WO2018118877A1 - Electrolyzer including a porous hydrophobic gas diffusion layer - Google Patents

Abstract

Various embodiments disclosed relate to an electrolyzer including a porous hydrophobic gas diffusion layer. The electrolyzer includes a membrane electrode assembly that includes a proton-exchange membrane having first and second opposed major surfaces. The membrane electrode assembly includes a cathode on the first major surface thereof, and an anode on the second major surface thereof. The membrane electrode assembly includes a gas diffusion layer contacting the cathode. The gas diffusion layer includes at least one of porous carbon paper or porous carbon cloth. The gas diffusion layer includes a hydrophobic material.

Description

ELECTROLYZER INCLUDING A POROUS HYDROPHOBIC GAS DIFFUSION LAYER

Cross Reference To Related Application

This application claims the benefit of U.S. Provisional Patent Application Number 62/436876, filed December 20, 2016, the disclosure of which is incorporated by reference herein in its entirety.

Background

[0001] There is great interest in harnessing energy from renewable sources to achieve environmental cleanliness in the energy industry. The desire to be able to convert and store all that renewable energy has rekindled interest in hydrogen as a clean and environmentally benign energy carrier. Likewise, the rising star of hydrogen-enabled mobility (e.g., motive fuel cells) adds further impetus to addressing needs for economical means to generate hydrogen, with the ultimate key to success for hydrogen as fuel in societal everyday transportation solutions. With the recent focus on hydrogen as an energy carrier there is increasing interest in low cost and high efficiency ¾ production.

[0002] Polymer electrolyte membrane (PEM) water electrolysis has emerged as one of the better choices to address the need for hydrogen fuel, by virtue of being compatible with the highly variable and unpredictable nature of renewable energy generation. Even though PEMs have been used for quite a few years, substantial improvements have not occurred.

[0003] Standard commercial gas diffusion layers (GDLs) are platinum plated sintered titanium plates. This type of material, however, is very expensive.

Summary

[0004] In various embodiments, the present disclosure provides an electrolyzer including a membrane electrode assembly. The membrane electrode assembly includes a proton-exchange membrane having first and second opposed major surfaces. The membrane electrode assembly includes a cathode on the first major surface of the proton-exchange membrane. The membrane electrode assembly includes an anode on the second major surface of the proton-exchange membrane. The membrane electrode assembly also includes a gas diffusion layer contacting the cathode. The gas diffusion layer includes at least one of porous carbon paper or porous carbon cloth. The gas diffusion layer also includes a hydrophobic material.

[0005] In various embodiments, the present disclosure provides an electrolyzer. The electrolyzer includes a proton-exchange membrane having first and second opposed major surfaces. The electrolyzer includes a cathode on the first major surface of the proton-exchange membrane. The electrolyzer includes an anode on the second major surface of the proton-exchange membrane. The electrolyzer includes a gas diffusion layer contacting the cathode. The gas diffusion layer includes at least one of porous carbon paper or porous carbon cloth. The gas diffusion layer includes a hydrophobic material that is present in a range of 0.001 wt.% to 30 wt.% of the gas diffusion layer, based on the total weight of the gas diffusion layer. The electrolyzer includes a cathode gasket contacting the cathode. The electrolyzer includes an anode gas diffusion layer contacting the anode. The electrolyzer includes an anode gasket contacting the anode gas diffusion layer.

[0006] In various embodiments, the present disclosure provides a method of making the electrolyzer. The method includes applying the gas diffusion layer to the cathode to form the electrolyzer.

[0007] In various embodiments, the present disclosure provides a method of using the electrolyzer. The method includes applying an electrical potential across the anode and the cathode. The method can include providing water to the anode of the membrane electrode assembly. The method includes generating hydrogen from water with the membrane electrode assembly.

[0008] In various embodiments, the present disclosure provides various advantages over other membrane electrode assemblies and methods of using the same, at least some of which are unexpected. For example, in various embodiments, the membrane electrode assembly of the present disclosure including the gas diffusion layer is less expensive than other membrane electrode assemblies, such as those including platinum plated sintered titanium plates, allowing for production of less expensive electrolyzers. In various embodiments, the gas diffusion layer of the present disclosure is thinner and less dense than other gas diffusion layers, allowing for smaller and lighter membrane electrode assemblies.

[0009] In various embodiments, the gas diffusion layer on the cathode of the present disclosure is more flexible than other gas diffusion layers, providing more conformity to the cathode, and allowing for application of the gas diffusion layer to the cathode via convenient and fast roll-to-roll processing. In various embodiments, the increased flexibility of the gas diffusion layer on the cathode of the present disclosure allows for a higher GDL compression and greater intimate contact of the gas diffusion layer with the cathode without puncturing the gas diffusion layer, which provides improved overall performance of the membrane electrode assembly, such as compared to membrane electrode assemblies including platinum plated sintered titanium plates.

[0010] During electrolyzer use of a membrane electrode assembly including a cathode gas diffusion layer, water is a reactant that needs to get through the anode gas diffusion layer to contact the anode for hydrogen gas to be generated. Hydrogen ions formed at the anode must travel through the proton- exchange membrane to the cathode, where they obtain electrons and become hydrogen gas. It is desirable that the hydrophilic proton-exchange membrane retain a high concentration of water in order to maintain high proton conductivity and current density. However, in various embodiments, surprisingly, the membrane electrode assembly of the present disclosure including the gas diffusion layer that includes the hydrophobic material generates hydrogen from water more efficiently, such as compared to corresponding membrane electrode assemblies having a cathode gas diffusion layer free of the hydrophobic material or including a hydrophilic material. Although not wanting to be bound by theory, it is believed that hydrophilicity of both gas diffusion layers (anodic and cathodic) in contact with the membrane will facilitate the membrane maintaining a highly hydrated (and therefore conductive) state, and hence facilitate generation of hydrogen. Surprisingly, some embodiments of the membrane electrode assembly of the present disclosure that include the gas diffusion layer with the hydrophobic material generate hydrogen from water more efficiently, such as compared to corresponding membrane electrode assemblies having a cathode gas diffusion layer free of the hydrophobic material or including a hydrophilic material.

Brief Description of the Drawings

[0011] The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.

[0012] FIG. 1 illustrates an exemplary membrane electrode assembly described herein.

[0013] FIG. 2 illustrates exemplary microstructured whiskers used in membrane electrode assemblies described herein, in accordance with various embodiments.

[0014] FIG. 3 illustrates cell voltage versus testing time for various electrolyzers, in accordance with various embodiments.

[0015] FIG. 4 illustrates cell voltage versus testing time for various electrolyzers, in accordance with various embodiments.

[0016] FIG. 5 illustrates cell voltage versus testing time for various electrolyzers, in accordance with various embodiments.

Detailed Description

[0017] Reference will now be made in detail to certain embodiments of the disclosed subject matter, examples of which are illustrated in part in the accompanying drawings. While the disclosed subject matter will be described in conjunction with the enumerated claims, it will be understood that the exemplified subject matter is not intended to limit the claims to the disclosed subject matter.

