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

Abstract

The invention relates to a method for producing an electrode (10) for use in alkaline electrolysis of water, the method comprising: providing a metal substrate (12); providing a coating material (26) comprising powder (28) consisting of a catalyst material (20), and comprising non-metal particles (24); and coating at least a portion of the substrate with the coating material. The invention also relates to electrodes produced in this way.

Description

[0001] Title: Method for producing an electrode for use in alkaline

[0002] Electrolysis of water and electrode

[0003] Description

[0004] The invention relates to a method for producing an electrode for use in the alkaline electrolysis of water, comprising a metallic substrate on which a catalyst layer is applied, at least in sections. The invention also relates to such an electrode.

[0005] Such electrodes and methods for their production are generally known from the prior art. Expanded metal meshes, for example, are used as a substrate. Porous nickel has proven particularly advantageous as a catalyst material. In this context, it is known to produce porous nickel by selectively dissolving a soluble component, such as aluminum or zinc, from an alloy of nickel and the soluble component. Such porous nickel and the alloy from which it is made are generally referred to as "Raney nickel" or "Raney alloy" after its inventor.

[0006] EP 4 198 174 A1 also discloses an anode for use in alkaline water electrolysis, which comprises a substrate in the form of an expanded metal mesh and a catalyst layer deposited thereon by thermal spraying. The catalyst layer has a lamellar structure consisting of metallic regions and empty regions. Specifically, EP 4 198 174 A1 proposes depositing a mixture of nickel and aluminum by thermal spraying, followed by dissolving the aluminum to obtain the lamellar structure described above.

[0007] Furthermore, DE 10 2022 124917 B3 discloses a method for providing an electrode of the type mentioned above. According to the method, a powder mixture of nickel powder and powder of an aluminum-nickel-molybdenum alloy is applied to a flat section of a metallic sheet by thermal spraying or laser deposition welding. The mixture is then heated at temperatures ranging 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. The invention addresses the problem of improving the efficiency of alkaline water electrolysis.

[0008] This object is achieved according to the invention by a method having the features of claim 1.

[0009] A method for producing an electrode for use in the alkaline electrolysis of water is proposed. The electrode comprises a metallic substrate, to which a catalyst layer comprising a catalyst material is applied, at least in sections. The method comprises providing a metallic substrate, providing a coating material, in particular a powder mixture, for coating the substrate, and coating at least a section of the substrate with the coating material to form the catalyst layer or a precursor of the catalyst layer. The coating material comprises a powder (or powder mixture) of a catalyst material for catalysis in the electrolysis of water (first component). In particular, the catalyst material is a catalytically active metal alloy.In this respect, the coating material can, in particular, comprise a powder made of a catalytically active metal alloy. The coating material also comprises non-metallic particles (second component). The non-metallic particles are, in particular, not catalytically active or are only catalytically active to a reduced extent compared to the catalyst material.

[0010] The proposed process makes it possible to create electrodes with improved mechanical and catalytic properties. Using such electrodes, the efficiency of water electrolysis can be improved.

[0011] In this context, the term "coating material" refers to the entirety of the first component (powder of catalyst material) and the second component (non-metallic particles). "Coating material" refers in particular to the starting material, which is subjected to a suitable coating process (e.g., thermal spraying or laser cladding, see below) and thus applied to the substrate. The coating material or components thereof can be modified in their shape and properties during coating (e.g., by melting and accelerating during thermal spraying). Preferably, the substrate is coated with the coating material by thermal spraying of the coating material (in particular, by at least partially melting the coating material and deposition of melt droplets from the coating material under pulsed action).Plasma spraying, preferably atmospheric plasma spraying, has proven particularly advantageous. Cold gas spraying, flame spraying, or high-velocity oxygen (HVOF) spraying are also possible.

[0012] Alternatively, the substrate can be coated using laser cladding.

[0013] The coating material can consist of a powder of catalyst material (first component) and, in particular, non-metallic particles mixed with the powder (second component). In this respect, the coating material can be a mixture of powder of catalyst material and non-metallic particles.

[0014] The coating material may comprise other components in addition to the powder of catalyst material (first component) and the non-metallic particles (second component).

[0015] In this context, the term "catalyst material" refers to a catalytically active material, i.e., a material that supports the alkaline electrolysis of water. The catalyst material is, in particular, a metal alloy designed to catalyze the anode reaction (oxygen formation) or the cathode reaction (hydrogen formation) during the alkaline electrolysis of water. In particular, the catalyst material is a catalytically active metal alloy.

[0016] Preferably, the catalyst material comprises or consists of a nickel-containing metal alloy, more preferably a nickel alloy with a nickel content of at least 25 wt.%.

[0017] The term "non-metallic" in the present context 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, e.g., metal powder or powder made of a metal alloy. However, the term "non-metallic" should not be understood to mean that the particles must not contain any metal atoms. As explained in more detail below, "non-metallic" particles within the meaning of the present application can also include, in particular, particles made of metal-non-metal compounds, e.g., glass particles.

