WO2024148419A1 - Titanium textile - Google Patents

Abstract

It is provided a metallic textile and a process for producing same, the metallic textile comprising a titanium textile layer having an interlocking dendritic microstructure, a porosity of from 20 to 95 %. The titanium textile layer can have a flexibility sufficient to allow the titanium textile layer to be rolled on itself. The metallic textile can be incorporated in a rolled product and/or used as porous transport layer in an electrolytic cell.

Description

TITANIUM TEXTILE

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application is claiming priority from U.S. Provisional Application No. 63/434,564 filed December 22, 2022, the content of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

[0002] This disclosure relates to the field of porous metallic textile, more specifically porous transport layers (PTL) and titanium containing PTL, methods of making same and methods of using same.

BACKGROUND OF THE ART

[0003] Porous metals and metallic foams have unique properties and characteristics and have been used in different applications. Thin metallic porous layers have been successfully used in batteries, filtration, gas getters, spargers, aerators, electromagnetic shields, catalysts or catalyst supports, electrodes, and transport layer. One application of porous metals is as metallic porous transport layers (PTL) which are useful to address the growing demand of renewable energy sources in electrochemistry. One example of usage of PTLs in electrochemistry is in proton exchange membrane water electrolysers (PEMWE). In such applications, the PTLs conduct electric charges and allow the transport of the water to the catalyst layers and the removal of gaseous oxygen. Various materials have been employed as PTLs, however titanium is preferred due to its unique corrosion resistance. Traditional titanium PTLs include meshes, expanded meshes, sintered fibers and powders. Meshes and expanded meshes are flexible and can be produced in large surfaces. However, they are essentially composed of perforations going through the layer and have low surface area. These characteristics impact their properties and limit their use in many applications. The structure and properties of sintered powders and fibers are limited by the packing of the particles or fibers used to produce the layer. Moreover, PTLs produced by sintering metal powders or fibers are limited to the size of the furnace in which they are produced. The flexibility of PTLs made of sintered powder is usually limited.

[0004] Accordingly, improvements in the properties of titanium textile are desired, particularly for use in electrolysers, batteries, filtration, catalysts, catalyst supports and the like. SUMMARY

[0005] It is provided a metallic textile, comprising a titanium textile layer having an interlocking dendritic microstructure and a porosity of from 20 to 95 %.

[0006] In one embodiment, the titanium textile layer has a flexibility sufficient to allow the titanium textile layer to be rolled on itself.

[0007] In an embodiment, the porosity is from 40 to 95%, from 50 to 90 %, or more preferably from 55 to 85 %.

[0008] In another embodiment, the textile layer has a thickness between 50 pm and 3 mm, or preferably of less than 500 pm.

[0009] In a further embodiment, the textile layer further comprises a metal or ceramic coating on its surface.

[0010] In another embodiment, the titanium textile layer comprises from 0.05 to 2 wt. % oxygen, preferably between 0.05 and 0.4% wt. %.

[0011] In a further embodiment, the titanium textile layer is used as a metallic porous transport layer.

[0012] In a further embodiment, the metallic porous transport layer is flexible and optionally rolled.

[0013] In an embodiment, the metallic textile is formed by deposition of the titanium powder on a substrate.

[0014] In another embodiment, the porosity is characterized by pores having a size of from 5 to 250 pm.

[0015] It is also provided a rolled product comprising the metallic porous transport layer as described herein being rolled on itself.

[0016] It is provided a rolled product comprising the metallic porous transport layer as defined herein being rolled on itself. [0017] It is additionally provided a process of producing a titanium textile, the process comprising the consolidation of titanium having a dendritic microstructure.

[0018] It is additionally provided a process to consolidate the titanium having a dendritic microstructure using sintering.

[0019] It is additionally provided a process where pressure is used during the sintering. The sintering is conducted by heating the material to a temperature from 800°C up to 80% of the melting point of titanium to obtain the titanium textile.

[0020] In an embodiment, the consolidation causes a permanent interlocking of the dendritic microstructure.

[0021] In an embodiment, the sintering comprises applying a pressure on the plate.

[0022] In a further embodiment, the pressure applied is during the sintering process with or without spacer to control a final thickness of the titanium textile.

[0023] In another embodiment, the sintering causes a permanent interlocking of the dendritic microstructure.

[0024] In an additional embodiment, the temperature is from 1000 to 1400°C.

