Method for producing an electrode for use in the alkaline electrolysis of water, and electrode

Abstract

The invention relates to a method for producing an electrode (10) for use in the alkaline electrolysis of water, comprising providing a metallic, in particular nickel-based, substrate (12), providing a spray material comprising a nickel-iron alloy, and coating at least one section of the substrate with the spray material by means of thermal spraying. The invention also relates to such an electrode and a spray material.

Description

[0001] Title: Method for manufacturing an electrode for use in alkaline water electrolysis, and electrode

[0002] Description

[0003] The invention relates to a method for producing an electrode for use in the alkaline electrolysis of water. The electrode comprises a metallic substrate on which a catalyst layer is applied, at least in sections.

[0004] Such electrodes and methods for their production are generally known from the prior art. Expanded metal meshes, for example, are used as substrates. Porous nickel, especially so-called "Raney nickel," has proven particularly advantageous as a catalyst material.

[0005] From EP 4 198 174 Al, an anode for use in alkaline water electrolysis is also known, which has a substrate in the form of an expanded metal grid and a catalyst layer deposited on it by thermal spraying. The catalyst layer has a lamellar structure consisting of metallic areas and empty areas.

[0006] Furthermore, a method for providing an electrode of the type mentioned above is known from DE 10 2022 124917 B3. According to the method, a powder mixture of nickel powder and powder from an aluminum-nickel-molybdenum alloy is applied to a planar section of a flat metallic material by thermal spraying or laser cladding and subsequently tempered at temperatures between 250°C and 650°C under a non-reducing nitrogen or argon atmosphere for a period of 10 minutes to form aluminum-nickel phases.

[0007] Furthermore, a method for manufacturing a cathode for the

[0008] Hydrogen production is known in which several catalyst layers are applied to a nickel grid by thermal spraying, wherein one of the catalyst layers may have a catalyst made of a transition metal alloy.

[0009] From CN 1 17344334 A, another method for producing a cathode for hydrogen production is known, wherein a catalyst is applied to a nickel wire grid by thermal spraying, the catalyst comprising 40-80 wt% nickel and additionally one or more of the elements Fe, Co, Mo and W.

[0010] The invention addresses the problem of improving the efficiency of water electrolysis.

[0011] This problem is solved according to the invention by a method with the features of claim 1. This method is for producing an electrode, in particular anode, for use in the alkaline electrolysis of water. The electrode comprises a metallic substrate on which a catalyst layer is applied, at least partially. The method comprises providing a metallic substrate, providing a spray material, and coating at least a section of the substrate with the spray material to form the catalyst layer or a precursor of the catalyst layer. The coating is carried out by thermal spraying, in particular by melting or partially melting the spray material and pulsed deposition of molten droplets from the spray material onto the substrate. The spray material comprises a nickel-iron alloy.

[0012] Electrodes manufactured in this way with thermally sprayed nickel-iron alloy exhibit improved catalytic and mechanical properties. In particular, it has been found that the use of a combination of nickel and iron can significantly reduce overpotential during the electrolysis of water.

[0013] In this context, "spray material" refers to the starting material that is fed into the thermal spraying process, in particular a thermal spray gun, and then applied to the substrate. The spray material, or its components, can be modified in form and properties during the coating process (e.g., by melting and acceleration during thermal spraying).

[0014] The injection molding material can consist of a nickel-iron alloy. The injection molding material can also include other components. For example, it is conceivable that the injection molding material also includes pure nickel. The pure nickel may contain unavoidable impurities in a total of no more than 1 wt.%, in particular no more than 0.8 wt.%, in particular no more than 0.5 wt.%, in particular no more than 0.3 wt.%.

[0015] In particular, the spray material comprises a catalyst component (first component) which consists of the nickel-iron alloy. The catalyst component may also include other components, e.g., pure nickel.

[0016] As part of a beneficial further development process, the spray material can also include aluminum. It has been found that combining aluminum with iron results in particularly high catalytic activity in thermally sprayed coatings.