[0018] The term "particles" in this context encompasses various particle shapes, such as (regular or irregular) grains, in particular powder grains, spheres, fibers, or the like. The particles can be regular or irregular in shape. The particles can be provided by comminuting a solid material (e.g., powder). The particles can also be preformed from a starting material, e.g., polymer melt or glass melt. The particles can be in bulk form. The particles can be in powder form.

[0019] It is conceivable that the non-metallic particles remain in the catalyst layer, even when the electrode is used in the electrolysis of water. It has been shown that the catalytic effect can be improved by using two different components (catalyst material and, in particular, non-metallic particles that are not catalytically active). It is assumed that the non-metallic particles, due to their different surface properties compared to the catalyst material, can serve as gas bubble nucleation centers during the electrolysis of water and thus reduce the overpotential.

[0020] According to a particularly advantageous development of the method, the non-metallic particles can be at least partially removed after coating the substrate with the coating material—and in particular before using the electrode in the electrolysis of water. In this way, a porous catalyst layer is formed, in particular in the form of a porous network made of the catalyst material. In such a (porous) catalyst layer, a surface area is enlarged, which increases catalytic activity and also promotes mass transport during electrolysis. The proposed two-stage procedure, comprising the introduction of non-metallic particles into the catalyst layer and the subsequent at least removal of these particles, makes it possible to specifically adjust porosity and, in particular, also to change porosity within the catalyst layer.

[0021] 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%, and more preferably more than 98%, of the non-metallic particles are removed. The at least partial removal of the non-metallic particles can be carried out in different ways, in particular depending on the non-metallic particles used.

[0022] The at least partial removal of the non-metallic particles can comprise heating at least a portion of the non-metallic particles. In particular, the at least partial removal of the non-metallic particles can comprise the thermal decomposition of at least a portion of the non-metallic particles. In this respect, the heating can be carried out in such a way that at least a portion 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 comprise heating the coated substrate, e.g., in an oven. The heating of the non-metallic particles can also comprise the local introduction of heat, e.g., by means of a laser.

[0023] Alternatively or additionally, the at least partial removal of the non-metallic particles can comprise dissolving at least a portion of the non-metallic particles using a dissolving fluid. The dissolving can comprise dissolving the non-metallic particles in the dissolving fluid. The dissolving can also comprise the chemical decomposition of the non-metallic particles using 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 method can comprise immersing the coated substrate in a bath of dissolving fluid. The at least partial removal of the non-metallic particles can also comprise performing an etching treatment, in particular using potassium hydroxide.

[0024] The non-metallic particles can be made of different materials. The coating material can comprise a single type of non-metallic particles. The coating material can also comprise mixtures of different non-metallic particles.

[0025] Silicon-containing particles, in particular glass particles, furthermore in particular glass powder or glass spheres, furthermore in particular made of borosilicate glass, furthermore in particular made of alkali borate glass, have proven particularly advantageous. The non-metallic particles can also comprise or be particles of precipitated silica. In the case of silicon-containing particles, the optional removal of the non-metallic particles can, for example, comprise at least partially dissolving the silicon-containing particles (e.g. glass particles) in a lye, in particular KOH. For example, the at least partial removal can comprise immersing the coated substrate in a bath of 30% KOH at 80°C for 24 hours.

[0026] Alternatively or additionally, the non-metallic particles may comprise or be plastic particles, in particular made of a polymer from 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 may involve saponification of the plastic particles (particularly in the case of PBT, PET, or PC) under alkaline conditions (e.g., by immersing the coated substrate in a NaOH solution).

[0027] Alternatively or additionally, the non-metallic particles may comprise or be salt particles, in particular made of a carbonate, more particularly of KH2CO3 or K2CO3. In such particles, the optional removal of the particles may in particular comprise dissolving the salt particles in a solvent, in particular water, optionally after prior or simultaneous heating of the coated substrate.

[0028] 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 comparatively light and, in particular, inexpensive. The optional removal of such carbon particles may, for example, comprise heating the carbon particles, in particular the coated substrate, in an oxygen-containing atmosphere, in particular at a temperature between 300 and 450°C.

[0029] Alternatively or additionally, the non-metallic particles may comprise or be particles of a mineral, in particular sodium tetraborate (borax) or potassium tetraborate. The optional removal of the non-metallic particles may, for example, comprise chemically dissolving the particles.

[0030] The non-metallic particles are preferably silicon-containing particles, more preferably glass particles, more preferably glass spheres, more preferably made of borosilicate glass, more preferably made of alkali borate glass. The layer structure of the catalyst layer can vary. Advantageously, the coating is carried out in such a way that - in the catalyst layer applied to the substrate - the non-metallic particles are distributed in the catalyst material. In this way, a homogeneous pore distribution can be provided after removal of the non-metallic particles. This can be provided, for example, by the catalyst material and the non-metallic particles being mixed, in particular homogeneously, in the coating material. For example, the coating material can be a homogeneous mixture of catalyst material and non-metallic particles.

[0031] Preferably, the coating is applied in such a way that the catalyst material (before and especially after removal of the non-metallic particles) forms a percolating network at least in sections (i.e., at least in partial areas of the coating). In this way, conductivity in the catalyst layer can be improved.

