene membrane, before phosphoric acid incorporation, was approximately 0.01 Q cm^-2 at room temperature, closely aligning with the overall resistance of the GP membrane (0.009 Q cm^-2) at the same temperature. This observation implies that the mixed conductivity of the GP membrane is predominantly limited by its proton conductivity. Additionally, figure 29B reveals an estimated activation energy of about 6.88 kJ/mol, significantly lower than the value reported in existing literature of 32.48 kJ/mol (in, Y. et al. Elevated-temperature H2 separation using a dense electron and proton mixed conducting polybenzimidazole-based membrane with 2D sulfonated graphene. Green Chem. 23, 3374-3385, 2021). This remarkably surprising and unexpected mixed conductivity may be primarily ascribed to the enhanced proton conductivity within the GP membrane, facilitated by the creation of rapid and multi-scale proton transport pathways based on proton-permeable monolayer graphene nanosheets and the nanoconfined phosphoric acid.

[00107] The gas separation performance of the GP membrane was analyzed through singlegas permeation tests conducted across a temperature range from 20°C to 250°C. As presented in figure 30, the GP membrane exhibited nearly impermeable behaviour to helium (He) and carbon dioxide (CO₂) gases, indicating its dense and stable structure maintained throughout the entire temperature testing range. In line with the Mixed Proton-Electron Conduction (MPEC) mechanism, only hydrogen gas could traverse the membrane via hydrogen-proton conversion at the electrode-membrane interfaces and associated electron-proton conduction within the membrane. Consequently, the GP membrane surprisingly and unexpectedly possesses nearly 100 % H2/CO2 selectivity. Furthermore, with rising temperature, the hydrogen permeance experiences a significant increase, ranging from 1 to 69 GPU, attributable to the improved mixed conductivity at elevated temperatures. When compared to advanced hydrogen-separation membranes based on size-sieving (as summarized in Table 1), the GP membrane presents exceptional selectivity and high hydrogen permeance. Notably, it also surpasses conventional MPEC-based counterparts at different temperatures, offering around four times higher hydrogen permeance.

Table 5: Performance comparison of the GP membrane with other advanced membranes for H2/CO2 separation.

.. . .. . Testing Hydrogen „ . .. ..

Membrane Mechanism . . ³ Selectivity temperature ( C) permeance (GPU) ³

GP MPEC 250 69

GP MPEC 200 41

GP MPEC 160 26

PBI-SG MPEC 300 22

PBI-SG MPEC 240 13

PBI-SG MPEC 180 6.9

PBI-PA Size-sieving 150 0.01 34

PIM/PBI Size-sieving 250 41 24

PBI/ZIF-8 Size-sieving 150 0.2 16

PBI/PPC Size-sieving 350 0.15 14

« means nearly no CO2 permeance

[00108] In one aspect, the present invention provides a membrane reactor using a graphene nanosheets/phosphoric acid (GP) membrane to achieve a nearly 100% H₂/CO₂ selectivity based on the mixed proton-electron conducting mechanism. Fabricated through a facile process of vacuum filtration and immersion, the GP membrane demonstrates exceptional mixed protonelectron conductivity, with a peak conductivity of 308 mS/cm at 250°C. This remarkable mixed conductivity is primarily attributed to the high electron conductivity of the graphene nanosheets and multi-scale proton conducting pathways formed by proton-permeable monolayer graphene nanosheets and a nanoconfined proton conductor in the form of phosphoric acid. After spraycoating with Pt/C as catalysts on both sides, the GP membrane-based membrane reactor achieves an exceptional hydrogen permeance of 61 GPU at 250°C. Additionally, the GP membrane displays impressive thermal stability, owing to the strong nanoconfinement effect within its 2D nanochannels. These accomplishments represent a significant step forward in the development of advanced membranes for high-purity hydrogen production and underline the promising future of hydrogen energy technology.

