Membrane electrode assembly and water electrolysis cell

Abstract

The invention relates to a membrane electrode assembly (1) for a water electrolysis cell, comprising an anode (2), a cathode (3) and a hydrocarbon membrane lying between the anode (2) and the cathode (3), further comprising a first gas recombination layer (5) which is arranged between the anode (2) and the hydrocarbon membrane (4), wherein the first gas recombination layer (5) comprises a noble metal (6), a ceramic material (7) and a proton-conductive polymer (8), and wherein a volume portion of proton-conductive polymer (8) is 24 to 84 volume %, in particular 35 to 75 volume % and in particular 46 to 65 volume %, based on the total volume of the gas recombination layer (5).

Description

[0001] Membrane electrode assembly and water electrolysis cell

[0002] Description

[0003] The invention relates to a membrane electrode assembly with a low membrane layer thickness and high power density and to a water electrolysis cell comprising this membrane electrode assembly.

[0004] Membrane electrode assemblies, including catalyst-coated membranes with a proton exchange membrane coated with an anode on one side and a cathode on the opposite side, are known in the art as CCMs (catalyst coated membranes). When CCMs are used in water electrolysis, the term PEM-WE (proton-exchange membrane water electrolysis) is commonly used.

[0005] Proton exchange membranes for use in PEM-WE are typically extruded perfluorosulfonic acid (PFSA)-based polymer membranes. The most established examples of PEM-WE are Nation® N115 and Nation® N117 from Chemours. Current literature also uses thinner, cast (i.e., solvent-printed) membranes such as Nation® NR212.

[0006] A catalyst for the oxidation of water (water splitting) is used in the anode electrode layer (anode for short). This catalyst is often referred to as an OER (oxygen evolution reaction) catalyst. OER catalysts are usually based on noble metals and comprise noble metal oxides that exhibit high catalytic activity for water splitting. Furthermore, a proton-conducting polymer, a so-called PFSA-type ionomer, is typically used as a binder in the anode, which is mixed with the OER catalyst.

[0007] A catalyst for the reduction of protons to hydrogen (hydrogen evolution reaction = HER catalyst) is used in the cathode electrode layer (short: cathode). These catalysts are usually based on platinum and / or palladium, with platinum and / or palladium preferably finely dispersed on carbon powders. Furthermore, the cathode also usually comprises a PFSA-based ionomer as a binder. Furthermore, a membrane electrode assembly for water electrolysis cells can comprise at least one gas recombination layer, which usually comprises a recombination catalyst, such as platinum particles. The platinum particles are preferably finely dispersed within an ionomer matrix arranged between the anode and the membrane. The gas recombination layer can be considered part of the membrane.The recombination catalyst catalyzes the reaction of hydrogen, which passes from the cathode to the anode, with oxygen from the anode side, thus preventing the formation of explosive mixtures on the anode side of a cell. The ionomer of the gas recombination layer is usually selected from the group of perfluorinated polymers, particularly perfluorinated sulfonic acid polymers, due to its oxidation stability.

[0008] EP 3 559 314 A1 teaches a membrane with a laminate structure, wherein an intermediate layer comprises a recombination catalyst comprising platinum or palladium supported on high-surface-area supports such as carbon, silica, titanium oxide, or zirconium oxide. Primarily, conventional PFSA membranes are described.

[0009] Hydrocarbon membranes are mostly used in fuel cell applications, as taught, for example, in EP 1 133 806 A1.

[0010] Compared to perfluorosulfonic acid (PFSA) membranes, hydrocarbon membranes offer several advantages. For example, they exhibit lower gas permeability through the membrane, allowing higher cell current yields to be achieved, even when using very thin membranes, which result in very low ionic resistance (and thus very good performance). Furthermore, they can operate for extended periods at high temperatures >100 °C with limited degradation, which is provided by the low gas permeability (even at high temperature) and the high glass transition temperature typical of hydrocarbon-based polymers. Operation at higher temperatures results in several system advantages: reduced cooling size, lower sensitivity to gas contaminants, and higher cell efficiency. Hydrocarbon membranes also emit lower amounts of aggressive degradation products, e.g.HF and superacidic sulfonic acid molecules released by PFSAs result in less damage to the metallic bipolar plates in the stack during operation, enabling a longer service life and / or the use of cheaper materials. Finally, hydrocarbon membranes have an improved environmental profile compared to perfluorinated ionomers because they do not contain perfluoroalkyl compounds and no perfluoroalkyl chemistry is required in their manufacture. However, a disadvantage of hydrocarbon membranes is their extremely poor adhesion and thus adhesion to conventional gas recombination layers and anodes, which often include PFSA ionomers as binders, especially under humid conditions such as those found in water electrolysis. This can lead to delamination of the gas recombination layer and the catalyst layers (anode and cathode), which in turn results in reduced cell performance and can even cause cell failure.

[0011] The transfer of design features of a fuel cell is not generally applicable to water electrolysis cells.

[0012] It is therefore an object of the present invention to provide a membrane electrode assembly for a water electrolysis cell, which comprises a hydrocarbon membrane and is characterized by very good adhesion properties to the gas recombination layer and the anode, thereby resulting in a permanently high power density (low cell voltage even at high current densities). Furthermore, it is an object of the present invention to provide a water electrolysis cell that, due to the use of the membrane electrode assembly, is also characterized by a permanently high power density.

[0013] These objects are achieved by the features of the independent claims. The dependent claims contain advantageous developments and refinements of the invention.

[0014] Accordingly, the object is achieved by a membrane electrode assembly (MEA) comprising an anode, a cathode and a hydrocarbon membrane located between the anode and the cathode and further comprising a specifically designed gas recombination layer located between the anode and the hydrocarbon membrane.

[0015] The membrane electrode assembly can be a laminate of layers with the layer sequence: anode / first gas recombination layer / hydrocarbon membrane / cathode. Additional layers can be provided as long as the first gas recombination layer is located between the anode and the hydrocarbon membrane. The layers can be laminated together. Alternatively, the membrane electrode assembly (MEA) can be a CCM (catalyst coated membrane), with the layers each applied directly to the hydrocarbon membrane.

