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, the method comprising providing a metallic substrate (12), providing a coating material (26) comprising a powder (28) of a catalyst material (20) and non-metallic 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

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.Electrodes of this type and methods for their production are known in principle from the prior art. Expanded metal grids, for example, are used as the substrate. Porous nickel in particular has proven to be advantageous as catalyst material. In this connection, 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 commonly referred to by the inventor as "Raney nickel" or "Raney alloy".Furthermore, EP 4 198 174 A1 discloses an anode for use in alkaline water electrolysis, which anode has a substrate in the form of an expanded metal lattice and a catalyst layer deposited thereon by means of thermal spraying. The catalyst layer has a lamellar structure of metallic regions and empty regions. In concrete terms, EP 4 198 174 A1 proposes depositing a mixture of nickel and aluminum by means of thermal spraying, and subsequently dissolving out the aluminum in order to obtain the lamellar structure described above.Furthermore, DE 10 2022 124 917 B3 discloses a method for providing an electrode of the type mentioned at the beginning. According to the method, a powder mixture of nickel powder and powder of an aluminum-nickel-molybdenum alloy is applied by thermal spraying or laser deposition welding to a flatly extended portion of a metallic flat material and subsequently tempered at temperatures in the range between 250° C. and 650° C. under a non-reducing nitrogen or argon atmosphere for a duration of 10 min to form aluminum-nickel phases.The invention is concerned with the problem of improving an efficiency in alkaline water electrolysis.This object is achieved according to the invention by a method having the features of claim 1. This is a method of manufacturing an electrode for use in alkaline electrolysis of water. The electrode comprises a metallic substrate, on 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 portion 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 comprise in particular a powder of a catalytically active metal alloy. The coating material also includes non-metallic particles (second component). The nonmetallic particles are in particular catalytically inactive or are active only to a reduced extent in comparison with the catalyst material.The proposed method makes it possible to provide electrodes with improved mechanical and catalytic properties. By using such electrodes, efficiency in electrolysis of water can be improved.The term "coating material" in the present context denotes the entity of the first component (powder of catalyst material) and the second component (non-metallic particles). By "coating material" is meant in particular the starting material which is fed to a suitable coating process (e.g. thermal spraying or laser deposition welding, see below) and is thus applied to the substrate. The coating material or components thereof can be changed in its shape and property during the coating (for example by melting and accelerating during thermal spraying).The coating of the substrate with the coating material is preferably carried out by thermal spraying of the coating material (in particular with at least partial melting of the coating material and pulse-applying deposition of melt droplets from the coating material). Plasma spraying, preferably atmospheric plasma spraying, has proven particularly advantageous. In addition, cold gas spraying, flame spraying or high-speed flame spraying (HVOF spraying) are conceivable.Alternatively, the coating of the substrate can be carried out by means of laser deposition welding.The coating material can consist of a powder of catalyst material (first component) and, in particular, non-metallic particles (second component) mixed with the powder. In this respect, the coating material can be a mixture of powder of catalyst material and nonmetallic particles.The coating material can comprise further components in addition to the powder of catalyst material (first component) and the non-metallic particles (second component).The term "catalyst material" in the present context means a catalytically active material, i.e. a material supporting the alkaline electrolysis of water. The catalyst material is in particular a metal alloy which is designed to catalyse the anode reaction (oxygen formation) or to catalyse the cathode reaction (hydrogen formation) in the alkaline electrolysis of water. In particular, the catalyst material is a catalytically active metal alloy.Preferably, the catalyst material comprises or consists of a nickel-containing metal alloy, more preferably a nickel alloy having a nickel content of at least 25 wt %.The term "non-metallic" in the present context means that the particles do not consist of a pure metal or a metal alloy. In this respect, the term "non-metallic" includes particles made of a pure metal or a metal alloy, for example. Metal powder or powder of a metal alloy. The term "non-metallic" is not to be understood, however, as meaning that the particles must not comprise metal atoms. As will be explained in detail below, "non-metallic" particles in the sense of the present application can in particular also be particles of metal-non-metal compounds, for example. Glass particles comprise.The term "particles" in the present context comprises various particle shapes, such as, for example, (regular or irregular) grains, in particular powder grains, spheres, fibers, or the like. The particles can be provided by crushing a solid material (for example. Powder). The particles can also be made of a starting material, for example. The melt of the polymer may be initially shaped. The particles can be present as bulk material. The particles may be present as powders.