[0025] In an embodiment, the titanium having a dendritic microstructure is rolled before the sintering (i.e., direct powder rolling).

[0026] In an additional embodiment, the titanium having a dendritic microstructure is mixed with a liquid to ease the shaping prior to sintering (such as e.g., spreading into a thin layer, tape casting, or rolling).

[0027] In another embodiment, the process described herein further comprises adding a binder to the titanium before sintering.

[0028] In an additional embodiment, the titanium having a dendritic microstructure is mixed with a binder and shaped before sintering (such as e.g., extrusion). [0029] In an embodiment, the process described herein further comprises hot rolling, cold rolling or warm rolling the textile after sintering to reduce the thickness, to modify the density, the structure or the surface finish of the titanium textile.

[0030] In an embodiment, the process described herein further comprises coating titanium textile with a metal or ceramic coating.

[0031] In an embodiment, the process described herein further comprises weaving or bonding the titanium textile with other pieces of titanium textile to increase its size.

[0032] In another embodiment, the titanium is in the form of wool ordeagglomerated dendrites produced by molten salt electrorefining.

[0033] In another embodiment, the titanium is in the form of wool ordeagglomerated dendrites produced by the Armstrong process, or any other method.

[0034] Many further features and combinations thereof concerning the present improvements will appear to those skilled in the art following a reading of the instant disclosure.

DESCRIPTION OF THE DRAWINGS

[0035] FIG. 1A is scanning electron microscopy (SEM) image of sintered titanium powder according to the prior art.

[0036] FIG. 1B is a SEM image of titanium textile produced with fibers according to the prior art.

[0037] FIG. 2A is a SEM image of titanium wool precursor at magnification 50x.

[0038] FIG. 2B is a SEM image of deagglomerated titanium wool precursor at magnification

50x.

[0039] FIG. 2C is a SEM image of titanium wool precursor at magnification 200x.

[0040] FIG. 2D is a SEM image of titanium wool precursor at magnification 500x.

[0041] FIG. 3A is a photograph of the device used to determine the properties of the titanium textile. [0042] FIG. 3B is a schematic showing the flow rate-pressure relationship in a radial-flow.

[0043] FIG. 3C is a photograph showing a close-up on the device of Fig. 3A.

[0044] FIG. 3D is a photograph showing a close-up of the donut shaped protector of the device of Fig. 3A.

[0045] FIG. 4A is a photograph of the titanium textile.

[0046] FIG. 4B is a photograph of the titanium textile being bent by hand.

[0047] FIG. 5A is a microscopy image of the titanium textile at 50x magnification.

[0048] FIG. 5B is a microscopy image of the titanium textile at 100x magnification.

[0049] FIG. 5C is a microscopy image of the titanium textile at 200x magnification.

[0050] FIG. 5D is a microscopy image of the titanium textile at 300x magnification.

[0051] FIG. 6A is a SEM image of the titanium textile at 50x magnification.

[0052] FIG. 6B is a SEM image of the titanium textile at 200x magnification.

[0053] FIG. 7 is a graph comparing the thickness under compression of the titanium textile, commercial porous Ti powder sheet A and commercial porous Ti fiber sheet B.

[0054] FIG. 8 is a graph showing the resistance under compression of the titanium textile, commercial porous Ti powder sheet A and commercial porous Ti fiber sheet B.

[0055] FIG. 9 is a graph showing the resistivity under compression of the titanium textile, commercial porous Ti powder sheet A and commercial porous Ti fiber sheet B.

[0056] FIG. 10 is a graph showing the in-plane permeability under compression of the titanium textile, commercial porous Ti powder sheet A and commercial porous Ti fiber sheet B.

[0057] FIG. 11 shows two photographs of an-house designed electrolyser cell with an active area of 5 cm² used for in-situ characterisation of the developed porous transport layer.

[0058] FIG. 12 is a graph showing polarization curves of the PEMWE assembly. [0059] FIG. 13 is a graph showing polarization curves of the PEMWE assembly corrected for ohmic losses.

[0060] FIG. 14A is a photograph of an example oftwo pieces oftitanium textile joined together by cold rolling.

[0061] FIG. 14B is a photograph of an example of two pieces of titanium textile rolled over a mandrel.

[0062] FIG. 15A is a 2D image of a cross section of the laminated felt composed of denser surfaces (approximately 100 pm thick) with smaller pore size and a more porous core with larger pore size (approximately 200 pm); extracted from the reconstructed volume of a 3D x-ray microtomography.

