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 (4) located 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 at least one adhesion layer (6) is arranged between the gas recombination layer (5) and the hydrocarbon membrane (4), wherein the adhesion layer (6) comprises at least one ceramic material (7) and a proton-conductive polymer (8).

Description

[0001] Applicant:

[0002] Greenerity GmbH Industrial Area South E11 63755 Alzenau

[0003] Membrane electrode assembly and water electrolysis cell

[0004] Description

[0005] The invention relates to a membrane electrode assembly with high power density and low membrane layer thickness and to a water electrolysis cell comprising this membrane electrode assembly.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] Hydrocarbon membranes are mostly used in fuel cell applications, as taught, for example, in EP 1 133 806 A1.

[0012] 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.

[0013] The transfer of design features of a fuel cell is not generally applicable to water electrolysis cells.

[0014] It is therefore an object of the present invention to provide a membrane electrode assembly for a water electrolysis cell comprising a hydrocarbon membrane and characterized by very good adhesion properties to the gas recombination layer, 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.

[0015] These objects are achieved by the features of the independent claims. The dependent claims contain advantageous developments and refinements of the invention.

[0016] 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, as well as a gas recombination layer located between the anode and the hydrocarbon membrane. To improve the adhesion between the hydrocarbon membrane and the gas recombination layer, at least one adhesion layer is present between the gas recombination layer and the hydrocarbon membrane, according to the invention.

[0017] The membrane electrode assembly can be designed as a laminate of layers with the layer sequence: anode / first

[0018] Gas recombination layer / adhesion layer(s) / hydrocarbon membrane / cathode are present. Additional layers can be provided, as long as the at least one adhesion layer is arranged between the gas recombination layer 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. 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 can also be present in combination. The hydrocarbon membrane is preferably free of fluorine-containing substances.

[0019] 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 annealed 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 reinforcement structures. A membrane comprising a fluorine-containing reinforcement 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.

[0020] The hydrocarbon membrane advantageously has a layer thickness of 5 to 120 pm, particularly 15 to 90 pm, and especially 35 to 75 pm. This achieves an optimal balance between efficiency, gas tightness, and dimensional stability.

[0021] 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.

[0022] Unless otherwise disclosed below, the anode and cathode are 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. The gas recombination layer, which can be present as a single layer or in the form of a laminate of two or more layers, is also not specifically restricted and can be designed as in the prior art and comprise at least one proton-conductive polymer and a recombination catalyst. As already explained above, the recombination catalyst catalyzes the reaction of hydrogen, which passes from the cathode to the anode, with oxygen from the anode side in order to prevent the formation of explosive mixtures on the anode side of a cell and comprises, in particular, platinum particles.Due to its oxidation stability, the ionomer of the gas recombination layer is usually selected from the group of perfluorinated polymers and in particular perfluorinated sulfonic acid polymers (PFSA polymers).

[0023] The adhesion layer can be present as a single layer or as a layer sequence with two or more adhesion layers. The adhesion layers can have the same or different structures. References to an adhesion layer below refer to an adhesion layer that is in direct contact with the hydrocarbon membrane. Additional adhesion layers can be arranged between this adhesion layer and the gas recombination layer. Unless otherwise stated, the following statements regarding the composition and design of the adhesion layer apply to all adhesion layers used according to the invention.

[0024] The adhesion layer in direct contact with the hydrocarbon membrane, which may also be referred to as the first adhesion layer, comprises at least one ceramic material and at least one proton-conductive polymer.

[0025] It goes without saying that the adhesion layer can also comprise two or more ceramic materials and / or two or more proton-conductive polymers.

[0026] Neither the proton-conductive polymer nor the ceramic material are specifically limited.

[0027] The ceramic material is not specifically limited and is dispersed, i.e., distributed, in the proton-conductive polymer(s). This can be achieved, for example, by preparing an adhesion layer dispersion during the production of the adhesion layer, in which the ceramic material and the proton-conductive polymer are sufficiently mixed before further processing into the adhesion layer.