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 found here that a catalytic effect can be improved by using two different components (catalyst material and, in particular, catalytically inactive, nonmetallic particles). It is assumed that the non-metallic particles, on account of the surface properties different from the catalyst material, can serve as gas bubble nucleation centers during the electrolysis of water and can thus reduce the overvoltage.According to a particularly advantageous development of the method, the nonmetallic particles can be at least partially removed after the coating of the substrate with the coating material-and in particular before use of 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 of the catalyst material. In such a (porous) catalyst layer, a surface area is increased, which increases catalytic activity and also promotes mass transport during electrolysis. The proposed two-stage procedure comprising the introduction of nonmetallic particles into the catalyst layer and the subsequent at least removal of these particles makes it possible to set a porosity in a targeted manner and in particular also to change a porosity within the catalyst layer.The removal of the nonmetallic 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%, more preferably more than 98%, of the nonmetallic particles are removed.The at least partial removal of the nonmetallic particles can be effected in various ways, in particular depending on the nonmetallic particles used.The at least partial removal of the non-metallic particles may include 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 nonmetallic 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 nonmetallic particles. Heating the non-metallic particles may include heating the coated substrate, for example, in an oven. The heating of the non-metallic particles can also comprise the local introduction of heat, for example by means of a laser.Alternatively or additionally, the at least partial removal of the non-metallic particles can comprise the extraction of at least a portion of the non-metallic particles by an extraction fluid. The dissolving out may comprise dissolving the non-metallic particles in the dissolving out fluid. The dissolving out may also comprise chemically decomposing the non-metallic particles by the dissolving out fluid. The dissolving-out fluid can be, for example, a chemical solvent, an acid, an alkali, water, or a chemical reagent. For example, the method may comprise immersing the coated substrate in a bath of release fluid. The at least partial removal of the non-metallic particles can also comprise carrying out an etching treatment, in particular using potassium hydroxide.The non-metallic particles may be made of different materials. The coating material may comprise a single grade of non-metallic particles. The coating material may also comprise mixtures of different non-metallic particles.Silicon-containing particles, in particular glass particles, more particularly glass powder or glass balls, more particularly of borosilicate glass, more particularly of alkali borate glass, have proven to be particularly advantageous. The non-metallic particles may also comprise or be particles of precipitated silica. In the case of silicon-containing particles, the optional removal of the nonmetallic particles can be, for example, the at least partial dissolution of the silicon-containing particles (for example. Glass particles) in an alkali solution, in particular KOH. By way of example, the at least partial removal may comprise immersing the coated substrate in a bath of 30% KOH at 80° C. for 24 h.Alternatively or additionally, the non-metallic particles can comprise or be plastic particles, in particular made of a polymer of the group comprising PBT, PET, PC and PEEK. Such particles are particularly easy and comparatively easy to remove. For example, the optional removal of the plastic particles can comprise the saponification of the plastic particles (in particular in the case of PBT, PET or PC) under alkaline conditions (for example by immersing the coated substrate in a NaOH solution).Alternatively or additionally, the non-metallic particles can comprise or be salt particles, in particular of a carbonate, further in particular of KH 2 CO 3 or K 2 CO 3. In the case of such particles, the optional removal of the particles can comprise, in particular, the dissolution of the salt particles in a solvent, in particular water, optionally after prior heating or with simultaneous heating of the coated substrate.Alternatively or additionally, the non-metallic particles can comprise or be carbon particles, i.e. particles made of a carbon material, in particular of graphite and / or carbon black. Carbon particles are available comparatively easily and in particular economically. The optional removal of such carbon particles can comprise, for example, heating the carbon particles, in particular the coated substrate, in an oxygen-containing atmosphere, in particular at a temperature between 300 and 450° C.Alternatively or additionally, the non-metallic particles can comprise or be particles made of a mineral, in particular sodium tetraborate (borax) or potassium