[0032] It may also be advantageous if the coating is applied in such a way that the catalyst material forms an open-pore structure. This facilitates the removal of non-metallic components, especially in deeper layers of the catalyst layer.

[0033] The ratio of catalyst material to non-metallic particles in the coating material can vary. It has proven particularly advantageous if the volume ratio of non-metallic particles to catalyst material in the coating material is at least 5:95, preferably at least 10:90, more preferably at least 15:85, and at most 40:60, more preferably at most 30:70, more preferably at most 25:75.

[0034] The volume ratio can be calculated in particular according to the following formula:

[0035] Formula 1):

[0036] The "mass" can be the weight of the individual components. In particular, the volume fraction of the non-metallic particles in the total volume of the

[0037] Coating material between 5 and 40 vol.%, more preferably between 5 and 25 vol.%.

[0038] The non-metallic particles can be of different sizes. It has proven particularly advantageous if the particle diameter, especially the average diameter, of the non-metallic particles is less than 150 pm, preferably 5-50 pm, more preferably 5-40 pm, more preferably 10-30 pm. The coating material can also comprise a mixture of non-metallic particles with different particle diameters.

[0039] The particle diameter can be determined according to ISO 13320:2020-01. In particular, the particle diameter can be determined by laser light scattering using a "Laser Scattering Particle Size Distribution Analyzer," e.g., the "Partica LA-960V2" from Horiba Scientific.

[0040] As mentioned above, the coating material may comprise other components in addition to the powder of catalyst material and the non-metallic particles.

[0041] In an advantageous further development, the coating material can also comprise an aluminum powder made of aluminum or a low-alloy aluminum alloy. "Low-alloy" is understood here to mean, in particular, alloys that consist of at least 80% metallic aluminum.

[0042] When thermally spraying such a coating material comprising catalyst material and aluminum, a layered structure can be formed, in particular, comprising catalyst regions made of catalyst material and aluminum regions made of aluminum or an aluminum alloy. The regions can be in the flat shape typical for thermal spraying, resulting in a lamellar structure consisting of catalyst regions and aluminum regions when viewed in cross-section.

[0043] The aluminum can remain in the catalyst layer after coating. It has been found that aluminum can increase the catalytic activity of the catalyst material. According to an advantageous development, however, the aluminum can also be removed from the catalyst layer after it has been applied. In this way, the surface area of ​​the catalyst layer can be further increased.

[0044] In particular, the process can—alternatively or in addition to removing the non-metallic particles—comprise at least partial removal of the aluminum, particularly by an etching treatment using potassium hydroxide. The aluminum regions present after coating can thus become "empty" regions. Thus, after the aluminum has been dissolved out, the catalyst layer can have a cross-sectionally lamellar structure consisting of catalyst regions and empty regions (in the places of the previously present aluminum regions).

[0045] It may also be advantageous if the aluminum is only partially removed, leaving a residual amount of aluminum in the catalyst layer. As described above, aluminum can improve catalytic activity.

[0046] The catalyst material preferably comprises nickel and / or a nickel alloy. In particular, the catalyst material can be selected from the group comprising: nickel, nickel-aluminum alloy, aluminum-nickel-molybdenum alloy, in particular aluminum(40-50)-nickel(35-40)-molybdenum(15-20) alloy, and combinations thereof.

[0047] In this respect, the powder of the catalyst material can be a powder or a powder mixture of two or more powders, wherein the powder or powders are selected from the group consisting of:

[0048] nickel powder,

[0049] Powder made of an aluminium-nickel-molybdenum alloy, in particular an aluminium(40-50)-nickel(35-40)-molybdenum(15-20) alloy,

[0050] Powder made of a nickel-aluminum alloy, and combinations thereof.

[0051] Preferably, the proportion of nickel powder in the powder of catalyst material is 5-25 wt.% (if present at all).

[0052] Nickel-aluminum alloys can, in particular, be so-called "Raney nickel" alloys. When using nickel-aluminum alloys, the process can optionally include dissolving the aluminum from the nickel-aluminum alloy after coating.

[0053] When reference is made here to an aluminium (40-50)-nickel (35-40)-molybdenum (15-20) alloy, this means that the alloy contains the quantities of the element indicated in brackets after the respective element in weight percent based on the total alloy.

[0054] When using aluminum-nickel-molybdenum alloy, in particular the aluminum(40-50)-nickel(35-40)-molybdenum(15-20) alloy, it may also be advantageous if the process, after coating the substrate, comprises tempering the coated section at temperatures in the range between 250°C and 650°C under a non-reducing nitrogen or argon atmosphere for a period of 10 - 120 min to form aluminum-nickel phases, in particular AhNi, AUNij phases.

[0055] In a particularly preferred embodiment, the catalyst material powder can be a powder mixture of nickel powder and powder of an aluminum (40-50)-nickel (35-40)-molybdenum (15-20) alloy, in particular with the proportion of nickel powder being 5-25 wt.% of the powder mixture. Glass particles, in particular, can be provided as non-metallic particles.

