Mo-ru catalyst materials for the electrolysis of water

Abstract

The invention relates to a catalyst material for an electrolyser for the electrolysis of water, wherein the catalyst material comprises molybdenum and ruthenium, and wherein the catalyst material has a ruthenium portion of between 5 atom% and 35 atom% and a molybdenum portion of between 40 atom% and 95 atom%, in each case based on the total atomic number of the catalyst material. The invention also relates to a catalyst comprising the above catalyst material. The invention also relates to an electrode and in particular to a cathode of an electrolyser for the electrolysis of water, comprising an electrically conductive carrier, wherein the carrier is coated with the above catalyst material. Furthermore, the invention relates to the use of the above catalyst material, the above catalyst, or the above electrode in the electrolysis of water.

Description

[0001] Mo-Ru catalyst materials for water electrolysis

[0002] The invention relates to the field of catalyst materials for water electrolysis. In particular, the invention relates to a catalyst material for an electrolyzer for water electrolysis.

[0003] Furthermore, the invention relates to a catalyst comprising the above catalyst material, wherein the catalyst material is applied to a particle, in particular microparticles.

[0004] Furthermore, the invention relates to an electrode, and in particular a cathode, of an electrolyzer for water electrolysis comprising the above catalyst material.

[0005] Furthermore, the invention relates to the use of the above catalyst material or the use of the above catalyst or the use of the above electrode in water electrolysis.

[0006] In water electrolysis, the water molecule is split into the gases hydrogen and oxygen using electrical energy at a cathode and anode of an electrolysis cell, respectively. An important application of water electrolysis is the production of hydrogen, as it has the potential to replace the production of hydrogen from fossil fuels in the course of the expansion of renewable energies. Furthermore, water electrolysis enables the chemical storage of surplus wind and solar power in the case of fluctuating electricity generation from renewable energies, particularly wind power and photovoltaics. The produced hydrogen can be used in chemical processes or fed into the natural gas grid directly or after subsequent methanation as methane.

[0007] The catalyst materials used in water electrolysis typically contain a very high proportion of precious metals, which is associated with high costs. Furthermore, the availability of sufficient quantities, as well as the environmental impact of mining or extracting the precious metals, are problematic. Furthermore, the stability or activity of the catalyst materials known to date is not always sufficient for water electrolysis. In particular, catalyst materials containing transition metals exhibit low activity, making water electrolysis with these catalyst materials uneconomical. Accordingly, there is a need to improve the efficiency of water electrolysis.

[0008] Based on this, the object of the invention is to improve water electrolysis and in particular to provide catalyst materials, catalysts or electrodes with high activity and stability at low cost.

[0009] According to the invention, the object is achieved by the features of the independent claims. Preferred embodiments of the invention are specified in the subclaims, each of which may represent an aspect of the invention individually or in combination.

[0010] This object is achieved by a catalyst material for an electrolyzer for water electrolysis, wherein the catalyst material comprises molybdenum and ruthenium, and wherein the catalyst material has a ruthenium content of between 5 atomic % and 35 atomic % and a molybdenum content of between 40 atomic % and 95 atomic %, each based on the total number of atoms in the catalyst material. Furthermore, the object is achieved by a catalyst comprising the above catalyst material, wherein the catalyst material is applied to a particle, in particular a microparticle.

[0011] In addition, the object is achieved by an electrode and in particular cathode of an electrolyzer for water electrolysis comprising an electrically conductive carrier, wherein the carrier is coated with the above catalyst material.

[0012] This object is preferably achieved by a cathode of an electrolyzer for water electrolysis comprising an electrically conductive support coated with a catalyst material, wherein the catalyst material comprises molybdenum and ruthenium, and wherein the catalyst material has a ruthenium content of between 5 atomic % and 35 atomic % and a molybdenum content of between 40 atomic % and 95 atomic % in each case based on the total number of atoms of the catalyst material.

[0013] In this context, catalyst material refers in particular to the catalytically active material of the anode or cathode of an electrolysis cell or electrolyzer for water electrolysis. Particularly preferred is the catalytically active material of the cathode. The catalytically active material of the cathode is also referred to as a hydrogen evolution catalyst.

