Catalyst-coated membrane and water electrolysis cell

Abstract

The present invention relates to a catalyst-coated membrane comprising a proton exchange membrane, an anode applied to a first side of the membrane and a cathode applied to a second side of the membrane, wherein the anode comprises at least one noble metal containing catalyst having a weight per unit area of the noble metal containing catalyst of less than or equal to 0.6 mg / cm2 based on the content of noble metal 2 and an area expansion of the catalyst-coated membrane of less than 20% after storage in hot water at 100°C for two hours at an air pressure of 1013 hPa.

Description

[0001] The present invention relates to a catalyst-coated membrane with high power density at low catalyst loadings and a water electrolysis cell comprising said catalyst-coated membrane.

[0002] A catalyst-coated membrane with a proton exchange membrane coated on one side with an anode and on the opposite side with a cathode is known in the prior art under the term CCM (catalyst-coated membrane). When a CCM is used in water electrolysis, the term PEM-WE (proton exchange membrane water electrolysis) is conventional.

[0003] The proton exchange membrane used in PEM-WE is usually an extruded polymer membrane based on perfluorosulfonic acid (PFSA). The most established example of a PEM is Nafion® from Chemours N115 and N117. Relatively thin cast membranes, i.e. membranes by means of solvent printing, such as NR212, continue to be used in the current literature.

[0004] In the anode electrode layer (short: anode), a catalyst is used to oxidize water (water splitting). This catalyst is generally referred to as OER (oxygen evolution reaction) catalyst. OER catalysts are usually based on noble metals and contain noble metal oxides that exhibit high catalytic activity for water splitting. In addition, a proton-conducting polymer, an ionomer of the type known as PFSA, is usually used in the anode as a binder present as a mixture with the OER catalyst.

[0005] In the cathode electrode layer (short: cathode), a catalyst is used to reduce protons to hydrogen. (hydrogen evolution reaction = HER catalyst). These catalysts are usually based on platinum, which is preferably present in finely dispersed form on a carbon powder. In addition, the cathode usually also comprises a PFSA-based ionomer as a binder.

[0006] The currently produced CCMs for PEM-WE applications have a high content of the noble metals iridium and / or ruthenium, a typical areal weight (also called (noble metal) loading) is 1 to 2 mg / cm 2 , which ensures sufficient OER rates. Here the areal weight (mg) refers to the mass of the catalyst metal and the area (cm 2 ) refers to the geometric area of the CCM on which the catalyst is present. This area is also referred to as active area. As indicated above, hitherto, a high areal weight was necessary in order to prevent efficiency losses. Studies (see for example M. Bernt et al., The Electrochemical Society, 165 (5) F305-F314 (2018)) have shown that at less than 0.4 mg / cm 2These losses are particularly significant at low iridium loadings. The above publications suggest to solve the problem by preparing thicker electrodes, but do not teach how to prepare thicker electrodes without at the same time increasing the iridium loading.

[0007] It is therefore an object of the present application to provide a catalyst-coated membrane featuring a good efficiency at low anode noble metal loading and a low voltage at a given current density. Furthermore, it is an object of the present application to provide a water electrolysis cell featuring likewise a good efficiency and thus also a reduced operating cost due to a reduced power consumption.

[0008] This object is achieved by the independent claims. The dependent claims include advantageous variants and embodiments of the present application.

[0009] Thus, according to the present application, a catalyst-coated membrane is described, comprising a proton exchange membrane (PEM for short), an anode applied to a first side of the membrane and a cathode applied to a second side of the membrane. The anode is characterized by a low catalyst loading and comprises for this purpose at least one noble metal containing catalyst having a weight per unit area of less than or equal to 0.6 mg / cm2, based on the noble metal content in the noble metal containing catalyst. 2 As explained below, this low loading of noble metal containing catalyst in the catalyst-coated membrane according to the present application is sufficient to obtain a low voltage at a given current density and thus a high efficiency.