[0017] Aluminum can be a component of the nickel-iron alloy. Therefore, the nickel-iron alloy can also contain aluminum. In other words, the nickel-iron alloy could be a nickel-iron-aluminum alloy. It is also conceivable that the catalyst component of the spray material is a mixture, particularly a powder mixture, of nickel-iron alloy and nickel-iron-aluminum alloy.

[0018] The aluminum can also be provided as part of another component of the spray material. In particular, the spray material—in addition to the catalyst component comprising the nickel-iron alloy—can include an aluminum component as a second component. The aluminum component can, in particular, consist of essentially pure aluminum and / or a low-alloy aluminum alloy. "Low-alloy" in the following refers specifically to alloys that consist of at least 80 wt.% metallic aluminum. When thermally spraying such a two-component spray material comprising a nickel-iron alloy and an aluminum component, a layered structure can be formed, comprising nickel regions made of nickel-iron alloy and aluminum regions made of aluminum or an aluminum alloy.The areas can be in the flat shape typical for thermal spraying, so that in a cross-section a lamellar structure is formed from the nickel areas and the aluminum areas.

[0019] The aluminum (in the nickel-iron alloy and / or as a separate aluminum component) can remain in the catalyst layer after coating.

[0020] According to an advantageous embodiment, the aluminum in the nickel-iron-aluminum alloy and / or in the aluminum component can be at least partially, and in particular only partially, removed after coating. The removal of the aluminum from the nickel-iron-aluminum alloy can result in a porous nickel-iron layer, similar to the "Raney nickel" method described above. The removal of the aluminum component can lead to a lamellar cross-sectional structure consisting of nickel regions encompassing the nickel-iron alloy and empty regions (at the locations of the previously present aluminum regions).

[0021] By removing the aluminum, the surface area of ​​the catalyst layer can be increased, thereby enhancing catalytic activity. It can be advantageous if the aluminum is not completely removed, but only partially, leaving a residual amount in the catalyst layer. This configuration has proven particularly beneficial, as it provides an increased surface area combined with the iron-aluminum material combination, which is advantageous for catalysis.

[0022] The removal of the aluminum can advantageously be achieved by an etching treatment using potassium hydroxide. For this purpose, for example, the coated substrate can be immersed in a potassium hydroxide solution. An advantageous method comprises – after coating with the spray material – immersing the coated substrate in a 30 wt% KOH solution at 80°C for 2 to 5 hours.

[0023] It is conceivable that the nickel-iron alloy contains only nickel and iron, and possibly unavoidable impurities. It has proven particularly advantageous if the nickel-iron alloy consists of:

[0024] - Nickel,

[0025] - Iron and

[0026] - possibly unavoidable impurities in a total of not more than 1.0 wt.%, in particular not more than 0.8 wt.%, in particular not more than 0.5 wt.%, in particular not more than 0.3 wt.%, wherein, based on wt.%, the nickel content in the nickel-iron alloy is 1.5 to 9 times greater than the iron content, preferably 1.5 to 3 times greater.

[0027] As mentioned above, it is particularly preferred if the nickel-iron alloy additionally comprises aluminum. A particularly preferred nickel-iron-aluminum alloy consists of

[0028] - at least 25 wt.%, in particular at least 30 wt.%, and at most 50 wt.%, in particular at most 40 wt.%, nickel,

[0029] - potentially unavoidable impurities in a total of not more than 1.0 wt.%, in particular not more than 0.8 wt.%, in particular not more than 0.5 wt.%, in particular not more than 0.3 wt.%,

[0030] - Remainder iron and aluminium, the proportions of iron and aluminium being calculated according to the following formula:

[0031] Ni(w%) = a(Fe(w%) - % AI(w%)), where a is a number between 1.5 and 3.

[0032] Therefore, in the proposed nickel-iron (aluminum) alloy, the nickel content, based on weight percent, is 1.5 to 3 times higher than the iron content, which is reduced by one-quarter of the aluminum content. Such a ratio has proven particularly advantageous with regard to high catalytic activity and a robust catalyst layer in thermal spraying.

[0033] The coating with the spray material can be done in different ways. It can

[0034] - especially when the spray material consists of the nickel-iron alloy - it may be advantageous if the substrate is coated with the spray material in such a way that the catalyst layer is essentially dense, i.e., exhibits at most a "natural" porosity that arises as a result of the thermal spraying process.