[0014] The catalyst material according to the invention thus has a low content of the noble metal ruthenium, which makes the catalyst material cost-effective—especially compared to noble metal-based catalyst materials. It has been shown that the activity of the catalyst material with respect to the hydrogen evolution reaction is comparable to that of platinum. Furthermore, the catalyst material exhibits high stability. The catalyst material is suitable for both alkaline and acidic water electrolysis in a membrane-electrode arrangement in PEM (proton exchange membrane) or AEM (anion exchange membrane) water electrolysis. Furthermore, it can also be used in the standard configuration of alkaline water electrolysis.

[0015] The catalyst material can comprise other elements besides molybdenum and ruthenium. Alternatively, the catalyst material can consist of molybdenum and ruthenium—i.e., it can contain no other elements. The molybdenum and ruthenium are preferably present in the catalyst material as elemental metals—i.e., in oxidation state 0. In other words, the molybdenum and ruthenium are preferably not present in the catalyst material as metal salts or metal oxides.

[0016] The ruthenium content of the catalyst material, which ranges between 5 atomic percent and 35 atomic percent, and the molybdenum content of the catalyst material, which ranges between 40 atomic percent and 95 atomic percent, each refer to the total number of atoms in the catalyst material. If the catalyst material contains no other elements, i.e., consists of molybdenum and ruthenium, the molybdenum content and the ruthenium content of the catalyst material add up to 100%.

[0017] As already mentioned, the catalyst material has a low ruthenium content. In this context, according to a preferred embodiment of the invention, the ruthenium content is between 5 atomic % and 30 atomic %; preferably between 5 atomic % and 25 atomic %; and particularly preferably between 5 atomic % and 20 atomic % based on the total number of atoms in the catalyst material. It has been shown that the catalyst is active despite the very low ruthenium content. For example, the ruthenium content can be 27 atomic % and the molybdenum content 40 atomic %. In another example, the ruthenium content can be 11 atomic % and the molybdenum content 89 atomic %.

[0018] In connection with the preferred development in which the catalyst material comprises further elements in addition to molybdenum and ruthenium, according to a preferred development of the invention it is provided that the catalyst material comprises up to 35 atomic % of further metals, based on the total number of atoms of the catalyst material, wherein the molybdenum content is between 40 atomic % and 90 atomic % in each case based on the total number of atoms of the catalyst material.

[0019] In this further development, the catalyst material is preferably a multinary material system comprising more than two elements. Multinary material systems have the advantage of being more stable under electrolytic conditions than binary material systems. In particular, multinary material systems are also suitable for the electrolytic reduction of CO2 to CO.

[0020] The proportion of other elements - i.e. not molybdenum and ruthenium - can be up to 35 atomic% based on the total number of atoms in the catalyst material.

[0021] In this context, according to a further development of the invention, the additional metals comprise titanium and silver. It has been shown that a catalyst material comprising molybdenum, ruthenium, and silver, or molybdenum, ruthenium, and titanium, or molybdenum, ruthenium, titanium, and silver, is particularly suitable for alkaline water electrolysis.

[0022] According to a further preferred development of the invention, the catalyst material consists of ruthenium and molybdenum and titanium and / or silver, wherein the molybdenum content is between 40 atomic % and 90 atomic % based on the total number of atoms in the catalyst material. In other words, the catalyst material is preferably made of molybdenum, ruthenium and silver, or of molybdenum, ruthenium and titanium, or of molybdenum, ruthenium, titanium and silver. The catalyst material is therefore preferably a ternary or quaternary material system. It is particularly preferably a ternary material system consisting of molybdenum, ruthenium and silver, or a quaternary material system consisting of molybdenum, ruthenium, silver and titanium. These material systems have shown particularly high catalytic activities, particularly in water electrolysis.

[0023] In the case of the quaternary catalyst material, or the ternary catalyst material consisting of molybdenum, ruthenium and silver, the ruthenium content is preferably between 20 atomic% and 35 atomic% and particularly preferably between 20 atomic% and 30 atomic%, based on the total number of atoms of the catalyst material.