[0010] The fact that the area expansion of the catalyst-coated membrane is less than 20% after being kept in hot water at 100°C for two hours at an air pressure of 1013 hPa makes this low loading possible. In other words, this means that the catalyst-coated membrane according to the present application has a high dimensional stability. The high dimensional stability of the catalyst-coated membrane described in the present application is essentially due to the high dimensional stability of the proton exchange membrane used, since the catalyst layer to be provided does not usually undergo any appreciable dimensional change when intended to be used according to the present application (even when kept in hot water at 100°C for two hours at an air pressure of 1013 hPa). In other words, this means that if the membrane used according to the present application has an area expansion of less than 20% after being kept in hot water at 100°C for two hours at an air pressure of 1013 hPa, then the catalyst-coated membrane prepared using this membrane will likewise have a corresponding area expansion of less than 20% (after conditioning at 21°C and 50% relative humidity, which corresponds to the baseline value of the dimensions of the catalyst-coated membrane under ambient conditions). Given that the dimensional stability of the catalyst-coated membrane as a whole is the key to the present application, according to the present application, area expansion means the area expansion of the catalyst-coated membrane. The dimensional stability of the catalyst-coated membrane of the present application and thus the area expansion are explicitly described in the experimental section below, wherein the catalyst-coated membrane is understood in the context of measuring the area expansion to mean the membrane coated with catalyst on one or both sides (depending on the preparation method).

[0011] The use of a dimensionally stable membrane as defined above allows to obtain good efficiency with a low anode loading of 0.6 mg / cm 2 or less, such as 0.2 mg / cm 2 or even 0.1 mg / cm 2 .

[0012] Without being bound by theory, it is assumed that the high efficiency when combining a dimensionally stable (catalyst-coated) membrane with an anode having a low noble metal loading is based on the fact that the dimensionally stable membrane ensures the integrity of the anode when installing the catalyst-coated membrane in the cell and during operation under wet conditions. In contrast, when using a membrane having a low dimensional stability (i.e. having an area expansion of more than 20%) according to the method described herein, the membrane swells excessively under wet operating conditions and the anode loses its integrity, increasing the electrode resistance, which in turn leads to a reduction in efficiency, especially at high current densities. This loss of electrode integrity is almost non-existent at high noble metal loadings, since sufficient anode connectivity is maintained, but at loadings below 0.6 mg / cm 2 the loss becomes significant and unacceptable.

[0013] On the other hand, in the dimensionally stable catalyst-coated film according to the invention, anodic integrity is maintained even at very low noble metal loadings. This can be further demonstrated by the fact that at low current densities where efficiency is determined by catalyst activity (rather than by resistance), very similar cell voltage values ​​are obtained for both film types (dimensionally stable and non-dimensionally stable) across the entire loading range. Furthermore, the trend in cell voltage corresponds to the theoretically expected trend in cell voltage. Conversely, in the context of the invention, films with high dimensional stability, and therefore catalyst-coated films with high dimensional stability, are suitable for high current densities (e.g., >1 A / cm²). 2 It has a significant advantage at this high current density, where the resistance becomes significant once the anode noble metal load decreases.

[0014] According to the present invention, the terms "loading," "precious metal loading," or "weight per unit area" refer only to the presence of precious metals in the catalyst used. Using a precious metal-based loading is advantageous because, in the case of precious metals, the metal accounts for a particularly high proportion of the catalyst cost.

[0015] Furthermore, the dimensional stability of the membrane used according to the invention, and therefore the dimensional stability of the catalyst-coated membrane according to the invention, is understood to refer to dimensional stability during the transition from a dry to a wet state. The expansion occurring in the membrane, and therefore also in the catalyst-coated membrane, describes area expansion resulting from expansion in two directions perpendicular to each other. The directions perpendicular to each other are understood here to refer to expansion directions within the same plane, rather than expansion of the catalyst-coated membrane in the direction of layer thickness or layer arrangement. More specifically, the directions perpendicular to each other are understood to refer to expansion directions in the longitudinal (MD) and transverse (TD) directions (also called machine transverse), where the change in area can be expressed as a percentage of area expansion. In the context of the invention, high dimensional stability always means low area expansion of less than 20%.

[0016] As an example, in a membrane having a length of 100 mm (MD) and a width of 100 mm (TD) when dry, and wherein the length and width increase to 115 mm (MD) and 125 mm (TD) after being immersed in hot water at 100°C for two hours at an air pressure of 1013 hPa, the area expansion is 43.75%, as explained in more detail below.

[0017] In the context of this invention, after being kept in hot water at 100°C for two hours at an air pressure of 1013 hPa, films with high dimensional stability and therefore less than 20% area expansion, as well as catalyst-coated films, can be obtained in various ways, and there are no specific limitations on the methods of preparing them.

[0018] According to a first exemplary method, one or more reinforcing structures are incorporated into the proton exchange membrane, such that the one or more reinforcing structures limit the swelling of the membrane. The reinforcing structures can be introduced, for example, during the preparation of the membrane from a dispersion or solution of ionomer. In this case, a previously formed reinforcing structure, such as a (bi-)axially stretched PTFE (ePTFE, expanded PTFE), is impregnated with a dispersion of ionomer and then dried, such that the pores of the reinforcing structure are filled with ionomer. The membrane can subsequently be heated in a high-temperature step, for example at about 150 to 200°C, in order to improve the stability of the membrane.