tetraborate. The optional removal of the non-metallic particles can comprise, for example, the chemical dissolution of the particles.The non-metallic particles are preferably silicon-containing particles, more preferably glass particles, more preferably glass spheres, more preferably borosilicate glass, more preferably alkali borate glass.The layer structure of the catalyst layer may be different. The coating is advantageously carried out in such a way that-in the catalyst layer applied to the substrate-the nonmetallic particles are distributed in the catalyst material. In this way, a homogeneous pore distribution can be provided after the removal of the non-metallic particles. This can be provided, for example, by the catalyst material and the nonmetallic particles being mixed, in particular homogeneously, in the coating material. For example, the coating material may be a homogeneous mixture of catalyst material and non-metallic particles.The coating is preferably carried out in such a way that the catalyst material (before and in particular also after the removal of the nonmetallic particles) forms a percolating network at least in sections (that is to say at least in partial regions of the coating). In this way, conductivity in the catalyst layer can be improved.It can furthermore be advantageous if the coating is carried out in such a way that the catalyst material forms an open-pore structure. In this way, removal of the nonmetallic components, in particular also in relatively low levels of the catalyst layer, is facilitated.The ratio of catalyst material and non-metallic particles in the coating material may vary. It has been found to be particularly advantageous if a volume ratio of nonmetallic 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.The volume ratio can be calculated in particular according to the following formula:The "mass" can be, in particular, the weighing-in of the individual components.In particular, a volume proportion of the non-metallic particles to the total volume of the coating material is between 5 and 40 vol %, more preferably between 5 and 25 vol %.The non-metallic particles can be of different sizes. It has proven to be particularly advantageous if an, in particular average, particle diameter of the non-metallic particles is less than 150 μm, preferably 5-50 μm, more preferably 5-40 μm, more preferably 10-30 μm. The coating material can also comprise a mixture of non-metallic particles with different particle diameters.The particle diameter can be determined according to ISO 13320:2020-01. In particular, the particle diameter can be determined by means of laser light scattering using a "Laser Scattering Particle Size Distribution Analyzer", for example the device "Particle LA-960V2" from Horiba Scientific.As mentioned above, the coating material may comprise further components in addition to the powder of catalyst material and the non-metallic particles.Within the scope of an advantageous development, the coating material can also comprise an aluminum powder made of aluminum or a low-alloy aluminum alloy. In the present case, "low-alloy" is understood to mean, in particular, alloys which consist at least to the extent of 80% by weight of metallic aluminum.During the thermal spraying of such a coating material comprising catalyst material and aluminum, a layer structure comprising catalyst regions of catalyst material and aluminum regions of aluminum or aluminum alloy can be formed in particular. The regions can be present in the form of a fin typical for thermal spraying, so that a lamellar structure of catalyst regions and aluminum regions results when viewed in a cross section.The aluminum may remain in the catalyst layer after coating. It has been found that aluminum can increase a catalytic activity of the catalyst material.According to an advantageous development, however, the aluminum can also be removed again from the catalyst layer after the application thereof. In this way, a surface area of the catalyst layer can be further increased.In particular, as an alternative or in addition to the removal of the nonmetallic particles, the method can comprise the at least partial removal of the aluminum, in particular by an etching treatment using potassium hydroxide. From the aluminum areas present after the coating, "empty" areas can thus become. In this respect, after the aluminum has been dissolved out, the catalyst layer can have a structure of lamellar cross section comprising catalyst regions and empty regions (at the locations of the aluminum regions present previously).It can furthermore be advantageous if the aluminum is only partially removed, i.e. a residual proportion of aluminum remains in the catalyst layer. As described above, aluminum can improve catalytic activity.The catalyst material preferably comprises nickel and / or a nickel alloy. In particular, the catalyst material may 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.