[0063] FIG 15B is a SEM image of the cross section with a zoom on the top portion providing a closer view of the denser surface over the more porous core.

[0064] FIG. 16A is a SEM image presenting a cross section of the felt covered with fine particles.

[0065] Figure 16B is a SEM image presenting the top surface covered with fine powder and the porosity that is much lower and the pores smaller compared to the opposite surface (Figure 16C).

[0066] Figure 16C is a SEM image presenting the opposite surface which is more porous than the surface covered with fine particles.

DETAILED DESCRIPTION

[0067] There is provided a metallic textile comprising a layer having an interlocking dendritic microstructure and a porosity from 20 to 95 %. Accordingly, the metallic textile can be referred to as a porous metallic textile.

[0068] Porous metallic textiles are used in different applications and are key components in electrolysers, fuel cells, batteries, electrodes, gas getters, spargers, aerators, electromagnetic shields, catalysts and catalyst supports as well as filtration media. [0069] In one particular example, the porous metallic textile is a porous transport layer (PTL), which is positioned between the bipolar plates (BPs) and catalyst coated membrane (CCM). The PTL is one of the key components of PEMWEs, and plays an important role in the cell performance. In some embodiments, the PTL is placed between the membrane electrode assembly (MEA) and the separator plates/bipolar plates (BPs) at both electrode sides. PTLs can also be referred to as gas diffusion layers (GDL), liquid/gas diffusion layers (LGDL) or current collectors (CO). The PTL is responsible for expediting the transport of the liquid and gas between the flow channels and electrodes, electrical conduction, and heat conduction within the cell. The multi-functions that the PTL plays on the anode or GDL on the cathode of a PEMWE are summarized as follows: transfers reactant water; removes evolved gases (hydrogen and oxygen); facilitates good electrical conductivity between the BPs and catalyst layers; removes heat from the reaction; and provides mechanical support for the CCM, especially under compression. In addition, the PTL is corrosion resistant because it has to survive the acidic environment of the solid electrolyte, and must remain stable enough to withstand the high overpotentials during operation. It is important to balance the PTL properties with respect to thickness, porosity, pore size, surface roughness, mechanical stability, flexibility, electrical and thermal conductivity, and surface passivation to ease the manufacturing and achieve the best PTL performance within the PEMWE. This can be achieved by the titanium textile described herein.

[0070] The metallic PTL of the present disclosure comprises a titanium textile layer having an interlocking dendritic microstructure. The PTL has a variable porosity from 20 to 95 %. The porosity can be optimized depending on the specific application of the PTL. The titanium textile layer is a flexible layer, and the flexibility is such that the titanium textile layer can be rolled on itself. This is an advantage because the production, transport and storage of titanium textile can be facilitated when rolled. The flexibility is achieved thanks in part to the interlocking dendritic microstructure obtained by solid state sintering as explained in further details herein below. The structure and properties of the titanium textile are unique (combination of porosity, pore size, flexibility and high surface area) and advantageous for the development of different devices (i.e., electrolyser, electrode, catalyst, catalyst support, filtration media, etc.).

[0071] As encompassed herein, the term textile is intended to encompass e.g., and not limited to, felt, mesh, foams and wool or fiber like material.

[0072] As will be apparent in the present disclosure, there are many advantages to the titanium textile described herein. First of all, the unique structure of the electrorefined product (i.e., dendritic microstructure) combined with the fabrication process allows to produce materials with unique structure, density and properties, which are very different from existing products obtained by sintering powders or fibres, meshes or expanded meshes. The traditional fabrication of porous layers using fibres and powders does not provide a lot of flexibility to control the density and texture (i.e., the texture and structure mostly rely on the stacking of the particles or fibres into the porous layer). The materials produced with powders are denser (porosity typically lower than 50%), have lower permeability, are not flexible and cannot be produced into a rolled product (requisite to produce large scale roll to roll production process). The materials produced with sintered powder are difficult to produce in very thin layer and are usually very expensive, thus limiting their use in numerous applications. Materials produced with fibres or chips usually have lower surface area.