[0019] The ionomer used is preferably a PFSA ionomer.

[0020] The reinforcing membrane can also be obtained by, for example, laminating one or more non-reinforced membranes having a reinforcing structure in a press or calendering process. A membrane having a plurality of reinforcing structures can be obtained, for example, by laminating (for example in a press or calendering process) two or more membranes, at least two of which have a reinforcing structure. This makes it possible to obtain a membrane having two or more reinforcing structures and very high dimensional stability, i.e. an area expansion of less than 10% when the membrane is held in hot water at 100°C for 2 hours at an air pressure of 1013 hPa.

[0021] Suitable reinforcing structures are, for example, woven or non-woven polymer structures, porous ceramic membranes, perforated polymer membranes or perforated inorganic membranes or (bi-)axially stretched porous polymer membranes. Preferred reinforcing structures are also porous membranes of expanded polytetrafluoroethylene (ePTFE) or polyolefins, which allow the preparation of thin and strong membranes with excellent electrochemical properties.

[0022] According to a second exemplary method, a dimensionally stable membrane can be obtained by increasing the equivalent weight (EW) of the ionomer, thereby limiting the absorption of water by the membrane. Here, the EW indicates the mass of polymer present per mole of ionic functionality in the ionomer. Depending on the type of ionomer used, the person skilled in the art can determine a suitable minimum equivalent weight which does not exceed the desired area expansion (for example less than 20%). A non-reinforced membrane comprising an ionomer having such an equivalent weight can be prepared, for example, by extrusion or solvent-based coating processes.

[0023] The above methods, i.e. the introduction of one or more reinforcing structures and the increase in the equivalent weight, can additionally be combined.

[0024] In principle, the method in which one or more reinforcing structures are introduced into the membrane can be preferred, since thin membranes, for example with a layer thickness of around 50 pm, having very good dimensional stability, good mechanical properties and low ionic resistance can be obtained, which is particularly advantageous for the use of the application in water electrolysis cells.

[0025] The ionomer used in the polymer electrolyte membrane used according to the application and in the catalyst layer is not particularly limited and can be a perfluorinated ionomer (PFSA), a partially fluorinated or hydrocarbon-based (non-fluorinated) ionomer, wherein different ionomers can be used in the different layers of the catalyst-coated membrane.

[0026] The membrane can also be composed of sub-layers which can comprise different ionomers. Examples of ionomers of the PFSA type are Nafion® from Chemours Nafion® from Chemours, Flemion® from Asahi Glass, Aciplex® from Asahi Kasei, HySultone® from Solvay Specialty Polymers, or Dow XUS-13456 from Dow. Nafion® from Chemours, Flemion® from Asahi Glass, Aciplex® from Asahi Kasei, HySultone® from Solvay Specialty Polymers, or Dow XUS-13456 from Dow. Nafion® from Chemours, Flemion® from Asahi Glass, Aciplex® from Asahi Kasei, HySultone® from Solvay Specialty Polymers, or Dow XUS-13456 from Dow. Examples of hydrocarbon-based ionomers are sulfonated polyether ketone (sPEK), sulfonated polyether ether ketone (sPEEK), sulfonated polyketone ketone (sPKK), sulfonated polysulfone (sPSU) and sulfonated polyether sulfone (sPES).

[0027] According to an advantageous variant, the area expansion of the catalyst-coated membrane is less than 15% and in particular less than 10% after two hours of immersion in hot water at 100°C under an air pressure of 1013 hPa, as described hereafter. This leads to an improved efficiency of the catalyst-coated membrane and to a particularly low voltage for a given current density.

[0028] In order to further reduce the cost of the catalyst-coated membrane while maintaining a high efficiency, the weight per area of the noble metal-containing catalyst is preferably less than or equal to 0.4 mg / cm 2 and in particular less than or equal to 0.35 mg / cm 2 .

[0029] When the weight per area of the noble metal-containing catalyst is preferably greater than or equal to 0.02 mg / cm 2 and in particular greater than or equal to 0.05 mg / cm 2 it is advantageous to optimize the catalytic performance of the catalyst-coated membrane while keeping the economic outlay minimal.

[0030] Due to the very good OER activity, the noble metal of the at least one noble metal-containing catalyst is more particularly chosen from iridium and ruthenium. This means that both iridium and ruthenium can be used as noble metal-containing catalysts, either individually or in combination.