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 the powders are selected from the group consisting of:nickel powder,Powder of an aluminum-nickel-molybdenum alloy alloy, in particular an aluminum (40-50)-nickel (35-40)-molybdenum (15-20) alloy,Nickel-aluminum alloy powders, and combinations thereof.Preferably, the proportion of nickel powder in the powder of catalyst material is 5-25 wt% (if any).The nickel-aluminum alloys can be, in particular, so-called "Raney nickel" alloys. When nickel-aluminum alloys are used, the method can optionally include, after coating, dissolving the aluminum from the nickel-aluminum alloys.When an aluminum (40-50)-nickel (35-40)-molybdenum (15-20) alloy is mentioned here, this means that the alloy has the respective amounts of the element stated in brackets behind the respective element in percent by weight, based on the total alloy.When using aluminum-nickel-molybdenum alloy alloy, in particular the aluminum(40-50)-nickel(35-40)-molybdenum(15-20) alloy, it may also be advantageous if the method comprises, after coating the substrate, 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 duration of 10-120 min to form aluminum-nickel phases, in particular Al 3 Ni, Al 3 Ni 2- phases.In the context of a particularly preferred embodiment, the powder of catalyst material can be a powder mixture of nickel powder and powder of aluminum(40-50)-nickel(35-40)-molybdenum(15-20) alloy, in particular wherein the proportion of the nickel powder is 5-25% by weight of the powder mixture. In particular, glass particles can be provided as nonmetallic particles.It is further considered to be advantageous if the aluminum(40-50)-nickel(35-40)-molybdenum(15-20) alloy consists of the elements mentioned aluminum, nickel and molybdenum and optionally up to 2 wt % titanium and unavoidable impurities in a sum of at most 1 wt %, in particular at most 0.8 wt %, in particular at most 0.5 wt %, in particular at most 0.3 wt %. It is further considered to be advantageous if the nickel content of the powder of aluminum-nickel-molybdenum alloy is at least 36 wt %, in particular at least 37 wt %, in particular at most 39 wt %, in particular at most 38 wt % and in particular 37 wt % nickel. It is further considered to be advantageous if the molybdenum content of the powder of aluminum-nickel-molybdenum alloy is at least 16% by weight, in particular at least 17% by weight, in particular at least 18% by weight, in particular at most 24% by weight, in particular at most 23% by weight, in particular at most 22% by weight, in particular at most 21% by weight, in particular at most 20% by weight and in particular 19% by weight of molybdenum. It is further considered to be advantageous if the aluminum content of the powder of aluminum-nickel-molybdenum alloy is at least 41 wt %, in particular at least 42 wt %, in particular at least 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 to be advantageous if a titanium content of the powder of aluminum-nickel-molybdenum alloy is at least 0.2% by weight, in particular at least 0.4% by weight, in particular at least 0.6% by weight, in particular at most 1.5% by weight and in particular at most 1.2% by weight of nickel.The nickel powder particles may comprise unavoidable impurities in a sum of at most 1% by weight, in particular at most 0.8% by weight, in particular at most 0.5% by weight, in particular at most 0.3% by weight.It is further considered to be advantageous if the proportion of the nickel powder in the powder mixture is at least 8% by weight, in particular at least 10% by weight, in particular at least 15% by weight, in particular at most 23% by weight, in particular at most 22% by weight, in particular at most 21% by weight and in particular 20% by weight.It has furthermore proven 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 μm, in particular at least 50 μm, in particular at least 80 μm, in particular at least 100 μm, and in particular at most 300 μm, in particular at most 200 μm, in particular at most 180 μm, in particular at most 160 μm, in particular at most 150 μm.Coating the substrate may include depositing a single layer of material forming the catalyst layer. The coating of the substrate can also comprise applying a plurality of material layers to one another, which together form the catalyst layer. The catalyst layer can thus be a multilayer material.The proposed method makes it possible in particular to produce catalyst layers having locally different pore contents or contents of nonmetallic particles. For example, the coating of the substrate can comprise the application of a plurality of material layers of coating material having different material compositions, in particular having different volume ratios of nonmetallic particles to catalyst material (see above).It has proven to be particularly advantageous if the coating of the substrate is carried out in such a way that a volume ratio of nonmetallic particles to catalyst material increases with an increasing number of layers, that is to say a volume fraction of nonmetallic particles per material layer increases with an increasing number of layers. After the removal of the nonmetallic particles, a volume fraction of the pores per material layer can therefore increase with increasing number of layers. In this respect, the coating can be carried out in such a way that, after the at least partial removal of the nonmetallic particles, material layers of the catalyst layer close to the surface have a higher porosity than material layers of the catalyst layer close to the substrate. In this way, catalytic activity can be increased at the material layers close to the surface. At the same time, the denser layers in the vicinity of the substrate can promote reliable adhesion of the catalyst layer to the substrate.The coating materials with different material compositions can be present, for example, as prefabricated powder mixtures which are fed successively to a coating unit, for example 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 of different material compositions, in particular a plurality of powder mixtures having different volume ratios of nonmetallic particles to catalyst powder. It is also conceivable