[0024] Furthermore, in the quaternary catalyst material, or in the ternary catalyst material consisting of ruthenium, molybdenum and silver, the molybdenum content is preferably between 40 atomic% and 50 atomic% and particularly preferably between 40 atomic% and 45 atomic%, based on the total number of atoms of the catalyst material.

[0025] Furthermore, in the quaternary catalyst material, or in the ternary catalyst material consisting of ruthenium, molybdenum and silver, the silver content is preferably between 15 atomic% and 50 atomic% and particularly preferably between 20 atomic% and 40 atomic%, based on the total number of atoms of the catalyst material.

[0026] Furthermore, in the quaternary catalyst material consisting of ruthenium, molybdenum, silver, and titanium, the titanium content is preferably between 0.001 atomic % and 5 atomic % and particularly preferably between 0.001 atomic % and 2 atomic % based on the total number of atoms in the catalyst material. A preferred catalyst material, for example, consists of 34.9 atomic % ruthenium, 42.85 atomic % molybdenum, 21.23 atomic % silver, and 1.02 atomic % titanium. With this exemplary quaternary catalyst material, a hydrogen evolution reaction at a potential of -100 mV resulted in a current of -13.86 pA with an electrode surface area of ​​0.735 mm 2 measured.

[0027] Another preferred catalyst material consists, for example, of 25.19 atomic percent ruthenium, 40.73 atomic percent molybdenum, 30.83 atomic percent silver, and 0.82 atomic percent titanium. With this exemplary quaternary catalyst material, a hydrogen evolution reaction at a potential of -100 mV resulted in a current of -13.69 pA at an electrode surface of 0.735 mm 2 measured.

[0028] Another preferred catalyst material consists, for example, of 25.19 atomic percent ruthenium, 40.03 atomic percent molybdenum, 34.03 atomic percent silver, and 0.75 atomic percent titanium. With this exemplary quaternary catalyst material, a hydrogen evolution reaction at a potential of -100 mV resulted in a current of -13.3 pA at an electrode surface of 0.735 mm 2 measured.

[0029] Another preferred catalyst material consists, for example, of 22.1 atomic percent ruthenium, 40.69 atomic percent molybdenum, and 37.21 atomic percent silver. With this exemplary ternary catalyst material, a hydrogen evolution reaction at a potential of -100 mV resulted in a current of -10.9 pA at an electrode surface of 0.735 mm 2 measured.

[0030] According to a further preferred alternative development of the invention, the catalyst material consists of molybdenum and ruthenium. The molybdenum content is preferably between 65 atomic percent and 95 atomic percent, based on the total number of atoms in the catalyst material. Thus, in this alternative development, the catalyst material is preferably a binary material system. Binary material systems have the advantage of being particularly easy to produce, since they consist of only two elements. This also makes the catalyst material cost-effective.

[0031] In this context, according to a further preferred development of the invention, the ruthenium content is between 5 atomic% and 30 atomic%, preferably between 5 atomic% and 25 atomic%, more preferably between 8 atomic% and 25 atomic%, even more preferably between 10 atomic% and 20 atomic%.

[0032] A preferred catalyst material, for example, consists of 18 atomic percent ruthenium and 82 atomic percent molybdenum. Another preferred catalyst material, for example, consists of 16 atomic percent ruthenium and 84 atomic percent molybdenum. Yet another preferred catalyst material, for example, consists of 11 atomic percent ruthenium and 89 atomic percent molybdenum. It has been shown that, in binary catalyst materials, these atomic ratios with a particularly low proportion of ruthenium represent a particularly active catalyst material that is low-cost due to the low ruthenium content.

[0033] Regardless of whether the catalyst material consists of ruthenium and molybdenum or whether the catalyst material can also comprise other elements, according to a further preferred development it is provided that the catalyst material comprises ruthenium as the only noble metal. Furthermore it is preferably provided that the catalyst material is free of platinum. Further preferably it is provided that the catalyst material is free of sulfur. Further preferably it is provided that the catalyst material is free of nickel. Further preferably it is provided that the catalyst material is free of molybdenum(IV) sulfide. Particularly preferably the catalyst material is free of platinum and free of molybdenum(IV) sulfide. Particularly preferably the catalyst material is free of platinum, free of nickel and free of molybdenum(IV) sulfide.Unlike other catalyst materials, platinum is preferably not present in the catalyst material, which makes the catalyst material particularly advantageous. Likewise, the catalyst material is preferably not based on molybdenum(IV) sulfide; rather, the molybdenum is present in the catalyst material as elemental molybdenum. As already mentioned, the invention also relates to the catalyst comprising the above catalyst material, wherein the catalyst material is applied to the particle, in particular the microparticle. In the present case, a microparticle is preferably understood to mean a particle whose diameter is in the range from 10 pm to 200 pm. The catalyst has the advantage of being particularly versatile and easy to handle. The technical features and advantages of the catalyst will become apparent to those skilled in the art from the description of the catalyst material.