[0018] Throughout this document, values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a range of "about 0.1% to about 5%" or "about 0.1% to 5%" should be interpreted to include not just about 0.1% to about 5%, but also the individual values (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.1% to 0.5%, 1.1% to 2.2%, 3.3% to 4.4%) within the indicated range. The statement "about X to Y" has the same meaning as "about X to about Y," unless indicated otherwise. Likewise, the statement "about X, Y, or about Z" has the same meaning as "about X, about Y, or about Z," unless indicated otherwise.

[0019] In this document, the terms "a," "an," or "the" are used to include one or more than one unless the context clearly dictates otherwise. The term "or" is used to refer to a nonexclusive "or" unless otherwise indicated. The statement "at least one of A and B" or "at least one of A or B" has the same meaning as "A, B, or A and B." In addition, it is to be understood that the phraseology or terminology employed herein, and not otherwise defined, is for the purpose of description only and not of limitation. Any use of section headings is intended to aid reading of the document and is not to be interpreted as limiting; information that is relevant to a section heading may occur within or outside of that particular section. All publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.

[0020] In the methods described herein, the acts can be carried out in any order without departing from the principles of the invention, except when a temporal or operational sequence is explicitly recited. Furthermore, specified acts can be carried out concurrently unless explicit claim language recites that they be carried out separately. For example, a claimed act of doing X and a claimed act of doing Y can be conducted simultaneously within a single operation, and the resulting process will fall within the literal scope of the claimed process.

[0021] The term "about" as used herein can allow for a degree of variability in a value or range, for example, within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range, and includes the exact stated value or range.

[0022] The term "substantially" as used herein refers to a majority of, or mostly, as in at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more, or 100%.

Electrolyzer

[0023] In various embodiments, the present disclosure provides an electrolyzer. The electrolyzer includes a membrane electrode assembly. The membrane electrode assembly includes a proton- exchange membrane having first and second opposed major surfaces. The membrane electrode assembly includes a cathode on the first major surface of the proton-exchange membrane. The membrane electrode assembly includes an anode on the second major surface of the proton-exchange membrane. The membrane electrode assembly includes a gas diffusion layer contacting the cathode. The gas diffusion layer includes at least one of porous carbon paper or porous carbon cloth. The gas diffusion layer includes a hydrophobic material.

[0024] Referring to FIG. 1, exemplary membrane electrode assembly 100 includes anode 105. Adjacent anode 105 is proton-exchange membrane 104 having first and second opposed major surfaces 1 10, 1 15. Cathode 103 is situated adjacent proton-exchange membrane 104 on first major surface thereof 1 10, while anode 105 is adjacent second major surface 1 15 of proton-exchange membrane 104. Gas diffusion layer 107 is situated adjacent cathode 103, and includes at least one of porous carbon paper or porous carbon cloth, as well as a hydrophobic material. Proton-exchange membrane 104 is electrically insulating and permits only hydrogen ions (e.g., protons) to pass through membrane 104.

[0025] In operation, water is introduced into anode 105 of membrane electrode assembly 100. At anode 105, the water is separated into molecular oxygen (O2), hydrogen ions (H⁺), and electrons. The hydrogen ions diffuse through proton-exchange membrane 104 while electrical potential 117 drives electrons to cathode 103. At cathode 103, the hydrogen ions combine with electrons to form hydrogen gas.

[0026] The membrane electrode assembly includes a gas diffusion layer contacting the cathode and includes at least one of porous carbon paper or porous carbon cloth, and additionally includes a hydrophobic material. The gas diffusion layer is a porous hydrophobic layer. The gas diffusion layer includes pores ranging in size from 10 nm to 100 micrometers (in some embodiments, 0.1 micrometer to 100 micrometers, or 1 micrometer to 50 micrometers, or 10 nm or less, or less than, equal to, or greater than 25 nm, 50, 75, 100, 150, 200, 250, 500, 750 nm, 1 micrometer, 2 micrometers, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 75 micrometers, or 100 micrometers or more). The pores can be substantially homogeneously distributed in the gas diffusion layer, such as with respect to a major surface thereof.

The pores can be through pores that pass from one major surface of the gas diffusion layer to the other opposed major surface of the gas diffusion layer.

[0027] The cathode gas diffusion layer can have a thickness in a range of 1 micrometer to 1 mm, for example, 10 micrometers to 500 micrometers, 100 micrometers to 300 micrometers, 150 micrometers to 300 micrometers, or 1 micrometer or less, or less than, equal to, or greater than 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 1 10, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 320, 340, 360, 380, 400, 420, 440, 460, 480, 500, 750 micrometers, or 1 mm or more.

[0028] The carbon paper or carbon cloth in the cathode gas diffusion layer can include carbon fibers. The carbon fibers can be any suitable carbon fibers, and can include carbonized polymer fibers, such as carbonized polyacrylonitrile (PAN), rayon, or carbonized petroleum pitch. At least one of the carbon paper or the carbon cloth further includes a binder that holds the carbon fibers together. The carbon paper can be non-woven, such that the carbon paper includes non-woven carbon fibers. The carbon cloth can be woven, such that the carbon cloth includes woven carbon fibers. The gas diffusion layer can include the carbon paper, the carbon fibers, or both the carbon paper and the carbon fibers. The gas diffusion layer can be free of the carbon cloth (i.e., contains none) and free of the carbon paper.

[0029] The hydrophobic nature of the cathode gas diffusion layer can result from a hydrophobic material that is part of the cathode gas diffusion layer. The hydrophobic material can be formed via a hydrophobizing treatment of the other components of the gas diffusion layer, such as via a

hydrophobizing treatment of at least one of the carbon paper or the carbon fibers. The hydrophobic material can be substantially homogeneously distributed on the gas diffusion layer, such as a coating

(e.g., surface coating, such as on the face that is in contact with the proton-exchange membrane) that is uniformly distributed with respect to a major surface of the gas diffusion layer, or throughout the gas diffusion layer. The hydrophobic material can form any suitable proportion of the gas diffusion layer, based on the total weight of the gas diffusion layer, for example, 0.001 wt.% to 30 wt.% of the gas diffusion layer, 1 wt.% to 10 wt.% of the gas diffusion layer, or 0.001 wt.% or less, or less than, equal to, or greater than 0.01 wt.%, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, or 30 wt.% or more. The hydrophobic material, resulting from the hydrophobizing treatment, can be any one or more suitable materials that causes the gas diffusion layer to increase in hydrophobicity relative to a corresponding gas diffusion layer that is free of said hydrophobic material. For example, the hydrophobic material can include at least one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorinated ethylene propylene (FEP), tetrafluoroethylene-hexafluoropropylene copolymer (TFE-HFP), tetrafluoroethylene-alkylvinyl ether co-polymer, polychlorotrifluoroethylene (PCTFE), ethylene-tetrafluoroethylene co-polymer (ETFE), ethylene-chlorotrifluoroethylene co-polymer (ECTFE), or a surfactant.