[0016] The hydrocarbon membrane comprises at least one ionomer that is not fluorinated, or whose fluorine content is a maximum of 5% by mass, based on the total mass of the ionomer. Thus, the hydrocarbon membrane comprises at least one hydrocarbon-based ionomer, although two or more hydrocarbon-based ionomers may also be present in combination. Preferably, the hydrocarbon membrane is free of fluorine-containing substances. The hydrocarbon membrane is, for example, mainly composed of one or more hydrocarbon-based ionomers, such assulfonated polyaryl ethers (SPAE), sulfonated polyaryl ether ether nitriles (SPAEEN), sulfonated polyaryl ether ketones (SPAEK), sulfonated polyaryl ether nitriles (SPAEN), sulfonated polyaryl ether sulfones (SPAES), sulfonated polyaryl ether sulfone ketones (SPAESK), sulfonated polyether ether ketones (SPEEK), sulfonated polyether ketones (SPEK), sulfonated polyether sulfones (SPES), sulfonated polyimides, sulfonated polyketone ketones (SPKK), sulfonated polyphosphazenes (SPPh), sulfonated polyphenylene sulfones (SPPSf), sulfonated polyphenylene sulfide sulfones (SPPSSf), sulfonated polyphenylene sulfide sulfonenitriles (SPPSSfN), sulfonated polystyrenes (SPS), sulfonated polysulfones (SPSf), sulfonated polyphenylenes (sPP), sulfonated phenylated polyphenylenes (sPPP), and mixtures thereof. The hydrocarbon membrane is preferably free of fluorine-containing substances.

[0017] Furthermore, according to the present invention, one or more reinforcing structures can be incorporated into the hydrocarbon membrane, such that the reinforcing structure(s) limit the expansion of the hydrocarbon membrane. A reinforcing structure can, for example, be introduced during the manufacturing process of the hydrocarbon membrane from an ionomer dispersion or ionomer solution. In this case, a previously formed reinforcement structure, such as ceramic materials or polymeric materials such as (bi-)axially stretched PTFE (ePTFE, English: expanded PTFE) or woven structures such as fabrics made of polyketone (PK) fibers, polyether ketone (PEK) fibers, polyether ether ketone (PEEK) fibers, perfluoroalkoxyalkane (PFA) fibers or polyphenylene sulfide (PPS) fibers, is impregnated with a corresponding ionomer dispersion and then dried so that the pores of the reinforcement structure are filled with ionomer.The hydrocarbon membrane can then be tempered in a high-temperature step, e.g., at approximately 150°C to 200°C, to improve its stability. The aforementioned maximum fluorine content of 5 mass% refers explicitly to the ionomer and not to the reinforcing fabric. A membrane comprising a fluorine-containing reinforcing structure, e.g., made of PTFE, and a hydrocarbon ionomer also falls under the definition of a hydrocarbon membrane within the meaning of the present invention. The hydrocarbon membrane advantageously has a layer thickness of 5 to 120 pm, in particular of 15 to 90 pm, and especially of 35 to 75 pm. This achieves an optimal balance between efficiency, gas tightness, and dimensional stability.

[0018] Furthermore, hydrocarbon membranes with a larger layer thickness of, for example, up to 200 pm can also be used, although this can lead to a significant reduction in efficiency due to the high membrane proton resistance, especially at high current densities.

[0019] The anode and the cathode are, unless otherwise disclosed below, designed as in the prior art for water electrolysis cells and comprise at least one binder and at least one catalyst catalyzing the respective electrolysis reaction.

[0020] The gas recombination layer used according to the invention can be present as a single layer or as a layer sequence with two or more gas recombination layers. The gas recombination layers can have the same or different structures. References to a gas recombination layer below refer to a gas recombination layer that is in direct contact with the hydrocarbon membrane. Additional gas recombination layers can be arranged between this (first) gas recombination layer and the anode. Unless otherwise stated, the following statements regarding the composition or configuration of the gas recombination layer apply to all gas recombination layers used according to the invention.

[0021] The gas recombination layer in direct contact with the hydrocarbon membrane, which can also be called the first gas recombination layer, comprises a noble metal, a ceramic material and a proton-conductive polymer.

[0022] It goes without saying that the gas recombination layer may also comprise two or more precious metals and / or two or more ceramic materials and / or two or more proton-conductive polymers.

[0023] Neither the precious metal nor the proton-conductive polymer nor the ceramic material are individually limited.

[0024] The ceramic material is dispersed, i.e., distributed, in the proton-conductive polymer(s). This can be achieved, for example, by preparing a gas recombination layer dispersion during the production of the first gas recombination layer, in which the ceramic material and the proton-conductive polymer are sufficiently mixed before further processing to form the first gas recombination layer takes place. Essential to the invention is that the amount of proton-conductive polymer, based on the total volume of the first gas recombination layer, is between 24 and 84% by volume. The total volume of the gas recombination layer is defined as the sum of the volumes of the individual components. At higher ionomer contents, as in the prior art, detachment occurs between the first gas recombination layer and the hydrocarbon membrane.At lower ionomer content (below 24% by volume), film formation is poor and proton conductivity is insufficient, leading to high resistances and thus low performance.

[0025] Due to the first gas recombination layer according to the invention, high adhesion is achieved between the hydrocarbon membrane and the first gas recombination layer, so that no detachment occurs between the first gas recombination layer and the hydrocarbon membrane under the humid conditions of water electrolysis. This leads to a particularly consistently high power density of the MEA according to the invention.

[0026] In light of the above advantages, a mass fraction of proton-conductive polymer in the gas recombination layer, based on the total volume of the first gas recombination layer, is preferably from 35 to 75 volume% and more preferably from 46 to 65 volume%.

[0027] The hydrocarbon membrane is not specifically limited. Particularly stable carbon membranes are selected from sulfonated polyether ketones, sulfonated polyetheretherketones, sulfonated polyketone ketones, sulfonated polyphenylenes, sulfonated phenylated polyphenylenes, and mixtures thereof.