[0028] Due to the (first) adhesion layer according to the invention, high adhesion is achieved between the hydrocarbon membrane and the gas recombination layer, so that even under the humid conditions of water electrolysis, no detachment occurs between the gas recombination layer and the hydrocarbon membrane. This leads to a particularly high power density of the MEA according to the invention.

[0029] The hydrocarbon membrane is not limited in detail. Particularly stable carbon membranes are selected from sulfonated 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 and are in particular selected from sulfonated polyether ketones,sulfonated polyetheretherketones, sulfonated polyketoneketones, sulfonated polyphenylenes, sulfonated phenylated polyphenylenes and mixtures thereof.

[0030] 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 gas recombination layer. In other words, the adhesion strength of the adhesion layer is improved. 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 the very good reduction stability, the ceramic material is particularly selected from silicon oxide, tantalum oxide, niobium oxide, tungsten oxide (WO3) and zirconium oxide (ZrO2), and is particularly selected from Nb2O5, Ta2O5, SiO2 and mixtures thereof.

[0031] 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 adhesion-promoting properties.

[0032] Due to the very good proton conductivity, the proton-conductive polymer of the adhesion layer is preferably selected from the group of fluorinated ionomers, perfluorinated ionomers, hydrocarbon-based ionomers and combinations thereof, and is in particular a perfluorinated proton-conductive polymer.

[0033] Further advantageously, in light of minimal additional proton resistance due to the MEA, the equivalent weight of the proton-conductive polymer of the adhesion layer can be less than 1050 g / mol, preferably less than 950 g / mol, and more preferably less than 850 g / mol. The equivalent weight indicates the weight of the ionomer per mole of functional groups, in particular sulfonic acid groups.

[0034] To improve adhesion properties and thus reduce delamination or detachment of individual layers or parts of layers of the membrane electrode assembly, it is advantageous if the volume fraction of proton-conductive polymer in the adhesion layer, based on the total volume of the adhesion layer, is between 24 and 84% by volume. The total volume of the adhesion layer is defined as the sum of the volumes of the individual components. At higher ionomer contents, detachment occurs between the gas recombination layer and the hydrocarbon membrane because the adhesion layer cannot establish sufficient adhesion to the hydrocarbon membrane. At lower ionomer contents (below 24% by volume), on the other hand, the proton conductivity is excessively reduced, which can lead to high resistance and thus to low performance and poor film formation, which can result in, for example, crumbling.

[0035] In light of the above advantages, a volume fraction of proton-conductive polymer in the adhesion layer, based on the total volume of the adhesion layer, is preferably from 35 to 75 volume% and more preferably from 46 to 65 volume%.

[0036] To improve the water electrolysis efficiency, the gas recombination layer comprises at least one proton-conductive polymer, wherein the proton-conductive polymer is in particular a fluorinated ionomer, a perfluorinated ionomer or a hydrocarbon-based ionomer and in particular a perfluorinated ionomer.

[0037] To further improve the adhesion between the hydrocarbon membrane and the gas recombination layer, the MEA advantageously comprises a second adhesion layer arranged between the gas recombination layer and the first adhesion layer. To particularly enhance the adhesion properties, the first adhesion layer, which is aligned with the hydrocarbon membrane, has a lower volume fraction of proton-conductive polymer than the second adhesion layer, which is aligned with the gas recombination layer.

[0038] Furthermore, a second adhesion layer can advantageously be provided in the MEA, which is arranged between the gas recombination layer and the hydrocarbon membrane. In light of the improved proton transport through the gas recombination layer and good cell bonding, the volume fraction of proton-conductive polymer in the first adhesion layer aligned with the hydrocarbon membrane is advantageously between 24 and 56% by volume. Furthermore, the volume fraction of proton-conductive polymer in the second adhesion layer aligned with the gas recombination layer is advantageously between 56 and 100% by volume, in each case based on the respective total volume of the corresponding first or second adhesion layer.

[0039] In order to improve the catalytic properties on the anode side of the MEA in addition to the adhesion, in particular to increase the hydrogen-oxygen recombination, the adhesion layer comprises in particular at least one noble metal and the noble 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.