[0073] In contrast, the titanium textile of the present disclosure is produced using titanium material having a dendritic microstructure in wool or deagglomerated form. It is encompassed in some embodiments that the titanium textile is in the form of wool or deagglomerated dendrites produced by molten salt electrorefining, the Armstrong process (reduction of titanium tetrachloride by sodium metal), or any other known method. The dendritic microstructure of the powder produced from the titanium wool interlocks after solid state sintering to obtain the titanium textile. The dendritic microstructure can be described as irregular and having branch-like protrusions. The dendrite or branch-like structure physically interlocks and improves bounding between the particles thus improving the textile’s mechanical properties.

[0074] A porosity of 20 to 95 % can be achieved in the PTL of the present disclosure. Porosity can have a direct effect on charge and mass transport inside the PTLs. A porosity between 50 and 95 % is usually preferred. It is recognized that high porosity facilitates gas removal but increases the ohmic resistance. The pore gradient may play a role to get the best compromise for the efficiency of a PTL in PEMWE (i.e., reactant and gas diffusion and contact resistance).

[0075] The titanium textile pore size (typically between 10 and 500 pm) may be modified by adjusting the precursor’s structure, particle size and felt fabrication process. Large porosity reduces the contact points at the PTL catalyst layer (CL) interface and increases the contact resistance. Large pore size (usually > 150 pm) may increase ohmic loss due to the poor contact between the PTL and the CL. Generally, larger pores facilitate water and gas transport at the expense of electrical and thermal conductivity, and vice versa for smaller pores. Moreover, a large pore size may compromise the mechanical integrity and the stability of the titanium textile.

Accordingly, the pore size should not exceed 500 pm.

[0076] The thickness of the titanium textile is an important parameter when considering its use in PTL. The thickness and the quality of the interface between the PTL and catalyst layer (CL) affect PTL and PEMWE performances. Accordingly, smaller thicknesses are usually preferred, typically less than 500 pm, less than 450 pm, less than 400 pm, less than 375 pm, less than 350 pm, less than 300 pm, less than 250 pm or less than 200 pm. Thicker products for other applications can be obtained by stacking or assembling layers of the titanium textile.

[0077] The important flexibility of the titanium textile is an advantage of the present textile material. The flexibility generally refers to how much the textile will bend without breaking, as well as its ability to return to its original shape after bending. The flexibility is affected by the material’s intrinsic properties but also its geometry, i.e., the thinner the textile, the higher the flexibility.

[0078] The titanium textile of the present disclosure is characterized by a high surface area. The surface area is a function of the shape of the precursor (i.e., dendritic), its thickness and the processing conditions.

[0079] The higher surface contact between the PTL and the CL reduces the contact resistance. The contact surface depends on the density of the PTL surface, the PTL surface roughness and the applied pressure.

[0080] Usually unavoidable, titanium contains a small amount of oxygen in solution or in the form of surface oxide. Consequently, the titanium textile layer usually comprises a small amount of oxygen. In one example, there can be from 0.05 to 2 wt. % oxygen, preferably from 0.05 to 1 wt. % oxygen, or from 0.1 to 0.4 wt. % oxygen. Oxygen in solution reduces the ductility of titanium and may impact the flexibility of the felt. Surface oxidation may impact the surface conductivity.

[0081] The flexible and permeable titanium textile as provided herewith is produced at low cost relative to other materials available on the market. The precursor material is electrorefined titanium, such as titanium wool, having a network of dendritic filaments. The dendritic structure is important as it provides a precursor with very low apparent density. The low apparent density of the textile allows adjusting the density of the textile. The dendritic structures help the interlocking and flexibility compared to sintered powders. As encompassed herein, a method of compaction could be used prior to sintering, e.g., loose powder distribution, direct powder rolling or compaction, etc. After sintering, the interlocking is permanent. The density of the textile can be adjusted by controlling the amount of precursor, the pressure (before, during and after sintering) and temperature of the sintering treatment. This allows for the production of materials with controlled porosity and porosity levels. As the density of the precursor is much lower than the powder normally used to produce sintered powders, a much lower density can be obtained, providing more flexibility in controlling the density of the textile. The limitations in flexibility observed with sintered powders are overcome with the flexible titanium textile. Since the product is flexible, it can be rolled and used in roll-to-roll processes. Moreover, the dimensions and rigidity of PTLs represent significant constraints during the fabrication of PEMWEs. This dimension limitation regarding traditional materials is also overcome herein because multiple pieces of titanium textile can be joined together to extend the total surface area. Accordingly, the size of the titanium textile is not limited by the size of the plate.