[0028] Surprisingly, it has been found that when the ceramic material is selected from at least one of oxides, nitrides, carbides, silicides, borides, fluorides, and mixtures thereof, particularly high adhesion is achieved between the hydrocarbon membrane and the first gas recombination layer. This applies even more to oxides, nitrides, carbides, silicides, borides, fluorides, and mixtures thereof of at least one selected from chromium, molybdenum, silicon, tantalum, niobium, tin, titanium, zirconium, cerium, tungsten, antimony, aluminum, and mixtures thereof. The metals can be present, in particular, in amounts typically used for doping. This also applies to the fluorine content in the ceramic material. Due to its very good reduction stability, the ceramic material is selected, in particular, from silicon oxide, tantalum oxide, tungsten oxide, zirconium oxide, and niobium oxide, and is particularly selected from Nb2O5, Ta2O5, SiO2, and mixtures thereof.

[0029] Further advantageously, a specific surface area of ​​the ceramic material, measured according to BET, is more than 1 m 2 / g and less than 1200 m 2 / g, especially more than 50 m 2 / g and less than 800 m 2 / g and especially more than 100 m 2 / g and less than 400 m 2 / g. The BET method is carried out according to DIN ISO 9277:2003-05 "Determination of specific surface area of ​​solids by gas adsorption using the BET method." A specific surface area in the specified range and in particular in the preferred range of more than 100 m 2 / g and less than 400 m 2 / g, the ceramic material is characterized by very good support properties for the gas recombination catalyst (precious metal).

[0030] Due to the very good proton conductivity, the proton-conductive polymer of the first gas recombination layer is preferably selected from the group of fluorinated ionomers, perfluorinated ionomers and combinations thereof, preferably of the sulfonated type, and is in particular a perfluorinated proton-conductive polymer, in particular perfluorosulfonic acid polymer (PFSA).

[0031] To further improve the adhesion between the hydrocarbon membrane and the first gas recombination layer, and also the anode, the MEA advantageously comprises a second gas recombination layer arranged between the anode and the hydrocarbon membrane. To particularly enhance the adhesion properties, the gas recombination layer facing the hydrocarbon membrane has a lower volume fraction of proton-conductive polymer than the gas recombination layer facing the anode.

[0032] Furthermore, a second gas recombination layer can advantageously be provided in the MEA, which is arranged between the anode and the hydrocarbon membrane. In light of the improved proton transport through the gas recombination layer and its adhesive properties, the gas recombination layer aligned with the hydrocarbon membrane is advantageously the first gas recombination layer, and the volume fraction of proton-conductive polymer in the first gas recombination layer is between 24 and 65% by volume. Furthermore, the gas recombination layer aligned with the anode is a second gas recombination layer, and the volume fraction of proton-conductive polymer in the second gas recombination layer is between 45 and 99% by volume, in each case based on the total volume of the corresponding gas recombination layer.

[0033] In order to improve not only adhesion but also the catalytic properties in terms of gas recombination properties on the anode side of the MEA, the precious metal is preferably selected from the group consisting of platinum, palladium, iridium, ruthenium, rhodium, rhenium, gold, and mixtures and alloys thereof, and is in particular platinum and / or palladium. If the precious metal is in the form of an alloy, it is further preferred if the precious metal is present as an alloy with copper, cobalt, nickel, iron, yttrium, and / or tin, and in particular as an alloy with cobalt and / or nickel. The alloys can be binary, ternary, or quaternary. Particularly advantageous alloys are PtCo, PtCoNi, and PtPdCo.

[0034] To maximize the adhesion properties of the first gas recombination layer, the precious metal content should not be too high. The weight per unit area of ​​the precious metal in the first gas recombination layer is advantageously 0.01 to 0.1 mg / cm 2 and in particular 0.01 to 0.05 mg / cm 2 .

[0035] Particularly when using PFSA ionomers in the first gas recombination layer, it is advantageous if the mass fraction of the noble metal, based on the sum of the mass of the noble metal and the ceramic material in the first gas recombination layer, is 0.1 mass% to 80 mass%, in particular 0.5 mass% to 30 mass%, and in particular 1 mass% to 10 mass%. The preferred ranges in particular demonstrate that the proportion of ceramic material is particularly important for improving the adhesion between the first gas recombination layer and the hydrocarbon membrane on the one hand, and the first gas recombination layer and the anode on the other.

[0036] To improve the catalytically supporting activity of the first gas recombination layer, the precious metal is advantageously supported on the ceramic material.

[0037] To further improve the homogeneity of the first gas recombination layer and thus also its adhesion strength, the precious metal is deposited as particles on the ceramic material, and the particle size of the ceramic material provided with precious metal particles is 1 to 30 nm and in particular 2 to 6 nm. The particle size is determined by transmission electron microscopy, with 500 particles being analyzed to calculate an average value.

[0038] The particle sizes can be within the specified ranges, whereby the particle distribution can be monomodal, bimodal, trimodal or higher-modal.

[0039] To improve the balance between increased adhesion and support of gas recombination, the thickness of the first gas recombination layer is preferably 0.1 to 20 pm, in particular 1 to 15 pm, and in particular 2 to 10 pm. The layer thicknesses are measured by scanning electron microscopy. A further aspect of the invention describes a water electrolysis cell comprising the membrane electrode assembly according to the invention as described above. Due to the use of the membrane electrode assembly according to the invention, the water electrolysis cell according to the invention is also characterized by very good adhesive properties between the individual layers and in particular between the anode, the first gas recombination layer, and the hydrocarbon membrane, so that a permanently high efficiency is also achieved in the water electrolysis cell.

[0040] Further details, advantages, and features of the present invention will become apparent from the following description of exemplary embodiments with reference to the drawings. It shows:

[0041] Fig. 1 shows an MEA according to a first embodiment in section,

[0042] Fig. 2 a measuring arrangement for determining the adhesion between the layers of the MEA,

[0043] Fig. 3 is a diagram obtained when carrying out the adhesion test with the measuring arrangement according to Fig. 3,

[0044] Fig. 4 is a diagram illustrating the adhesion test results of the prepared examples and

[0045] Fig. 5 is a diagram illustrating the test results for the gas purity of an MEA according to the invention.