for the components of the coating material, in particular the powder of catalyst material and the nonmetallic particles, to be kept separate from one another, for example in separate containers, and then in situ, for example in one of the coating units (for example. Spray gun) can be mixed upstream of the mixing device.It has furthermore proven to be advantageous if, before the coating of the substrate with the coating material, an intermediate layer of catalyst material without nonmetallic particles, acting in particular as adhesion promoter, is applied to the substrate. It has been found that such an intermediate layer improves 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.It can further be advantageous if, before the coating of the substrate with the coating material, in particular also before the application of the optional intermediate layer, at least the section of the substrate to be coated is mechanically blasted, for example. Sand blasted is used, in particular for cleaning and preparation for a coating.The metallic substrate is in particular a nickel-based substrate (i.e. made of nickel or nickel alloy or nickel-plated metal).The substrate may have various shapes. Advantageously, the substrate is a metallic flat material. Preferably, the substrate has a plurality of through-holes. For example, the substrate can be formed in the form of a perforated sheet with a plurality of through-openings. Further advantageous configurations of the substrate comprise: expanded metal mesh, woven wire fabric or knitted fabric, metal fleece, and metal foam.The substrate may be regular or irregular in shape. The substrate may be formed to be bent. Preferably, however, the substrate is planar.The substrate preferably has two opposite sides. The method may comprise coating one or both of these sides with the spray material, preferably only one of these sides.Within the scope of an advantageous development, the substrate can be a section of a metallic flat material, in particular flat strip material. In this respect, the provision of the substrate can comprise the provision of a metallic flat material, in particular flat strip material. In particular, the flat material is conveyed along a conveying direction, preferably continuously, and coated during this. In order to obtain a respective electrode, a section can then be cut to length and / or cut (for example punched out or laser cut) from the coated flat material, in particular flat strip material. In this way, a continuous and thus particularly economical production of electrodes having a large surface area is made possible.The invention also relates to a coating material, in particular a mixture or powder mixture. The coating material is designed in particular for use in a method described above.In particular, the coating material is a spraying material for thermal spraying. The coating material comprises a powder of a catalyst material (first component), in particular of at least one catalytically active metal alloy, and nonmetallic particles (second component).Preferably, a volume ratio of non-metallic particles to the powder of catalyst material to that 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, see above.The coating material can be, in particular, a, in particular homogeneous, mixture of the powder of the catalyst material and the nonmetallic particles. For example, the powder of the catalyst material and the non-metallic particles may have been mixed in a tumbler mixer.The optional features and advantages described above with respect to the method can also serve for further development of the coating material, so that reference is made to the above disclosure in this regard in order to avoid repetitions.The invention also relates to an electrode for use in 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 of nickel alloy or of nickel-plated metal), substrate on which a catalyst layer, in particular a thermally sprayed catalyst layer, is applied at least in sections (substrate is therefore 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 nonmetallic particles distributed in the catalyst material.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 nonmetallic particles to the substrate by means of thermal spraying.The shape of the non-metallic particles in the catalyst layer may be different from a shape of the non-metallic (starting) particles in the coating material. In the case of coating by means of thermal spraying, the particles can, for example, first at least partially melt and then strike the substrate with pulses. The particles can be deformed in this case. For example, at least some particles in the catalyst layer may assume a flat shape characteristic of thermal spraying.The catalyst layer may be a single layer of material. The catalyst layer can also have a plurality of material layers applied to one another, each comprising catalyst material and nonmetallic particles distributed in the catalyst material.