[0030] The membrane electrode assembly includes a cathode on the first major surface of the proton- exchange membrane, and an anode on the second major surface of the proton-exchange membrane. The anode, the cathode, or both the anode and the cathode, can be or can include catalyst coatings, such as on the proton-exchange membrane or on a catalyst support (e.g., coatings having a substantially uniform thickness). The anode and the cathode can independently have any suitable thickness, for example, in a range from 1 micrometer to 10 mm, 10 micrometers to 300 micrometers, or 1 micrometer or less, or less than, equal to, or greater than 2, 4, 6, 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 1 10, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, or 300 micrometers or more. The anode and the cathode can independently include or be free of a catalyst support (i.e., does not have a catalyst support). For example, the cathode or anode can independently include a catalyst support and a catalyst material.

[0031] The membrane electrode assembly includes a proton-exchange membrane having first and second opposed major surfaces. The proton-exchange membrane is electrically insulating but ionically conductive toward protons. The proton-exchange membrane can include any suitable materials that provide the electrically insulating and ionically conductive property. The proton-exchange membrane can include or can be a polymeric perfluorinated sulfonic acid. The proton-exchange membrane can have any suitable thickness, for example, in a range from 1 micrometer to 10 mm, 10 micrometers to 300 micrometers, 1 micrometer or less, or less than, equal to, or greater than 2, 4, 6, 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 1 10, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, or 300 micrometers or more.

[0032] The anode or cathode can include any suitable catalyst material, such that the electrolyzer can be used as described herein. For example, a catalyst material of at least one of the cathode or the anode includes at least one of platinum, gold, ruthenium, iridium, palladium, rhodium, nickel, iron, molybdenum, tungsten, niobium, copper, cobalt, manganese, titanium, or an alloy thereof. A catalyst material of the cathode can include platinum. A catalyst material of the anode can include iridium.

[0033] The electrolyzer of the present disclosure can have any suitable operational current density consistent with the membrane electrode assembly described herein, for example, an operational current density at 80°C in a range from 0.001 A/cm² to 30 A/cm², 0.5 A/cm² to 25 A/cm², 1 A/cm² to 20 A/cm², 2 A/cm² to 10 A/cm², or less than, equal to, or greater than 0.001 A/cm², 0.01, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1, 12, 13, 14, 15, 16, 17, 18, 19, 20, 22, 24, 26, 28 A/cm², or 30 A/cm² or more.

[0034] In addition to the membrane electrode assembly including the cathode gas diffusion layer, cathode, proton-exchange membrane, and anode, the electrolyzer can further include a cathode gasket in contact with the cathode gas diffusion layer. The electrolyzer can further include an anode gasket in contact with an anode gas diffusion layer on the anode.

[0035] The cathode and anode gasket can independently have any suitable GDL compression consistent with the electrolyzer structures described herein, wherein GDL compression is determined by one minus gasket thickness (which does not change before and after compression) divided by the initial pre- compression thickness of the gas diffusion layer corresponding to that gasket. For example, in the

Examples, the thickness of a cathode gas diffusion layer was 9.7 mil, the thickness of a cathode gasket was 5.3 mil, so the cathode GDL compression was 45% (i.e., l-(5.3/9.7)). For example, a cathode GDL compression of 45% indicates that the cathode gasket thickness divided by the initial cathode gas diffusion layer thickness is 1-0.45 (i.e., 0.55 or 55%). For example, the cathode gasket can have a GDL compression in a range from 0.01% to 90%, 1% to 50%, 15% to 90% (e.g., greater than 15% to less than or equal to 90%), or 0.01% or less, or less than, equal to, or greater than 0.1%, 0.5, 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 82, 84, 86, 88, or 90% or more.

Nano-Structured Thin Film

[0036] In various embodiments, at least one of the anode or the cathode includes a nano-structured thin film (NSTF) catalyst support. For example, at least one of the cathode or the anode can include nanostructured elements (e.g., catalyst) including microstructured (e.g., small, not necessarily micro- scale) support whiskers having an outer surface at least partially coated by a catalyst material of at least one of the cathode or anode. In the membrane electrode assembly, the whiskers including the catalyst material can be embedded in the proton-exchange membrane.

[0037] Referring to FIG. 2, exemplary NSTF-supported catalyst material 200 on substrate 208 (e.g., microstructured catalyst transfer substrate) has nanostructured elements 202 with microstructured whiskers 204 (e.g., catalyst support) having outer surface 205 at least partially covered by catalyst material 206. After embedding the catalyst material-coated whiskers in the proton-exchange membrane, the microstructured catalyst transfer substrate can be removed, leaving behind the whiskers embedded in the membrane. [0038] Suitable whiskers can be provided by techniques known in the art, including those described in U.S. Pat. Nos. 4,812,352 (Debe), 5,039,561 (Debe), 5,338,430 (Parsonage et al.), 6, 136,412 (Spiewak et al.), and 7,419,741 (Vernstrom et al), the disclosures of which are incorporated herein by reference. In general, microstructured whiskers can be provided, for example, by vacuum depositing (e.g., by sublimation) a layer of organic or inorganic material onto a substrate (e.g., a microstructured catalyst transfer polymer sheet), and then, in the case of perylene red deposition, converting the perylene red pigment into microstructured whiskers by thermal annealing. Typically, the vacuum deposition steps are carried out at total pressures at or below about 10^"3 Torr or 0.1 Pascal. Exemplary microstructures are made by thermal sublimation and vacuum annealing of the organic pigment C.I. Pigment Red 149 (i.e., N,N'-di(3,5-xylyl)perylene-3,4:9, 10-bis(dicarboximide)). Methods for making organic nanostructured layers are disclosed, for example, in Materials Science and Engineering, A158 ( 1992), pp. 1-6; J. Vac. Sci. Technol. A, 5 (4), July/August 1987, pp. 1914- 16; J. Vac. Sci. Technol. A, 6, (3), May/August 1988, pp. 1907-1 1; Thin Solid Films, 186, 1990, pp. 327-47; J. Mat. Sci., 25, 1990, pp. 5257-68; Rapidly Quenched Metals, Proc. of the Fifth Int. Conf. on Rapidly Quenched Metals, Wurzburg, Germany (Sep. 3-7, 1984), S. Steeb et al., eds., Elsevier Science Publishers B.V., New York, ( 1985), pp. 1 1 17-24;

Photo. Sci. and Eng., 24, (4), July/August 1980, pp. 21 1- 16; and U.S. Pat. Nos. 4,340,276 (Maffitt et al.) and 4,568,598 (Bilkadi et al), the disclosures of which are incorporated herein by reference. Properties of catalyst layers using carbon nanotube arrays are disclosed in the article "High Dispersion and Electrocatalytic Properties of Platinum on Well-Aligned Carbon Nanotube Arrays", Carbon, 42, (2004), 191-197. Properties of catalyst layers using grassy or bristled silicon are disclosed, for example, in U.S. Pat. Pub. No. 2004/0048466 Al (Gore et al).

[0039] Vacuum deposition may be carried out in any suitable apparatus (see, e.g., U.S. Pat. Nos.

5,338,430 (Parsonage et al.), 5,879,827 (Debe et al), 5,879,828 (Debe et al.), 6,040,077 (Debe et al.), and 6,319,293 (Debe et al.), and U.S. Pat. Pub. No. 2002/0004453 Al (Haugen et al.)). One exemplary apparatus is depicted schematically in FIG. 4A of U.S. Pat. No. 5,338,430 (Parsonage et al.), and discussed in the accompanying text, wherein the substrate is mounted on a drum which is then rotated over a sublimation or evaporation source for depositing the organic precursor (e.g., perylene red pigment) prior to annealing the organic precursor in order to form the whiskers.

