MANUFACTURING METHOD OF A CATALYTIC COATED DREIDI-MENSIONAL STRUCTURED ELECTRODE

Description

[0001] The invention relates to a method for producing a catalyst-coated, three-dimensionally structured electrode. In a first method step, a three-dimensionally structured metal substrate is provided. Subsequently, a mesoporous catalyst layer is synthesized on the three-dimensionally structured metal substrate. The synthesis preferably takes place by first generating a solution or suspension of a template, a metal precursor, and a solvent. The solution or suspension is then applied to the three-dimensionally structured metal substrate, so that a film forms on the three-dimensionally structured metal substrate. The three-dimensionally structured metal substrate is then dried at a temperature T 1 so that the solvent within the film evaporates and a layer of a catalyst precursor with integrated template structures is obtained.Finally, the three-dimensionally structured metal substrate containing catalyst precursors is subjected to a thermal treatment to form a mesoporous catalyst layer.

[0002] Furthermore, the invention relates to an electrode produced by the method of the type mentioned above, as well as to an electrochemical cell comprising such an electrode. Background and state of the art

[0003] In electrolysis cells for water splitting and fuel cells for reconverting gaseous hydrogen to electricity, catalyst powders dispersed with a binder are typically applied to a membrane using spraying, screen printing, or doctor blade coating techniques. Such processes are known, for example, from publications DE19544323A1 and US20120094210A1.

[0004] When producing a catalyst layer using the above-mentioned techniques, it is not possible to achieve a uniform coating with adjustable porosity and without the use of a binder. Binder-free and mesoporously templated anode materials, in particular, show improved oxygen evolution (OER) activities on a half-cell scale. It has been shown that iridium-containing mesoporous layers achieve a significantly higher Ir mass activity than comparable binder-based catalyst layers produced using ink methods (see also Fig. 4 ).

[0005] Direct coating of the membrane with a binder-free, mesoporous catalyst template is not possible, as the synthesis of such a catalyst (without a binder) requires thermal treatment. Thermal treatment leads to membrane destruction.

[0006] In order to use the highly active catalyst layers in an electrolyzer or a fuel cell, an alternative method had to be found that enables the transfer of the mesoporous layer from the half-cell to the full-cell scale.

[0007] US 2019 / 0211464 A1 discloses a method for producing an electrode for electrolysis. For this purpose, a coating solution comprising a platinum group metal precursor, a rare earth metal precursor, an organic solvent, and an amine-based solvent is first prepared. The coating solution is applied to a metal substrate to form a catalyst layer. The catalyst layer is then dried and subjected to a heat treatment. The choice of metal substrate is not limited and can be porous, for example, a grid, a metal foam, or an expanded metal. The catalyst layer itself is not described as porous. As a result, the catalyst layer does not have a suitable specific surface area and is disadvantageously formed in terms of its mass.

[0008] EP 3617348 A1 discloses an oxide-dispersed porous metal body. This can be provided by a metallic porous body that is added to a coating bath containing nickel sulfamate. The coating is used for the production of an electrode. The coating itself does not contain any pores.

[0009] CN 110783574 A discloses a method for producing a fuel cell electrode. The manufacturing method uses a foam metal, which is placed in an organic solution and then removed again. Additional process steps such as washing with deionized water can also be performed. Furthermore, a catalyst powder, a polymer binder, and an organic solvent are uniformly mixed to obtain a catalyst slurry. The catalyst slurry is applied to the metal foam. Macroporosity is achieved through the structure of the foam metal. However, this limits the distribution, size, and configuration of the pores to those of the metal foam, particularly to macropores. Macropores are disadvantageous for increasing the efficiency of a catalyst, for example, because they result in an unfavorable surface-to-volume ratio.

[0010] US 2021 / 0140058 A1 also discloses a method for producing a catalyst layer for an electrode. For this purpose, a coating solution is first prepared and applied to a metal substrate. The metal substrate can be pretreated, for example, by sandblasting, chemical etching, or thermal spraying. This is used to obtain irregularities (or "roughnesses"). irregularities ). Further pretreatment steps include salt or acid treatment. The coating solution can then be applied to the pretreated substrate and heat-treated in a convection drying and / or electric furnace. Efficient application of the coating solution to the metal substrate is only possible to a limited extent.

[0011] Therefore, there is a need to obtain an efficient catalyst layer, especially in the context of a coating for electrodes. Object of the invention

[0012] The object of the invention was therefore to eliminate the disadvantages of the prior art and to provide an electrochemical cell comprising a highly active, binder-free, mesoporously templated catalyst layer. In particular, the object of the invention was to provide an electrode for such an electrochemical cell and a method for producing this electrode. Summary of the invention

[0013] The object of the invention is achieved by the features of the independent claims. Advantageous embodiments of the invention are described in the dependent claims.