[0082] The electrorefined titanium is consolidated by sintering at high temperature (at least 800°C), optionally under pressure to produce a thin porous layer (i.e., textile). The consolidation is done below the melting point of titanium. In some embodiments, the temperature is from 1000°C to 1400°C. The titanium wool can be extended and homogeneously distributed on a substrate and sintered under a plate that provides the pressure for levelling and controlling the thickness of the thin flat textile. In some embodiments, the sintering is performed under a non-oxidizing atmosphere for example under vacuum or in an inert gas such as Ar or He. Another method which can improve the uniformity of the textile starts with a step in which the wool is deagglomerated and then distributed and sintered as described above. This deagglomeration can be realized by various shearing methods such as milling, carding or blade cutting in various gas or liquid media. Following this deagglomeration process, the powder is optionally further sieved, filtered or separated to isolate a given particle size distribution favorable to PTL performance (i.e., elimination of ultrafine or oversize particles). The amount of wool or titanium powder distributed on the substrate, the temperature and pressure (weight of the plate above the precursor during the sintering) as well as the thickness of spacers between the plates determines the thickness of the titanium textile.

[0083] The wool or titanium powder can be spread into a thin layer using a liquid, a binder or a combination thereof. The shaping can be done when the binder is melted. Also, the materials can be shaped using pressure prior to sintering using for example direct powder rolling. In some embodiments, a slurry of titanium particles in liquid suspension is formed and then deposited on a substrate surface to form a textile. In other embodiments, a cold spray can be used in a similar fashion using dry particles.

[0084] Coatings could be used to avoid the bonding of the textile to the plate during sintering or to minimise contamination of the textile during processing. The density and properties of the resulting textile can be adjusted by modifying the structure of the electrorefined precursor, the amount of materials, the pressure (i.e., weight of the plate), the thickness of spacers between the plates, the sintering temperature and time.

[0085] The materials can be assembled (e.g., bonding or welding the textile sheets together) to produce rolls of textiles. The precursor and method allow the production of textiles with porosity ranging from 20 to 95%, so that one may tailor the properties of the textile and PTLs. These attributes are important for the mass production of porous transport layers, but also for the production of many other devices, including for example electrodes, catalyst supports, filtration medias, etc.

[0086] The density and properties of the resulting textile can be adjusted by modifying the structure of the electrorefined precursor, the method to depose the materials on the plate, the amount of electrorefined precursor, the method to consolidate the material, the pressure (i.e., weight of the plate), the spacing between the plates, the sintering temperature and time. The density, structure, properties, thickness and surface finish can be modified by cold, warm or hot rolling the textile to the desired thickness. The structure and properties of the PTLs can be adjusted by stacking layers to produce laminates of different structures or properties (e.g., denser layers on the external surfaces and more porous layer in the core). The sintered textile may also be coated to modify its structure (e.g., apply and sinter powders on the surface of the textile). The surface of the titanium may be treated or coated to modify the composition of the surface, the surface properties and its corrosion resistance.

[0087] Ti-based PTL materials preferably have a coating (typically noble metals like Pt, Ir, Au or Ta to serve as protective layers, prevent the formation of an oxide layer and minimise the interfacial contact resistance). Platinum, tantalum or iridium coated titanium are possible. Alternatively, due to the cost of noble metals, a surface treatment can be performed instead by etching Ti with an acid such as HCI. During etching in acid, a Ti hydride under-layer with considerable thermal and chemical strength can be formed, serving as a protective layer against passivation. The formation of Ti hydride occurs when the hydrogen content in the metal surpasses the solubility limit. Other potential surface treatments to improve conductivity such as incorporating a microporous layer, gas nitriding and antimony doped TiO2 coating have also been used.

[0088] There are many applications for the PTL described herein, for example, in the production of hydrogen, which is a substantial market. With the increasing global consumption of energy and interest in the development of sustainable ways of producing energy, hydrogen production and consumption are expected to grow very significantly in the coming years. Reduction in the cost of PTLs is required for the commercially viable green hydrogen production using the PEMWE technology. Water electrolysis is currently the most eco-friendly way of producing high purity hydrogen and this production method is expected to grow. Porous transport layers (PTLs) are essential components in the fabrication of PEMWE and represent a significant portion of the cost of these devices (typically 15-25%; Doan et al., International Journal of Energy Research, 2021 , 45, 14207). A reduction of the cost of the PTL should help reducing the cost of the electrolyser and make this production method more attractive. The access to rolls of PTLs as achieved herein make the development of roll-to-roll fabrication processes possible (the process is currently a batch process) and helps reduce the cost of the electrolyser. Better PTLs also help improve efficiency and longevity of the devices and make this production method more attractive. Currently, water electrolysis accounts for only 4% of the global hydrogen production and the market share for PEMWE is expected to grow, especially if the electrolysers become cheaper, more efficient and more reliable (Yu et al., Applied Catalysis B: Environmental, 2018, 239, 133).