[0056] It is further considered advantageous if the aluminum(40-50)-nickel(35-40)-molybdenum(15-20) alloy consists of the aforementioned elements aluminum, nickel, and molybdenum, and optionally up to 2% by weight of titanium, and unavoidable impurities in a total of not more than 1% by weight, in particular not more than 0.8% by weight, in particular not more than 0.5% by weight, in particular not more than 0.3% by weight. It is further considered advantageous if the nickel content of the aluminum-nickel-molybdenum alloy powder is at least 36% by weight, in particular at least 37% by weight, in particular not more than 39% by weight, in particular not more than 38% by weight, and in particular 37% by weight nickel. It is further considered advantageous if the molybdenum content of the powder of aluminum-nickel-molybdenum alloy is at least 16 wt.%, in particular at least 17 wt.%, in particular at least 18 wt.%, in particular at most 24 wt.%, in particular at most 23 wt.%, in particular at most 22 wt.-%, in particular at most 21 wt.%, in particular at most 20 wt.% and in particular 19 wt.% molybdenum. It is further considered advantageous if the aluminum proportion of the powder made of aluminum-nickel-molybdenum alloy is at least 41 wt.%, in particular at least 42 wt.%, in particular at most 43 wt.%, in particular at most 49 wt.%, in particular at most 48 wt.%, in particular at most 47 wt.%, in particular at most 47 wt.%, in particular at most 46 wt.%, in particular at most 45 wt.% and in particular 44 wt.% aluminum. It is further considered advantageous if a titanium proportion of the powder made of aluminum-nickel-molybdenum alloy is at least 0.2 wt.%, in particular at least 0.4 wt.%, in particular at least 0.6 wt.%, in particular at most 1.5 wt.% and in particular at most 1.2 wt.% nickel.

[0057] The nickel powder particles may contain unavoidable impurities in a total of not more than 1 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.%.

[0058] It is further considered advantageous if the proportion of nickel powder in the powder mixture is at least 8 wt.%, in particular at least 10 wt.%, in particular at least 15 wt.%, in particular at most 23 wt.%, in particular at most 22 wt.%, in particular at most 21 wt.% and in particular 20 wt.%.

[0059] Furthermore, it proves to be advantageous if the coating of the substrate is carried out in such a way that the catalyst layer has a layer thickness of at least 15 pm, in particular at least 50 pm, in particular at least 80 pm, in particular at least 100 pm, and in particular at most 300 pm, in particular at most 200 pm, in particular at most 180 pm, in particular at most 160 pm, in particular at most 150 pm.

[0060] Coating the substrate may comprise applying a single layer of material that forms the catalyst layer. Coating the substrate may also comprise applying a plurality of material layers on top of one another, which together form the catalyst layer. The catalyst layer may thus be a multilayer material.

[0061] The proposed method makes it possible, in particular, to produce catalyst layers with locally varying pore fractions or proportions of non-metallic particles. For example, coating the substrate can comprise applying a plurality of material layers made of coating material with different material compositions, in particular with different volume ratios of non-metallic particles to catalyst material (see above). It proves particularly advantageous if the substrate is coated in such a way that the volume ratio of non-metallic particles to catalyst material increases with the number of layers, i.e., the volume fraction of non-metallic particles per material layer increases with the number of layers. After removal of the non-metallic particles, the volume fraction of pores per material layer can thus increase with the number of layers.In this respect, the coating can be carried out in such a way that, after at least partial removal of the non-metallic particles, the material layers of the catalyst layer near the surface exhibit a higher porosity than the material layers of the catalyst layer near the substrate. This can increase catalytic activity at the material layers near the surface. At the same time, the denser layers near the substrate can promote reliable adhesion of the catalyst layer to the substrate.

[0062] The coating materials with different material compositions can, for example, be present as prefabricated powder mixtures, which are successively fed to a coating unit, e.g., a spray gun for thermal spraying. In this respect, the provision of the coating material can comprise the provision of a plurality of coating materials with different material compositions, in particular a plurality of powder mixtures with different volume ratios of non-metallic particles to catalyst powder. It is also conceivable for the components of the coating material, in particular the powder of catalyst material and the non-metallic particles, to be kept separate from one another, e.g., in separate containers, and then mixed in situ, e.g., in a mixing device upstream of the coating unit (e.g., spray gun).

[0063] Furthermore, it proves advantageous if, prior to coating the substrate with the coating material, an intermediate layer of catalyst material without non-metallic particles, particularly acting as an adhesion promoter, is applied to the substrate. It has been found that such an intermediate layer improves the adhesion of the catalyst layer to the substrate. The intermediate layer can, in particular, be applied directly to a surface of the substrate. In this respect, the intermediate layer can be a base layer.

[0064] Furthermore, it may be advantageous if, before coating the substrate with the

[0065] Coating material, in particular before the application of the optional intermediate layer, at least the section of the substrate to be coated is mechanically blasted, e.g. sandblasted, in particular for cleaning and preparation for coating.

[0066] The metallic substrate is in particular a nickel-based substrate (i.e. made of nickel or nickel alloy or nickel-plated metal).

[0067] The substrate can have various shapes. Advantageously, the substrate is a flat metallic material. Preferably, the substrate has a plurality of through-openings. For example, the substrate can be designed in the form of a perforated sheet with a plurality of through-openings. Further advantageous embodiments of the substrate include: expanded metal mesh, wire mesh or knitted fabric, metal fleece, and metal foam.