[0040] Typically, the nominal thickness of deposited perylene red pigment is in a range from about 50 nm to 500 nm. Typically, the whiskers have an average cross-sectional dimension in a range from 20 nm to 60 nm and an average length in a range from 0.3 micrometer to 3 micrometers.

[0041] In some embodiments, the whiskers are attached to a backing (e.g., substrate). Exemplary backings include polyimide, nylon, metal foils, or other material that can withstand the thermal annealing temperature up to 300°C. In some embodiments, the backing has an average thickness in a range from 25 micrometers to 125 micrometers. The backing or substrate can be removed after embedding the catalyst material -coated whiskers in the proton-exchange membrane. [0042] In some embodiments, the backing has a microstructure on at least one of its surfaces. In some embodiments, the microstructure is included of substantially uniformly shaped and sized features at least three (in some embodiments, at least four, five, ten, or more) times the average size of the whiskers. The shapes of the microstructures can, for example, be V-shaped grooves and peaks (see, e.g., U.S. Pat. No. 6, 136,412 (Spiewak et al.)) or pyramids (see, e.g., U.S. Pat. No. 7,901,829 (Debe et al.)). In some embodiments, some fraction of the microstructure features extend above the average or majority of the microstructured peaks in a periodic fashion, such as every 31^st V-groove peak being 25% or 50% or even 100% taller than those on either side of it. In some embodiments, this fraction of features that extend above the majority of the microstructured peaks can be up to 10% (in some embodiments up to 3%, 2%, or even up to 1%). Use of the occasional taller microstructure features may facilitate protecting the uniformly smaller microstructure peaks when the coated substrate moves over the surfaces of rollers in a roll-to-roll coating operation. The occasional taller feature touches the surface of the roller rather than the peaks of the smaller microstructures, so much less of the nanostructured material or whisker material is likely to be scraped or otherwise disturbed as the substrate moves through the coating process. In some embodiments, the microstructure features are substantially smaller than half the thickness of the membrane that the catalyst will be transferred to in making a membrane electrode assembly. This is so that during the catalyst transfer process, the taller microstructure features do not penetrate through the membrane where they may overlap the electrode on the opposite side of the membrane. In some embodiments, the tallest microstructure features are less than l/3^rd or l/4^th of the membrane thickness. For the thinnest ion exchange membranes (e.g., about 10 micrometers to 15 micrometers in thickness), it may be desirable to have a substrate with microstructured features no larger than about 3 micrometers to 4.5 micrometers tall. The steepness of the sides of the V-shaped or other microstructured features or the included angles between adjacent features may in some embodiments be desirable to be on the order of 90° for ease in catalyst transfer during a lamination-transfer process and to have a gain in surface area of the electrode that comes from the square root of two (1.414) surface area of the microstructured layer relative to the planar geometric surface of the substrate backing.

Method of Making the Electrolyzer

[0043] In various embodiments, the present disclosure provides a method of making the electrolyzer. For example, the method can be any suitable method that forms an embodiment of the electrolyzer described herein. In some embodiments, the method includes applying the gas diffusion layer to the cathode to form the electrolyzer.

[0044] The method can include applying a gas diffusion layer to a cathode to form an electrolyzer including a membrane electrode assembly. The membrane electrode assembly includes a proton- exchange membrane having first and second opposed major surfaces. The membrane electrode assembly includes the cathode on the first major surface of the proton-exchange membrane. The membrane electrode assembly includes an anode on the second major surface of the proton-exchange membrane. The membrane electrode assembly includes the gas diffusion layer contacting the cathode. The gas diffusion layer includes at least one of porous carbon paper or porous carbon cloth. The gas diffusion layer includes a hydrophobic material.

[0045] In some embodiments, the method includes using a roll-to-roll process to apply the gas diffusion layer to the cathode.

Method of Using the Electrolyzer

[0046] In various embodiments, the present disclosure provides a method of using the electrolyzer. The method can be any suitable method of using any embodiment of the electrolyzer described herein. For example, the method can include applying an electrical potential across the anode and the cathode. The method can also include generating hydrogen from water with the membrane electrode assembly. The method can include generating oxygen gas at the anode side and hydrogen gas at the cathode side. The method can include providing water (e.g., any suitable water, such as deionized water) to the anode, and optionally to the cathode.

Exemplary Embodiments

[0047] The following exemplary embodiments are provided, the numbering of which is not to be construed as designating levels of importance: 1A. An electrolyzer comprising a membrane electrode assembly, the membrane electrode assembly comprising:

a proton-exchange membrane having first and second opposed major surfaces;

a cathode on the first major surface of the proton-exchange membrane;

an anode on the second major surface of the proton-exchange membrane; and

a gas diffusion layer contacting the cathode, the gas diffusion layer comprising at least one of porous carbon paper or porous carbon cloth, and a hydrophobic material.

2A. The electrolyzer of Exemplary Embodiment 1 A, wherein the gas diffusion layer has pores ranging in size from 10 nm to 100 micrometers (in some embodiments, 0.1 micrometer to 100 micrometers, or 1 micrometer to 50 micrometers, or 10 nm or less, or less than, equal to, or greater than 25 nm, 50, 75, 100, 150, 200, 250, 500, 750 nm, 1 micrometer, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 75, or 100 micrometers or more).

3A. The electrolyzer of any one of the preceding A Exemplary Embodiments, wherein the gas diffusion layer has pores that are substantially homogeneously distributed therein. 4A. The electrolyzer of any one of the preceding A Exemplary Embodiments, wherein the gas diffusion layer has a thickness in a range from 1 micrometer to 1 mm (in some embodiments, 10 micrometers to 500 micrometers, 100 micrometers to 300 micrometers, 150 micrometers to 300 micrometers, or 1 micrometer or less, or less than, equal to, or greater than 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 320, 340, 360, 380, 400, 420, 440, 460, 480, 500, 750 micrometers, or 1 mm or more).

5A. The electrolyzer of any one of the preceding A Exemplary Embodiments, wherein at least one of the carbon paper or carbon cloth comprises carbon fibers.

6A. The electrolyzer of Exemplary Embodiment 5A, wherein at least one of the carbon paper or the carbon cloth further comprises a binder that holds the carbon fibers together. 7A. The electrolyzer of either Exemplary Embodiment 5 A or 6A, wherein the carbon fibers comprise carbonized polymer fibers.

8A. The electrolyzer of any one of the preceding A Exemplary Embodiments, wherein the carbon paper comprises non-woven carbon fibers.

9A. The electrolyzer of any one of the preceding A Exemplary Embodiments, wherein the carbon cloth comprises woven carbon fibers.

10A. The electrolyzer of any one of the preceding A Exemplary Embodiments, wherein the gas diffusion layer comprises the carbon paper.