[0046] Fig. 1 shows only the essential components of the MEA. All other components are omitted for clarity.

[0047] In detail, Fig. 1 shows an MEA 1 that can be used for a water electrolysis cell.

[0048] The MEA 1 is shown in section and comprises an anode 2, a cathode 3, and a hydrocarbon membrane 4 located between the anode 2 and the cathode 3. A first gas recombination layer 5 is present between the hydrocarbon membrane 4 and the anode 2. The first gas recombination layer 5 serves to improve gas purity, i.e., only a small proportion of hydrogen converts to oxygen on the anode side, and a small proportion of oxygen converts to hydrogen on the cathode side.

[0049] Anode 2 serves to oxidize water and, for this purpose, comprises an OER (oxygen evolution reaction) catalyst, which is formed from noble metals and may comprise noble metal oxides that exhibit high catalytic activity for water splitting. Due to their very good catalytic activity and stability against dissolution during operation, iridium- and ruthenium-containing OER catalysts, such as iridium oxide, ruthenium oxide, or an iridium-ruthenium mixed oxide, are preferred. Furthermore, anode 2 comprises at least one proton-conductive polymer, a so-called PFSA-type ionomer, which is used as a binder and is mixed with the OER catalyst.

[0050] Cathode 3 is used to reduce protons to hydrogen and comprises a hydrogen evolution reaction (HER) catalyst. This HER catalyst is based on platinum and / or palladium, with platinum and / or palladium preferably finely dispersed on carbon powders. Furthermore, cathode 3 also comprises a PFSA-based ionomer as a binder.

[0051] The first gas recombination layer 5 has, in particular, a layer thickness of 0.1 to 20 pm and comprises a noble metal 6, a ceramic material 7 and a proton-conductive polymer 8. Two or more noble metals 6 and / or two or more ceramic materials 7 and / or two or more proton-conductive polymers 8, which are, in particular, fluorinated ionomers and, in particular, perfluorinated ionomers, can also be contained in the first gas recombination layer 5.

[0052] The precious metal 6 is in particular selected from the group consisting of platinum, palladium, iridium, ruthenium, rhodium, rhenium, gold, and mixtures and alloys thereof, and is in particular platinum and / or palladium. If the precious metal 6 is present as an alloy, it is in particular an alloy with copper, cobalt, nickel, iron, yttrium, and / or tin. The weight per unit area of ​​the precious metal 6 in the first gas recombination layer 5 is in particular 0.01 to 0.1 mg / cm 2 and in particular 0.01 to 0.05 mg / cm 2 . If two or more precious metals 6 are used, the basis weight refers to the basis weight of the sum of all precious metals 6.

[0053] The ceramic material 7 is in particular selected from at least one of oxides, nitrides, carbides, silicides, borides, fluorides, and mixtures thereof, and from at least one selected from chromium, molybdenum, silicon, tantalum, niobium, tin, titanium, zirconium, cerium, tungsten, antimony, aluminum, and mixtures thereof. Silicon oxide, tantalum oxide, tungsten oxide, zirconium oxide, and niobium oxide are particularly suitable.

[0054] Preferably, the ceramic material 7 has a specific surface area, measured according to BET, of more than 1 m 2 / g and less than 1200 m 2 / G.

[0055] Preferably, the mass fraction of the noble metal 6, based on the sum of the masses of the noble metal 6 and the ceramic material 7 in the first gas recombination layer 5, is 0.1 mass% to 80 mass%, in particular 0.5 mass% to 30 mass%, and in particular 1 mass% to 10 mass%. Advantageously, the noble metal 6 is supported on the ceramic material 7; in particular, the noble metal 6 is deposited as particles on the ceramic material 7, and the particle size of the ceramic material 7 provided with noble metal particles is 1 to 30 nm, and in particular 2 to 6 nm.

[0056] As already explained, the membrane is a hydrocarbon membrane 4. It is therefore mainly made of one or more hydrocarbon-based ionomers, such assulfonated polyaryl ethers (SPAE), sulfonated polyaryl ether ether nitriles (SPAEEN), sulfonated polyaryl ether ether ketones (SPAEK), sulfonated polyaryl ether nitriles (SPAEN), sulfonated polyaryl ether sulfones (SPAES), sulfonated polyaryl ether ether sulfone ketones (SPAESK), sulfonated polyether ether ketones (SPEEK), sulfonated polyether ketones (SPEK), sulfonated polyether sulfones (SPES), sulfonated polyimides, sulfonated polyketone ketones (SPKK), sulfonated polyphosphazenes (SPPh), sulfonated polyphenylene sulfones (SPPSf), sulfonated polyphenylene sulfide sulfones (SPPSSf), sulfonated Polyphenylene sulfide sulfone nitriles (SPPSSfN), sulfonated polystyrenes (SPS), sulfonated polysulfones (SPSf), sulfonated polyphenylenes (sPP), sulfonated phenylated polyphenylenes (sPPP) and mixtures thereof and the proportion of fluorine is, based on the total mass of the ionomer in the hydrocarbon membrane 4,, at a maximum of 5 mass%.

[0057] Hydrocarbon ionomers can be linear polymers, cross-linked polymers, branched polymers, grafted polymers, and / or block polymers. They may optionally also contain heteroatoms such as F, N, S, and P. Block copolymers containing sulfonic acid-rich blocks alternating with sulfonic acid-poor or non-sulfonated blocks are particularly advantageous in terms of the combination of high proton conductivity, good mechanical properties, and high dimensional stability.