[0034] As already mentioned, the invention also relates to an electrode, and particularly preferably a cathode, of an electrolyzer for water electrolysis comprising the electrically conductive support, wherein the support is coated with the catalyst material described above. The technical features and advantages of the electrode will become apparent to those skilled in the art from the description of the catalyst material.

[0035] According to a further preferred embodiment of the invention, the carrier is porous. Alternatively and / or additionally, the carrier can be designed as a foam, a mesh, a sheet with holes, or a nonwoven.

[0036] In this context, it is further provided that the carrier comprises nickel, titanium, stainless steel, and / or carbon. It is further preferred that the carrier be made of nickel, titanium, stainless steel, and / or carbon. For example, the carrier is nickel foam. Nickel foam is a cost-effective and readily available carrier that makes water electrolysis economical.

[0037] With regard to the production of the cathode, according to a further preferred development of the invention, the cathode is obtained by the following steps:

[0038] - Providing the support, - Applying the catalyst material using a PVD process, plasma spraying process, thermal spraying process, airbrush spraying process, and / or using a wet chemical synthesis process.

[0039] The support can be coated with the catalyst material using a PVD process—that is, a physical vapor deposition process, such as sputtering. Alternatively, the material can be applied via wet chemical synthesis using an airbrush spraying process. Both manufacturing methods result in an active and stable electrode.

[0040] With regard to the wet-chemical synthesis process, according to a further preferred embodiment of the invention, the step of applying the catalyst material comprises applying a polymer-containing precursor solution to the support by means of the airbrush spraying method. The polymer-containing precursor solution is preferably polyvinylpyrrolidone dissolved in a mixture of water and ethanol, wherein the precursor solution comprises the metals molybdenum and ruthenium in the form of salts in the appropriate atomic ratio. If a ternary or quaternary catalyst material is to be produced, the precursor solution also comprises the metals silver and / or titanium in the form of salts. For application, the precursor solution is preferably sprayed onto the support, particularly preferably while the support is on a hot plate. The hot plate is preferably set such that the support preferably has a temperature of 120°C during application.

[0041] According to a further preferred development of the invention, a heat treatment is carried out following the application of the precursor solution to the support. Particularly preferably, the support to which the precursor solution is applied is heated to 800°C. The heat treatment preferably brings about a stable bond between the catalyst material and the support. Further preferably, the heat treatment takes place under a reducing atmosphere, particularly preferably under a 10% H2 / 90% Ar atmosphere.

[0042] Furthermore, it can be provided that the heat treatment is followed by a further heat treatment. The further heat treatment preferably takes place in an oxidizing atmosphere, particularly preferably in a 10% O2 / 90% Ar atmosphere. This further heat treatment preferably forms an oxide layer on the surface of the catalyst material.

[0043] In connection with the application of the catalyst material to the support using the PVD process, according to an alternative development of the invention, the step of applying the catalyst material is carried out using the PVD process and starting from exactly one sputtering target or several sputtering targets of the same design. In particular, therefore, several different sputtering targets are not used, for example a sputtering target consisting of molybdenum and a sputtering target consisting of ruthenium. Instead, preferably only one sputtering target or several similarly designed sputtering targets comprising molybdenum and ruthenium are used. When producing a binary catalyst material, the sputtering target or sputtering targets preferably consist of molybdenum and ruthenium.Further preferably, when producing a ternary catalyst material, the sputtering target(s) consists of molybdenum, ruthenium, and silver. Further preferably, when producing a quaternary catalyst material, the sputtering target(s) consists of molybdenum, ruthenium, silver, and titanium.