[0031] When the noble metal containing catalyst is selected from iridium oxide, ruthenium oxide, mixtures thereof and alloys thereof, it is particularly advantageous in terms of high catalyst stability and excellent OER activity. Other elements can be added to improve the activity and / or stability of the OER catalyst. Any alloying metal can be particularly selected from tin (Sn), niobium (Nb), nickel (Ni), tantalum (Ta), titanium (Ti), cobalt (Co), zinc (Zn), platinum (Pt), iron (Fe), silicon (Si) and cerium (Ce), wherein the alloying metal is present in the alloy in an amount of less than 50 wt.-%.

[0032] Iridium oxide and ruthenium oxide can for example be present in the form of (nano)particles or as thin films coated on a substrate. In the case of (nano)particles, the catalyst oxide can be self-supporting, aggregated or finely dispersed on a substrate, typically a powder with a high specific surface area, such as titanium oxide. When the catalyst is present in the form of a thin film, inorganic, for example ceramic, or organic compounds, for example polyaromatic molecules such as perylene, can be used as a substrate.

[0033] The OER catalyst oxide can be obtained by wet-chemical methods, for example precipitation of hydroxides starting from soluble salts followed by heat treatment in air, or by thermal, dry methods (for example the "Adam's fusion method") or by gas phase methods. Various methods for the synthesis of iridium oxide are summarized, for example, in J. Hansaem and L. Jaeyoung (Journal of Energy Chemistry, Volume 46, July 2020, pages 152-172).

[0034] In order to further improve the efficiency of the noble metal containing catalyst at low loadings and high anode conductivity, the noble metal containing catalyst is preferably supported on inorganic and / or ceramic carriers, in particular on titanium oxide and / or niobium oxide and / or antimony-doped niobium oxide and / or tin oxide and / or antimony-doped tin oxide.

[0035] According to a further advantageous variant, the cathode comprises a platinum containing and / or palladium containing cathode catalyst, wherein the platinum containing and / or palladium containing cathode catalyst is more particularly present on a carbon containing carrier material. This is advantageous because the platinum containing and / or palladium containing cathode catalyst has a particularly high HER activity, which contributes to the power density of the catalyst coated membrane according to the application. It should also be noted here that the dimensional stability of the catalyst coated membrane is essentially not influenced by the provision of a cathode, so that this is also the case for a catalyst coated membrane having an anode and a cathode. The area expansion of the catalyst coated membrane is less than 20% after two hours in hot water at 100°C at an air pressure of 1013 hPa.

[0036] It is further advantageous when the proton exchange membrane has a layer thickness of 5 to 120 pm, more particularly 15 to 90 pm, and more particularly 35 to 75 pm. This achieves an optimal balance between efficiency and dimensional stability.

[0037] It is also possible to use films of greater thickness, for example up to 200 pm, however thereby a significant reduction in efficiency due to the high membrane proton resistance, especially at high current densities. If films in the lower thickness range, i.e. about 50 pm or less, are used, the hydrocarbon-based ionomer is preferably included in at least one sublayer of the membrane in order to reduce the gas permeability from the side of the catalyst-coated membrane to the other side of the catalyst-coated membrane. Hydrocarbon-based ionomers inherently have a lower gas permeability than PFSA ionomers. In particular, in order to prevent the formation of an explosive mixture on the anode side and / or a loss of current efficiency, the crossing-over of hydrogen should be minimized. Furthermore, in the lower thickness range, it is preferred to use reinforced films in order to improve the mechanical properties and long-term stability - thousands of operating hours.

[0038] It is further advantageous when the proton exchange membrane comprises at least one recombination catalyst, in particular comprising platinum particles. The platinum particles are preferably finely dispersed within the membrane. The recombination catalyst catalyzes the reaction of hydrogen crossing over from the cathode to oxygen from the anode side in order to prevent the formation of an explosive mixture on the anode side of the cell.

[0039] The anode and the cathode of the catalyst-coated membrane of the present invention can be produced by conventional methods. This can be done, for example, by dispersing a powdered noble metal-containing catalyst together with an ionomer binder in an organic solvent or a mixture of water and one or more organic solvents. The dispersion is then optionally stirred in a high-energy mixer to make good dispersion possible and to reduce the size of catalyst agglomerates. Using a coating device or a printing device, the ink or paste thus obtained is then coated or printed directly onto the membrane surface (first or second face of the proton exchange membrane) or initially onto an inert substrate called a decal. The coating device or printing device employed can be, for example, a doctor blade, a slot nozzle, a coating roller, or a screen or gravure printing. The liquid medium is then evaporated, resulting in a thin electrode layer. When one or both electrodes are coated onto an inert substrate, the dried electrode is then transferred onto the membrane surface by applying heat and pressure, i.e. by the so-called decal transfer method.