[0058] This reveals a further advantageous effect of the first gas recombination layer 5: The first gas recombination layer 5 improves the adhesion between the hydrocarbon membrane 4 and the first gas recombination layer 5, as well as between the hydrocarbon membrane 4 and the anode 2, resulting in a very good layer bond. The very good adhesion is achieved by a volume fraction of proton-conductive polymer, based on the total volume of the gas recombination layer 5, of 24 to 84 volume%, and the first gas recombination layer 5 further comprising at least one ceramic material 7 and at least one noble metal 6. Higher volume fractions, such as more than 84 volume%, cannot guarantee sufficiently high adhesion, and lower volume fractions are not sufficient for proton conduction.In the light of an improvement in adhesion, the volume fraction of proton-conductive polymer in the gas recombination layer 5 is in particular from 35 to 75 volume% and in particular from 46 to 65 volume%.

[0059] The proton-conductive polymer 8 of the first gas recombination layer 5 is advantageously selected from the group of fluorinated ionomers, perfluorinated ionomers and combinations thereof, and is in particular a perfluorinated proton-conductive polymer.

[0060] The membrane electrode assembly according to the invention can be manufactured as follows:

[0061] To prepare the gas recombination layer dispersion, the precious metal, the ceramic material, and the fluorine-containing ionomer can be ground together in a ball mill (grinding medium: ZrO2 balls). The grinding time can be, for example, 120 minutes, but depends on the dispersibility of the ceramic material and can be adjusted accordingly.

[0062] Alternatively or additionally, ultrasound or various grinding media mills can also be used to produce dispersions. Grinding media mills include, for example, ball mills, stirred bead mills, agitator mills, attritors, and specific roller mills.

[0063] In a further process step, the gas recombination layer dispersion is applied to an anode or a hydrocarbon membrane. Common application techniques such as slot nozzles, doctor blades, spiral applicators, screen printing, or spraying devices are used.

[0064] The gas recombination layer dispersion is then dried to obtain the gas recombination layer on the anode or the hydrocarbon membrane.

[0065] If the gas recombination layer dispersion has been applied to the anode, a further process step can be performed by lamination of the anode coated with the gas recombination layer and the hydrocarbon membrane. The lamination temperature is typically 150 to 190 °C, and the pressure is 1 to 3 MPa. The lamination time can be approximately one minute.

[0066] The above procedure also applies if the gas recombination layer dispersion has been applied to the hydrocarbon membrane. It is then laminated to the anode. This first procedure is easily implemented using conventional technologies and enables the production of an MEA with high adhesion and gas purity.

[0067] According to a second method, the production of the MEA according to the invention first comprises the production of a gas recombination layer dispersion, which can be carried out as described for the first method. The gas recombination layer dispersion again comprises at least one noble metal, a ceramic material, and at least one fluorine-containing ionomer.

[0068] The gas recombination layer dispersion is then applied to a substrate. The substrate is inert to the gas recombination layer dispersion, meaning it exhibits no chemical or physical reactivity with the gas recombination layer dispersion.

[0069] In a further process step, the gas recombination layer dispersion is dried to produce the gas recombination layer and thus a so-called decal is obtained.

[0070] The gas recombination layer is then transferred to the anode or to the hydrocarbon membrane and the substrate is subsequently removed.

[0071] Depending on whether the gas recombination layer has been transferred to the anode or to the hydrocarbon membrane by the decal process, lamination may further be carried out with either a hydrocarbon membrane or an anode, as set forth above for the first method of the invention.

[0072] This second process is also easy to implement using conventional technologies and enables the production of an MEA with high adhesion and gas purity.

[0073] According to a third method, as already explained above, a gas recombination layer dispersion is first prepared which comprises at least one noble metal, a ceramic material and at least one fluorine-containing ionomer.

[0074] Furthermore, an anode dispersion is prepared. The anode dispersion comprises, in particular, at least one catalytically active substance, as described for the MEA according to the invention.

[0075] A further decal process is then carried out, in which the anode dispersion and then the gas recombination layer dispersion are first applied to the anode dispersion applied to the substrate. This creates a layer arrangement: substrate / anode dispersion / gas recombination layer dispersion. The dispersions are dried. No particular sequence is required. For example, the anode dispersion can be dried first before the gas recombination layer dispersion is applied, or the gas recombination layer dispersion is applied to the still undried anode dispersion, and both dispersions are dried simultaneously, producing the anode layer and the gas recombination layer on the substrate.

[0076] The decal, i.e. the dried anode layer-gas recombination layer arrangement, is then transferred to the hydrocarbon membrane so that the gas recombination layer is arranged between the hydrocarbon membrane and the anode.

[0077] The third method allows the production of an MEA with high adhesion and gas purity easily using conventional technologies.

[0078] The above process steps of the third process according to the invention may be followed by a step of laminating the anode layer-gas recombination layer arrangement and the hydrocarbon membrane, as already explained for the first and second processes according to the invention.

[0079] According to a fourth method, as already explained above, a gas recombination layer dispersion is first prepared which comprises at least one noble metal, a ceramic material and at least one fluorine-containing ionomer.

[0080] Furthermore, an anode dispersion is prepared. The anode dispersion comprises, in particular, at least one catalytically active substance, as described for the MEA according to the invention.

[0081] The gas recombination layer dispersion is then applied to the hydrocarbon membrane and subsequently the protective anode dispersion is applied to the gas recombination layer dispersion.

[0082] The dispersions are then dried to produce the anode layer and the gas recombination layer, whereby the dispersions can be dried sequentially or together.

[0083] All of the processes disclosed above can be followed by a further process step of annealing in a temperature range of 150 to 200°C to consolidate the mechanical properties of the gas recombination layer. This step can possibly coincide with one of the decal processes. The fabrication of the inventive MEA according to the processes is simple and can be achieved at high production rates using state-of-the-art techniques and equipment already used in the production of water electrolysis cell membrane electrode assemblies.

[0084] Furthermore, the following tests were carried out:

[0085] An anode catalyst ink was prepared by mixing an iridium oxide catalyst in water, solvent, and a D79-25BS PFSA ionomer dispersion from Solvay Specialty Polymers. The catalyst-to-ionomer ratio was 9.7:1. The anode catalyst ink was milled for 120 minutes in a ball mill (grinding media: ZrO2 balls with a diameter of 1 mm). An anode catalyst layer was prepared by applying and drying the catalyst ink to a substrate (decal process).