[0035] It can also be advantageous if the substrate is coated with the spray material in such a way that the catalyst layer is porous, i.e., has intentionally introduced pores beyond the "natural" porosity. Such porosity can be created, for example, by the leaching of aluminum as described above. Alternatively or additionally, such porosity can be created by introducing non-metallic particles into the catalyst material and subsequently removing at least some of these non-metallic particles.

[0036] In a further advantageous development, the spray material can, for example, contain non-metallic particles in addition to the nickel-iron alloy. These non-metallic particles can be designed, in particular, to form pores in the catalyst layer. The non-metallic particles can be provided as an alternative or in addition to the aluminum component described above.

[0037] In this context, "non-metallic" means that the particles do not consist of a pure metal or a metal alloy. Therefore, the term "non-metallic" excludes particles made of a pure metal or a metal alloy, such as metal powder or powder made from a metal alloy. However, the term "non-metallic" should not be understood to mean that the particles must not contain any metal atoms.

[0038] The non-metallic particles can remain in the catalyst layer. In embodiments of the process where the coating material comprises aluminum and the aluminum is at least partially removed after coating, the particles can, for example, serve as reinforcement, stabilizing the porous catalyst layer. Furthermore, it is hypothesized that, due to their surface properties differing from those of the nickel-iron alloy, the non-metallic particles can act as gas bubble nucleation centers during the electrolysis of water, thus improving mass transport within the catalyst layer. Alternatively, it may be advantageous to at least partially remove the non-metallic particles after coating.The removal of the non-metallic particles is preferably carried out in such a way that - at least in a surface layer of the catalyst layer - more than 90%, preferably more than 95%, further preferably more than 98%, of the non-metallic particles are removed.

[0039] The at least partial removal of the non-metallic particles can be carried out in different ways, especially depending on the non-metallic particles used.

[0040] The at least partial removal of non-metallic particles can involve heating at least a subset of them. In particular, the at least partial removal of non-metallic particles can involve the thermal decomposition of at least a subset of them. In this respect, the heating can be carried out in such a way that at least a subset of the non-metallic particles are thermally decomposed. Alternatively, the heating can be used merely as an auxiliary step before or during a further process step for removing the non-metallic particles. The heating of the non-metallic particles can be achieved by heating the coated substrate, for example, in an oven. The heating of the non-metallic particles can also involve the localized application of heat, for example, using a laser.

[0041] Alternatively or additionally, the at least partial removal of the non-metallic particles can involve dissolving at least a subset of the non-metallic particles using a dissolving fluid. Dissolving the non-metallic particles can involve dissolving them in the dissolving fluid. Dissolving the non-metallic particles can also involve chemical decomposition by the dissolving fluid. The dissolving fluid can be, for example, a chemical solvent, an acid, an alkali, water, or a chemical reagent. For example, the process can involve immersing the coated substrate in a bath of dissolving fluid. At least partial removal of the non-metallic particles can also involve performing an etching treatment, particularly using potassium hydroxide. The non-metallic particles can be made of different materials.The spray material can consist of a single type of non-metallic particles. It can also consist of mixtures of different non-metallic particles.

[0042] Silicon-containing particles, especially glass particles, particularly glass powders or glass spheres, especially borosilicate glass, and especially alkali borate glass, have proven particularly advantageous. The non-metallic particles can also include or consist of precipitated silica particles. For silicon-containing particles, the optional removal of the non-metallic particles can, for example, involve at least partially dissolving the silicon-containing particles (e.g., glass particles) in an alkaline solution, especially KOH. As an example, at least partial removal can involve immersing the coated substrate in a bath of 30% KOH at 80°C for 24 hours.

[0043] Alternatively or additionally, the non-metallic particles can comprise or be plastic particles, particularly those made from a polymer belonging to the group comprising PBT, PET, PC, and PEEK. Such particles are particularly lightweight and relatively easy to remove. For example, the optional removal of the plastic particles can involve saponifying the plastic particles (especially in the case of PBT, PET, or PC) under alkaline conditions (e.g., by immersing the coated substrate in a NaOH solution).