Example 6

Synthesis of nanosheets from a solid inorganic proton conductor - phosphotungstic acid

[00109] Phosphotungstic acid (PWA) is a solid acid with high proton conductivity and thermal stability up to 450°C, making it promising for high-temperature proton-conducting membranes. PWA nanosheets can be synthesized via a simple hydrothermal reaction. Phosphotungstic acid (PWA) nanosheets were prepared via a hydrothermal reaction following the previously reported protocol of Yang, M. et al. (Roll-to-roll fabricated polymer composites filled with subnanosheets exhibiting high energy density and cyclic stability at 200 °C. Nat Energy 9, 143-153, 2024). First, a homogeneous solution was formed by mixing 10 mL tetralin and 3 mmol aliphatic amine in a 40 mL Teflon autoclave. While stirring vigorously, a solution of 0.5 mmol H₃PO₄ and 100 mg H3PW12O40 in 1 mL ethanol was added. After stirring for 10 min, the autoclave was sealed and heated at 180°C for 48 h. Once cooled to room temperature, the nanosheets settled at the bottom were dispersed in 8 mL of cyclohexane and centrifuged at 10,000 rpm for 5 min. This dispersioncentrifugation process was repeated three times, after which the nanosheets were dried at 50°C, ground into a fine powder, and stored for further use.

[00110] The prepared PWA nanosheets have a lateral size of approximately 1.2 pm and a thickness of about 1 .3 nm, as determined from the AFM results in Figure 31 . Due to their relatively high aspect ratio, the PWA nanosheets are favourable for facilitating the formation of nanosheet membranes with a well-aligned lamellar structure.

Example 7

Fabrication of PWA/BN composite membranes

[00111 ] During synthesis of PWA nanosheets, dehydrated phosphotungstic acid clusters and phosphoric acid self-assemble into 2D nanosheets, with oleylamine acting as a surfactant. However, thermogravimetric analysis (TGA) revealed that the grafted surfactant molecules begin to volatilize around 210 °C, compromising the nanosheets' structural integrity (Figure 32G). To address this problem with the physicochemical stability of PWA nanosheets, instead of using PWA nanosheets alone to form a freestanding membrane, the present inventors have incorporated PWA nanosheets with BN nanosheets to create a nanocomposite membrane.

[00112] In a first method, Phosphotungstic acid boron nitride (PWA/BN) nanosheet membranes were fabricated using a vacuum filtration process. First, a specific amount of PWA nanosheets was dispersed into a 0.5 mg/mL BN nanosheet suspension to ensure a homogeneous mixture. Then, 15 mL of the mixed dispersion was sequentially filtered through a 0.2 pm-pore- size Nylon membrane filter with a 25 mm diameter, forming a uniform membrane structure. After filtration, the membrane was allowed to dry completely under ambient conditions, ensuring structural integrity. Finally, the dried membrane was carefully peeled off from the polymer substrate, yielding a free-standing PWA/BN composite membrane suitable for further application.

[00113] Alternatively, in a second method, PWA nanosheets and BN nanosheets may be separately dispersed in DI water to produce 0.5 mg/mL nanosheet dispersions respectively. Specific volumes of each dispersion may then be filtered onto a Nylon membrane filter (with 0.2 pm pore size and 25 mm diameter) sequentially in orderto fabricate multilayer membranes having alternating BN and PWA layers with different layer thicknesses, tunable according to the volume of dispersion filtered at each step. After fully drying under ambient conditions, the resulting membranes may be peeled off from the polymer substrate, to provide PWA/BN membranes with alternating BN and PWA layers in accordance with Scheme 4: Phosphotungstic - BN nanosheet

Scheme 4: Schematic illustrating the structure of the PWA/BN membrane

[00114] The PWA/BN membrane obtained from the first method was fabricated with a thickness of approximately 60 pm (Figure 32A). The uniform distribution of boron, nitrogen, oxygen, tungsten, and phosphorus in the EDX maps (Figure 32B-F) confirms the homogeneous mixing of PWA and BN nanosheets. TGA results show that the thermal decomposition of surfactant molecules grafted onto PWA nanosheets begins at approximately 213 °C (Figure 32G). Meanwhile, the primary components of the PWA/BN nanosheet membrane remain surprisingly thermally stable up to 300 °C, making it suitable for high-temperature applications. Additionally, the PWA nanosheet content in the membrane is estimated to be around 5 wt%.

[00115] Based on nitrogen adsorption-desorption isotherms, the PWA/BN membrane exhibits a pore size of around 2.2 nm (Figure 32H), which provides a nanoconfinement effect for PWA nanosheets and their chemisorbed water at elevated temperatures. The proton conductivity of the PWA/BN nanosheet membrane was measured at various temperatures under 3% relative humidity (RH), showing a steady increase and reaching approximately 34.4 mS/cm at 260 °C (Figure 33A). Notably, in a 24-hour stability test, the membrane retained about 97% of its initial proton conductivity, demonstrating excellent stability (Figure 33B).