[0089] The PTLs used for the production of PEMWE were initially developed for other applications (e.g., filtration) and are not perfectly adapted for the production of the electrolysers. The cost of these materials are presently more than 2 orders of magnitude higher than the cost of dense titanium. The optimisation of new PTLs adapted to the specific needs of PEMWEs allows the reduction of the cost of PEMWEs which may contribute to the expansion of this alternative method of producing and transporting clean energy. This is achieved herein with the titanium textile.

[0090] Besides PTLs used in PEMWEs, the unique structure of the materials produced herein makes them valuable in many other applications (filtration, catalyst support, medical applications and the like). The dimensions and rigidity of the titanium PTL are characteristics determining their limitations in various applications. However, the titanium textile overcomes these traditional limitations. For example, as explained above, access to rolls of titanium felt enables the continuous production of devices, such as the cells.

EXAMPLE 1

[0091] For the purpose of comparison, scanning electron microscopy images showing the microstructure of commercial sintered titanium powder (Fig. 1A) and commercial titanium fiber (Fig. 1 B) are provided. These two materials have been traditionally used as PTLs. None of these materials have the dendritic microstructure of the titanium textile achieved herein. In addition, the resulting properties of the titanium textile are also different from those of the materials presented in Figs. 1A-1 B.

[0092] In the present Example, all the scanning electron microscopy images were performed using scanning electron microscopy (SEM) and secondary electron image (SEI) mode to evaluate the morphology of the powder and textile at various magnifications.

[0093] The titanium textile as encompassed herein was produced with a titanium wool manufactured by electrorefining in molten salts. Scanning electron microscopy images of the titanium wool precursor were taken and are shown in Figs. 2A-2D. As can be seen in Figs. 2A- 2D, the titanium wool has a dendritic microstructure characterized by inhomogeneous tree-like grain protrusions visible at all magnifications shown.

[0094] A titanium textile was produced by solid state sintering of the titanium wool. The titanium wool was consolidated at a temperature of 1000°C under pressure to produce a thin porous layer (i.e., the titanium textile). The pressure was applied by placing the titanium wool under a plate which provided the pressure for leveling and controlling the thickness of the thin flat sheets. The weight on the plate can be varied to adjust the pressure applied and the density of the resulting material.

[0095] A 3-in-1 device was used to measure the thickness under compression (TUC), the resistivity under compression (RUC) and the in-plane permeability (IPP) simultaneously (Fig. 3A). This was achieved with the flow rate-pressure relationship in a radial-flow using an annulus of gas diffusion layer (GDL) samples (Fig. 3B). The device offered a pneumatic compression under a varying load up to 10 MPa. A two-piece through-plane permeability (TPP) adaptor was designed for TPP measurement. A donut shaped protector was used for the bottom plate and disk shaped protector for the upper plate (Figs. 3C-3D). The sample GDL was 24 mm in diameter and the active TPP area was 12 mm in diameter.

[0096] A photograph of the resulting titanium textile is shown in Fig. 4A. The flexibility obtained allowed the titanium textile to bend as shown in Fig. 4B without breaking. The microstructure was observed by optical microscopy imaging (Figs. 5A-5D) and scanning electron microscopy imaging (Figs. 6A-6B). As can be seen from the microscopy imaging, the dendritic microstructures have interlocked to form the titanium textile. None of the prior art microstructures (Figs. 1A-1 B) resemble the presently obtained titanium textile as they all lack the interlocking dendritic microstructure of the titanium textile.

[0097] Two materials (a commercial porous Ti sheet A made from Ti powders and commercial porous Ti sheet B made from Ti fiber) were used to compare the properties of the titanium textile obtained as provided herewith (Table 1). The titanium textile produced using the process described herein had an average thickness of 344 pm with a standard deviation of 9 pm. The average porosity was 75 % with a standard deviation of 2%.