[0044] In connection with the application of the catalyst material to the support using the PVD process, according to a further preferred development, the step of providing the support includes removing a surface oxide of the support. Thus, an additional step can be provided prior to the application of the catalyst material, in which surface oxides of the support are removed. Alternatively, a support can be provided whose surface has been modified to provide a surface that is as oxide-free as possible. It has been shown that reducing oxides on the surface of the support is beneficial for the produced electrode.

[0045] The invention further relates to the use of the above-described catalyst material, or the use of the above-described catalyst in water electrolysis, or the use of the above-described electrode in water electrolysis, in particular as a cathode. Preferably, the invention further relates to the use of the above-described cathode in water electrolysis.

[0046] The catalyst material, the catalyst and the cathode show overpotentials for hydrogen evolution of only 50 mV at a current density of 100 mA / cm 2 , and 130 mV at a current density of 2 A / cm 2 , which enables very efficient water electrolysis.

[0047] The water electrolysis can be acidic water electrolysis, alkaline water electrolysis, PEM water electrolysis, or AEM water electrolysis. Use in alkaline water electrolysis, PEM water electrolysis, and / or AEM water electrolysis is preferred.

[0048] The person skilled in the art will derive further technical aspects and advantages of the use of the catalyst material and / or the use of the cathode from the above description of the catalyst material and / or the cathode.

[0049] The invention will be explained below by way of example with reference to the accompanying drawings using preferred embodiments, wherein the features presented below can represent an aspect of the invention both individually and in combination. They show: Fig. 1 SEM-EDX and TEM images of two cathodes according to a preferred embodiment of the invention, wherein the cathodes were manufactured using different heat treatment methods (Methods A and B).

[0050] Fig. 2 is a current-voltage diagram for the two cathodes from Figure 1,

[0051] Fig. 3 in a) and b) each shows a CP diagram for the two cathodes from Figure 1,

[0052] Fig. 4 SEM-EDX images of the cathode according to method A of Figure 1 after being exposed to a long-term hydrogen evolution reaction,

[0053] Fig. 5 is a CP diagram for another cathode according to a preferred embodiment of the invention, this cathode being manufactured by means of heat treatment method A,

[0054] Fig. 6 in a) a CP diagram for another cathode according to a preferred embodiment of the invention, this cathode being manufactured by means of heat treatment method A, during a long-term chronopotentiometry measurement, and in b) the current-voltage diagram before and after the long-term chronopotentiometry measurement,

[0055] Fig. 7 shows SEM-EDX images of the cathodes from Figure 6 after exposure to the long-term hydrogen evolution reaction, and

[0056] Fig. 8 shows a CP diagram for a cathode produced by a sputtering process according to a preferred embodiment of the invention, compared to a Ni cathode. Cathodes coated with catalyst material for water electrolysis according to a preferred embodiment of the invention were produced using the wet-chemical synthesis process described below:

[0057] A metal precursor solution of ethanol and water 50 / 50 V / V containing metal salts with an atomic ratio of molybdenum to ruthenium of 77 to 23 was mixed with polyvinylpyrrolidone (PVP) and sprayed evenly onto the surface of a nickel foam carrier.

[0058] To form a catalyst material consisting of ruthenium and molybdenum on the support, a heat treatment is performed. The following two types of heat treatment (methods A and B) were performed on two supports identically coated with precursor solutions:

[0059] Method A heat treatment is a single-step annealing at 800 °C with a 9:1 Ar and EL flow for 2 hours. This leads to the degradation of the PVP and the metal precursors, as well as to the graphitization of the carbon and the alloying of the metals.

[0060] Method B heat treatment consists of two steps: Heat treatment A is followed by a 2-hour oxidation step at 250 °C with a flow of Ar and O2 (9:10 ratio), resulting in the formation of a surface oxide layer. The formation of the oxide layer was confirmed by the higher mass of the cathodes prepared using this method, the same initial loading of catalyst precursors, and SEM-EDX and TEM imaging.