[00116] Confined within the 2D nanochannels formed by BN nanosheets, PWA nanosheets are both structurally reinforced and physicochemically stabilized at elevated temperatures, mitigating the effects of surfactant decomposition observed without nanoconfinement. Additionally, due to their strong affinity for water, PWA nanosheets in the composite membrane are adapted to chemisorb water molecules from, for example, a feed water or steam during water electrolysis at elevated temperatures. This ability to chemisorb water helps form continuous hydrogen-bonded networks, creating efficient pathways for proton transport. As a result, the PWA/BN membrane is well-suited for medium-temperature water electrolysis, where reliable proton conduction and thermal stability are essential for improved water electrolysis efficiency and durability.

Example 8

Application of Graphene/BN/Phosphoric acid (GBP) membranes to steam electrolysis

[00117] The Graphene/BN/Phosphoric acid (GBP) membranes produced in accordance with Example 3 were assessed for their steam electrolysis performance using a single cell with a 1 cm² effective area. Dry N₂ (40 mL/min) under ambient pressure was utilized to transport steam generated in a water vaporizer with varying relative humidity to the anode, while N₂ (40 mL/min) under ambient pressure flowed on the cathode side (Scheme 5). Current-voltage (IV) curves were obtained under different operating conditions through linear sweep voltammetry in the voltage range of 0-2 V with a 0.05 V step size. Electrochemical Impedance Spectroscopy (EIS) was conducted at 1 .6 V over a frequency range from 100 kHz to 1 Hz at different temperatures to evaluate ohmic and polarization resistance. Single-cell durability testing was performed at a constant current density of 0.2 mA cm^-2 at 250 °C.

Scheme 5: Schematic showing the set-up for the steam electrolysis test [00118] With the optimized steam flow rate and Oxygen Evolution Reaction (OER) catalyst, the GBP membrane-based electrolyzer was then assessed at different temperatures to investigate the impact of operating temperature on the electrolysis performance. In Figure 34A, the electrolysis performance improved with increasing temperature from 160 to 250 °C, reflected in higher achievable current density at the same applied voltage. The enhanced performance can be attributed to two key factors. Firstly, the improved proton conductivity, as indicated by the reduced ohmic resistance (decreasing from 0.12 to 0.06 Q cm²) of the GBP membrane in Figure 34B, highlights its potential for medium-temperature water electrolysis. Additionally, the improved OER kinetics, evident from the decreased polarization resistance (reducing from 1.25 to 0.44 Q cm²), suggests the importance of elevating the operating temperature to above 100 °C for optimal performance. The peak current density of about 2.26 A cm^-2 can be achieved at 2 V and 250 °C. The operating durability of the electrolyzer at 200 mA cm^-2 and 250 °C was examined by continuously measuring the cell voltage change over 21 hours. In Figure 34C, minimal voltage vibration was observed with an increasing rate of around 9.96 mV/h and a slight fluctuation in corresponding efficiency (maintained above 86%) relative to the thermal-neutral voltage of 1 .29 V, indicating excellent operating stability of the electrolyzer. Besides, the GBP-membrane-based water electrolyzer exhibits outstanding performance at elevated temperatures, achieving higher current density at relatively low applied voltage compared to the state-of-the-art mediumtemperature water electrolyzers in Figure 34D. These results underscore the GBP membrane's potential for application to medium-temperature water electrolysis, attributed to its exceptional proton conductivity and thermal stability at elevated temperatures.

[00119] Non-noble metal catalysts have attracted attention as cost-effective and environmentally friendly alternatives to noble metals for the OER in medium-temperature water electrolysis. These catalysts offer advantages such as high electrical conductivity, structural tunability, and competitive electrocatalytic performance. To harness the benefits of improved OER kinetics at elevated temperatures, a single-atom catalyst known as Fe-NSC, characterized by atomically dispersed iron atoms with precise sulfur modifications at the periphery, was synthesized in accordance with the protocols of Jia, Y. et al. (“Atomically Dispersed Fe-N4 Modified with Precisely Located S for Highly Efficient Oxygen Reduction.” Nano-Micro Lett. 12, 1 16, 2020) and employed in the GBP membrane-based water electrolysis system due to its high thermal stability and catalytic activity in acidic environments. The sulfur modification played a pivotal role in adjusting the electronic structure of iron-nitrogen complexes (Fe-N₄ moiety), thereby impacting reactant and intermediate absorption/desorption characteristics at the iron center. The Fe-NSC catalysts exhibited a platelet-like morphology of approximately 20 nm in size, as presented in Figure 35A. Additionally, the XRD analysis in Figure 35B indicated a crystal structure similar to graphite, suggesting a predominant graphite-like phase. In Figure 35C, a comparison of catalytic activity in strong acid media revealed that the Fe-NSC displayed a higher current density per pm of metal, implying superior catalytic activity at the active sites compared to the commercial lrO₂ catalyst.