Table 1 . Properties of the materials tested

[0098] Using the 3-in-1 device the TUC of the titanium textile was measured under a compression of up to 4 MPa. The TUC of the titanium textile was also compared to the one of commercial porous Ti sheet A and commercial porous Ti sheet B under the same compression conditions (Fig. 7). Similar resistance to thickness reduction under compression was observed for the Ti textile and the commercial porous Ti sheet A and B. The resistance and the resistivity were also measured in function of the compression using the 3-in-1 device (Figs. 8 and 9). The titanium textile achieved a similar reduction of the resistance and the resistivity when compared to commercial porous Ti sheet A and commercial porous Ti sheet B. The in-plane permeability was also measured (Fig. 10). The titanium textile achieved a permeability under compression very similar to commercial porous Ti sheet A, but different to the commercial porous Ti sheet B.

EXAMPLE 2

[0099] To further characterise and compare the developed titanium textile with commercial PTL, this material was tested as a porous transport layer (PTL) in a proton exchange membrane water electrolyser (PEMWE). To do so, the Ti sheet A and the titanium textile as described herein were assembled in an in-house designed PEM water electrolyser cell with an active area of 5 squared centimetres (Fig. 11). The test station used as a capacity of up to 150 W power with maximum current of 36 A and voltage of 5 V; its operating temperature ranging from ambient to 90°C with an air bladder compression of 50-100 psi. On the anode side, the uncoated PTL materials were inserted in the fixture with a cathode gas diffusion layer (GDL) consisting of a Toray carbon paper TGP-H-120 with 5% PTFE available commercially. Between the anode PTL and the cathode GDL, a catalyst coated membrane (COM) was inserted. The COM was made of Nation 117 incorporating a 2.0 mg IrOx/cm² catalyst on the anode side, and 1.0 mg Pt/cm² (as Pt/C) on the cathode side.

[0100] The detailed above cell stack was initially tested under various current densities to create a polarisation curve with the commercial Ti sheet A to evaluate the variability of the measurement in as conditioned state two times (repeat), and with a new sheet of the same material (also repeated). After that, the Ti textile described herein was measured under similar conditions and the Ti sheet A was tested again. Figure 12 confirms that the Ti textile does perform similarly as the Ti sheet A as its measurements are within the variability of the measurements realized on the Ti sheet A material. Similar behavior can be observed when the cell voltage is corrected for the ohmic losses of the assembly, but it does amplify the fact that the COM might have suffered from multiple assemblies/disassemblies realized in this test which increased the cell charge transfer resistance (Figure 13).

EXAMPLE 3 [0101] Roll-to-roll process may be of interest for the industrialisation, automation and mass production of some products. In these applications, there is an interest to have long pieces of felt and have the possibility to roll the felt over a mandrel. When the size of the felts is limited by the size of the equipment and the process used (e.g., sintering), it may be interesting to join different pieces of felt together to produce longer pieces of material and roll the resulting product over a mandrel. Different approaches for joining could be considered such as welding, brazing, bonding with adhesives and cold forming. This example presents the use of cold rolling to bond pieces of felt together.

[0102] Pieces of felt were produced using a process similar to the one presented in Example 1 . The pieces of felt (300 pm thick) were bonded by rolling them together while the extremities of consecutive felts (i.e., the end of one felt over the beginning of the following felt) were overlapped (3 cm overlap). The felts were rolled to 300 pm thickness. The reduction of the overlapped section (2 x 300 pm = 600 pm) down the 300 pm lead to the entanglement of the two layers of the felt and the bonding of the two pieces of felt together. The resulting pieces is longer (Figure 14A) and flexible, and it can be handled and rolled over a mandrel (Figure 14B).

EXAMPLE 4

[0103] In some applications, differences in porosity through the section of the felt may represent an advantage. Different methods could be used to obtain different levels of porosity at the core and surfaces of the felt. This example provides two methods to produce felts with graded porosity. The first method involved the lamination of felts with different porosity level. Precursors were produced using similar commercially pure titanium metal particles of size between 63 and 212 pm that were pre-sintered into 1 mm thick felts. One of the felt was cold rolled down to 200 pm. Two pieces of that 200 pm thick felt were then sandwiched over an as-sintered felt (i.e., not rolled). The resulting laminate was then rolled down to 400 pm. The cold rolling allowed the different layers of felt to bond together and provided a sandwich structure with higher density and smaller pore size on the top and bottom surface of the felt (Figure 15B).