[0068] The substrate may be regularly or irregularly shaped. The substrate may be curved. However, the substrate is preferably flat.

[0069] The substrate preferably has two opposing sides. The method may comprise coating one or both of these sides with the spray material, preferably only one of these sides.

[0070] In an advantageous further development, the substrate can be a section of a metallic flat material, in particular a flat strip material. In this respect, the provision of the substrate can comprise the provision of a metallic flat material, in particular a flat strip material.

[0071] In particular, the flat material is conveyed along a conveying direction, preferably continuously, and coated during this process. To obtain a respective electrode, a section of the coated flat material, in particular flat strip material, can then be cut to length and / or separated (e.g., punched out or laser cut). This enables the continuous and thus particularly economical production of large-area electrodes.

[0072] The invention also relates to a coating material, in particular a mixture or powder mixture. The coating material is particularly designed for use in a method described above. In particular, the coating material is a spray material for thermal spraying. The coating material comprises a powder made of a catalyst material (first component), in particular of at least one catalytically active metal alloy, and non-metallic particles (second component).

[0073] Preferably, a volume ratio of non-metallic particles to the powder of catalyst material to the coating material is at least 5:95, preferably at least 10:90, more preferably at least 15:85, and at most 40:60, more preferably at most 30:70, more preferably at most 25:75 - see above.

[0074] The coating material can, in particular, be a homogeneous mixture of the catalyst material powder and the non-metallic particles. For example, the catalyst material powder and the non-metallic particles can be mixed in a tumble mixer.

[0075] The optional features and advantages described above with regard to the method can also serve to further develop the coating material, so that in order to avoid repetition, reference is made to the above disclosure in this regard.

[0076] The invention also relates to an electrode for use in the alkaline electrolysis of water. The electrode is produced, in particular, by 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, to which a catalyst layer, in particular a thermally sprayed one, is applied at least in sections (i.e., the substrate is coated at least in sections with a catalyst material), wherein the catalyst layer comprises a catalyst material, in particular at least one catalytically active metal alloy, and non-metallic particles distributed in the catalyst material.

[0077] The catalyst layer is preferably thermally sprayed. In this respect, the catalyst layer can be obtained by applying a coating material comprising a powder of catalyst material and non-metallic particles to the substrate by thermal spraying.

[0078] The shape of the non-metallic particles in the catalyst layer can differ from the shape of the non-metallic (starting) particles in the coating material. When coated using thermal spraying, for example, the particles can initially melt at least partially and then impact the substrate with a pulse. This can deform the particles. For example, at least some particles in the catalyst layer can take on a flat-shaped form, typical of thermal spraying.

[0079] The catalyst layer may be a single material layer. The catalyst layer may also comprise a plurality of material layers applied to one another, each comprising catalyst material and non-metallic particles distributed within the catalyst material.

[0080] The invention also relates to an electrode for use in the alkaline electrolysis of water, in particular produced by a method described above, comprising a metallic, in particular nickel-based (i.e., made of nickel or a nickel alloy or nickel-plated metal), substrate, to which a catalyst layer, in particular a thermally sprayed one, is applied at least in sections. The catalyst layer comprises a catalyst material, in particular at least one catalytically active metal alloy, and pores distributed in the catalyst material. The pores are obtained in particular by removing non-metallic particles previously distributed in the catalyst material. The catalyst layer can additionally have pores formed "naturally" during thermal spraying.

[0081] Such an electrode exhibits an increased catalyst surface area, which has a positive effect on catalytic activity due to the increased number of catalytically active regions. Furthermore, mass transport through the pores is favored.

[0082] The catalyst layer may be a single layer of material. The catalyst layer may also comprise a plurality of material layers applied to one another, each comprising catalyst material and pores distributed within the catalyst material.

[0083] Within the scope of an advantageous development, the volume fraction of pores per material layer can increase with increasing number of layers. In this respect, material layers of the catalyst layer near the surface can have a higher porosity than material layers of the catalyst layer near the substrate. In this way, catalytic activity can be increased at the material layers near the surface. At the same time, the denser layers near the substrate can promote reliable adhesion of the catalyst layer to the substrate. It also proves advantageous if the catalyst layer has a porosity of more than 5%, preferably more than 8%, preferably more than 10%, and in particular less than 40%, preferably less than 35%, more preferably less than 30%, more preferably less than 25%.

[0084] In this respect, a volume fraction of the catalyst material in the catalyst layer (i.e., a volume of the catalyst material in the catalyst layer relative to the total volume of the catalyst layer) can be more than 60 vol.%, preferably more than 65 vol.%, more preferably more than 70 vol.%, more preferably more than 75 vol.%. In particular, however, a volume fraction of the catalyst material in the catalyst layer is less than 95 vol.%, preferably less than 90 vol. A volume fraction of the catalyst material in the catalyst layer between 60 and 95 vol.%, preferably between 70 and 90 vol.%, is particularly advantageous.

[0085] The porosity can be determined, for example, according to ISO / TR 26946:2011.