11A. The electrolyzer of any one of the preceding A Exemplary Embodiments, wherein the gas diffusion layer is a porous hydrophobic layer. 12A. The electrolyzer of any one of the preceding A Exemplary Embodiments, wherein the hydrophobic material is substantially homogeneously distributed on the gas diffusion layer.

13 A. The electrolyzer of any one of the preceding A Exemplary Embodiments, wherein the hydrophobic material is 0.001 wt.% to 30 wt.% of the gas diffusion layer, based on the total weight of the gas diffusion layer (in some embodiments, 1 wt.% to 10 wt.% of the gas diffusion layer, or 0.001 wt.% or less, or less than, equal to, or greater than 0.01 wt.%, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, or 30 wt.% or more). 14A. The electrolyzer of any one of the preceding A Exemplary Embodiments, wherein the hydrophobic material comprises at least one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorinated ethylene propylene (FEP), tetrafluoroethylene-hexafluoropropylene copolymer (TFE-HFP), tetrafluoroethylene-alkylvinyl ether co-polymer, polychlorotrifluoroethylene (PCTFE), ethylene-tetrafluoroethylene co-polymer (ETFE), ethylene-chlorotrifluoroethylene co-polymer (ECTFE), or a surfactant.

15 A. The electrolyzer of any one of the preceding A Exemplary Embodiments, wherein at least one of the anode or the cathode comprises a catalyst coating on the proton-exchange membrane.

16A. The electrolyzer of any one of the preceding A Exemplary Embodiments, wherein the anode and the cathode both comprise catalyst coatings. 17A. The electrolyzer of any one of the preceding A Exemplary Embodiments, wherein the anode and the cathode independently have a thickness in a range from 1 micrometer to 10 mm (in some embodiments, 10 micrometers to 300 micrometers, or 1 micrometer or less, or less than, equal to, or greater than 2, 4, 6, 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, or 300 micrometers or more).

18A. The electrolyzer of any one of the preceding A Exemplary Embodiments, wherein the proton- exchange membrane has a thickness in a range from 1 micrometer to 10 mm (in some embodiments, 10 micrometers to 300 micrometers, or 1 micrometer or less, or less than, equal to, or greater than 2, 4, 6, 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 1 10, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, or 300 micrometers or more).

19A. The electrolyzer of any one of the preceding A Exemplary Embodiments, wherein the proton- exchange membrane has a thickness in a range from 10 micrometers to 300 micrometers. 20A. The electrolyzer of any one of the preceding A Exemplary Embodiments, wherein the proton- exchange membrane comprises a polymeric perfluorinated sulfonic acid membrane.

21 A. The electrolyzer of any one of the preceding A Exemplary Embodiments, wherein at least one of the anode or the cathode comprises a nanostructured thin film (NSTF). 22A. The electrolyzer of Exemplary Embodiment 21 A, wherein at least one of the cathode or the anode comprises nanostructured elements comprising microstructured support whiskers having an outer surface at least partially coated by a catalyst material of at least one of the cathode or anode. 23A. The electrolyzer of any one of the preceding A Exemplary Embodiments, wherein at least one of the cathode or the anode independently comprises a catalyst support.

24A. The electrolyzer of any one of the preceding A Exemplary Embodiments, wherein a catalyst material of at least one of the cathode or the anode comprises at least one of platinum, gold, ruthenium, iridium, palladium, rhodium, nickel, iron, molybdenum, tungsten, niobium, copper, cobalt, manganese, titanium, or an alloy thereof.

25A. The electrolyzer of any one of the preceding A Exemplary Embodiments, wherein a catalyst material of the cathode comprises platinum.

26A. The electrolyzer of any one of the preceding A Exemplary Embodiments, wherein a catalyst material of the anode comprises iridium.

27A. The electrolyzer of any one of the preceding A Exemplary Embodiments, having an operational current density at 80°C in a range from 0.001 A/cm² to 30 A/cm² (in some embodiments, 0.5 A/cm² to 25 A/cm², 1 A/cm² to 20 A/cm², 2 A/cm² to 10 A/cm², or less than, equal to, or greater than 0.001, 0.01, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1, 12, 13, 14, 15, 16, 17, 18, 19, 20, 22, 24, 26, 28 A/cm², or 30 A/cm² or more). 28A. The electrolyzer of any one of the preceding A Exemplary Embodiments, further comprising: a cathode gasket in contact with the gas diffusion layer; and

an anode gasket in contact with an anode gas diffusion layer on the anode.

29A. The electrolyzer of Exemplary Embodiment 28A, wherein the cathode gasket has a GDL compression in a range from 0.01% to 90% (in some embodiments, 1% to 50%, 15% to 90% (e.g., greater than 15% to less than or equal to 90%), or 0.01% or less, or less than, equal to, or greater than 0.1, 0.5, 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 82, 84, 86, 88, or 90% or more). IB. A method of making the electrolyzer of any A Exemplary Embodiment, the method comprising: applying the gas diffusion layer to the cathode to form the electrolyzer. 2B. The method of Exemplary Embodiment IB, wherein the method comprises using a roll-to-roll process to apply the gas diffusion layer to the cathode.

IC. A method of using the electrolyzer of any A Exemplary Embodiment, the method comprising: applying an electrical potential across the anode and the cathode;

providing water to the anode; and

generating hydrogen from the water with the membrane electrode assembly.

ID. An electrolyzer comprising:

a proton-exchange membrane having first and second opposed major surfaces;

a cathode on the first major surface of the proton-exchange membrane;

an anode on the second major surface of the proton-exchange membrane; and

a gas diffusion layer contacting the cathode, the gas diffusion layer comprising at least one of porous carbon paper or porous carbon cloth, and a hydrophobic material that is present in a range of 0.001 wt.% to 30 wt.% of the gas diffusion layer, based on the total weight of the gas diffusion layer (in some embodiments, 1 wt.% to 10 wt.% of the gas diffusion layer, or 0.001 wt.% or less, or less than, equal to, or greater than 0.01, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, or 30 wt.% or more);

a cathode gasket contacting the cathode;

an anode gas diffusion layer contacting the anode; and

an anode gasket contacting the anode gas diffusion layer.

Examples

[0048] Various embodiments of the present invention can be better understood by reference to the following Examples which are offered by way of illustration. The present invention is not limited to the Examples given herein.

[0049] Table 1 shows the sources of the gas diffusion layer (GDL) materials used in these Examples.

Table 1 Gas Diffusion Layer Material Source

Pt/Ti GDL, platinized porous titanium gas diffusion layer, 50 Giner, Inc., Newton, MA

cm²

Pt/Ti GDL obtained under the trade designation "BEKIPOR Bekaert Company, Zwevegam, TITANIUM" Belgium

Hydrophobic treated carbon paper obtained under the trade Toray Industries, Inc., New York, designation "TORAY 060" NY

Untreated (i.e., no hydrophobic treatment) carbon paper Mitsubishi Rayon Co., Ltd., Tokyo, obtained under the trade designation "U105" Japan

Hydrophobic treated carbon paper obtained under the trade Freudenberg Vliesstoffe SE & Co. designation "FREUDENBERG H2315 C2" KG, Weinheim, Germany

Hydrophobic treated carbon paper available under the trade 3M Company, St. Paul, MN designation "2979"

-General Method for Preparing Nanostructured Whiskers for Catalyst Supports

[0050] Nanostructured whiskers were prepared by thermal annealing a layer of perylene red pigment (C.I. Pigment Red 149, also known as "PR149", obtained from Clariant, Charlotte, NC), which was sublimation vacuum coated onto microstructured catalyst transfer polymer substrates (MCTS) with a nominal thickness of 200 nm, as described in detail in U.S. Pat. No. 4,812,352 (Debe), the disclosure of which is incorporated herein by reference.