[0044] Alternatively or additionally, the non-metallic particles can comprise or be salt particles, in particular made of a carbonate, further specifically of KHCO3 or K2CO3. In the case of such particles, the optional removal of the particles can in particular comprise dissolving the salt particles in a solvent, in particular water, optionally after prior or simultaneous heating of the coated substrate.

[0045] Alternatively or additionally, the non-metallic particles may comprise or be carbon particles, i.e., particles made of a carbon material, in particular graphite and / or carbon black. Carbon particles are relatively easy to obtain and, in particular, inexpensive. The optional removal of such carbon particles may, for example, involve heating the carbon particles, especially the coated substrate, in an oxygen-containing atmosphere, particularly at a temperature between 300 and 450°C. Alternatively or additionally, the non-metallic particles may comprise or be particles made of a mineral, in particular sodium tetraborate (borax) or potassium tetraborate. The optional removal of the non-metallic particles may, for example, involve chemically dissolving the particles.

[0046] In a particularly advantageous embodiment, the spray material can comprise, or preferably consist of, a nickel-iron alloy, in particular a nickel-iron-aluminium alloy (as the first component / catalyst component) and glass particles (as the second component).

[0047] The spray material can be supplied as a powder or powder mixture. It can include a powder made of nickel-iron alloy and / or a nickel-iron-aluminum alloy (catalyst component). The spray material can also include a powder made of aluminum or a low-alloy aluminum alloy (aluminum component). Furthermore, the spray material can contain non-metallic particles.

[0048] The coating with the spray material can be carried out using various thermal spraying processes. Preferably, the coating is applied by plasma spraying, in particular atmospheric plasma spraying (APS) or vacuum plasma spraying. It is advantageous if the spray material is provided as a powder or powder mixture. Cold gas spraying, flame spraying, or high-velocity oxygen fuel (HVOF) spraying are also conceivable.

[0049] It is also conceivable that the coating material is provided as wire or multiple wires (e.g., a wire made of a nickel-iron alloy and a wire made of the aluminum component). With such a configuration, coating can be carried out, in particular, by arc wire spraying.

[0050] The metallic substrate can be of various designs. Advantageously, the substrate is a flat metallic material. Preferably, the substrate has a plurality of openings. For example, the substrate can be in the form of a perforated sheet with a plurality of openings. Other advantageous embodiments of the substrate include: expanded metal mesh, wire woven or knitted wire, metal fleece, and metal foam.

[0051] The substrate can have one or more three-dimensional contact structures for contacting the electrode.

[0052] The substrate can be regularly or irregularly shaped. The substrate can be curved. Preferably, however, the substrate is flat.

[0053] Preferably, the substrate is a nickel-containing substrate, i.e., made of nickel or a nickel alloy or of nickel-plated metal.

[0054] The substrate preferably has two opposite sides. The process can include coating one or both of these sides with the spray material, preferably only one of these sides.

[0055] Furthermore, it can be advantageous if, before coating the substrate with the spray material, at least the section of the substrate to be coated is mechanically blasted, e.g. sandblasted, especially for cleaning and preparation for the coating.

[0056] In a further advantageous embodiment, the substrate provision can include the provision of a metallic flat material, in particular flat strip material, wherein the flat material is conveyed along a conveying direction, preferably continuously, and coated during this process. To obtain a specific electrode, a section can then be cut to length and / or separated (e.g., punched out or laser-cut) from the coated flat material, in particular flat strip material. In this way, continuous and therefore particularly economical production of large-area electrodes is enabled.

[0057] The invention also relates to a sprayable material, in particular a powder mixture or a plurality of wires, for use in one of the processes described above. The sprayable material is designed for thermal spraying. The sprayable material comprises a first component (catalyst component) comprising a nickel-iron alloy and / or a nickel-iron-aluminum alloy, and a second component comprising an aluminum component and / or non-metallic particles.

[0058] The optional features and advantages described above in relation to the process can also serve to shape the injection molding material, so reference is made to the above disclosure in order to avoid repetition.