[0086] A gas recombination layer ink was prepared by mixing a Pt precursor salt, SiC>2 (20 mass% Pt based on the sum of Pt and SiC>2) in water, solvent, and a D2020 PFSA ionomer dispersion from Chemours. A gas recombination layer was prepared by applying and drying the gas recombination layer ink onto the dried anode catalyst layer (decal method). The ionomer content of the gas recombination layer can be found in the table below.

[0087] A cathode catalyst ink was prepared by mixing a Pt / C (60 wt% Pt on carbon) catalyst, water, solvent, and a D2020 PFSA ionomer dispersion from The Chemours Company. The ionomer-to-carbon ratio was 0.8:1. The cathode catalyst ink was milled for 120 minutes in a ball mill (grinding media: ZrO2 balls with a diameter of 1 mm). A cathode catalyst layer was prepared by applying and drying the catalyst ink to a substrate (decal process).

[0088] Catalyst-coated membranes (CCM) were prepared from anode catalyst layers containing an unsupported iridium oxide catalyst with an iridium loading of 2.25 mglr / cm 2and were optionally coated with a gas recombination layer. The exact composition of the gas recombination layer can be found in the table below. Cathode catalyst layers contained a catalyst with 60 mass% Pt on carbon with a platinum loading of 0.80 mg Pt / cm 2 Catalyst-coated membranes (CCMs) were then fabricated using a decal process (standard decal transfer method), in which an ionomer membrane was sandwiched between an anode layer / gas recombination layer assembly and the cathode layer opposite the membrane. Lamination was carried out at a temperature of 160 °C and a pressure of 3 MPa for 1 minute, after which the substrates (decals) were removed. The active area of ​​both catalyst layers was 50 mm x 50 mm, and the membrane size was 80 mm x 80 mm. Table 2 summarizes the CCM compositions.

[0089] Production of the gas recombination layer

[0090] Example 1

[0091] To prepare the gas recombination dispersion, 0.16 g of a platinum precursor compound (H2Pt(OH)e), 0.38 g of silicon dioxide, 7.18 g of D2020 (The Chemours Company, PFSA ionomer dispersion, 20.9 mass%), 4.97 g of water, and 39.65 g of organic solvent were mixed and ground for 120 minutes in a ball mill (grinding medium: ZrO2 balls with a diameter of 1 mm). The mass ratio of the ceramic material to ionomer was 2:8. This corresponded to a volume fraction of ionomer of 83.0 volume%. The conversion is carried out using the density of the silicon dioxide of 2.65 g / cm3. 3 , the density of platinum is 21.45 g / cm 3 and the density of the ionomer of 2.1 g / cm 3The edge of the anode was then covered with a frame made of 50 μm thick PET film and coated with the gas recombination dispersion using a spiral doctor blade (30 μm wire diameter) and dried in an oven at 120 °C for 5 minutes. The resulting platinum weight per unit area was 0.16 mg / cm 2 The thickness of the gas recombination layer was about 3 pm.

[0092] Example 2

[0093] To prepare the gas recombination dispersion, 0.27 g of a platinum precursor compound (H2Pt(OH)e), 0.64 g of silicon dioxide, 7.18 g of D2020 (The Chemours Company, PFSA ionomer dispersion, 20.9 mass%), 4.97 g of water, and 39.65 g of organic solvent were mixed and ground for 120 minutes in a ball mill (grinding medium: ZrO2 balls with a diameter of 1 mm). The mass ratio of the ceramic material to ionomer was 3:7. This corresponded to a volume fraction of ionomer of 74.1 volume%. The conversion is carried out using the density of the silicon dioxide of 2.65 g / cm3. 3 , the density of platinum is 21.45 g / cm 3 and the density of the ionomer of 2.1 g / cm 3The edge of the anode was then covered with a frame made of 50 μm thick PET film and coated with the gas recombination dispersion using a spiral doctor blade (30 μm wire diameter) and dried in an oven at 120 °C for 5 minutes. The resulting platinum weight per unit area was 0.18 mg / cm 2 The thickness of the gas recombination layer was about 3 pm. Example 3

[0094] To prepare the gas recombination dispersion, 0.41 g of a platinum precursor compound (H2Pt(OH)e), 1.00 g of silicon dioxide, 7.18 g of D2020 (The Chemours Company, PFSA ionomer dispersion, 20.9 mass%), 4.97 g of water, and 39.65 g of organic solvent were mixed and ground for 120 minutes in a ball mill (grinding medium: ZrO2 balls with a diameter of 1 mm). The mass ratio of the ceramic material to ionomer was 4:6. This corresponded to a volume fraction of ionomer of 64.7 volume%. The conversion is carried out using the density of the silicon dioxide of 2.65 g / cm 3 , the density of platinum is 21.45 g / cm 3 and the density of the ionomer of 2.1 g / cm 3The edge of the anode was then covered with a frame made of 50 μm thick PET film and coated with the gas recombination dispersion using a spiral doctor blade (30 μm wire diameter) and dried in an oven at 120 °C for 5 minutes. The resulting platinum weight per unit area was 0.17 mg / cm 2 The thickness of the gas recombination layer was about 3 pm.

[0095] Example 4

[0096] To prepare the gas recombination dispersion, 0.62 g of a platinum precursor compound (H2Pt(OH)e), 1.50 g of silicon dioxide, 7.18 g of D2020 (The Chemours Company, PFSA ionomer dispersion, 20.9 mass%), 4.97 g of water, and 39.65 g of organic solvent were mixed and ground for 120 minutes in a ball mill (grinding medium: ZrO2 balls with a diameter of 1 mm). The mass ratio of the ceramic material to ionomer was 5:5. This corresponded to a volume fraction of ionomer of 55.0 volume%. The conversion is carried out using the density of the silicon dioxide of 2.65 g / cm 3 , the density of platinum is 21.45 g / cm 3 and the density of the ionomer of 2.1 g / cm 3The edge of the anode was then covered with a frame made of 50 μm thick PET film and coated with the gas recombination dispersion using a spiral doctor blade (30 μm wire diameter) and dried in an oven at 120 °C for 5 minutes. The resulting platinum weight per unit area was 0.16 mg / cm 2 The thickness of the gas recombination layer was about 3 pm.