[0040] 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.

[0041] To maximize the adhesion properties of the adhesion layer, the precious metal content should not be too high. The ideal weight of the precious metal in the adhesion layer is 0.01 to 0.1 mg / cm³. 2 and in particular 0.01 to 0.05 mg / cm 2 .

[0042] Particularly when using PFSA ionomers in the adhesion layer, it is advantageous if the mass fraction of the precious metal, based on the sum of the masses of the precious metal and the ceramic material in the adhesion layer, is 0.1 mass% to 80 mass%, in particular 0.5 mass% to 30 mass%, 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 gas recombination layer and the hydrocarbon membrane. To improve the catalytically supporting activity of the adhesion layer, the precious metal is advantageously supported on the ceramic material.

[0043] To further improve the homogeneity of the adhesion 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.

[0044] The particle size distribution can be monomodal, bimodal, or multimodal. One particle size distribution may be at 1.5 nm and another at 5 nm.

[0045] To improve the balance between increased adhesion and the smallest possible layer thickness to reduce the weight of the MEA, the adhesion layer thickness is preferably in the range of 0.1 to 20 pm, particularly 0.2 to 10 pm, and especially 0.5 to 2 pm. The layer thicknesses are measured using scanning electron microscopy.

[0046] As a further aspect of the invention, a water electrolysis cell is described that comprises 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 gas recombination layer and the hydrocarbon membrane, so that a permanently high efficiency is also achieved in the water electrolysis cell.

[0047] 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:

[0048] Fig. 1 shows an MEA according to a first embodiment in section,

[0049] Fig. 2 a measuring arrangement for determining the adhesion between the layers of the MEA,

[0050] Fig. 3 is a diagram obtained when carrying out the adhesion test with the measuring arrangement according to Fig. 2 and

[0051] Fig. 4 is a diagram illustrating the adhesion test results of the prepared examples. Fig. 1 shows only the essential components of the MEA. All other components are omitted for clarity.

[0052] In detail, Fig. 1 shows an MEA 1 that can be used for a water electrolysis cell.

[0053] 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 gas recombination layer 5 is present between the hydrocarbon membrane 4 and the anode 2. Furthermore, an adhesion layer 6 is present between the hydrocarbon membrane 4 and the gas recombination layer 5 to improve the adhesion between the hydrocarbon membrane 4 and the gas recombination layer 5.

[0054] The gas recombination layer 5 serves to improve gas purity, meaning that 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. The gas recombination layer comprises at least one recombination catalyst, which in particular comprises platinum particles. Furthermore, the gas recombination layer 5 comprises at least one perfluorinated ionomer, in particular a PFSA ionomer.

[0055] 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 include 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.

[0056] 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.

[0057] In this embodiment, the adhesion layer 6 is arranged between the hydrocarbon membrane 4 and the gas recombination layer 5 and, in particular, has a layer thickness of 0.1 to 20 pm. The adhesion layer 6 comprises at least one ceramic material 7 and at least one proton-conductive polymer 8, and optionally a noble metal 9. Two or more noble metals 9 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 adhesion layer 6.

[0058] The precious metal 9 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 9 is present as an alloy, it is in particular an alloy with copper, cobalt, nickel, iron, yttrium, and / or tin. The surface weight of the precious metal 9 in the first gas recombination layer 5 is in particular 0.01 to 0.05 mg / cm 2 , but can also be 0 mg / cm 2 If two or more precious metals 9 are used, the basis weight refers to the basis weight of the sum of all precious metals 6.

[0059] 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, niobium oxide, tungsten oxide (WO3), and zirconium oxide (ZrO2) are particularly suitable.

[0060] 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.

[0061] Preferably, a mass fraction of the noble metal 9, based on the sum of the mass of the noble metal 9 and the ceramic material 7 in the adhesion layer 6 is 0.1 mass% to 80 mass%, in particular 0.5 mass% to 30 mass% and in particular 1 mass% to 10 mass%.