[0040] In alternative embodiments, the ink or paste for the preparation of the cathode can also be applied or printed directly on the porous transport layer, in particular on the gas diffusion layer. In this case, the term gas diffusion electrode (GDE) is used. The anode is applied to the membrane via a decal method or via direct film coating, thus obtaining a single-sided catalyst-coated membrane or so-called half-CCM. Subsequently, a catalyst-coated membrane (on both sides) is obtained upon installation in an electrolysis cell, wherein the connection between the cathode catalyst layer and the membrane is obtained under the operating conditions of the cell.

[0041] A water electrolysis cell comprising a catalyst-coated membrane as disclosed above is also described according to the present application. The use of the catalyst-coated membrane of the present application confers to the water electrolysis cell according to the present application the features of high power density and high efficiency at relatively low manufacturing costs. Examples

[0042] Method

[0043] Determination of dimensional stability (area expansion) of the membrane / catalyst coated membrane (CCM) during water uptake

[0044] The membrane or the membrane coated on one or both sides with catalyst (half-CCM or CCM) is conditioned at 21 °C and 50% relative humidity until the size / dimension does not further change. Then a square with edge length (L) of 80 mm x 80 mm is precisely cut out using a cutting die (L 干 = 80 mm). The two edges are aligned respectively in the longitudinal and transverse direction. The directions are marked with a permanent marker. Then the square piece (membrane, half-CCM or CCM) is kept in hot water at 100 °C for 2 h under an air pressure of 1013 hPa. Then the piece is taken out of the water, the excess water droplets are quickly wiped off and the edge length of the square is measured with a caliper with a resolution of 0.01 mm, resulting in the edge length L 1,湿 and L 2,湿 .

[0045] The area change (%) is calculated according to the following formula:

[0046] 100 x [(L 1,湿 x L 2,湿 - L 干 2 ] / L 干 2 .

[0047] The measurement of the swelling behavior at 100°C, which corresponds to the temperature of hot water at 1013 hPa air pressure at 1013 hPa air pressure at 100°C, and thus of the area expansion of the membrane, semi-CCM or CCM is an established condition in the prior art and is also linked to the swelling behavior of the membrane and thus of the semi-CCM or CCM in water at other conditions, for example at room temperature and in particular in hot water, which are normal operating conditions for the membrane, semi-CCM or CCM. In other words, a membrane / semi-CCM / CCM with a greater swelling behavior at 100°C and thus with a high area expansion also shows a greater swelling behavior at lower temperatures. However, the measurement of the swelling behavior at 100°C offers the advantage that this temperature is strictly controlled by the boiling point of water and is thus applied according to the present application.

[0048] Power / efficiency in water electrolysis cells

[0049] The efficiency of the CCM was measured in a single cell with an active area of 25 cm 2 The cell consisted of platinized titanium plates with a channel flow field design on the anode side and the cathode side. The flow field plate on the cathode side was additionally gold plated. Titanium sinter (1 mm thickness) and carbon paper (Toray TGP-H-120) were used as porous transport and gas diffusion layers on the anode side and the cathode side. The cell was closed with six M8 screws with a torque of 10 Nm. Deionized water with a conductivity of less than 1 μS / cm was circulated on the anode side. The cell was heated from room temperature to 60°C by a heating mat placed on the end plate over a period of 20 minutes. Then the temperature was increased to 80°C over a period of 20 minutes. The cell was conditioned by cycling from 0 to 1 A / cm 2 over a period of 20 minutes. The cell was conditioned by cycling from 0 to 1 A / cm 2 over a period of 20 minutes. The cell was conditioned by cycling from 0 to 1 A / cm

[0050] The current-voltage characteristics (polarization curves) were recorded by increasing the current density from a low value to a high value (A / cm 2 ) at 80°C and 65°C, with a holding time of 10 min each. The steps were as follows:

[0051] 0.01 - 0.02 - 0.03 - 0.05 - 0.08 - 0.1 - 0.2 - 0.4 - 0.6 - 0.8 - 1.0 - 1.2 - 1.4 - 1.6 - 1.8 - 2.0 - 2.25 - 2.5 - 2.75 - 3.0 (in each case in A / cm 2 ).