[0014] In a preferred embodiment, the invention relates to a method for producing a catalyst-coated three-dimensionally structured electrode comprising the following steps: a) Providing a three-dimensionally structured metal substrate; b) Preparing a suspension comprising a template, a metal precursor and a solvent; c) Applying the suspension to the three-dimensionally structured metal substrate so that a suspension film forms on the three-dimensionally structured metal substrate; d) Drying the suspension film on the three-dimensionally structured metal substrate at a temperature T 1 in a range between 18°C-250°C so that the solvent within the suspension film evaporates and a layer of a catalyst precursor with integrated template structures is obtained; e) Thermally treating the three-dimensionally structured metal substrate comprising the catalyst precursor at a second temperature T 2 in a range between 200°C and 1000°C and a calcination time t 2 in a range between 1 minute and 1440 minutes so that a mesoporous catalyst layer is formed.

[0015] The process according to the invention represents a departure from the prior art, as catalysts are not applied to a substrate via a binder-based dispersion using a suitable method (spraying, brushing, screen printing, doctor blade coating), as is frequently the case, but rather are deposited binder-free and with defined pore structures onto a three-dimensional substrate (dip coating) and subsequently implemented on a full-cell scale. The omission of a binder advantageously does not lead to a reduction in the volume-related electrical conductivity of the catalytically active material – in contrast to known binder-containing catalysts from the prior art. Accordingly, the process according to the invention achieves higher catalyst efficiency.In addition, densely packed pore structures lead to a crack-free coating and, in the case of small mesopores, to the best possible compromise between surface area and accessibility of reactants and products while avoiding diffusion limitations.

[0016] It has been shown that the use of three-dimensionally structured electrodes offers significant advantages in various applications, particularly in electrochemical cells. Three-dimensionally structured electrodes have a particularly large specific surface area per unit volume, which thus enables improved interaction between the electrode and the surrounding medium. In particular, the increased surface area per unit volume can advantageously enable improved gas bubble removal. A method for producing a three-dimensionally structured electrode with a nanostructured, mesoporous templated catalyst layer was previously neither known nor suggested in the prior art.

[0017] As already discussed at the beginning, a significant advantage of the present invention lies in the binder-free production of a catalyst. Binders are typically necessary to ensure mechanical adhesion of the particles of a catalyst powder both to each other and to a substrate, as well as—as in the case of water electrolysis—rapid proton transport. The process according to the invention leads to covalently bonded networks of the catalyst, which—without the use of binders—creates sufficient internal structural cohesion. A significant disadvantage of the binder is the reduction in electronic conductivity, which noticeably reduces the catalytic efficiency of active sites. A further disadvantage of the binder is the blocking of active sites.

[0018] For the purposes of the invention, a three-dimensionally structured substrate is preferably designed in such a way that it assumes a spatial structure, i.e., an extension in every spatial direction. This sequence of terms preferably refers to a three-dimensional, i.e., spatial, arrangement of structural elements within (or on the surface) of a substrate. The geometry of a three-dimensional structuring advantageously aims to enable an increased surface area per substrate volume. This can be achieved, for example, by regular pores, elevations, depressions, and openings in a three-dimensional substrate. An increased surface area advantageously leads to improved interaction between the substrate and its surrounding medium.

[0019] The three-dimensionally structured metal substrate is preferably cleaned or pretreated in a step prior to the process. In particular, such pretreatment can be accomplished by etching. This leads to improved adhesion of the subsequently applied mesoporous catalyst layer, as unwanted oxides and dirt are advantageously removed. It is understood that the pretreatment can also be performed using other methods for removing oxides and dirt.

[0020] The combination of the present process steps leads to a surprising synergistic effect, which results in the advantageous properties and the associated overall success of the invention, with the individual features interacting with each other. Another important advantage of the process according to the invention is the extremely rapid, reproducible, and economical synthesis procedure.

[0021] The use of a three-dimensionally structured metal substrate was far from conceivable for a person skilled in the art. Due to the thermal treatment involved in the synthesis process, it was expected that the three-dimensionally structured metal substrate would suffer from distortion. Furthermore, it was expected that thermal treatment of the three-dimensional metal substrate would lead to detrimental residual stresses and, under certain circumstances, cracks within the material. Lattice structures, nets, etc., in particular, have thin meshes that cannot withstand high temperatures.

[0022] Therefore, it was surprising to the inventors that the influence of the applied suspension largely prevented such material behavior. It was not expected that the applied suspension / catalyst precursor, in addition to the advantageous properties as a highly active catalyst in electrochemical cells (obtained later after thermal treatment), would also have a protective effect on the electrode in connection with thermal treatment.