[0097] Example 5 To prepare the gas recombination dispersion, 0.93 g of a platinum precursor compound (H2Pt(OH)e), 2.25 g of silicon dioxide, 7.18 g of D2020 (The Chemours Company, PFSA ionomer dispersion, 20.9 mass%), 4.97 g of water, and 39.65 g of organic solvent were mixed and ground for 120 minutes in a ball mill (grinding medium: ZrO2 balls with a diameter of 1 mm). The mass ratio of the ceramic material to ionomer was 6:4. This corresponded to a volume fraction of ionomer of 44.9 volume%. The conversion is carried out using the density of the silicon dioxide of 2.65 g / cm3. 3 , the density of platinum is 21.45 g / cm 3 and the density of the ionomer of 2.1 g / cm 3The edge of the anode was then covered with a frame made of 50 μm thick PET film and coated with the gas recombination dispersion using a spiral doctor blade (30 μm wire diameter) and dried in an oven at 120 °C for 5 minutes. The resulting platinum weight per unit area was 0.17 mg / cm 2 The thickness of the gas recombination layer was about 3 pm.

[0098] Comparative Example 1 and Comparative Example 2

[0099] The catalyst-coated membrane of Comparative Example 1 and Comparative Example 2 did not include a gas recombination layer.

[0100] Comparative Example 3 and Comparative Example 4

[0101] To prepare the gas recombination dispersion, 0.25 g of a platinum precursor compound (H2Pt(OH)e), 21.67 g of D2020 (The Chemours Company, PFSA ionomer dispersion, 20.9 mass%), 3.54 g of water, and 44.54 g of organic solvent were mixed and ground for 120 minutes in a ball mill (grinding medium: ZrO2 balls with a diameter of 1 mm). This corresponded to a mass fraction of the ionomer of 95 mass% and a volume fraction of the ionomer of 99.5 volume%. The conversion is carried out using the density of the platinum of 21.45 g / cm 3 and the density of the ionomer of 2.1 g / cm 3 The edge of the anode was then covered with a frame made of 50 μm thick PET film and coated with the gas recombination dispersion using a spiral doctor blade (30 μm wire diameter) and dried in an oven at 120 °C for 5 minutes. The resulting platinum weight per unit area was 0.17 mg / cm 2The thickness of the gas recombination layer was about 3 pm.

[0102] Comparison example 5

[0103] To prepare the gas recombination dispersion, 0.068 g of a platinum precursor compound (H2Pt(OH)e), 0.17 g of silicon dioxide, 7.18 g of D2020 (The Chemours Company, PFSA ionomer dispersion, 20.9 mass%), 4.97 g of water, and 39.65 g of organic solvent were mixed and ground for 120 minutes in a ball mill (grinding medium: ZrO2 balls with a diameter of 1 mm). The mass ratio of the ceramic material to ionomer was 1:9. This corresponded to a volume fraction of ionomer of 91.7 volume%. The conversion is carried out using the density of the silicon dioxide of 2.65 g / cm 3 , the density of platinum is 21.45 g / cm 3 and the density of the ionomer of 2.1 g / cm 3. The edge of the anode was then covered with a frame made of a 50 pm thick PET film and coated with the

[0104] Gas recombination dispersion and dried in an oven at 120 °C for 5 minutes. The resulting platinum area weight was 0.17 mg / cm 2 The thickness of the gas recombination layer was about 3 pm.

[0105] CCM production (membrane electrode assemblies in the sense of the present invention)

[0106] Anode and cathode layers were prepared as described above. A PFSA membrane, Nation N115 (The Chemours Company, United States) or a hydrocarbon membrane, Fumasep FKE-50 (Fumatech

[0107] GmbH, Germany) with a thickness of 50 pm according to the table. Measurement of adhesion

[0108] The adhesion force was determined using a measuring arrangement 10 as shown in Fig. 2. Each half-MEA (MEA without a cathode) was arranged with the membrane side 4 on a glass substrate 12 using an adhesive tape 11. In addition, a piece of paper 13 (printer paper, 80 g / m²) was attached to the anode 2 using an adhesive tape 11. The paper 13 is longer than the half-MEA and is clamped into the measuring instrument so that it serves as a pull tab. A pull was then applied in the direction of the arrow. When the tensile force reaches the adhesion or cohesion force of one of the layers used in the half-MEA, a plateau is reached, and the layer is delaminated with a constant force. The adhesion force is calculated as the average value over the length of the plateau divided by the sample width. The sample width was 2 cm. With regard to the measurement results obtained using this measuring arrangement, reference is also made to Fig. 3.

[0109] Measurement of gas purity

[0110] The gas purity of a CCM was measured in a single cell with an active area of ​​25 cm 2 measured. The cell consisted of platinized titanium plates with a column-bar flow field design on both the anode and cathode sides. Uncoated titanium sinter (1 mm thick) served as the porous transport layer on the anode side. Carbon paper (Toray TGP-H-120) served as the gas diffusion layer on the cathode side in all test series. Deionized water with a conductivity of less than 1 pS / cm was circulated on the anode side. The cell was heated from room temperature to 60 °C within 20 minutes. The temperature was then increased to 80 °C within 20 minutes. The gas purity was measured at a current density of 0.2 A / cm 2, a temperature of 50 °C, a cathode pressure of 16 bar, and an anode pressure of 1 bar. The hydrogen formed under these conditions, which diffused from the cathode side to the anode side, was determined using a Rosemount™ X-STREAM Enhanced XEGP continuous gas analyzer at the anode side outlet.

[0111] Fig. 3 shows exemplary measurement curves for Comparative Example 1 obtained using the measurement setup from Fig. 2. Different samples from Comparative Example 1 were measured, and the measurement curves for Sample 2 and Sample 3 are arbitrarily shown in Fig. 3. The plateau is reached at approximately 17 to 18 N, thus indicating delamination. For a sample width of 2 cm, approximately 9 N / cm is reached, as indicated in Fig. 4 for Comparative Example 5. The adhesion force in N / cm was determined from the tensile force, which was measured in Newtons. An overview of the adhesion forces of the above examples is shown in Fig. 4.