[0059] The invention also relates to the use of a nickel-iron alloy, in particular a nickel-iron-aluminium alloy, for producing a catalyst layer for the alkaline electrolysis of water on a metallic substrate, in particular expanded metal mesh or perforated sheet, by thermal spraying of this alloy.

[0060] The optional features and advantages described above in relation to the process can also serve to shape its use, so reference is made to the preceding disclosure in this regard to avoid repetition.

[0061] The invention also relates to an electrode, in particular anode, for use in the alkaline electrolysis of water. The electrode is produced, in particular, according to one of the methods described above. The electrode comprises a metallic, in particular nickel-based (i.e., made of nickel or a nickel alloy or nickel-plated metal), substrate on which at least partially a thermally sprayed catalyst layer is applied (i.e., the substrate is coated at least partially with a catalyst material). The catalyst layer comprises a nickel-iron alloy.

[0062] The optional features and advantages described above in relation to the method can also serve to design the electrode, so reference is made to the above disclosure in this regard to avoid repetition.

[0063] The catalyst layer may also contain nickel and / or nickel oxide. The catalyst layer may also include oxide or hydroxide compounds that may optionally form during thermal spraying, e.g., NiO, Ni(OH)₂, FeO, FezOa, FeO(OH), etc. The catalyst layer may also contain non-metallic particles. The catalyst layer may also contain aluminum or an aluminum alloy.

[0064] It has proven particularly advantageous if the catalyst layer has a nickel-iron alloy consisting of the following components:

[0065] - Nickel,

[0066] - Iron and

[0067] - possibly unavoidable impurities in a total of not more than 1.0 wt.%, in particular not more than 0.8 wt.%, in particular not more than 0.5 wt.%, in particular not more than 0.3 wt.%, wherein, based on wt.%, the nickel content in the nickel-iron alloy is 1.5 to 9 times greater than the iron content, preferably 1.5 to 3 times greater.

[0068] As part of an advantageous further training, the catalyst layer can also include aluminum.

[0069] Aluminum can be a component of the nickel-iron alloy. Therefore, the nickel-iron alloy can contain aluminum. In other words, the nickel-iron alloy can be a nickel-iron-aluminum alloy. It is also conceivable that the catalyst layer, in addition to the nickel-iron alloy, comprises a nickel-iron-aluminum alloy.

[0070] One particularly preferred nickel-iron-aluminum alloy consists of:

[0071] - at least 25 wt.%, in particular at least 30 wt.%, and at most 50 wt.%, in particular at most 40 wt.%, nickel,

[0072] - potentially unavoidable impurities in a total of not more than 1.0 wt.%, in particular not more than 0.8 wt.%, in particular not more than 0.5 wt.%, in particular not more than 0.3 wt.%,

[0073] - Remainder iron and aluminium, where the proportions of iron and aluminium are calculated according to the following formula: Ni(w%) = a(Fe(w%) - % AI(w%)), where a is a number between 1.5 and 3.

[0074] Therefore, in the proposed nickel-iron-aluminum alloy, the nickel content, based on weight percent, is 1.5 to 3 times higher than the iron content, which is reduced by one-quarter of the aluminum content. Such a ratio has proven particularly advantageous with regard to high catalytic activity and a robust catalyst layer during thermal spraying.

[0075] The aluminum can also be a residue of a dissolved aluminum component. For example, the aluminum in the catalyst layer can be obtained by applying an aluminum component to the substrate by thermal spraying, particularly in conjunction with the nickel-iron alloy, and then partially removing this aluminum component (e.g., by dissolution in a KOH solution, see above). The aluminum component can, in particular, consist essentially of pure aluminum or a low-alloy aluminum alloy.

[0076] The catalyst layer can be "dense," meaning it may exhibit at most a "natural" porosity resulting from the thermal spraying process. The average pore diameter can then be less than 5 pm, preferably less than 3 pm.

[0077] Alternatively, the catalyst layer can be porous. This increases the surface area of ​​the catalyst layer, which enhances catalytic activity and also promotes mass transport during electrolysis.

[0078] It has proven particularly advantageous if the catalyst layer has a porosity of more than 5%, preferably more than 10%, and in particular less than 40%, preferably less than 35%, further preferably less than 30%, and further preferably less than 25%.