[0051] A roll-good web of the MCTS (made on a polyimide film obtained from E.I. du Pont de Nemours, Wilmington, DE, under trade designation "KAPTON") was used as the substrate on which the PR149 was deposited. The MCTS substrate surface had V-shaped features with about 3 micrometer tall peaks, spaced 6 micrometers apart. A nominally 100 nm thick layer of Cr was then sputter deposited onto the MCTS surface using a DC magnetron planar sputtering target and typical background pressures of Ar and target powers known to those skilled in the art sufficient to deposit the Cr in a single pass of the MCTS web under the target at the desired web speed. The Cr coated MCTS web then continued over a sublimation source containing the PR149 pigment material. The PR149 was heated to a controlled temperature near 500°C so as to generate sufficient vapor pressure flux to deposit 0.022 mg/cm², or about 220 nm thick layer of the PR149 in a single pass of the web over the sublimation source. The mass or thickness deposition rate of the sublimation can be measured in any suitable fashion known to those skilled in the art, including optical methods sensitive to film thickness, or quartz crystal oscillator devices sensitive to mass. The PR149 coating was then converted to the whisker phase by thermal annealing, as described in detail in U.S. Pat. No. 5,039,561 (Debe), the disclosure of which is incorporated herein by reference, by passing the PR149 coated web through a vacuum having a temperature distribution sufficient to convert the PR149 as-deposited layer into a layer of oriented crystalline whiskers at the desired web speed, such that the whisker layer has an average whisker areal number density of 68 whiskers per square micrometer, determined from SEM images, with an average length of 0.6 micrometer.

-General Method for Preparing Nanostructured Thin Film (NSTF) Catalyst

[0052] Nanostructured thin film (NSTF) catalysts, specifically Ir-based oxygen evolution reaction (OER) catalyst and Pt-based hydrogen evolution reaction (HER) catalyst, were prepared by sputter coating Ir catalyst films or Pt catalyst films onto a layer of nanostructured whiskers (which were prepared as described above).

[0053] A vacuum sputter deposition system with 6 cryo-pumps (obtained from Brooks Automation, Chelmsford, MA) and the sputtering pressure is between 0.4 Pa and 0.66 Pa, ultimate pressure before sputtering is as low as lxlO^"4 Pa. The rectangular sputter targets with 12.7 cm x 38.1 cm (5 inch x 15 inch) (obtained from Materion Advanced Materials Group, Buffalo, NY) were used. The coatings were deposited by using ultra high purity Ar as the sputtering gas and magnetron power range from 2.5 to 3.5 kW. High purity (99.9+ %), Pt or Ir were used for the sputtering targets. A pre-sputter of each target was performed to clean the surface before deposition. The substrate to be sputtered on was positioned away from the sputtering targets. Each target was then lit for a given duration to eliminate any contaminants that may have formed on the target surfaces when the system was exposed to atmospheric pressure for sample loading. For the cathode catalyst, a Pt layer was coated directly on top of the nanostructured whiskers to obtain a Pt loading of about 250 microgram/cm². For the anode catalyst, Ir catalyst was sputtered onto the nanostructured whiskers to obtain an Ir loading of 250 microgram/cm².

-General Method for Preparing Catalyst-Coated Membrane (CCM)

[0054] Catalyst-coated-membranes (CCMs) were made by transferring the catalyst coated whiskers described above onto both surfaces (full CCM) of a proton exchange membrane (PEM) using the processes as described in detail in U.S. Pat. No. 5,879,827 (Debe et al). The hydrogen evolution reaction catalyst for the cathode was 0.25 mg/cm² Pt on NSTF whiskers, and the oxygen evolution reaction catalyst for the anode was 0.25 mg/cm² Ir on NSTF whiskers. The catalyst transfer was accomplished by hot roll lamination onto perfluorinated sulfonic acid membrane obtained from 3M Company, with a nominal equivalent weight of 825 g/mol and thickness of 50 micrometers (used as-made). CCMs were made with 825 equivalent weight PEM (obtained from 3M Company), the hot roll temperatures were 350°F (177°C) and the gas line pressure fed to force laminator rolls together at the nip ranged at 150 psi (1.03 MPa). The catalyst coated MCTS was precut into 15.2 cm x 11.4 cm shapes and sandwiched onto both side(s) of a 10.8 cm x 10.8 cm portion of PEM. The PEM with catalyst coated MCTS on both side(s), was placed between 1 mil (25 micrometer) thick polyimide film and then covered with paper on the outside prior to passing the stacked assembly through the nip of the hot roll laminator at a speed of 1.2 ft./min. (37 cm/min.). Immediately after passing through the nip, while the assembly was still warm, the layers of polyimide and paper were quickly removed and the Cr-coated MCTS substrates were peeled off the CCM by hand, leaving the catalyst coated whiskers stuck to the PEM surface(s).

-General Electrolyzer Assembly Procedure

[0055] The membrane electrode assemblies were formed as follows:

1) A nominally incompressible cathode gasket made from a glass reinforced

polytetrafluoroethylene (PTFE) film (obtained under the trade designation "CHR TAPE" from Saint Gobain Performance Plastics, Hoosick Falls, NY). The thickness of the selected film for a particular Example had a thickness calculated to provide the desired gas diffusion layer compression in the assembled cell. The prepared gasket, having 10 cm x 10 cm outside size and 7 cm x 7 cm inside hollow, was put on the surface of the graphite flow field block of a 50 cm² electrochemical cell (obtained as Model SCH50 from Fuel Cell Technologies

Albuquerque, NM);

2) A selected cathode porous carbon paper was put in the hollow part of the gasket, with the hydrophobic surface (when present) facing up to contact with the cathode catalyst side of the CCM;

3) The prepared CCM was put on the surface of the carbon paper, the cathode side with H₂ evolution reaction (HER) catalyst was placed in contact with the (hydrophobic) surface of the carbon paper;

4) An anode gasket with 10 cm x 10 cm outside size and 7 cm x 7 cm inside hollow was placed on the oxygen evolution catalyst-coated surface of the CCM;

5) The anode gas diffusion layer (platinum-plated titanium sheet) was placed in the hollow part of the anode gasket with the platinum-plated side facing the anode catalyst (Ir) side of the CCM; and

6) The platinized titanium flow field block was placed on the surface of the anode gas diffusion layer and gasket. Then, the titanium flow field block, anode gas diffusion layer, CCM, cathode gas diffusion layer, and the graphite flow field block were compressed together with screws. The parts were checked to ensure they could be uniformly assembled and sealed.