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 of nickel alloy or of nickel-plated metal), substrate on which a catalyst layer, in particular thermally sprayed catalyst layer, is applied at least in sections, wherein 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 nonmetallic particles previously dispersed in the catalyst material. The catalyst layer can additionally have pores formed "naturally" during thermal spraying.Such an electrode has an increased catalyst surface area, which has a positive effect on catalytic activity, since the number of catalytically active regions is increased. In addition, mass transport through the pores is promoted.The catalyst layer may be a single layer of material. The catalyst layer can also have a plurality of material layers applied to one another, each comprising catalyst material and pores distributed in the catalyst material.Within the scope of an advantageous development, a volume proportion of the pores per material layer can increase with an increasing number of layers. In this respect, material layers of the catalyst layer close to the surface can have a higher porosity than material layers of the catalyst layer close to the substrate. In this way, catalytic activity can be increased at the material layers close to the surface. At the same time, the denser layers in the vicinity of the substrate can promote reliable adhesion of the catalyst layer to the substrate.It has furthermore proven to be 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%.In this respect, a volume proportion of the catalyst material in the catalyst layer (i.e. a volume of the catalyst material in the catalyst layer based on the total volume of the catalyst layer) can be more than 60% by volume, preferably more than 65% by volume, more preferably more than 70% by volume, more preferably more than 75% by volume. In particular, however, a proportion by volume of the catalyst material in the catalyst layer is less than 95% by volume, preferably less than 90% by volume. A proportion by volume of the catalyst material in the catalyst layer is particularly advantageous between 60 and 95% by volume, preferably between 70 and 90% by volume.The porosity can be determined, for example, according to ISO / TR 26946:2011.The optional features and advantages described above with respect to the method can also serve for the configuration of the electrode, so that reference is made to the above disclosure in this regard in order to avoid repetitions.The following optional features apply to both the non-metallic particle electrode (claim 15) and the pore electrode (claim 16).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.The catalyst layer can additionally comprise optionally formed oxide or hydroxide compounds during coating, in particular during thermal spraying, for example. NiO, Ni(OH) 2, etc.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.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.The substrate can be designed, for example, as a metallic flat material, preferably in the form of a perforated plate having a plurality of through openings, an expanded metal grid, wire mesh or knitted fabric, metal fleece or metal foam or perforated plate, in particular each made of nickel or of nickel alloy or of nickel-plated metal.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.The invention is explained in more detail below with reference to the figures. The following are shown: FIG. 1 is a simplified schematic illustration of an exemplary electrode; FIG. 2 is a flow chart for explaining an exemplary method for producing an electrode according to FIG. 1 ; FIG. 3 shows measured values for specific current density and voltage required for this purpose; FIG. 4 is a scanning electron micrograph of a section of an electrode with catalyst layer comprising nonmetallic particles; FIG. 5 shows a scanning electron micrograph of a section of an electrode with dissolved-out nonmetallic particles; FIG. 6 shows a scanning electron micrograph of a section of an electrode with catalyst layer without nonmetallic particles.In the following description and in the figures, the same reference numerals are used in each case for identical or corresponding features.FIG. 1 shows a simplified schematic illustration of an electrode 10.The electrode 10 comprises a metallic substrate 12, which is formed as an expanded metal grid in the example. In embodiments not shown, the substrate 12 can also be formed, for example, as perforated sheet, wire mesh or knitted fabric, metal fleece, metal foam or the like.The substrate 12 is coated in sections with a catalyst layer 14. In the specific example, the substrate 12 has a first side 16 and an opposing second side 18, with the catalyst layer 14 coated only on 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.The catalyst layer 14 includes a catalyst material 20 and pores 22 dispersed in the catalyst material 20, and as explained in detail below, the pores 22 are formed by removing non-metallic particles 24 previously dispersed in the catalyst material 20.FIG. 1 shows the catalyst layer 14 in a simplified schematic illustration. In particular, size ratios and volume fractions are shown merely by way of example for visualizing the individual components. The "mold" of the catalyst material 20 shown in FIG. 1 is merely exemplary in order to visualize a structure typically formed during the preferred thermal spraying (see below). However, the catalyst material 20 is not limited to such a structure.Exemplary layer structures are described below with reference to FIGS. 4 to 6.The catalyst material 20 is preferably a metal and / or a metal alloy. In particular, the catalyst material 20 may 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.An exemplary method for producing such an electrode 10 is explained below with reference to FIG. 2.According to the method, in a first step 100, the metallic substrate 12 and a coating material 26 are provided. The substrate 12 can be, for example, an expanded metal grid made of nickel, nickel alloy or nickel-coated metal, as mentioned above.