[0062] Advantageously, the noble metal 9 is supported on the ceramic material 7. In particular, the noble metal 9 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.

[0063] 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 of the hydrocarbon membrane 4, a maximum of 5 mass%.

[0064] 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.

[0065] According to the present embodiment, the adhesion layer 6 significantly improves the adhesion between the hydrocarbon membrane 4 and the gas recombination layer 5, resulting in a very good layer bond. This very good adhesion is achieved by the adhesion layer comprising at least one ceramic material distributed in at least one proton-conductive polymer. As a result, the adhesion layer 6 acts as a mediator between the hydrocarbon membrane and the PFSA ionomer-containing gas recombination layer, preventing delamination or defects, even under the humid conditions prevailing in water electrolysis.

[0066] The equivalent weight of the proton-conductive polymer (8) of the adhesion layer is less than 1050 g / mol and in particular less than 950 g / mol and in particular less than 850 g / mol, so that even with a limited amount of ionomer, a sufficient number of proton-conductive sulfonic acid groups are present and thus the protective layer as a whole has a high proton conductivity.

[0067] In the light of an improvement in adhesion, the volume fraction of proton-conductive polymer in the adhesion layer 6 is in particular from 24 to 84 volume% and in particular from 35 to 75 volume%.

[0068] The membrane electrode assembly according to the invention can be manufactured as follows.

[0069] To produce an adhesion layer dispersion, a ceramic material and a fluorine-containing ionomer are ground together in a ball mill (grinding medium: ZrO2 balls). The grinding time is, for example, 120 minutes and depends on the dispersibility of the ceramic material. Thus, the grinding time can generally be adjusted accordingly.

[0070] 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.

[0071] In a further process step, the adhesion layer dispersion is applied to an anode (including a gas recombination layer) or a hydrocarbon membrane. The application method is generally not limited. Common technologies such as slot nozzles, doctor blades, spiral applicators, screen printing, or spraying devices are particularly suitable.

[0072] The adhesion layer dispersion was then dried to obtain an adhesion layer on the anode (including the gas recombination layer) or the hydrocarbon membrane.

[0073] Once the adhesion layer dispersion has been applied to the anode, a further process step can involve lamination of the anode with the adhesion layer and the hydrocarbon membrane. The lamination temperature can be, in particular, 150 to 190 °C, and the pressure can be 1 to 3 MPa. The lamination time can be approximately one minute.

[0074] The above procedure also applies if the adhesion layer dispersion has been applied to the hydrocarbon membrane. It is then laminated to the anode, including the gas recombination layer.

[0075] This first method according to the invention is easy to implement using conventional technologies and enables the production of an MEA with high adhesion and gas purity.

[0076] According to a second method according to the invention, the production of the MEA according to the invention first comprises the production of an adhesion layer dispersion, which can be carried out as described for the first method. The adhesion layer dispersion again comprises at least one ceramic material and at least one fluorine-containing ionomer.

[0077] The adhesion layer dispersion is then applied to a substrate. The substrate is inert to the adhesion layer dispersion, meaning it exhibits no chemical or physical reactivity with the adhesion layer dispersion.

[0078] In a further process step, the adhesion layer dispersion is dried to form the adhesion layer, thus obtaining a so-called decal. The adhesion layer is then transferred to the anode, including the gas recombination layer, or to the hydrocarbon membrane, and the substrate is subsequently removed.

[0079] Depending on whether the adhesion layer was transferred to the anode including gas recombination layer or to the hydrocarbon membrane by the decal process, lamination with either a hydrocarbon membrane or an anode including gas recombination layer can be carried out, as explained above for the first method according to the invention.

[0080] This second method according to the invention can also be easily implemented using conventional technologies and enables the production of an MEA with high adhesion and gas purity.

[0081] According to a third method according to the invention, as already explained above, an adhesion layer dispersion is first prepared which comprises at least one ceramic material and at least one fluorine-containing ionomer.

[0082] Furthermore, an anode dispersion and a gas recombination layer dispersion are prepared. The anode dispersion and the gas recombination layer dispersion each comprise, in particular, at least one catalytically active substance, as described for the MEA according to the invention.