[0086] The optional features and advantages described above with regard to the method can also be used to design the electrode, so that in order to avoid repetition, reference is made to the above disclosure in this regard.

[0087] The following optional features apply both to the electrode with non-metallic particles (claim 15) and to the electrode with pores (claim 16).

[0088] As explained in detail above, the catalyst material preferably comprises nickel and / or a nickel alloy. In particular, the catalyst material is selected from the group consisting of: nickel, nickel alloy, nickel-aluminum alloy, aluminum-nickel-molybdenum alloy, or combinations thereof.

[0089] The catalyst layer may also comprise oxide or hydroxide compounds optionally formed during coating, particularly during thermal spraying, e.g. NiO, Ni(OH)j, etc.

[0090] The non-metallic particles in the catalyst layer are preferably 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.

[0091] Preferably, the catalyst material is a catalytically active metal alloy, in particular aluminum-nickel-molybdenum alloy, further in particular an aluminum(40-50)-nickel(35-40)-molybdenum(15-20) alloy, and the non-metallic particles are glass particles.

[0092] The substrate can be formed, for example, as a metallic flat material, preferably in the form of a perforated sheet with a plurality of through-openings, an expanded metal grid, wire mesh or knitted fabric, metal fleece or metal foam or perforated sheet, in particular in each case made of nickel or nickel alloy or nickel-plated metal.

[0093] 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 production in a half-cell of an electrochemical cell.

[0094] The invention is explained in more detail below with reference to the figures. They show:

[0095] Figure 1 simplified schematic representation of an exemplary electrode;

[0096] Figure 2 Flowchart to explain an exemplary method for producing a

[0097] Electrode according to Figure 1;

[0098] Figure 3 Measured values ​​of specific current density and the voltage required for this;

[0099] Figure 4 Scanning electron micrograph of a section of an electrode with

[0100] Catalyst layer comprising non-metallic particles;

[0101] Figure 5 Scanning electron micrograph of a section of an electrode with dissolved non-metallic particles;

[0102] Figure 6 Scanning electron micrograph of a section of an electrode with

[0103] Catalyst layer without non-metallic particles.

[0104] 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 is designed for use in the alkaline electrolysis of water.

[0105] The electrode 10 comprises a metallic substrate 12, which in the 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.

[0106] The substrate 12 is coated in sections with a catalyst layer 14. In this specific example, the substrate 12 has a first side 16 and an opposite 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 for the substrate 12 to be coated on both sides with a catalyst layer 14.

[0107] The catalyst layer 14 comprises a catalyst material 20 and pores 22 distributed in the catalyst material 20. As explained in detail below, the pores 22 are formed by removing non-metallic particles 24 previously distributed in the catalyst material 20.

[0108] Figure 1 shows the catalyst layer 14 in a simplified schematic representation. In particular, the size ratios and volume fractions are shown merely as examples to visualize the individual components. The "flat-sheet shape" of the catalyst material 20 shown in Figure 1 is merely an example to visualize a structure typically formed during the preferred thermal spraying process (see below). However, the catalyst material 20 is not limited to such a structure.

[0109] Exemplary layer structures are described below with reference to Figures 4 to 6.

[0110] The catalyst material 20 is preferably a metal and / or a metal alloy. In particular, the catalyst material 20 can be selected from the group comprising: nickel, nickel-aluminum alloy, aluminum-nickel-molybdenum alloy, in particular aluminum(40-50)-nickel(35-40)-molybdenum(15-20) alloy, and combinations thereof. As mentioned above, an average layer thickness of the catalyst layer 14 is preferably at least 15 μm and in particular at most 300 μm. A porosity is preferably more than 5% and less than 40%. An average pore diameter of the pores 22 is at least 5 μm, preferably at least 10 μm.

[0111] In the following, an exemplary method for producing such an electrode 10 is explained with reference to Figure 2.

[0112] According to the method, the metallic substrate 12 and a coating material 26 are provided in a first step 100. As mentioned above, the substrate 12 can be, for example, an expanded metal mesh made of nickel, a nickel alloy, or a nickel-coated metal.

[0113] The coating material 26 comprises a powder 28 of catalyst material 20 and non-metallic particles 24. In particular, the coating material 26 can be a homogeneous mixture of powder 28 of catalyst material 20 and non-metallic particles 24.

[0114] As mentioned above, the non-metallic particles 24 can, 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.

[0115] The powder grains of the powder 28 of catalyst material 20 and the non-metallic particles 24 are shown only schematically as spheres in Figure 2. However, the powder grains and the non-metallic particles 24 are not limited to this shape, but can have various shapes and, in particular, can also be irregularly shaped.

[0116] In a further step 102, at least a portion of the substrate 12, in particular only the first side 16, is then coated with the coating material 26.

[0117] By way of example and preferably, the coating is carried out by means of thermal spraying, in particular by means of atmospheric plasma spraying. A spray gun 30 for thermal spraying is only schematically indicated in Figure 2. During thermal spraying (generally known and therefore not explained in detail here), the catalyst material 20 and optionally also the non-metallic particles 24 are melted, and the melt droplets are accelerated toward the substrate 12. The momentum upon impact with the substrate 12 creates—at least in the case of metallic catalyst material 20—in particular the schematically illustrated "flat cake" shape.