[0052] Preparation of anode ink

[0053] 20.00 g of a commercially available iridium-based catalyst (Elyst Ir75 0480; Umicore, Germany, IrO2 supported on TiO2; 75 wt% iridium) was mixed with 10.20 g of a catalyst with an ionomer content of 20.2 wt%. The D2020 ionomer dispersion (Chemours; USA) was mixed. Then, 0.5 g of water and 69.30 g of 2-propanol were added. The mixture was dispersed for 30 min using spherical zirconia beads with a diameter of 1 mm in a bead mill. The stirring disc had a diameter of 45 mm and was set to a speed of 2130 rpm. The quality of the dispersion was ensured by visually inspecting for the absence of catalyst aggregates. The quality of the dispersion was further confirmed by good coating quality, i.e., no visible aggregates or textures in the wet or dry layer.

[0054] Preparation of anodes with different iridium loadings on the decal paper

[0055] Anodized ink is applied to a glass fiber reinforced PTFE substrate, or in other words, to a decal, using a spiral coater (wire bar). The wet film thickness is gradually increased by selecting different spiral coaters with progressively increasing wire thicknesses to achieve a thickness of 0.15 mg / cm². 2 0.25 mg / cm 2 0.5 mg / cm 2 1.0 mg / cm 2 and 2.25 mg / cm 2 The iridium metal loading (weight per unit area) was determined. The wet layer thickness varied from 10 μm to 285 μm by selecting a spiral coater with an appropriate wire diameter. After coating, these wet layers were dried in an oven at 110°C for 5 min. The actual iridium metal loading was determined by gravimetric analysis by recording the precise decal weight before and after CCM lamination, as described in Example 1.

[0056] Example 1 : Catalysts with high dimensional stability (low area expansion) and different anode catalyst loadings Preparation of coated membranes (CCM)

[0057] A membrane with high dimensional stability and a thickness of 41 μm, comprising two expanded PTFE (ePTFE) reinforcement structures, was obtained by laminating an unreinforced PFSA membrane with a thickness of 25 μm between two reinforced PFSA membranes, each with a thickness of 8 μm. The membranes were laminated in a press at a temperature of 160 °C and a pressure of 1.5 MPa for 1 min. The longitudinal directions of the three membranes were arranged parallel to each other in each case. The linear expansion of the membrane due to water absorption (100 °C) was measured according to the described method, yielding values ​​of 2.0% and 3.3%. The resulting area expansion was 5.4%.

[0058] Five CCMs were prepared in a press by means of the decal method using this type of membrane. This was done by arranging the membranes between the anode and cathode decal (5 cm x 5 cm) and pressing them at a temperature of 180 °C and a pressure of 1.5 MPa for 1 min, thereby transferring the electrode layers from the decal substrate to the membranes.

[0059] The cathode was the same for all CCMs and consisted of a catalyst of platinum and ionomer binder on a carbon support. The weight ratio of catalyst to ionomer in the cathode was 3:1 and the platinum loading was 0.3 mg / cm 2 The cathode was likewise applied to the glass-fiber reinforced PTFE.

[0060] However, in the preparation of these CCMs, the anode loading of the different CCMs was varied by using anode decals with different loadings, as described in the section “Preparation of anodes with different iridium loadings on decal”. The actual anode loading was determined gravimetrically by determining the weight of the anode decal before transfer (anode electrode on PTFE substrate) and after transfer (pure PTFE substrate). The weight per area of iridium (loading) was calculated by determining the difference (anode decal minus pure PTFE substrate) and including the known composition of the dried electrode layer. For the five CCMs, the following anode iridium loadings were obtained: 0.162 mg / cm 2 , 0.261 mg / cm 2 , 0.474 mg / cm 2 , 1.029 mg / cm 2 and 2.072 mg / cm 2 .

[0061] In addition, the CCM with an anode iridium loading of 0.261 mg / cm 2 was investigated to measure the dimensional stability upon water uptake (100 °C, see method description). The CCM showed a dimensional change of 1.6% in length and 3.0% in width. This corresponds to an area expansion of 4.6%.

[0062] By using membranes with high dimensional stability, the respective CCMs also exhibit high dimensional stability.

[0063] The swelling behavior of the same CCM with an anode iridium loading of 0.261 mg / cm 2 was also investigated in a water bath at a lower temperature. At room temperature, the area expansion was 3.9%, while at a temperature of 80 °C, the area expansion was 4.1%.

[0064] Comparative Example 1 : Preparation of CCMs according to the prior art and with different anode iridium loadings

[0065] The CCM according to the prior art was prepared in a similar way to the procedure of Example 1, with the difference that the film used was Halar® NR212 (Chemours, USA). This film has a thickness of about 50 pm and is a film already established in the PEM-WE publication.

[0066] The linear dimensional changes of the Halar® NR212 film upon water uptake (100 °C) were 20.0% and 19.7%. The resulting area expansion was 43.6%.