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.As mentioned above, the non-metallic particles 24 can be selected, for example, 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.The powder grains of the powder 28 of catalyst material 20 and the non-metallic particles 24 are only schematically shown as balls in FIG. 2. However, the powder grains and the non-metallic particles 24 are not limited to this shape, but may have various shapes, and particularly may be irregularly shaped.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.By way of example and with preference, the coating is effected by means of thermal spraying, in particular by means of atmospheric plasma spraying. A spray gun 30 for thermal spraying is merely indicated schematically in FIG. 2.During thermal spraying (basically known and therefore not explained in detail here), the catalyst material 20 and optionally also the nonmetallic particles 24 are melted and the melt droplets are accelerated in the direction of the substrate 12. The impulse upon impingement on the substrate 12 produces-at least in the case of metallic catalyst material 20-in particular the schematically illustrated "curtain shape".In embodiments not shown, the coating can also be carried out by means of laser deposition welding.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.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 coating of the substrate 12 and the above-mentioned pores 22 are thus formed.As mentioned above, the manner of removing the non-metallic particles 24 may vary depending on the non-metallic particles 24 used. For example, removing the particles may include thermally decomposing the non-metallic particles 24 and / or dissolving the non-metallic particles 24 with a dissolving fluid (e.g., for example. Alkali, solvent, water) can be carried out.The electrodes 10 described above with intentionally introduced pores 22 have an improved catalytic activity in the electrolysis of water.FIG. 3 shows measured values for specific current density 32 (ordinate, in particular measured in A cm -2 ) and overvoltage 34 (abscissa, in particular measured in mV) for an electrode 10 described above with catalyst layer 14 with intentionally introduced pores 22 (curve 36, electrode according to Example 1, see Table 1) and for an electrode with 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 may have a certain process-related "natural" porosity.As can be seen from FIG. 3, overvoltage is reduced for the electrode 10 having pores 22, which improves efficiency in electrolysis of water.To determine the measured values according to FIG. 3, the electrodes 10 produced according to Tables 1 and 2 were applied under the same conditions in an electrolyte of 30% KOH solution to a voltage against a working electrode likewise immersed in the electrolyte. In this case, the voltage in question here was measured substantially electrolessly against a hydrogen normal electrode likewise immersed in the electrolyte in a three-electrode arrangement. In FIG. 3, the voltage required for a specific current density is plotted against the hydrogen normal electrode. It can be seen that in order to achieve a predefined specific current density, a lower voltage must be applied to the section in question or the electrode in question. Table 1 Table 1Example 1Catalyst MaterialAluminum-Nickel-Molybdenum alloy (concretely, Al44Ni37Mo19)Non-metallic particlesType: glass beads (mixture with diameters of 30-130 μm)volume ratio of nonmetallic particles to catalyst material in the coating material: 25:75Coating MethodAtmospheric Plasma SprayingManner of Dissolving Non-Metallic Particlesimmersing the coated substrate in 30% KOH solution at 80°C for 24 hours.Table 2Table 2Comparative ExampleCatalyst MaterialAluminum-Nickel-Molybdenum alloy (concretely, Al44Ni37Mo19)Non-metallic particlesNone of them wereCoating MethodAtmospheric Plasma SprayingFIGS. 4 to 6 show scanning electron micrographs (cross sections) of exemplary electrodes 10.FIG. 4 shows a section of an electrode 10 with expanded nickel metal grids as substrate 12 and catalyst layer 14 applied thereto by means of atmospheric plasma spraying. A mixture of powder of an aluminum-nickel-molybdenum alloy (specifically: Al44Ni37Mo19, i.e. an aluminum-nickel-molybdenum alloy with 44% by weight aluminum, 37% by weight nickel, 19% by weight molybdenum) and glass beads (specifically: mixture of glass beads with diameters between 30 and 130 μm, volume ratio of nonmetallic particles to catalyst material in the coating material: 15:85) was used as coating material 26. FIG. 4 shows the catalyst layer 14 before the optional detachment of the glass balls 24. in this respect, the catalyst layer 14 comprises the catalyst material 20 (aluminum-nickel-molybdenum alloy) and nonmetallic particles 24 (glass balls) embedded therein.FIG. 5 shows a section of a further electrode 10 in which the nonmetallic particles 24 have been dissolved out. In this respect, the catalyst layer 14 comprises catalyst material 20 and pores 22 distributed therein. A nickel expanded metal grid was again used as substrate 12 and a mixture of powder of an aluminum-nickel-molybdenum alloy (specifically: Al44Ni37Mo19) and glass beads (specifically: mixture of glass beads having diameters between 30 and 130 μm, volume ratio of nonmetallic particles to catalyst material in the coating material: 25:75) was used as coating material 26. The coating is also carried out by means of atmospheric plasma spraying. To dissolve out the glass beads 24, the substrate 12 coated in this way was immersed for 24 h in a 30% KOH solution at 80° C.FIG. 6 shows a comparative example of an electrode 10 with a catalyst layer 14, which consists only of catalyst material 20 (i.e. without nonmetallic particles 24 or pores 22). In the specific example, a powder of aluminum-nickel-molybdenum alloy (specifically: Al44Ni37Mo19) was applied to a nickel expanded metal grid by means of atmospheric plasma spraying.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedEP 4 198 174 A1