[0083] A further decal process is then carried out, in which the anode dispersion, then the gas recombination layer dispersion, and then the adhesion layer dispersion are applied to the previously applied dispersion on the substrate. This creates a layer arrangement: substrate / anode dispersion / gas recombination layer dispersion / adhesion layer dispersion.

[0084] The dispersions are dried. No particular sequence is required. For example, the anode dispersion can be dried first before the gas recombination layer dispersion and the adhesion layer dispersion are applied, or the gas recombination layer dispersion and the adhesion layer dispersion are applied to the still undried anode dispersion, and all three dispersions are dried simultaneously to produce the anode layer, the gas recombination layer dispersion, and the adhesion layer on the substrate.

[0085] The decal, i.e., the dried anode layer-gas recombination layer dispersion-adhesion layer arrangement, is then transferred to the hydrocarbon membrane, so that the adhesion layer is positioned between the hydrocarbon membrane and the gas recombination layer. The third method according to the invention makes it easy to produce an MEA with high adhesion and gas purity using conventional technologies.

[0086] 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 dispersion-adhesion layer arrangement and the hydrocarbon membrane, as already explained for the first and second processes according to the invention.

[0087] According to a fourth method according to the invention, as already explained above, an adhesion layer dispersion is first prepared which comprises at least one ceramic material and at least one fluorine-containing ionomer.

[0088] Furthermore, an anode dispersion and a gas recombination layer dispersion are prepared. The anode dispersion and the gas recombination layer dispersion each comprise, in particular, at least one catalytically active substance, as described for the MEA according to the invention.

[0089] The adhesion layer dispersion is then applied to the hydrocarbon membrane and then the gas recombination layer dispersion and then the anode dispersion are applied to the adhesion layer dispersion.

[0090] The dispersions are then dried to produce the anode layer, the gas recombination layer and the adhesion layer, whereby the dispersions can be dried sequentially or together.

[0091] All of the processes disclosed above may be followed by a further annealing step at a temperature range of 150 to 200 °C to strengthen the mechanical properties of the adhesion layer. This step may possibly coincide with one of the decal processes.

[0092] The production of the MEA of the invention according to the methods of the invention can be realized simply and at high production rates using state-of-the-art techniques and equipment already used in the production of water electrolysis cell membrane electrode assemblies.

[0093] Examples

[0094] 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).

[0095] To prepare the gas recombination dispersion, 0.25 g of a platinum black, 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 based on the density of 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 2 The thickness of the gas recombination layer was about 3 pm

[0096] 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).

[0097] Catalyst-coated membranes (CCM) were prepared from anode catalyst layers containing an unsupported iridium oxide catalyst with an iridium loading of 2.25 mgi r / cm 2 and were optionally coated with a gas recombination layer. Cathode catalyst layers contained a 60 mass% Pt-on-carbon catalyst with a platinum loading of 0.80 mg Pt / cm 2Catalyst-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.

[0098] Table 1 summarizes the CCM compositions. Preparation of the adhesion layers

[0099] Example 1

[0100] To prepare the adhesion layer, 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 83.5 volume%. The conversion is carried out using the density of the silicon dioxide of

[0101] 2.65 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 adhesion layer dispersion using a spiral doctor blade (30 pm wire diameter) and dried for 5 minutes at 120 °C in an oven.

[0102] Example 2

[0103] To prepare the adhesion layer, 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 74.6 volume%. The conversion is carried out using the density of the silicon dioxide of

[0104] 2.65 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 μm thick PET film. The adhesive layer dispersion was applied using a spiral doctor blade (30 μm wire diameter) and dried in an oven at 120 °C for 5 minutes. The thickness of the gas recombination layer was approximately 3 μm.

[0105] Example 3

[0106] To prepare the adhesion layer, 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 the ionomer of 65.4 volume%. The conversion is carried out using the density of the silicon dioxide of

[0107] 2.65 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 μm thick PET film. The adhesive layer dispersion was applied using a spiral doctor blade (30 μm wire diameter) and dried in an oven at 120 °C for 5 minutes. The thickness of the gas recombination layer was approximately 3 μm.