[00120] To assess the efficacy of the non-noble metal catalyst Fe-NSC, it was employed as the OER catalyst on the anode, with Pt/C serving as the Hydrogen Evolution Reaction (HER) catalyst on the cathode in the GBP membrane-based water electrolyzer. In Figure 35D, the electrolysis performance improved as the temperature rose, attributed to enhanced proton conductivity of the GBP membrane and accelerated reaction kinetics. The highest current density, reaching approximately 440 mA cm'², was achieved at 2 V and 250 °C. While this performance falls short of that attained with lrO₂, it is still considered acceptable, particularly given the relatively low loading of total single atoms (about 8.3 at%). As displayed in Figure 35E, the increase in temperature from 160 to 250 °C corresponded to a reduction in polarization resistance related to OER, from 4.7 to 2.1 Q cm², indicating high thermal stability and temperature-dependent catalytic activity. The operational durability of the electrolyzer was also evaluated by maintaining its operation at 100 mA cm^-2 and 250 °C for 20 hours (Figure 35F). The cell voltage exhibited a gradual increase at a rate of approximately 16 mV/h, and the corresponding efficiency experienced a slight reduction from 88 to 72 %. These results demonstrate the successful application of non-noble metal catalysts for medium-temperature water electrolysis.

CLAUSES

[00121 ] Additional embodiments are also described by the following enumerated clauses. Any of the following embodiments in combination with any applicable embodiments described in the preceding sections of the specification, or the claims of this patent application, are also contemplated.

Clause 1 . A proton conducting membrane comprising nanosheets, and 2D-nanochannels formed between the nanosheets, wherein the 2D-nanochannels comprise a proton conductor confined within the 2D-nanochannels, and wherein the proton conductor is physically and chemically stable at temperatures of 150°C and above.

Clause 2. A proton conducting membrane comprising nanosheets, and 2D-nanochannels formed between the nanosheets, wherein the 2D-nanochannels comprise an inorganic proton conductor confined within the 2D-nanochannels.

Clause 3. The proton conducting membrane of any preceding clause, comprising a plurality of microlayers, wherein at least one microlayer comprises a plurality of nanosheets.

Clause 4. The proton conducting membrane of any preceding clause, comprising boron nitride nanosheets. Clause 5. The proton conducting membrane of any preceding clause, comprising graphene nanosheets.

Clause 6. The proton conducting membrane of any preceding clause, comprising boron nitride nanosheets and graphene nanosheets.

Clause 7. The proton conducting membrane of any preceding clause, comprising;

(i) a first microlayer and a second microlayer, wherein the first microlayer is nonconductive to electrons, and the second microlayer is conductive to electrons; preferably wherein the first microlayer comprises a plurality of boron nitride nanosheets, and the second microlayer comprises a plurality of graphene nanosheets; or

(ii) a first microlayer, a second microlayer and a third microlayer, wherein the first microlayer comprises a plurality of nanosheets of a first substance, the second microlayer comprises a plurality of nanosheets of a second substance which is different to the first substance, and the third microlayer comprises a plurality of nanosheets of a third substance which is different to the second substance; optionally wherein the substance of the first microlayer and the substance of the third microlayer are the same; preferably wherein the second microlayer comprises a plurality of boron nitride nanosheets; most preferably wherein the first microlayer and/or the third microlayer each comprise a plurality of graphene nanosheets; or

(iii) a first microlayer and a second microlayer, wherein the first microlayer is nonconductive to electrons, and the second microlayer is conductive to protons; preferably wherein the first microlayer comprises a plurality of boron nitride nanosheets, and the second microlayer comprises a plurality of phosphotungstic acid (PWA) nanosheets; or