-General Method for Testing Electrolyzer Cells

[0056] Full CCMs fabricated as described above were tested in an H2/O2 electrolyzer single cell. The full CCMs were installed with appropriate gas diffusion layers directly into a 50 cm² test cell (obtained under the trade designation "50SCH" from Fuel Cell Technologies), with quad serpentine flow fields. The normal graphite flow field block on the anode side was replaced with a Pt-plated Ti flow field block of the same dimensions and flow field design (obtained from Giner, Inc.) in order to withstand the high anode potentials during electrolyzer operation. This flow field block and a corresponding "Giner Pt/Ti" GDL, which was used in these examples, were described in Lewinski, K.A., Van Der Vliet, D., Luopa, S.M., "NSTF Advances for PEM Electrolysis - "The Effect of Alloying on Activity of NSTF Electrolyzer Catalysts and Performance of NSTF Based PEM electrolyzers," 2015, ECS Transactions, 69, (17), pp. 893-917, the disclosure of which is incorporated herein by reference. Purified water with a resistivity of 18 Megaohms was supplied to the anode at 75 mL/min. An 800A/10kW power supply (obtained under the trade designation "ESS", Model ESS 12.5-800-2-D-LB-RSTL from TDK-Lambda, Neptune, NJ), was connected to the cell and used to control the applied cell voltage or current density.

Conditions of Evaluation

[0057] In PEM electrolyzer test mode, the testing measured the potential difference across the cell (cell voltage, V) at 2 A/cm² current density at 80°C. As described above, highly purified deionized water having a resistivity of 18 Megohms was supplied to the anode at a flow rate of 75 ml/min. Lower cell voltage at a fixed current density is preferred, because it reduces the electrical energy requirements and operating cost of the electrolyzer, and it also reduces the production of high-energy intermediates such as peroxides and hydroxyl radicals that can produce undesirable side reactions and degrade the cell materials.

Comparative Example and Examples 1-17

[0058] A control electrolyzer and the electrolyzers of Examples 1-17 were formed using the general electrolyzer formation procedure described above, using the standard CCM, and using the cathode GDL, anode GDL, and gasket compression shown in Table 2, below.

Table 2

Comparative Example

[0059] A Control cell was assembled according to the "General Electrolyzer Formation Procedure" above, using a Giner Pt/Ti gas diffusion layer for both the cathode GDL and the anode GDL. The gasket thicknesses for the cathode and anode were selected to be such that the degree of GDL compression for both GDLs in the assembled Comparative Example cell would be 3%. The resulting control water electrolyzer cell was operated at a current density of 2 A/cm² at 80°C for 53.5 hours, with the cell voltage being measured periodically during that time, as shown in FIGS. 3 to 5. Example 1

[0060] The electrolyzer cell for Example 1 was assembled as described for the Comparative Example, except that the cathode GDL used was a hydrophobic treated carbon paper obtained from Toray Industries, Inc., under the trade designation "TORAY 060." The cathode gasket thickness was selected such that the cathode GDL compression of the carbon paper was 4%. Cell voltage test results for Example 1 are shown in FIG. 3, and the final voltage reading after 53.5 hours is listed in Table 2, above.

Example 2

[0061] The electrolyzer cell for Example 2 was assembled as described for the Comparative Example, except that the cathode GDL used was an untreated carbon paper (as-received) obtained from Mitsubishi Rayon Co., Ltd., under the trade designation "U105." The cathode gasket thickness was selected such that the cathode GDL compression of the carbon paper was 3%. Cell voltage test results for Example 2 are shown in FIG. 3, and the final voltage reading after 53.5 hours is listed in Table 2, above.

Example 3

[0062] The electrolyzer cell for Example 3 was assembled as described for the Comparative Example, except that the cathode GDL used was an untreated carbon paper (as-received) obtained from Mitsubishi Rayon Co., Ltd., under the trade designation "U105." The cathode gasket thickness was selected such that the cathode GDL compression of the carbon paper was 45%. While both the platinum-coated titanium porous sheet GDL and the carbon paper GDL were porous and electrically conductive, the carbon paper was much more flexible and compressible than the metallic Pt/Ti GDL construction. Cell voltage test results for Example 3 are shown in FIG. 3, and the final voltage reading after 53.5 hours is listed in Table 2, above.

Example 4

[0063] The electrolyzer cell for Example 4 was assembled as described for the Control cell above, except that the cathode GDL used was a commercial hydrophobic treated carbon paper (as-received) obtained from Freudenberg Vliesstoffe SE & Co. KG, under the trade designation "FREUDENBERG H2315 C2." The cathode gasket thickness was selected such that the cathode GDL compression of the carbon paper was 10%. Cell voltage test results for Example 4 are shown in FIG. 3, and the final voltage reading after 53.5 hours is listed in Table 2, above.

Example 5

[0064] The electrolyzer cell for Example 5 was assembled as described for Example 4 above, except that the cathode GDL compression of the carbon paper was 15%. Cell voltage test results for Example 5 are shown in FIG. 3, and the final voltage reading after 53.5 hours is listed in Table 2, above.

Example 6

[0065] The electrolyzer cell for Example 6 was assembled as described for Example 4 above, except that the cathode GDL compression of the carbon paper was 30%. Cell voltage test results for Example 6 are shown in FIG. 3, and the final voltage reading after 53.5 hours is listed in Table 2, above. Example 7

[0066] The electrolyzer cell for Example 7 was assembled as described for Example 4 above, except that the cathode GDL compression of the carbon paper was 45%. Cell voltage test results for Example 7 are shown in FIG. 3, and the final voltage reading after 53.5 hours is listed in Table 2, above.

Example 8

[0067] The electrolyzer cell for Example 8 was assembled as described for the Control cell above, except that the cathode GDL used was a commercial hydrophobic treated carbon paper (as-received) obtained from 3M Company, under the trade designation "2979." The cathode gasket thickness was selected such that the cathode GDL compression of the carbon paper was 10%. Cell voltage test results for Example 8 are shown in FIG. 3, and the final voltage reading after 53.5 hours is listed in Table 2, above. Example 9

[0068] The electrolyzer cell for Example 9 was assembled as described for Example 8 above, except that the cathode gasket thickness was selected such that the cathode GDL compression of the carbon paper was 15%. Cell voltage test results for Example 9 are shown in FIG. 3, and the final voltage reading after 53.5 hours is listed in Table 2, above.

Example 10

[0069] The electrolyzer cell for Example 10 was assembled as described for Example 8 above, except that the cathode gasket thickness was selected such that the cathode GDL compression of the carbon paper was 30%. Cell voltage test results for Example 10 are shown in FIG. 3, and the final voltage reading after 53.5 hours is listed in Table 2, above.

Example 11

[0070] The electrolyzer cell for Example 11 was assembled as described for Example 8 above, except that the cathode gasket thickness was selected such that the cathode GDL compression of the carbon paper was 45%. Cell voltage test results for Example 11 are shown in FIG. 3, and the final voltage reading after 53.5 hours is listed in Table 2, above.