[0104] The second method involves the coating of the felts with a suspension of fine titanium particles (-20 pm) followed by a sintering for 1 h at 1000°C under vacuum. A felt was produced using the method described in Example 1. The precursors (made of commercially pure titanium metal particles of size between 63 and 212 pm) were pre-sintered into 1 mm thick felts and then cold rolled down to 450 pm. One of the surfaces was coated using a suspension of -20 pm titanium particles. The felt was dried and the heat treated at 1000°C for 1 h under vacuum. The resulting felt had one surface with finer porosity than the core of the felt. Figure 16A presents a cross section of the felt. The top surface (Figure 16B) is covered with fine powder and the porosity is much lower and smaller compared to the other surface (Figure 16C). This approach can be used to tailorthe porosity in the core and surface and optimised the properties of the felt (e.g., optimise surface contact, reduce contact resistance while maintaining high core permeability).

[0105] While the present disclosure has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses, or adaptations including such departures from the present disclosure as come within known or customary practice within the art and as may be applied to the essential features hereinbefore set forth, and as follows in the scope of the appended claims.

Claims (26)

WHAT IS CLAIMED IS:

1 . A metallic textile, comprising: a titanium textile layer having an interlocking dendritic microstructure; and a porosity of from 20 to 95 %.

2. The metallic textile of claim 1 , wherein the titanium textile layer has a flexibility sufficient to allow the titanium textile layer to be rolled on itself.

3. The metallic textile layer of claim 1 or 2, wherein the porosity is from 40 to 95%, from 50 to 90 %, or from 55 to 85 %.

4. The metallic textile of any one of claims 1 to 3, wherein the textile layer has a thickness between 50 pm and 3 mm, or of less than 500 pm.

5. The metallic textile layer of any one of claims 1 to 4, further comprising a metal or ceramic coating on its surface.

6. The metallic textile layer of any one of claims 1 to 5, wherein the titanium textile layer comprises from 0.05 to 2 wt. % oxygen, or between 0.05 and 0.4% wt. %.

7. The metallic textile of any one of claims 1 to 6 is used as a metallic porous transport layer.

8. The metallic textile of claim 7, wherein the metallic porous transport layer is flexible and optionally rolled.

9. The metallic textile of any one of claims 1 to 8, wherein the metallic textile is formed by deposition of the titanium powder on a substrate.

10. The metallic textile of any one of claims 1 to 9, wherein the porosity is characterized by pores having a size of 5 to 250 pm.

11. A rolled product comprising the metallic porous transport layer as defined in claim 7 being rolled on itself.

12. A process of producing a titanium textile, the process comprising consolidating titanium having a dendritic microstructure to obtain a titanium textile.

13. The process of claim 12, wherein the consolidating comprises: providing titanium having a dendritic microstructure on a plate; and sintering the titanium by heating to a temperature of from 800°C up to 80% of the melting point of titanium to obtain the titanium textile.

14. The process of claim 13, wherein the sintering comprises applying a pressure on the plate.

15. The process of claim 14, wherein the pressure applied is during the sintering process with or without spacer to control a final thickness of the titanium textile.

16. The process of any one of claims 12 to 15, wherein the sintering causes a permanent interlocking of the dendritic microstructure.

17. The process of any one of claims 12 to 16, wherein the temperature is from 1000 to 1400 °C.

18. The process of any one of claims 12 to 17, further comprising rolling the titanium before sintering.

19. The process of claim 18, wherein the titanium is rolled using powder rolling.

20. The process of any one of claims 12 to 19, wherein the titanium is provided mixed with a liquid to facilitate shaping before sintering.

21. The process of any one of claims 12 to 20, further comprising adding a binder to the titanium before sintering.

22. The process of any one of claims 12 to 21 , further comprising hot rolling, cold rolling or warm rolling the textile after sintering to reduce the thickness, to modify the density, the structure or the surface finish of the titanium textile.

23. The process of any one of claims 12 to 22, further comprising coating the titanium textile with a metal or ceramic coating.

24. The process of any one of claims 12 to 23, further comprising weaving or bonding the titanium textile with other pieces of titanium textile to increase its size.

25. The process of any one of claims 12 to 24, wherein the titanium is in the form of wool or deagglomerated dendrites produced by molten salt electrorefining.

26. The process of any one of claims 12 to 24, wherein the titanium is in the form of wool or deagglomerated dendrites produced by the Armstrong process, or any other method.