[0067] The anode and cathode used correspond to the anode and cathode from Example 1.

[0068] For the following five CCMs, the following anode iridium loadings were obtained: 0.155 mg / cm 2 , 0.303 mg / cm 2 , 0.504 mg / cm 2 , 1.068 mg / cm 2 and 2.102 mg / cm 2 .

[0069] Although the same electrodes as in Example 1 were used, slightly different loadings were obtained compared to the CCM of Example 1, due to slight inhomogeneities in the loading that occurred during the coating on the decal substrate. However, the differences are small enough to allow a comparison of the series of CCMs with high informative value.

[0070] A CCM with Halar® NR212 with an anode iridium loading of 0.303 mg / cm 2 was additionally investigated to measure the dimensional stability upon water uptake (100 °C, see method description). The CCM showed dimensional changes of 15.7% in length and 15.9% in width. This corresponds to an area expansion of 34.1%.

[0071] By using a film with low dimensional stability, the corresponding CCM likewise exhibits low dimensional stability.

[0072] The swelling behavior of the same CCM with an anode iridium loading of 0.303 mg / cm 2 was also investigated in a water bath at a lower temperature. At room temperature, the area expansion was 14.4%, while at a temperature of 80 °C, the area expansion was 26.6%.

[0073] The swelling behavior in water heated to 100 °C at an air pressure of 1013 hPa, as already described in the method section, is also relevant to the swelling behavior at lower temperatures.

[0074] Comparison of power / efficiency in water electrolysis cells - CCMs from Example 1 and Comparative Example 1

[0075] The CCMs from Example 1 and Comparative Example 1 were electrochemically characterized in a water electrolysis cell according to the method described above (see the section "Power / efficiency in a water electrolysis cell"). The results, i.e. the cell voltage as a function of the anode catalyst loading (anode noble metal loading) at a given current density, are shown in Figures 1 to 4 From the data it can be seen that, at the two temperatures studied and at an anode catalyst loading equal to or less than 0.6 mg / cm 2 and a current density greater than 1 A / cm 2 , the CCMs with high dimensional stability exhibit a better efficiency than the CCMs with low dimensional stability. It should be mentioned that, in order to produce a large amount of hydrogen per unit area of electrolyser and per unit of time, the relevant current density used is at a higher current density (> 1 A / cm 2 ).

[0076] Further details, advantages and features of the application will become apparent from the following description of exemplary embodiments with reference to the attached drawings. In these drawings:

[0077] Figure 1 shows the cell voltage as a function of the anode catalyst loading at a cell temperature of 80°C, at a current density of 3.0 A / cm 2 ,

[0078] Figure 2 shows the cell voltage as a function of the anode catalyst loading at a cell temperature of 80°C, at a current density of 1.2 A / cm 2 ,

[0079] Figure 3 shows the cell voltage as a function of the anode catalyst loading at a cell temperature of 80°C, at a current density of 0.05 A / cm 2 ,

[0080] Figure 4 shows the cell voltage as a function of the anode catalyst loading at a cell temperature of 65°C, at a current density of 3.0 A / cm 2 .

[0081] Figure 1 shows the cell voltage as a function of the anode catalyst loading at a cell temperature of 65°C, at a current density of 3.0 A / cm 2The current density and battery voltage of the water electrolysis cells from Example 1 and Comparative Example 1 at a battery temperature of 80°C. A comparison between the CCM (triangular; Example 1) with a membrane possessing high dimensional stability and therefore low area expansion according to the invention and the CCM (circular; Comparative Example 1) with a membrane possessing low dimensional stability and therefore high area expansion clearly shows that below 0.6 mg / cm²... 2 The advantage of using a size-stable membrane under high anodic load is that the battery voltage is improved by 40mV and higher.

[0082] Figure 2 The results show the iridium loading for various anodes at 1.2 A / cm². 2 The current density and battery voltage of the water electrolysis cells from Example 1 and Comparative Example 1 at a battery temperature of 80°C. A comparison between the CCM (triangular; Example 1) with a membrane possessing high dimensional stability and therefore low area expansion according to the invention and the CCM (circular; Comparative Example 1) with a membrane possessing low dimensional stability and therefore high area expansion clearly shows that below 0.6 mg / cm²... 2 The advantage of using size-stable membranes under anode loading.