[0061] Figures 1a) and 1b) show SEM-EDX elemental mapping obtained using a combination of scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The SEM-EDX elemental mapping was recorded after fabrication of the cathodes after heat treatment A (Figure 1a) and after heat treatment B (Figure 1b). The measured atomic ratio of the catalyst material of the cathode after heat treatment A is M082RU18, and that after heat treatment B is M084RU16.

[0062] Figures 1c) and 1d) show a TEM-EDX elemental mapping recorded using a combination of transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). The TEM-EDX elemental mapping was recorded after fabrication of the cathodes after heat treatment A (Figure 1c) and after heat treatment B (Figure 1d). The atomic ratio of the catalyst material of the cathode measured by SEM-EDX after heat treatment A is M082RU18, and that after heat treatment B is M084RU16.

[0063] The cathodes prepared according to A and B were used in a three-electrode flow cell with a thin iridium film on stainless steel as anode for water electrolysis in 1 M potassium hydroxide (KOH).

[0064] Since molybdenum is known to oxidize easily in air, after the first reduction a current-voltage diagram was recorded using linear sweep voltammetry (LSV) in the potential range of the hydrogen evolution reaction.

[0065] Figure 2 shows the resulting LSV diagram. The cathode after heat treatment method A appears to be characterized by higher activity.

[0066] After the LSV measurements, chronopotentiograms (CP measurements) were measured using galvanostatic measurements at three different current densities, namely -100 mA cm' 2 , -300 mA cm' 2 and -500 mA cm' 2, each recorded for 4 hours. Figure 3 shows the CP diagrams obtained, in Figure 3a) for the cathode produced after heat treatment A, and in Figure 3b) for the cathode produced after heat treatment B. Comparing the CP diagrams, it is clearly evident that the cathode after heat treatment A exhibits a lower overpotential for each current density.

[0067] Figure 4 shows an SEM-EDX elemental mapping obtained using a combination of scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The SEM-EDX elemental mapping was recorded for the cathode after heat treatment A after a long-term hydrogen evolution reaction in a flow cell structure. From Figure 4, it can be concluded that the cathode after heat treatment A remains unchanged in terms of the cathode coating even after a long-term hydrogen evolution reaction. The measured atomic ratio of the cathode after heat treatment A is MosgRun.

[0068] It can also be observed that the composition of the cathode produced by heat treatment A does not change significantly. Additional potassium signals can also be observed, which is to be expected after prolonged contact with the electrolyte.

[0069] Another cathode, prepared as described above using heat treatment A, was measured in a flow electrolyzer with a three-electrode system in a membrane electrode assembly (MEA) configuration. A thin iridium film electrode on stainless steel, cut to the same size, was used as the anode. Six CP measurements were performed consecutively at increasing current densities.

[0070] Each step lasted 1 hour. The selected current densities were: -0.100 A cm' 2 , -0.300 A cm' 2 , -0.500 A cm' 2 , -1 A cm' 2 , -1.5 A cm' 2 , -2 A cm' 2Due to the strong bubbling during hydrogen evolution, the chronopotentiometry plot shown in Figure 5 exhibits a high level of noise. For this reason, the data were also smoothed using a 50% percentile filter (shown as a less noisy line on the raw data in Figure 5). This smoothing method eliminates noise with abnormal amplitude by replacing the signal value at each point with the mean of a group of surrounding points.

[0071] The obtained overpotential for the hydrogen evolution reaction increases from 51.7 mV to 132.3 mV by changing the applied current density from -0.1 A cm' 2 to -2 A cm' 2 , which indicates a high activity of the cathode and the cathode material.

[0072] Furthermore, another cathode prepared as described above after heat treatment A was subjected to a 24-hour long-term chronopotentiometry measurement at -1 A cm 2 in 1 M KOH (Figure 6a). The anode material was again iridium. The obtained potential values ​​did not change significantly during the reaction, which also agrees with the LSV diagrams recorded before and after the long-term measurement, shown in Figure 6b (compared at the current density of -1 Acm' 2 ). This indicates a high stability of the cathode.

[0073] The potential value measured from the first and last during the 24-hour CP measurement at -1 A cm' 2 calculated degradation rate is 0.382 mV h' 1 Using the average values ​​of the 50 first and last measured potential values, the decay rate is calculated to be 0.361 mV h' 1 .