[0079] Furthermore, it proves advantageous if the catalyst layer has a specific surface area of ​​5-20 m². 2 / g BET. Preferably, the (porous) catalyst layer is obtained by thermally spraying a layer of a spray material comprising a first component (catalyst component) having a nickel-iron alloy, and a second component, in particular comprising an aluminum component and / or non-metallic particles, and subsequently at least partially removing the second component.

[0080] The invention also relates to the use of an electrode described above in the alkaline electrolysis of water, in particular as an anode for oxygen generation in a half-cell of an electrochemical cell.

[0081] Examples:

[0082] The following table lists exemplary and preferred compositions of a nickel-aluminium alloy.

[0083] The invention will be explained in more detail below with reference to the figures. They show:

[0084] Figure 1 simplified schematic representation of an exemplary electrode;

[0085] Figure 2 Flowchart to illustrate an exemplary process for manufacturing an electrode according to Figure 1; and

[0086] Figure 3 shows measured values ​​for specific current density and the voltage required for this.

[0087] In the following description and in the figures, the same reference numerals are used for identical or corresponding features. Figure 1 shows a simplified schematic representation of an electrode 10. The electrode 10 is designed for use in the alkaline electrolysis of water.

[0088] The electrode 10 comprises a metallic substrate 12, which in this example is designed as an expanded metal mesh. In embodiments not shown, the substrate 12 can also be designed, for example, as a perforated sheet, wire mesh or knitted fabric, metal fleece, metal foam, or the like.

[0089] The substrate 12 has a thermally sprayed catalyst layer 14 in sections. In the specific example, the substrate 12 has a first side 16 and an opposing second side 18, with the catalyst layer 14 being applied only to the first side 16. In embodiments not shown, however, it is also conceivable that the substrate 12 is coated on both sides with a catalyst layer 14.

[0090] As mentioned above, the catalyst layer 14 can be essentially dense. In the example shown, however, the catalyst layer 14 comprises a catalyst material 20 and pores 22 distributed within the catalyst material 20.

[0091] Figure 1 shows the catalyst layer 14 in a simplified schematic representation. In particular, the size ratios and volume fractions are shown only as examples to visualize the individual components. The "flat shape" of the catalyst material 20 shown in Figure 1 is merely an example to visualize a structure typically formed during thermal spraying (see below).

[0092] The catalyst material 20 comprises one of the nickel-iron (aluminum) alloys described above. The catalyst material 20 may additionally include pure nickel and / or oxide or hydroxide compounds that may optionally form during thermal spraying, e.g., NiO, Ni(OH)₂, FeO, Fe₂O₃, FeO(OH), etc.

[0093] An exemplary method for manufacturing such an electrode 10 is described below with reference to Figure 2. According to the method, in a first step 100, the metallic substrate 12 and a spray material 24 are provided. As mentioned above, the substrate 12 can be, for example, an expanded metal mesh or fabric made of nickel, a nickel alloy, or nickel-plated metal.

[0094] The spray material 24 comprises a first component 26 comprising the nickel-iron alloy (catalyst component) and a second component 28. In particular, the spray material 24 can be a homogeneous mixture of the catalyst component 26 and the second component 28.

[0095] In a further step 102, at least a section of the substrate 12, in particular only the first side 16, is then coated with the spray material 24.

[0096] The coating is applied by thermal spraying, in particular by atmospheric plasma spraying. A spray gun 30 for thermal spraying is only schematically indicated in Figure 2.

[0097] In thermal spraying (a process generally known and therefore not explained in detail here), the spray material 24 is partially or fully melted, and the molten droplets are accelerated towards the substrate 12. The momentum upon impact with the substrate 12 creates, in particular, the schematically depicted "flat shape".

[0098] In an optional further step 104 (after coating the substrate 12) the second component 28 is at least partially removed from the catalyst layer 14, thus forming the pores 22 mentioned above.