[0118] In designs not shown, the coating can also be carried out by laser deposition welding.

[0119] As mentioned above, it is conceivable that the electrode 10 with catalyst layer 14 comprising catalyst material 20 and non-metallic particles 24 is used in the electrolysis of water.

[0120] Preferably, however, in a further step 104, at least a portion of the non-metallic particles 24 are removed from the catalyst layer 14 after the substrate 12 has been coated, thus forming the above-mentioned pores 22.

[0121] As mentioned above, the method of removing the non-metallic particles 24 can vary depending on the non-metallic particles 24 used. For example, the removal of the particles can be achieved by thermally decomposing the non-metallic particles 24 and / or dissolving the non-metallic particles 24 with a dissolving fluid (e.g., alkali, solvent, water).

[0122] The electrodes 10 described above with intentionally introduced pores 22 have improved catalytic activity in the electrolysis of water.

[0123] Figure 3 shows measured values ​​of specific current density 32 (ordinate, especially in A cm' 2 measured) and overpotential 34 (abscissa, measured in particular in mV) for an electrode 10 described above with a catalyst layer 14 with intentionally introduced pores 22 (curve 36, electrode according to Example 1, see Table 1) and for an electrode with a catalyst layer 14 without intentionally introduced pores 22 (curve 38, comparative example, see Table 2). As mentioned above, the catalyst layer 14 according to the comparative example can have a certain process-related "natural" porosity. As can be seen from Figure 3, for the electrode 10 with pores 22, an overpotential is reduced, which improves the efficiency in the electrolysis of water.

[0124] To determine the measured values ​​according to Figure 3, the electrodes 10 manufactured according to Tables 1 and 2 were placed under identical conditions in an electrolyte consisting of 30% KOH solution and subjected to a voltage applied to a working electrode also immersed in the electrolyte. The voltage in question was measured essentially without current against a standard hydrogen electrode, also immersed in the electrolyte, in a three-electrode arrangement. Figure 3 shows the voltage required for a given specific current density against the standard hydrogen electrode. It can be seen that to achieve a given specific current density, a lower voltage must be applied to the relevant section or electrode.

[0125] Table 1

[0126] Table 2

[0127] Figures 4 to 6 show scanning electron micrographs (cross sections) of exemplary

[0128] Electrodes 10. Figure 4 shows a section of an electrode 10 with nickel expanded metal grid as substrate 12 and catalyst layer 14 applied thereto by means of atmospheric plasma spraying. A mixture of powder from an aluminum-nickel-molybdenum alloy (specifically: AI44Ni37Mol9, ie an aluminum-nickel-molybdenum alloy with 44 wt.% aluminum, 37 wt.% nickel, 19 wt.% molybdenum) and glass spheres (specifically: mixture of glass spheres with diameters between 30 and 130 pm, volume ratio of non-metallic particles to catalyst material in the coating material: 15:85) was used as coating material 26. Figure 4 shows the catalyst layer 14 before the optional removal of the glass beads 24. In this respect, the catalyst layer 14 comprises the catalyst material 20 (aluminum-nickel-molybdenum alloy) and non-metallic particles 24 (glass beads) embedded therein.

[0129] Figure 5 shows a section of another electrode 10 from which the non-metallic particles 24 were removed. The catalyst layer 14 thus comprises catalyst material 20 and pores 22 distributed therein. A nickel expanded metal mesh was again used as the substrate 12, and a mixture of powder from an aluminum-nickel-molybdenum alloy (specifically: Al44Ni37Mol9) and glass spheres (specifically: a mixture of glass spheres with diameters between 30 and 130 pm, volume ratio of non-metallic particles to catalyst material in the coating material: 25:75) was used as the coating material 26. The coating was also applied by atmospheric plasma spraying. To remove the glass spheres 24, the coated substrate 12 was immersed in a 30% KOH solution at 80°C for 24 hours.

[0130] Figure 6 shows a comparative example of an electrode 10 with a catalyst layer 14 consisting solely of catalyst material 20 (i.e., without non-metallic particles 24 or pores 22). In this specific example, a powder of aluminum-nickel-molybdenum alloy (specifically: AI44Ni37Mol9) was applied to a nickel expanded metal mesh by atmospheric plasma spraying.

Claims

Patent claims 1. A method for producing an electrode (10) for use in the alkaline electrolysis of water, comprising a metallic substrate (12) on which a catalyst layer (14) is applied at least in sections, the method comprising: - Providing a metallic, in particular nickel-based, substrate (12), in particular in the form of a metallic flat material, further in particular in the form of a perforated sheet, expanded metal mesh, wire mesh or knitted fabric, metal II fleece, or metal foam; - providing a coating material (26), - Coating at least a portion of the substrate (12) with the coating material (26), characterized in that the coating material (26) comprises a powder (28) made of a catalyst material (20), in particular of at least one catalytically active metal alloy, and non-metallic particles (24), wherein a volume ratio of non-metallic particles (24) to catalyst material (20) in the coating material (26) is at least 5:95, wherein a particle diameter of the non-metallic particles (24) is less than 150 pm.