(iv) a first microlayer, a second microlayer and a third microlayer, wherein the first microlayer comprises a plurality of nanosheets of a first substance, the second microlayer comprises a plurality of nanosheets of a second substance which is different to the first substance, and the third microlayer comprises a plurality of nanosheets of a third substance which is different to the second substance; optionally wherein the substance of the first microlayer and the substance of the third microlayer are the same; preferably wherein the second microlayer comprises a plurality of phosphotungstic acid (PWA) nanosheets; most preferably wherein the first microlayer and/or the third microlayer each comprise a plurality of boron nitride nanosheets nanosheets. Clause 8. The proton conducting membrane of any preceding clause, wherein the proton conductor is selected from the group(s) consisting of; solid acids, inorganic acids, protonic ceramics, protic inorganic polymers, protic ionic plastic crystals, protic organic ionic plastic crystals (POIPCs), zirconate based perovskites, rare-earth ortho-niobates, rare-earth ortho- tantalates, rare-earth tungstates, heteropolyoxometallates, silico-aluminates, transition metal oxides, zeolites, and protonic Metal-Organic Frameworks (MOFs), including nanosheets comprising any of the aforementioned proton conductors.

Clause 9. The proton conducting membrane of any preceding clause, wherein the proton conductor is selected from the group consisting of; phosphoric acid, sulfuric acid, boric acid, perchloric acid, phosphotungstic acid (PWA), cesium hydrogen sulfate, aluminium phosphate, silico-aluminophosphate, sulphated zirconia, titanium phosphate, zirconia, niobium phosphate, niobic acid, 1 ,2,4-triazolium perfluorobutanesulfonate, imidazolium methanesulfonate, acceptor doped SrCeO₃, acceptor doped BaCeO₃, and acceptor doped BaZrO₃, including nanosheets comprising any of the aforementioned proton conductors.

Clause 10. The proton conducting membrane of any preceding clause, wherein the proton conducting membrane further comprises a residual exfoliating agent.

Clause 1 1. The proton conducting membrane of any preceding clause, wherein the proton conducting membrane further comprises a residual exfoliating agent selected from the group consisting of high-viscosity amine-functionalized polymers, high-viscosity polyamines, high-viscosity polyesteramides, high-viscosity polyimides, high-viscosity polyesters, high-viscosity polyepoxides, high-viscosity polyethers, high-viscosity polyvinylamines, high-viscosity polyallylamines and high-viscosity polyamidoamines; preferably wherein the residual exfoliating agent is a high-viscosity polyethylenimine or a high-viscosity polyacrylamide.

Clause 12. The proton conducting membrane of any preceding clause, wherein the intersheet spacing between adjacent nanosheets falls within the range of 1-20 nm or 1 -10 nm, or 0.5- 5 nm, or 0.5-4 nm, or 0.5-3 nm, or 0.5-2 nm.

Clause 13. The proton conducting membrane of any preceding clause, wherein the thickness of the membrane falls within the range of 10-1000 pm.

Clause 14. The proton conducting membrane of any preceding clause, wherein the amount of proton conductor as a percentage of the overall weight of the membrane falls within the range of 10-90 wt%, or 10-80 wt%, or 10-70 wt%, or 10-60 wt%.

Clause 15. The proton conducting membrane of any preceding clause, wherein the proton conductivity of the membrane at 250°C falls within the range of 50-250 mS cm'¹; preferably 105-170 mS cm'¹. Clause 16. The proton conducting membrane of any preceding clause, wherein the proton conducting membrane is thermally stable when exposed to air at 250°C.

Clause 17. Use of the proton conducting membrane of any preceding clause, for hydrogen purification, or for hydrogen production, or for water electrolysis, or for steam electrolysis, or for carbon dioxide conversion, or for carbon dioxide reduction, or for ammonia synthesis, or in a fuel cell, or in energy storage applications.

Clause 18. An electrochemical device comprising the proton conducting membrane of any one of clauses 1 to 16.

Clause 19. The electrochemical device of clause 18, comprising;

(i) one or more catalysts, preferably wherein the one or more catalysts are applied as one or more additional microlayers, to one or more microlayers of the proton exchange membrane; or

(ii) one or more electrodes, preferably wherein the one or more electrodes are applied as one or more additional microlayers, to one or more microlayers of the proton exchange membrane.

Clause 20. The electrochemical device of clause 19, wherein the one or more catalysts, or the one or more electrodes, are independently selected in each instance from the group consisting of; heterogeneous catalysts, noble metal catalysts, transition metal catalysts, alkali metal catalysts, alkaline earth metal catalysts, noble metals, transition metals, alkali metals, alkaline earth metals, main group metals, metallic lanthanides and metallic actinides; preferably wherein the one or more catalysts, or the one or more electrodes, are independently selected in each instance from the group consisting of; Pt/C, PtRu/C, RuC>2, lrO₂, Cu, Al, Ag, Fe, Co, Ni, Mn, and Pd.