[0099] As mentioned above, the second component 28 can be a

[0100] The component may be aluminum. For example, the spray material 24 could be a powder mixture of nickel-iron (aluminum) alloy powder and aluminum powder. The aluminum can then be removed, for example, by an etching treatment using potassium hydroxide. For example, the coated substrate can be immersed in a 30 wt% KOH solution at 80°C for 2 to 5 hours.

[0101] As mentioned above, it is also conceivable that the second component 28 comprises non-metallic particles – in addition to or as an alternative to the aluminum component. The non-metallic particles could, for example, be selected from the group consisting of: silicon-containing particles, in particular glass particles, particles of precipitated silica (gel), plastic particles, salt particles, particles of carbon material, particles of minerals, and combinations thereof.

[0102] The method of removing non-metallic particles can vary depending on the type of non-metallic particles used. For example, removal can be achieved through thermal decomposition of the non-metallic particles and / or dissolving them with a dissolving fluid (e.g., alkali, solvent, water).

[0103] As mentioned above, it is also possible that the injection molding material 24 contains or consists solely of the first component 26 (catalyst component). In this case, the steps described above for removing or dissolving the second component 28 can be omitted.

[0104] Figure 3 shows measured values ​​for specific current density 32 (x-axis, in particular in A cm'). 2measured) and overvoltage 34 (y-axis, measured in particular in mV) for an electrode 10 with a catalyst layer 14 made of pure Ni (curve 36), for an electrode 10 with a catalyst layer 14 made of Ni70Fe30 alloy (curve 38), and for an electrode 10 with a catalyst layer 14 made of Ni35Fe25Al30 alloy (curve 40). A nickel fabric was used as the metallic substrate in each case. The catalyst layers 14 were applied to the nickel fabric by atmospheric plasma spraying, without the use of a second component 28.

[0105] As can be seen from Figure 3, the overvoltage for electrodes 10 with an iron-containing catalyst layer (curves 38 and 40) is significantly reduced compared to electrode 10 with a pure nickel catalyst layer (curve 36). Furthermore, the overvoltage for the electrode with a nickel-iron-aluminum alloy (curve 40) is even further reduced compared to the electrode with a nickel-iron alloy (curve 38) without aluminum.

[0106] To determine the measured values ​​shown in Figure 3, the electrodes 10 were immersed in a 30% KOH solution electrolyte under identical conditions and subjected to a voltage against a counter electrode also immersed in the electrolyte. The voltage in question was measured against a hydrogen reference electrode, also immersed in the electrolyte, in a three-electrode arrangement, essentially without current. Figure 3 shows the voltage against the hydrogen reference electrode required for a given specific current density.

Claims

Patent claims 1. Method for producing an electrode (10), in particular anode, for use in the alkaline electrolysis of water, comprising: - Providing a metallic, in particular nickel-containing, substrate (12), in particular in the form of a metallic flat material, further in particular in the form of an expanded metal mesh, wire mesh or knitted fabric, metal fleece or metal foam or perforated sheet; - Providing a spraying material (24) comprising a nickel-iron alloy; - Coating at least one section of the substrate (12) with the spray material (24) by thermal spraying.

2. Method according to claim 1, wherein the spray material (24), in particular the nickel-iron alloy, also contains aluminium.

3. The method of claim 1, wherein the nickel-iron alloy consists of nickel, Iron and any unavoidable impurities in a total of at most 1.0 wt. %, in particular at most 0.8 wt. %, in particular at most 0.5 wt. %, in particular at most 0.3 wt. %, wherein, based on wt. percent, the nickel content in the nickel-iron alloy is 1.5 to 9 times greater than the iron content, preferably 1.5 to 3 times greater.

4. The method of claim 1 or 2, wherein the nickel-iron alloy consists of - at least 25 wt.%, in particular at least 30 wt.%, and at most 50 wt.%, in particular at most 40 wt.%, nickel, - potentially unavoidable impurities in a total of no more than 1.0 wt.%, in particular no more than 0.8 wt.%, in particular no more than 0.5 wt.%, in particular no more than 0.3 wt.%, - Residual iron and aluminum, where, in terms of weight percent, the nickel content is 1.5 to 3 times greater than the iron content, which is reduced by a quarter of the aluminum content.