2. The method according to claim 1, wherein the coating of the substrate (12) with the coating material (26) is carried out by thermal spraying, preferably by plasma spraying, more preferably by atmospheric plasma spraying.

3. The method of claim 1 or 2, further comprising: at least partially removing the non-metallic particles (26).

4. The method according to the preceding claim, wherein the removal of the non-metallic particles (24) comprises heating at least a subset of the non-metallic particles (24), in particular the thermal decomposition of at least a subset of the non-metallic particles (24).

5. The method according to claim 3 or 4, wherein removing the non-metallic particles (24) comprises dissolving at least a portion of the non-metallic particles (24) by a dissolving fluid.

6. Method according to one of the preceding claims, wherein the non-metallic particles (24) are selected from the group comprising: - silicon-containing particles, in particular glass particles, further in particular glass spheres or glass powder, 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 (24) comprises at least partially dissolving the silicon-containing particles in a lye, in particular KOH; - Particles of precipitated silica; - plastic particles, in particular made of a polymer from the group comprising PBT, PET, PC and PEEK, in particular wherein the removal of the non-metallic particles (24) comprises saponification of the plastic particles under alkaline conditions; - salt particles, in particular made of a carbonate, further in particular of KH2CO3 or K2CO3, in particular wherein the removal of the non-metallic particles (24) comprises dissolving the salt particles in a solvent, in particular water, optionally after prior or simultaneous heating of the coated substrate (12); - particles made of a carbon material, in particular graphite and / or carbon black, wherein the removal of the non-metallic particles (24) comprises heating the coated substrate (12) in an oxygen-containing atmosphere, in particular at a temperature between 300 and 450°C; - Particles of a mineral, in particular sodium tetraborate or potassium tetraborate; and combinations thereof.

7. Method according to one of the preceding claims, wherein a volume ratio of non-metallic particles (24) to catalyst material (20) in the coating material (26) is at least 10:90, preferably at least 15:85, and at most 40:60, more preferably at most 30:70, more preferably at most 25:

75.

8. Method according to one of the preceding claims, wherein a particle diameter of the non-metallic particles (24) is 5-50 pm, preferably 5-40 pm, more preferably 10-30 pm.

9. Method according to one of the preceding claims, wherein the coating material (26) further comprises an aluminum powder made of aluminum or a low-alloy aluminum alloy.

10. Method according to the preceding claim, further comprising, after coating, at least partially removing the aluminum, in particular by an etching treatment using potassium hydroxide.

11. The method according to any one of the preceding claims, wherein the powder (28) of the catalyst material (20) is selected from the group comprising: nickel powder, Powder of an aluminium-nickel-molybdenum alloy, in particular an aluminium(40-50)-nickel(35-40)-molybdenum(15-20) alloy, Powder made of a nickel-aluminum alloy, and combinations thereof.

12. The method according to any one of the preceding claims, wherein the catalyst material (20) is a metal alloy, preferably an aluminum-nickel-molybdenum alloy, more preferably an aluminum (40-50)-nickel (35-40)-molybdenum (15-20) alloy, and wherein the non-metallic particles are glass particles, in particular glass spheres.

13. The method according to any one of the preceding claims, wherein the coating of the substrate (12) comprises the application of a plurality of material layers of coating material (26) with different material compositions, in particular with different volume ratios of non-metallic particles (24) to catalyst material (20), wherein the coating of the substrate (12) is carried out in such a way that a volume fraction of non-metallic particles (24) in the catalyst layer (14) increases with increasing number of layers.

14. Coating material (26) for use in a method according to one of the preceding claims, in particular spray material for thermal spraying, comprising a powder (28) made of a catalyst material (20), in particular of at least one catalytically active metal alloy, and non-metallic particles (24), wherein a volume ratio of non-metallic particles (24) to catalyst material (20) in the coating material (26) is at least 5:95, wherein a particle diameter of the non-metallic particles (24) is less than 150 pm.

15. Electrode (10) for use in the alkaline electrolysis of water, in particular produced according to a method according to one of the preceding claims, comprising a metallic, in particular nickel-based, substrate (12), on which a catalyst layer (14) is applied at least in sections, wherein the catalyst layer (14) comprises a catalyst material (20), in particular at least one catalytically active metal alloy, and non-metallic particles (24) distributed in the catalyst material (20).

16. An electrode (10) for use in the alkaline electrolysis of water, in particular produced by a method according to any one of the preceding claims, comprising a metallic, in particular nickel-based, substrate (12), on which a catalyst layer (14) is applied at least in sections, wherein the catalyst layer (14) comprises a catalyst material (20), in particular at least one catalytically active metal alloy, and pores (22) distributed in the catalyst material (20), wherein the pores (22) are obtained by removing non-metallic particles (24) previously distributed in the catalyst material (20).

17. Electrode (10) according to the preceding claim, wherein the catalyst layer (14) has a porosity of more than 5%, preferably more than 10%, and in particular less than 40%, preferably less than 35%, more preferably less than 30%, more preferably less than 25%.

18. Use of an electrode according to any one of claims 15 to 17 for oxygen production in a half-cell of an electrochemical cell for the alkaline electrolysis of water.

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