Example 12

[0071] The electrolyzer cell for Example 12 was assembled as described for the Control cell above, except that the cathode GDL used a commercial hydrophobic treated carbon paper (as-received) obtained from Freudenberg Vhesstoffe SE & Co. KG, under the trade designation "FREUDENBERG H2315 C2," and the anode GDL was a platinum-coated titanium construction obtained from Bekaert Company, under the trade designation "BEKIPOR TITANIUM." The cathode gasket thickness was selected such that the cathode GDL compression of the carbon paper was 15%, and the anode gasket thickness was selected such that the anode GDL compression was again 4%. Cell voltage test results for Example 12 are shown in FIG. 4, and the final voltage reading after 53.5 hours is listed in Table 2, above.

Example 13

[0072] The electrolyzer cell for Example 13 was assembled as described for Example 12 above, except that the cathode gasket thickness was selected such that the cathode GDL compression of the carbon paper was 20%. Cell voltage test results for Example 13 are shown in FIG. 4, and the final voltage reading after 53.5 hours is listed in Table 2, above.

Example 14

[0073] The electrolyzer cell for Example 14 was assembled as described for Example 12 above, except that the cathode gasket thickness was selected such that the cathode GDL compression of the carbon paper was 25%. Cell voltage test results for Example 14 are shown in FIG. 4, and the final voltage reading after 53.5 hours is listed in Table 2, above.

Example 15

[0074] The electrolyzer cell for Example 15 was assembled as described for Example 12 above, except that the cathode GDL used was a commercial hydrophobic carbon paper obtained from 3M Company, under the trade designation "2979," and the cathode gasket thickness was selected such that the cathode GDL compression of the carbon paper was 15%. Cell voltage test results for Example 15 are shown in FIG. 5, and the final voltage reading after 53.5 hours is listed in Table 2, above. Example 16

[0075] The electrolyzer cell for Example 16 was assembled as described for Example 15 above, except that the cathode gasket thickness was selected such that the cathode GDL compression of the carbon paper was 20%. Cell voltage test results for Example 16 are shown in FIG. 5, and the final voltage reading after 53.5 hours is listed in Table 2, above.

Example 17

[0076] The electrolyzer cell for Example 17 was assembled as described for Example 15 above, except that the cathode gasket thickness was selected such that the cathode GDL compression of the carbon paper was 25%. Cell voltage test results for Example 17 are shown in FIG. 5, and the final voltage reading after 53.5 hours is listed in Table 2, above.

Analysis [0077] Cell voltages versus test time were measured for Examples 1-1 1 having Giner Pt/Ti as the anode GDL. The current density was kept constant at 2 A/cm² and the temperature was kept at 80°C. The cell voltage values after 53.5 hours are summarized in Table 2, above. FIG. 3 illustrates the cell voltages (V) vs. test timing (hours) of the different carbon papers as cathode GDLs for PEM water electrolysis.

[0078] Cell voltage versus test time was measured for Examples 12- 14 having the carbon paper obtained under the trade designation "FREUDENBERG H2315 C2" as the cathode GDL and using Bekaert Pt/Ti as the anode GDL. The current density was kept constant at 2 A/cm² and the temperature was kept at 80°C. The cell voltage values after 53.5 hours are summarized in Table 2, above. FIG. 4 illustrates the cell voltage (V) versus test time (h) for PEM water electrolysis.

[0079] Cell voltage versus test time was measured for Examples 15- 17 having carbon paper 2979 as cathode GDL and Bekaert Pt/Ti as anode GDL. The current density was kept constant at 2 A/cm² and the temperature was kept at 80°C. The cell voltage values after 53.5 hours are summarized in Table 2, above.

[0080] The terms and expressions that have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the embodiments of the present invention. Thus, it should be understood that although the present invention has been specifically disclosed by specific embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those of ordinary skill in the art, and that such modifications and variations are considered to be within the scope of embodiments of the present invention.

Claims

What is claimed is:

1. An electrolyzer comprising a membrane electrode assembly, the membrane electrode assembly comprising:

a proton-exchange membrane having first and second opposed major surfaces;

a cathode on the first major surface of the proton-exchange membrane;

an anode on the second major surface of the proton-exchange membrane; and

a gas diffusion layer contacting the cathode, the gas diffusion layer comprising at least one of porous carbon paper or porous carbon cloth, and a hydrophobic material.

2. The electrolyzer of claim 1, wherein the gas diffusion layer has pores ranging in size from 10 nanometers to 100 micrometers.

3. The electrolyzer of either one of claims 1 or 2, wherein the gas diffusion layer has pores that are substantially homogeneously distributed therein.

4. The electrolyzer of any one of claims 1 to 3, wherein the hydrophobic material is substantially homogeneously distributed on the gas diffusion layer.

5. The electrolyzer of any one of claims 1 to 4, wherein the hydrophobic material is 0.001 wt.% to 30 wt.% of the gas diffusion layer, based on the total weight of the gas diffusion layer.

6. The electrolyzer of any one of claims 1 to 5, wherein the hydrophobic material comprises at least one of polytetrafluoroethylene, polyvinylidene fluoride, fluorinated ethylene propylene,

tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene -alky 1 vinyl ether co-polymer, polychlorotrifluoroethylene, ethylene -tetrafluoroethylene co-polymer, ethylene-chlorotrifluoroethylene co-polymer, or a surfactant.

7. The electrolyzer of any one of claims 1 to 6, wherein at least one of the anode or the cathode comprises a catalyst coating.

8. The electrolyzer of any one of claims 1 to 7, wherein at least one of the anode or the cathode comprises a nano-structured thin film.

9. The electrolyzer of claim 8, wherein at least one of the cathode or the anode comprises nanostructured elements comprising microstructured support whiskers having an outer surface at least partially coated by a catalyst material of at least one of the cathode or anode.

10. The electrolyzer of any one of claims 1 to 9, wherein at least one of the cathode or the anode independently comprises a catalyst support.

1 1. The electrolyzer of any one of claims 1 to 10, wherein a catalyst material of at least one of the cathode or the anode comprises at least one of platinum, gold, ruthenium, iridium, palladium, rhodium, nickel, iron, molybdenum, tungsten, niobium, copper, cobalt, manganese, titanium, or an alloy thereof.

12. The electrolyzer of any one of claims 1 to 1 1, further comprising:

a cathode gasket in contact with the gas diffusion layer; and

an anode gasket in contact with an anode gas diffusion layer on the anode.

13. A method of making the electrolyzer of any one of claims 1 to 12, the method comprising: applying the gas diffusion layer to the cathode to form the electrolyzer.

14. A method of using the electrolyzer of any one of claims 1 to 12, the method comprising: applying an electrical potential across the anode and the cathode;

providing water to the anode; and

generating hydrogen from water with the membrane electrode assembly.

15. An electrolyzer comprising:

a proton-exchange membrane having first and second opposed major surfaces;

a cathode on the first major surface of the proton-exchange membrane;

an anode on the second major surface of the proton-exchange membrane; and

a gas diffusion layer contacting the cathode, the gas diffusion layer comprising at least one of porous carbon paper or porous carbon cloth, and a hydrophobic material that is present in a range of 0.001 wt.% to 30 wt.% of the gas diffusion layer, based on the total weight of the gas diffusion layer; a cathode gasket contacting the cathode;

an anode gas diffusion layer contacting the anode; and

an anode gasket contacting the anode gas diffusion layer.