[0074] After the 24-hour measurement in the MEA setup, no structural changes were observed on the cathode. SEM-EDX analysis of the cathode after electrolysis shows a uniform layer of all starting elements, with the measured element ratio not changing significantly, as shown in Figure 7. The measured atomic ratio of the cathode is MosgRun. Before the 24-hour measurement, the measured atomic ratio of the cathode was MOSTRUB. Thus, the atomic ratio has not changed within the SEM-EDX error of + / - 1%. Figure 8 shows the measurement of an electrode produced using a sputtering process, according to another embodiment of the invention. The electrode, consisting of 80% molybdenum and 20% ruthenium, is compared to a pure Ni electrode as a cathode in water electrolysis. The cathodes, measuring 1 cm 2were tested in a flow-through electrolysis cell at 80 °C and 30% potassium hydroxide solution at a current of 0.5 A / cm 2 Measured using the three-electrode method. The anode was a Ni anode in both measurements. The separator was a commercially available diaphragm. The electrolysis cell was a 3 mm gap electrolysis cell. The voltage values ​​were measured directly and not corrected for resistances of the electrolysis system and the measurement system. A significantly reduced cathode potential is observed compared to the pure Ni cathode.

[0075] The invention originates from a funded research project with the funding number 03EFTNW306. Funding was provided as part of the "BMBF Exist" funding program.

Claims

Patent claims 1. Cathode of an electrolyzer for water electrolysis comprising an electrically conductive support coated with a catalyst material, wherein the catalyst material comprises molybdenum and ruthenium, and wherein the catalyst material has a ruthenium content of between 5 atomic% and 35 atomic% and a molybdenum content of between 40 atomic% and 95 atomic%, in each case based on the total number of atoms of the catalyst material.

2. Cathode according to claim 1, wherein the ruthenium content is between 5 atomic% and 30 atomic%, preferably between 5 atomic% and 25 atomic%, and particularly preferably between 5 atomic% and 20 atomic%, based on the total number of atoms of the catalyst material.

3. Cathode according to claim 1 or 2, wherein the catalyst material comprises up to 35 atomic % of further metals, based on the total number of atoms of the catalyst material, and wherein the molybdenum content is between 40 atomic % and 90 atomic % in each case based on the total number of atoms of the catalyst material.

4. A cathode according to claim 3, wherein the further metals comprise titanium and silver.

5. Cathode according to claim 1 or 2, wherein the catalyst material consists of ruthenium and molybdenum and titanium and / or silver, and wherein the molybdenum content is between 40 atomic% and 90 atomic%, each based on the total number of atoms of the catalyst material.

6. Cathode according to claim 1 or 2, wherein the catalyst material consists of molybdenum and ruthenium, and wherein the molybdenum content is between 65 atomic % and 95 atomic%, based on the total number of atoms in the catalyst material.

7. Cathode according to claim 6, wherein the ruthenium content is between 8 atomic% and 25 atomic%, preferably between 10 atomic% and 20 atomic%.

8. Cathode according to one of the preceding claims, wherein the catalyst material comprises ruthenium as the only noble metal and / or wherein the catalyst material is free of platinum, sulfur, nickel and / or molybdenum(IV) sulfide.

9. Cathode according to one of the preceding claims, wherein the carrier is porous and / or wherein the carrier is configured as a foam, a mesh, a sheet with holes, and / or a fleece and / or wherein the carrier comprises nickel, titanium, stainless steel, and / or carbon; or wherein the carrier consists of nickel, titanium, stainless steel, and / or carbon.

10. Cathode according to one of the preceding claims, obtained by the following steps: - Providing the carrier, - Application of the catalyst material using a PVD process, Plasma spraying, thermal spraying, airbrush spraying, and / or using a wet chemical synthesis process.

11. The cathode of claim 10, wherein the step of applying the catalyst material comprises applying a polymer-containing precursor solution to the support by means of the airbrush spraying method and a subsequent heat treatment.

12. The cathode of claim 10, wherein the step of applying the catalyst material is carried out using the PVD method and starting from exactly one sputtering target or several sputtering targets of the same design.

13. Use of a cathode according to one of claims 1 to 12 in water electrolysis.

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