Clause 21. The electrochemical device of any one of clauses 18 to 20, wherein the electrochemical device is an electrolyzer for gas purification or for gas production, or for gas conversion, or for water electrolysis, or for ammonia production, or wherein the electrochemical device is a fuel cell, or a proton battery, or a redox flow battery.

Clause 22. The electrochemical device of clause 21 , wherein the electrochemical device is a fuel cell, having a power density falling within the range of 0.5 to 1 .5 W cm^-2, preferably having a power density falling within the range of 0.8 to 1 .2 W cm^-2.

Clause 23. The fuel cell of clause 22, wherein the fuel cell possesses long term operational stability; preferably wherein long term operational stability is indicated by a voltage decay rate of not more than 0.5 mV tr¹ at 400 mA cm^-2 and 250 °C over a period of 150 hours or more. Clause 24. The fuel cell of clause 22 or clause 23, wherein the fuel cell is a direct methanol fuel cell, capable of operating at high power densities when fed with high concentration methanol solutions; preferably wherein a high power densitiy is defined as a power density of not less than 0.2 W cm'²; preferably wherein a high concentration methanol solution is defined as a methanol solution wherein the concentration of the methanol is not less than 5 M.

Clause 25. A process for manufacturing the proton conducting membrane of any one of clauses 1 to 16, wherein the process comprises the steps of; a. obtaining a dispersion of first nanosheets in a liquid; and b. filtering or tape casting the dispersion from step a. onto a substrate, to form a first microlayer comprising a plurality of first nanosheets, situated on the substrate; c. optionally obtaining a dispersion of second nanosheets in a liquid, and filtering or tape casting the dispersion of second nanosheets in a liquid, onto the first microlayer comprising a plurality of first nanosheets, situated on the substrate from step b., to form a second microlayer comprising a plurality of second nanosheets, adjacent to the first microlayer comprising a plurality of first nanosheets, situated on the substrate; d. optionally repeating step c. one or more times with one or more further dispersions of further nanosheets in a liquid, to thereby sequentially build up additional laminarly arranged stacked microlayers each comprising a plurality of further nanosheets, situated on the substrate; e. drying the product of step b. or step c. or step d., to form a membrane comprising nanosheets, and having 2D-nanochannels formed between the nanosheets; f. removing the membrane produced in step e. from the substrate; and g. incorporating a proton conductor into the 2D-nanochannels of the membrane.

Clause 26. The process of clause 25, wherein the, or each, dispersion of nanosheets in a liquid, is obtained by a process of exfoliation, facilitated by milling in the presence of an exfoliating agent selected from the group consisting of high-viscosity amine-functionalized polymers, high-viscosity polyamines, high-viscosity polyesteramides, high-viscosity polyimides, high-viscosity polyesters, high-viscosity polyepoxides, high-viscosity polyethers, high-viscosity polyvinylamines, high-viscosity polyallylamines and high-viscosity polyamidoamines; preferably wherein the exfoliating agent is a high-viscosity polyethylenimine or a high-viscosity polyacrylamide; preferably wherein the milling is facilitated by ball milling; and/or wherein the, or each, dispersion of nanosheets in a liquid, is a mixed dispersion of nanosheets in a liquid, wherein the mixed dispersion of nanosheets in a liquid comprises nanosheets of more than one substance.

Clause 27. The process of clause 25 or clause 26, wherein the filtering is vacuum assisted filtration.

Clause 28. The process of any one of clauses 25 to 27, wherein the substrate is a polymer substrate.

Clause 29. The process of any one of clauses 25 to 28, wherein step f. of removing the membrane produced in step e. from the substrate is performed by peeling the membrane off the substrate.

Clause 30. The process of any one of clauses 25 to 29, wherein step g. of incorporating a proton conductor into the 2D-nanochannels of the membrane comprises immersing the membrane into a solution of the proton conductor for a period of time sufficient to incorporate the proton conductor into the 2D-nanochannels of the membrane, followed by removing the membrane from the solution and drying the membrane; or, wherein step g. of incorporating a proton conductor into the 2D-nanochannels of the membrane comprises incorporating a proton conductor into the dispersion of first nanosheets in a liquid at step a., prior to filtration or tape casting (step b.), and/or incorporating a proton conductor into the dispersion of second nanosheets in a liquid at step c., prior to filtration or tape casting; and/or incorporating a proton conductor into the one or more further dispersions of further nanosheets in a liquid at step d., prior to filtration or tape casting.