5. Method according to any of the preceding claims, wherein the spray material (24) further comprises an aluminum component made of aluminum or of a low-alloy aluminum alloy.

6. A method according to one of claims 2, 4 or 5, the method further comprising, after coating: at least partial removal of the aluminium, in particular by an etching treatment using potassium hydroxide.

7. Method according to one of the preceding claims, wherein the spray material (24) further comprises non-metallic particles, in particular for the formation of pores (22).

8. Method according to the preceding claim, further comprising, after coating: at least partial removal of the non-metallic particles.

9. The method of claim 7 or 8, wherein the non-metallic particles are selected from the group consisting of: - Silicon-containing particles, in particular glass particles, further in particular glass powder or glass spheres, further in particular made of borosilicate glass, further in particular made of alkali borate glass, in particular wherein the removal of the non-metallic particles comprises at least partially dissolving the silicon-containing particles in an alkali, in particular KOH; - Particles of precipitated silica; - Plastic particles, in particular made of a polymer of the group comprising PBT, PET, PC and PEEK, in particular wherein the removal of the non-metallic particles comprises saponification of the plastic particles under alkaline conditions; - Salt particles, in particular of a carbonate, further in particular of KHCO3 or K2CO3, in particular wherein the removal of the non-metallic particles comprises dissolving the salt particles in a solvent, in particular water, optionally after prior or simultaneous heating of the coated substrate; - Particles made of a carbon material, in particular graphite and / or carbon black, wherein the removal of the non-metallic particles involves heating the coated Substrates in an oxygen-containing atmosphere, especially at a temperature between 300 and 450°C; Particles made of a mineral, in particular sodium tetraborate or potassium tetraborate; and combinations thereof.

10. Spray material, in particular for use in a method according to one of the preceding claims, comprising a first component (26) comprising a nickel-iron alloy, in particular a nickel-iron-aluminium alloy, and a second component (28) comprising an aluminum component and / or non-metallic particles.

11. Use of a nickel-iron alloy, in particular a nickel-iron-aluminium alloy, for the production of a catalyst layer for the alkaline electrolysis of water on a metallic substrate, in particular expanded metal mesh or perforated sheet, by means of thermal spraying.

12. Electrode (10), in particular anode, for use in the alkaline electrolysis of water, comprising a metallic, in particular nickel-based, substrate (12) on which at least partially a thermally sprayed catalyst layer (14) is applied, wherein the catalyst layer (14) comprises a nickel-iron alloy.

13. Electrode (10) according to the preceding claims, wherein the nickel-iron alloy consists of Nickel, iron and any unavoidable impurities in a total of at most 1.0 wt. %, in particular at most 0.8 wt. %, in particular at most 0.5 wt. %, in particular at most 0.3 wt. %, wherein the nickel content in the nickel-iron alloy is 1.5 to 9 times greater than the iron content, preferably 1.5 to 3 times greater.

14. Electrode (10) according to claim 12, wherein the catalyst layer (14), in particular the nickel-iron alloy, also comprises aluminium.

15. Electrode (10) according to claim 12 or 14, wherein the nickel-iron alloy consists of - at least 25 wt.%, in particular at least 30 wt.%, and at most 50 wt.%, in particular at most 40 wt.%, nickel, - potentially unavoidable impurities in a total of no more than 1.0 wt.%, in particular no more than 0.8 wt.%, in particular no more than 0.5 wt.%, in particular no more than 0.3 wt.%, - Remainder iron and aluminum, wherein, based on weight percent, the nickel content is 1.5 to 3 times greater than the iron content reduced by one quarter of the aluminum content.

16. Electrode (10) according to claim 14 or 15, wherein the catalyst layer (14) is porous, wherein the porous catalyst layer (14) is obtained by thermally spraying a layer of a spray material (24) comprising a first component (26) and a second component (28), and subsequently at least partially removing the second component, wherein the first component (26) comprises the nickel-iron alloy, in particular wherein the second component (28) comprises a aluminum component and / or contains non-metallic particles.

17. Use of an electrode (10) according to one of claims 12 to 16 as an anode for oxygen generation in the alkaline electrolysis of water.

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