[0108] Example 4

[0109] To prepare the adhesion layer, 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 55.8 volume%. The conversion is based on the density of the silicon dioxide of 2.65 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 μm thick PET film. The adhesive layer dispersion was applied using a spiral doctor blade (30 μm wire diameter) and dried in an oven at 120 °C for 5 minutes. The thickness of the gas recombination layer was approximately 3 μm.

[0110] Example 5

[0111] To prepare the adhesion layer, 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 45.7 volume%. The conversion is based on the density of the silicon dioxide of 2.65 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 μm thick PET film. The adhesive layer dispersion was applied using a spiral doctor blade (30 μm wire diameter) and dried in an oven at 120 °C for 5 minutes. The thickness of the gas recombination layer was approximately 3 μm.

[0112] Comparative Example 1 and Comparative Example 2

[0113] The catalyst-coated membrane of Comparative Example 1 and Comparative Example 2 does not comprise a gas recombination layer and an adhesion layer.

[0114] Comparative Example 3 and Comparative Example 4

[0115] The catalyst-coated membrane of Comparative Example 3 and Comparative Example 4 comprises a gas recombination layer corresponding to the above-mentioned composition and no adhesion layer. Comparative Example 5

[0116] To prepare the adhesion layer, 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 91.9 volume%. The conversion is based on the density of the silicon dioxide of 2.65 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 μm thick PET film. The adhesive layer dispersion was applied using a spiral doctor blade (30 μm wire diameter) and dried in an oven at 120 °C for 5 minutes. The thickness of the gas recombination layer was approximately 3 μm.

[0117] CCM production (membrane electrode assemblies in the sense of the present invention)

[0118] Anode and adhesion layers were prepared as described above. For the fabrication of the CCM, a PFSA membrane, Nation N115 (The Chemours Company, United States), or a hydrocarbon membrane, Fumasep FKE-50 (Fumatech GmbH, Germany), with a thickness of 50 μm was used, as shown in the table. The adhesion force was determined by a measuring arrangement 1 as shown in Fig. 2. Each half-MEA (MEA without cathode) was arranged with the membrane side 4 on a glass substrate 12 using an adhesive tape 11. In addition, a paper 13 (printer paper, 80 g / m 2) was attached to the anode 2 using adhesive tape 11. The paper 13 was longer than the half-MEA and was clamped into the measuring instrument so that it served as a pull tab. Tension 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.

[0119] 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, indicating delamination. With a sample width of 2 cm, approximately 9 N / cm is achieved, as indicated in Fig. 4 for Comparative Example 5.

[0120] 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. It was found that MEAs according to the present invention exhibit very good adhesion between the membrane, adhesion layer, and gas recombination layer-anode assembly.

[0121] Furthermore, the examples show that the advantage of an adhesion layer only becomes necessary with the use of a gas recombination layer, since MEAs without a gas recombination layer (Comparative Examples 1 and 2) do not exhibit adhesion problems, but also do not exhibit improved gas purity. However, MEAs with a gas recombination layer and a hydrocarbon membrane but without an adhesion layer exhibit low adhesion (Comparative Example 4). A PFSA membrane, on the other hand, does not require an additional adhesion layer and already exhibits good adhesion to a gas recombination layer (Comparative Example 3).

[0122] 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.

[0123] It is shown that the MEA 1 according to the invention exhibits very good adhesion forces due to the adhesive layer 6 used. In addition to the above written description of the invention, reference is hereby explicitly made to the graphic representation of the invention in Figures 1 to 4 for its supplementary disclosure.