Clause 31. The process of any one of clauses 25 to 30, further comprising applying one or more catalysts, or one or more electrodes, to one or more of the microlayers; preferably wherein the one or more catalysts, or the one or more electrodes, is applied to one or more of the microlayers, via spray coating.

Clause 32. The process of clause 31 , wherein the one or more catalysts, or the one or more electrodes, are independently selected in each instance from the group consisting of; heterogeneous catalysts, noble metal catalysts, transition metal catalysts, alkali metal catalysts, alkaline earth metal catalysts, noble metals, transition metals, alkali metals, alkaline earth metals, main group metals, metallic lanthanides and metallic actinides; preferably wherein the one or more catalysts, or the one or more electrodes, are independently selected in each instance from the group consisting of; Pt/C, PtRu/C, RuO₂, lrC>2, Cu, Ag, Fe, Co, Ni, Mn, and Pd.

Claims

1 . A proton conducting membrane comprising nanosheets, and 2D-nanochannels formed between the nanosheets, wherein the 2D-nanochannels comprise a proton conductor confined within the 2D-nanochannels, and wherein the proton conductor is physically and chemically stable at temperatures of 150°C and above.

2. A proton conducting membrane comprising nanosheets, and 2D-nanochannels formed between the nanosheets, wherein the 2D-nanochannels comprise an inorganic proton conductor confined within the 2D-nanochannels.

3. The proton conducting membrane of any preceding claim, comprising a plurality of microlayers, wherein at least one microlayer comprises a plurality of nanosheets.

4. The proton conducting membrane of any preceding claim, comprising boron nitride nanosheets.

5. The proton conducting membrane of any preceding claim, comprising graphene nanosheets.

6. The proton conducting membrane of any preceding claim, comprising boron nitride nanosheets and graphene nanosheets.

7. The proton conducting membrane of any preceding claim, comprising;

(i) a first microlayer and a second microlayer, wherein the first microlayer is nonconductive to electrons, and the second microlayer is conductive to electrons; preferably wherein the first microlayer comprises a plurality of boron nitride nanosheets, and the second microlayer comprises a plurality of graphene nanosheets; or

(ii) a first microlayer, a second microlayer and a third microlayer, wherein the first microlayer comprises a plurality of nanosheets of a first substance, the second microlayer comprises a plurality of nanosheets of a second substance which is different to the first substance, and the third microlayer comprises a plurality of nanosheets of a third substance which is different to the second substance; optionally wherein the substance of the first microlayer and the substance of the third microlayer are the same; preferably wherein the second microlayer comprises a plurality of boron nitride nanosheets; most preferably wherein the first microlayer and/or the third microlayer each comprise a plurality of graphene nanosheets; or

(iii) a first microlayer and a second microlayer, wherein the first microlayer is nonconductive to electrons, and the second microlayer is conductive to protons; preferably wherein the first microlayer comprises a plurality of boron nitride nanosheets, and the second microlayer comprises a plurality of phosphotungstic acid (PWA) nanosheets; or

(iv) a first microlayer, a second microlayer and a third microlayer, wherein the first microlayer comprises a plurality of nanosheets of a first substance, the second microlayer comprises a plurality of nanosheets of a second substance which is different to the first substance, and the third microlayer comprises a plurality of nanosheets of a third substance which is different to the second substance; optionally wherein the substance of the first microlayer and the substance of the third microlayer are the same; preferably wherein the second microlayer comprises a plurality of phosphotungstic acid (PWA) nanosheets; most preferably wherein the first microlayer and/or the third microlayer each comprise a plurality of boron nitride nanosheets nanosheets.

8. The proton conducting membrane of any preceding claim, wherein the proton conductor is selected from the group(s) consisting of; solid acids, inorganic acids, protonic ceramics, protic inorganic polymers, protic ionic plastic crystals, protic organic ionic plastic crystals (POIPCs), zirconate based perovskites, rare-earth ortho-n io bates, rare-earth ortho- tantalates, rare-earth tungstates, heteropolyoxometallates, silico-aluminates, transition metal oxides, zeolites, and protonic Metal-Organic Frameworks (MOFs), including nanosheets comprising any of the aforementioned proton conductors.