[0003] DE 10 2022 124 917 B3

[0004] Cited Non-Patent LiteratureLaser Scattering Particle Size Distribution Analyzer", for example the "Particle LA-960V2" device from Horiba Scientific

[0038]

Claims

Method for producing an electrode (10) for use in 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 grid, wire mesh or knitted fabric, metal fleece, or metal foam; - providing a coating material (26), in particular in the form of a powder mixture, comprising a powder (28) made of a catalyst material (20), in particular made of at least one catalytically active metal alloy, and nonmetallic particles (24); - coating at least one section of the substrate (12) with the coating material (26).Method according to claim 1, wherein the coating of the substrate (12) with the coating material (26) is effected by thermal spraying, preferably by plasma spraying, further preferably by atmospheric plasma spraying.The method of claim 1 or 2, further comprising: at least partially removing the non-metallic particles (26).The method according to the preceding claim, wherein the removal of the non-metallic particles (24) comprises heating at least a portion of the non-metallic particles (24), in particular thermally decomposing at least a portion of the non-metallic particles (24).The method of 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.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 balls or glass powder, further in particular borosilicate glass, further in particular alkali borate glass, in particular wherein the removal of the non-metallic particles (24) comprises the at least partial dissolution of the silicon-containing particles in an alkali solution, in particular KOH; - particles of precipitated silica; - plastic particles, in particular of a polymer from the group comprising PBT, PET, PC and PEEK, in particular wherein the removal of the non-metallic particles (24) comprises the saponification of the plastic particles under alkaline conditions; - salt particles, in particular made of a carbonate, further in particular made of KH 2 CO 3 or K 2 CO 3, in particular wherein the removal of the non-metallic particles (24) comprises the dissolution of the salt particles in a solvent, in particular water, optionally after prior heating or while simultaneously heating 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 the heating of the coated substrate (12) in an oxygen-containing atmosphere, in particular at a temperature between 300 and 450° C.; - particles made of a mineral, in particular sodium tetraborate or potassium tetraborate; and combinations thereof.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 5:95, preferably at least 10:90, further preferably at least 15:85, and at most 40:60, further preferably at most 30:70, further preferably at most 25:75.The method according to any one of the preceding claims, wherein a particle diameter of the non-metallic particles (24) is less than 150 μm, preferably 5-50 μm, more preferably 5-40 μm, more preferably 10-30 μm.The method of any preceding claim, wherein the coating material (26) further comprises an aluminum powder of aluminum or a low alloy aluminum alloy.The method according to the preceding claim, further comprising, after the coating, at least partially removing the aluminum, in particular by an etching treatment using potassium hydroxide.The method according to any of the preceding claims, wherein the powder (28) of the catalyst material (20) is selected from the group comprising: nickel powder, powder of an aluminum-nickel-molybdenum alloy, in particular an aluminum (40-50)-nickel (35-40)-molybdenum (15-20) alloy, powder of a nickel-aluminum alloy, and combinations thereof.Method according to one of the preceding claims, wherein the catalyst material (20) is a metal alloy, preferably aluminum-nickel-molybdenum alloy, further preferably an aluminum (40-50)-nickel (35-40)-molybdenum (15-20) alloy, and wherein the non-metallic particles are glass particles, in particular glass balls.Method according to 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 proportion of non-metallic particles (24) in the catalyst layer (14) increases with an increasing number of layers.Coating material (26) for use in a method according to one of the preceding claims, in particular injection material for thermal spraying, comprising a powder (28) made of a catalyst material (20), in particular made of at least one catalytically active metal alloy, and nonmetallic particles (24).Electrode (10) for use in 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 nonmetallic particles (24) distributed in the catalyst material (20).Electrode (10) for use in alkaline electrolysis of water, in particular produced by 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 pores (22) distributed in the catalyst material (20), wherein the pores (22) are obtained by removing nonmetallic particles (24) previously distributed in the catalyst material (20).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%.Use of an electrode according to any one of claims 15 to 17 for oxygen generation in a half-cell of an electrochemical cell for alkaline electrolysis of water.

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