[0112] It is shown that the MEA 1 according to the invention has very good adhesion forces due to the gas recombination layer 5 used.

[0113] Fig. 5 shows the gas purity of an inventive MEA 1 according to Example 5 compared to the gas purity of a prior art MEA with an HC membrane without a gas recombination layer according to Comparative Example 2, as well as a prior art, PFSA-rich gas recombination layer and a PFSA membrane according to Comparative Example 3. It can be seen that the inventive MEA 1 exhibited improved gas purity compared to an MEA with a gas recombination layer and further exhibited slightly improved gas purity compared to a thicker PFSA membrane with a conventional gas recombination layer. In addition to the above written description of the invention, explicit reference is hereby made to the drawings of the invention in Figures 1 to 5 for the purpose of supplementing the disclosure.

[0114] List of reference symbols

[0115] 1 MEA

[0116] 2 anode

[0117] 3 Cathode 4 Hydrocarbon membrane

[0118] 5 first gas recombination layer

[0119] 6 Precious metal

[0120] 7 ceramic material

[0121] 8 proton-conductive ionomer 10 measuring arrangement

[0122] 11 Adhesive tape

[0123] 12 Glass substrate

[0124] 13 Paper

Claims

Claims 1. Membrane electrode assembly (1) for a water electrolysis cell, comprising an anode (2), a cathode (3) and a hydrocarbon membrane (4) located between the anode (2) and the cathode (3), further comprising a first gas recombination layer (5) arranged between the anode (2) and the hydrocarbon membrane (4), wherein the first gas recombination layer (5) comprises a noble metal (6), a ceramic material (7) and a proton-conductive polymer (8), and wherein a volume fraction of proton-conductive polymer (8), based on the total volume of the gas recombination layer (5), is from 24 to 84% by volume, in particular from 35 to 75% by volume and in particular from 46 to 65% by volume.

2. Membrane electrode assembly (1) according to claim 1, wherein the hydrocarbon membrane (4) comprises sulfonated polyether ketones, sulfonated polyether ether ketones, sulfonated polyketone ketones, sulfonated polysulfones, sulfonated polyether sulfones and mixtures thereof.

3. Membrane electrode assembly (1) according to one of the preceding claims, wherein the ceramic material (7) is selected from at least one of oxides, nitrides, carbides, silicides, borides, fluorides and mixtures thereof, of at least one selected from chromium, molybdenum, silicon, tantalum, niobium, tin, titanium, zirconium, cerium, tungsten, antimony, aluminum and mixtures thereof, wherein the ceramic material (7) is in particular selected from silicon oxide, tantalum oxide, tungsten oxide, zirconium oxide and niobium oxide.

4. Membrane electrode assembly (1) according to one of the preceding claims, wherein a specific surface area of ​​the ceramic material (7), measured according to BET, is more than 1 m 2 / g and less than 1200 m 2 / g, especially more than 50 m 2 / g and less than 800 m 2 / g and especially more than 100 m 2 / g and less than 400 m 2 / g.

5. Membrane electrode assembly (1) according to one of the preceding claims, wherein the equivalent weight of the proton-conductive polymer (8) of the gas recombination layer (5) is less than 1050 g / mol and in particular less than 950 g / mol and in particular less than 850 g / mol.

6. Membrane electrode assembly (1) according to one of the preceding claims, wherein the proton-conductive polymer (8) of the first gas recombination layer (5) is selected from the group of fluorinated ionomers, perfluorinated ionomers and combinations thereof, and in particular is a perfluorinated proton-conductive polymer.

7. Membrane electrode assembly (1) according to one of the preceding claims, further comprising a second gas recombination layer arranged between the anode (2) and the hydrocarbon membrane (4), wherein the gas recombination layer aligned with the hydrocarbon membrane (4) has a lower mass fraction of proton-conductive polymer (8) than the gas recombination layer aligned with the anode (2).

8. Membrane electrode assembly (1) according to one of the preceding claims, further comprising a second gas recombination layer arranged between the anode (2) and the hydrocarbon membrane (4), wherein the gas recombination layer aligned with the hydrocarbon membrane (4) corresponds to the first gas recombination layer (5) and has a volume fraction of proton-conductive polymer (8) of 24 to 65% by volume, and the second gas recombination layer aligned with the anode (2) has a volume fraction of proton-conductive polymer (8) of 46 to 99% by mass, in each case based on the respective total volume of the corresponding gas recombination layer (5).

9. Membrane electrode assembly (1) according to one of the preceding claims, wherein the noble metal (6) is selected from the group consisting of platinum, palladium, iridium, ruthenium, rhodium, rhenium, gold and mixtures and alloys thereof, and in particular is platinum and / or palladium and / or wherein the noble metal (6) is present as an alloy with copper, cobalt, nickel, iron, yttrium and / or tin and in particular is present as an alloy with cobalt and / or nickel and / or wherein a surface weight of the noble metal (6) in the first gas recombination layer (5) is 0.01 to 0.1 mg / cm 2 and in particular 0.01 to 0.05 mg / cm 2 and / or wherein a mass fraction of the noble metal (6), based on the sum of the mass of the noble metal (6) and the ceramic material (7) in the first gas recombination layer (5) is 0.1 mass% to 80 mass%, in particular 0.5 mass% to 30 mass% and in particular 1 mass% to 10 mass% and / or wherein the noble metal (6) is supported on the ceramic material (7) and / or wherein the noble metal (6) is deposited as particles on the ceramic material (7) and the particle size of the ceramic material (7) provided with noble metal particles is 1 to 30 nm and in particular 2 to 6 nm and / or wherein a layer thickness of the first gas recombination layer (5) is 0.1 to 20 pm, in particular 1 to 15 pm and in particular 2 to 10 pm.

10. A water electrolysis cell comprising a membrane electrode assembly (1) according to one of the preceding claims.

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