9. The proton conducting membrane of any preceding claim, wherein the proton conductor is selected from the group consisting of; phosphoric acid, sulfuric acid, boric acid, perchloric acid, phosphotungstic acid (PWA), cesium hydrogen sulfate, aluminium phosphate, silico- aluminophosphate, sulphated zirconia, titanium phosphate, zirconia, niobium phosphate, niobic acid, 1 ,2,4-triazolium perfluorobutanesulfonate, imidazolium methanesulfonate, acceptor doped SrCeOs, acceptor doped BaCeOs, and acceptor doped BaZrOs, including nanosheets comprising any of the aforementioned proton conductors.

10. The proton conducting membrane of any preceding claim, wherein the proton conducting membrane further comprises a residual exfoliating agent.

1 1. The proton conducting membrane of any preceding claim, wherein the proton conducting membrane further comprises a residual exfoliating agent selected from the group consisting of high-viscosity amine-functionalized polymers, high-viscosity polyamines, high-viscosity polyesteramides, high-viscosity polyimides, high-viscosity polyesters, high-viscosity polyepoxides, high-viscosity polyethers, high-viscosity polyvinylamines, high-viscosity polyallylamines and high-viscosity polyamidoamines; preferably wherein the residual exfoliating agent is a high-viscosity polyethylenimine or a high-viscosity polyacrylamide.

12. The proton conducting membrane of any preceding claim, wherein the intersheet spacing between adjacent nanosheets falls within the range of 1 -20 nm or 1 -10 nm, or 0.5-5 nm, or 0.5-4 nm, or 0.5-3 nm, or 0.5-2 nm.

13. The proton conducting membrane of any preceding claim, wherein the thickness of the membrane falls within the range of 10-1000 pm.

14. The proton conducting membrane of any preceding claim, wherein the amount of proton conductor as a percentage of the overall weight of the membrane falls within the range of 10-90 wt%, or 10-80 wt%, or 10-70 wt%, or 10-60 wt%.

15. The proton conducting membrane of any preceding claim, wherein the proton conductivity of the membrane at 250°C falls within the range of 50-250 mS cm'¹; preferably 105-170 mS cm ¹.

16. The proton conducting membrane of any preceding claim, wherein the proton conducting membrane is thermally stable when exposed to air at 250°C.

17. Use of the proton conducting membrane of any preceding claim, for hydrogen purification, or for hydrogen production, or for water electrolysis, or for carbon dioxide conversion, or for carbon dioxide reduction, or for ammonia synthesis, or in a fuel cell, or in energy storage applications.

18. An electrochemical device comprising the proton conducting membrane of any one of claims 1 to 16.

19. The electrochemical device of claim 18, comprising;

(i) one or more catalysts, preferably wherein the one or more catalysts are applied as one or more additional microlayers, to one or more microlayers of the proton exchange membrane; or

(ii) one or more electrodes, preferably wherein the one or more electrodes are applied as one or more additional microlayers, to one or more microlayers of the proton exchange membrane.

20. The electrochemical device of claim 19, wherein the one or more catalysts, or the one or more electrodes, are independently selected in each instance from the group consisting of; heterogeneous catalysts, noble metal catalysts, transition metal catalysts, alkali metal catalysts, alkaline earth metal catalysts, noble metals, transition metals, alkali metals, alkaline earth metals, main group metals, metallic lanthanides and metallic actinides; preferably wherein the one or more catalysts, or the one or more electrodes, are independently selected in each instance from the group consisting of; Pt/C, PtRu/C, RuO₂, I rC>2, Cu, Al, Ag, Fe, Co, Ni, Mn, and Pd.

21 . A process for manufacturing the proton conducting membrane of any one of claims 1 to 16, wherein the process comprises the steps of; a. obtaining a dispersion of first nanosheets in a liquid; and b. filtering or tape casting the dispersion from step a. onto a substrate, to form a first microlayer comprising a plurality of first nanosheets, situated on the substrate; c. optionally obtaining a dispersion of second nanosheets in a liquid, and filtering or tape casting the dispersion of second nanosheets in a liquid, onto the first microlayer comprising a plurality of first nanosheets, situated on the substrate from step b., to form a second microlayer comprising a plurality of second nanosheets, adjacent to the first microlayer comprising a plurality of first nanosheets, situated on the substrate; d. optionally repeating step c. one or more times with one or more further dispersions of further nanosheets in a liquid, to thereby sequentially build up additional laminarly arranged stacked microlayers each comprising a plurality of further nanosheets, situated on the substrate; e. drying the product of step b. or step c. or step d., to form a membrane comprising nanosheets, and having 2D-nanochannels formed between the nanosheets; f. removing the membrane produced in step e. from the substrate; and g. incorporating a proton conductor into the 2D-nanochannels of the membrane.