[0083] Figure 3 The results show the iridium loading for various anodes at 0.05 A / cm². 2 The cell voltages from the water electrolysis cells of Example 1 and Comparative Example 1 were measured at a current density and a cell temperature of 80°C. The power / efficiency in this low current density region was similar for both membrane types across the entire anode load range. At 2 mg / cm³... 2 Below and at 0.2 mg / cm 2 The voltage difference between the loading rates is in the range of 45 to 50 mV, which corresponds to a slope of 45-50 mV / decade and thus to the theoretical expectation of the iridium oxide OER catalyst. Strictly speaking, the slope should be calculated based on the resistance-corrected cell voltage, but at such low current densities, a correction of only a few mV is negligible, and since no correction is considered for either loading rate, the slope and the conclusions drawn from it remain unchanged.

[0084] Figure 4 The results show the iridium loading for various anodes at 3.0 A / cm². 2cell voltage of water electrolysis cells from Example 1 and from Comparative Example 1 at a current density of 0.6 mg / cm2and a cell temperature of 65 °C. The comparison between the CCM with a membrane according to the present application having a high dimensional stability and thus a low area expansion (triangle; Example 1) and the CCM with a membrane having a low dimensional stability and thus a high area expansion (circle; Comparative Example 1) clearly indicates the advantage of using a dimensionally stable membrane at an anode loading of below 0.6 mg / cm2, the improvement of the cell voltage is 40 mV and higher. 2

[0085] In addition to the above written description of the application, explicit reference is hereby made to the graphic representation of the application in Figures 1 to 4 for its supplementary disclosure.​

Claims

1. A water electrolysis battery, comprising a catalyst-coated membrane, said catalyst-coated membrane comprising: Proton exchange membrane, • An anode applied to the first surface of the membrane, comprising at least one noble metal-containing catalyst, wherein the area weight of the noble metal-containing catalyst is less than or equal to 0.35 mg / cm² based on the noble metal content. 2 The precious metals mentioned are selected from iridium and ruthenium, and • The cathode applied to the second side of the membrane, After being kept in hot water at 100°C for two hours, the area expansion of the catalyst-coated membrane was less than 20%. This area expansion was measured and calculated by adjusting the membrane (either a half-CCM or a CCM with catalyst coated on one or both sides) at 21°C and 50% relative humidity until the dimensions no longer changed. Then, a cutting die L was used. 干 A square with an edge length L of 80mm × 80mm is precisely cut out from 80mm. These two edges are aligned longitudinally and laterally, and the orientation is marked with a permanent marker. The square sheet, i.e., a half-CCM or CCM, is then kept in hot water at 100°C for 2 hours under an air pressure of 1013 hPa. The sheet is then removed from the water, excess water droplets are quickly scraped off, and the edge length L is measured using calipers with a resolution of 0.01mm. 1,湿 and L 2,湿 ; The change in area (%) is calculated using the following formula: 100×[(L 1,湿 ×L 2,湿 )-L 干 2 ] / L 干 2 。 2. The water electrolysis battery of claim 1, wherein after being kept in hot water at 100°C for two hours, the area of ​​the catalyst coating film expands by less than 15%.

3. The water electrolysis battery of claim 1, wherein after being kept in hot water at 100°C for two hours, the area of ​​the catalyst coating film expands by less than 10%.

4. The water electrolysis battery of claim 1, wherein, based on the precious metal content, the area weight of the precious metal-containing catalyst is greater than or equal to 0.02 mg / cm². 2 .

5. The water electrolysis battery of claim 1, wherein, based on the precious metal content, the area weight of the precious metal-containing catalyst is greater than or equal to 0.05 mg / cm². 2 .

6. The water electrolysis battery of claim 1, wherein the noble metal-containing catalyst is selected from iridium oxide, ruthenium oxide, mixtures thereof, and alloys thereof.

7. The water electrolysis battery of claim 1, wherein the precious metal-containing catalyst is supported on an inorganic and / or ceramic support.

8. The water electrolysis battery of claim 1, wherein the noble metal-containing catalyst is supported on titanium oxide and / or niobium oxide and / or antimony-doped niobium oxide and / or tin oxide and / or antimony-doped tin oxide.

9. The water electrolysis battery of claim 1, wherein the cathode comprises a platinum- and / or palladium-containing cathode catalyst, the platinum- and / or palladium-containing cathode catalyst being present on a carbon-containing support material.

10. The water electrolysis battery of claim 1, wherein the proton exchange membrane has a layer thickness of 5 to 120 μm, and / or The proton exchange membrane contains at least one recombinant catalyst, which is platinum particles.

11. The water electrolysis battery of claim 10, wherein the proton exchange membrane has a layer thickness of 15 to 90 μm.

12. The water electrolysis battery of claim 10, wherein the proton exchange membrane has a layer thickness of 35 to 75 μm.

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