[0124] List of reference symbols

[0125] 1 MEA

[0126] 2 anode

[0127] 3 Cathode 4 Hydrocarbon membrane

[0128] 5 Gas recombination layer

[0129] 6 Adhesive layer

[0130] 7 ceramic material

[0131] 8 proton-conductive ionomer 9 precious metal

[0132] 10 Measuring arrangement

[0133] 11 Adhesive tape

[0134] 12 Glass substrate

[0135] 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 gas recombination layer (5) arranged between the anode (2) and the hydrocarbon membrane (4), wherein at least one adhesion layer (6) is arranged between the gas recombination layer (5) and the hydrocarbon membrane (4), wherein the adhesion layer (6) comprises at least one ceramic material (7) and a proton-conductive polymer (8).

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 polyphenylenes, sulfonated phenylated polyphenylenes 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 silicon, tantalum, niobium, tin, titanium, zirconium, cerium, tungsten, antimony and mixtures thereof, wherein the ceramic material (7) is in particular selected from silicon oxide, tantalum oxide, niobium oxide, tungsten oxide and zirconium oxide and / or 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 and / or wherein the proton-conductive polymer (8) of the adhesion layer is selected from the group of fluorinated ionomers, perfluorinated ionomers and hydrocarbon-based ionomers and combinations thereof, and is in particular a perfluorinated proton-conductive polymer and / or wherein the equivalent weight of the proton-conductive polymer (8) of the adhesion layer (6) is less than 1050 g / mol and in particular less than 950 g / mol and in particular less than 850 g / mol.

4. Membrane electrode assembly (1) according to one of the preceding claims, wherein a volume fraction of the proton-conductive polymer in the adhesion layer (6), based on the total volume of the adhesion layer (6), is 24 to 84 volume%, in particular 35 to 75 volume% and in particular 46 to 65 volume%.

5. Membrane electrode assembly (1) according to one of the preceding claims, wherein the gas recombination layer (5) comprises at least one proton-conductive polymer, wherein the proton-conductive polymer is in particular a fluorinated ionomer, a perfluorinated ionomer or a hydrocarbon-based ionomer, in particular a perfluorinated ionomer.

6. Membrane electrode assembly (1) according to one of the preceding claims, further comprising a second adhesion layer, wherein an adhesion layer (6) aligned with the hydrocarbon membrane (4) has a lower mass fraction of proton-conductive polymer (8) than an adhesion layer aligned with the gas recombination layer (5).

7. Membrane electrode assembly (1) according to one of the preceding claims, further comprising a second adhesion layer, wherein in an adhesion layer (6) aligned with the hydrocarbon membrane (4) a mass fraction of proton-conductive polymer (8) of 24 to 56 volume% and in an adhesion layer aligned with the gas recombination layer (5) a mass fraction of proton-conductive polymer (8) of 56 to 100 volume%, in each case based on the respective total mass of the corresponding adhesion layer.

8. Membrane electrode assembly (1) according to one of the preceding claims, wherein the adhesion layer comprises at least one noble metal (9) and the noble metal is in particular selected from the group consisting of platinum, palladium, iridium, ruthenium, rhodium, rhenium, gold and mixtures and alloys thereof, and in particular platinum and / or palladium, wherein in particular wherein the noble metal (9) 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 and in particular in the form of PtCo, PtCoNi or PtPdCo, ​​wherein in particular, a weight per unit area of ​​the noble metal (9) in the adhesion layer is 0 to 0.1 mg / cm 2 and in particular 0.01 to 0.05 mg / cm 2wherein in particular a mass fraction of the precious metal (9), based on the sum of the mass of the precious metal (9) and the ceramic material (7) in the adhesion layer (6) is 0.1 mass% to 80 mass%, in particular 0.5 mass% to 30 mass%, in particular 1 mass% to 10 mass%, wherein in particular the precious metal (9) is supported on the ceramic material (7), wherein in particular the precious metal (9) is present as particles on the ceramic material (7) deposited and the particle size of the ceramic material (7) provided with precious metal particles, measured by transmission electron microscopy, wherein 500 particles are analyzed, is 1 to 30 nm and in particular 2 to 6 nm.

9. Membrane electrode assembly (1) according to one of the preceding claims, wherein the thickness of the adhesion layer (6) is 0.1 to 20 pm, in particular 0.2 to 10 pm, and in particular 0.5 to 2 pm.

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

Images