[0023] It has also been shown to be advantageous that the suspension is present homogeneously and evenly on all geometric shapes (extensions, undercuts, curves, elevations, etc.) of the structured three-dimensional substrate after application, preferably by dip coating. Particularly compared to a substrate with a consistently planar surface, the three-dimensionally structured substrate leads to improved adhesion of the suspension.

[0024] Surprisingly, the occurrence of so-called edge effects was not particularly pronounced during dip coating. Although edge effects are known to lead to thicker film segments, coatings with a homogeneous layer thickness can be achieved by selecting the correct composition.

[0025] In further preferred embodiments, a solution comprising a template, a metal precursor and a solvent can also be prepared in step b).

[0026] In further preferred embodiments, multiple templates, metal precursors, and / or solvents can also be used. Furthermore, the template is preferably a pore template.

[0027] The preferred film may be selected from a group comprising a solution film (film through a solution) or a suspension film (film through a suspension).

[0028] It is also preferred that several mesoporous catalyst layers are formed in step e).

[0029] It has proven advantageous that mesoporous coatings produced via dip coating adhere particularly well to the substrate. Adhesion tests using a tape test showed that the coating material is difficult to remove from the substrate. In comparison, for example, sprayed substrates that were thermally treated under the same conditions show significantly poorer adhesion. This can be explained by the uniform film morphology. Multilayer coatings also showed good adhesion. A further advantage is the ability of mesoporous coatings to be easily applied in multiple layers. This allows, for example, a desired geometric metal loading to be specifically adjusted over a wide range during dip coating. The mesoporous morphology helps achieve a high geometric loading, as the porous structure can better compensate for stresses within the layer.During calcination / removal of the template, the film shrinks along the surface normal (creating ellipsoidal pores), compensating for stresses within the layer that could lead to detachment. Surprisingly, the preferential use of a template made it possible to produce multilayer mesoporous catalyst layers, which allowed for particularly efficient electrolysis.

[0030] In particular, the use of a metal substrate is advantageous for adopting a geometrically structured three-dimensional shape, while the substrate still exhibits sufficiently high rigidity due to the material (metal). This enables a stable design of a substrate that can withstand tensile and compressive loads and is therefore particularly suitable for installation in a full-cell scale without damage. Furthermore, metal is very easy to process, so any geometric shape can be achieved with the metal substrate.

[0031] In a preferred embodiment, the metal substrate comprises a metal selected from the group consisting of nickel, silver, titanium, iron, manganese, cobalt, gold, iridium, copper, platinum, palladium, osmium, rhodium, ruthenium, aluminum, tungsten, tin, zinc, lead, germanium, silicon, and their alloys. The aforementioned materials are advantageous because they generally exhibit good electrical conductivity, but also good chemical stability with respect to the surrounding medium, particularly when used in electrolytic cells or galvanic cells. It is understood that the metal substrate also comprises combinations of the aforementioned materials.

[0032] In a preferred embodiment, the process is characterized by producing mesoporous catalyst layers on three-dimensionally structured Ti substrates with different geometries. Ti substrates are particularly suitable because they have a naturally thin oxide layer on their surface. If these substrates are coated, oxygen functions present on the substrate surface can form covalent and / or ionic bonds with the catalyst layer during the thermal treatment, resulting in strong mechanical adhesion.

[0033] In a preferred embodiment, the metal substrate also comprises other electrically conductive materials selected from the group comprising glassy carbon, boron-doped diamond, carbides, nitrides, and oxides. These are preferably present in smaller amounts in the metal substrate, with smaller amounts describing a range of preferably small volume percentages of the total substrate. In further preferred embodiments, the metal substrate essentially completely comprises one or more of the aforementioned electrically conductive materials.

[0034] The synthesized mesoporous catalyst layer is preferably nanostructured. Nanostructuring is preferably understood as the structuring of a solid at the atomic level. Targeted modification (implantation) alters atomic, chemical, etc., properties of the solid, usually near the surface.

[0035] A nanostructured mesoporous catalyst layer is preferably understood as an ordered nanostructure of the mesoporous catalyst layer. This means that a catalyst layer comprises approximately identical structural elements in a repetitive (periodic) manner (e.g., arranged in a row). Surprisingly, it has been shown that the formation of an ordered mesostructure is not disrupted by the geometric configuration (e.g., curvature, depression) of the substrate surface.

[0036] Furthermore, one or more metal salts are preferably dispersed as a catalyst precursor together with one or more templates in one or more suitable solvents, and this mixture is transferred to the three-dimensional metal substrate. The subsequent evaporation of the solvent leads to a favorable periodic arrangement of the template surrounded by a catalyst precursor. Subsequent thermal treatment at preferred temperatures between 300°C and 800°C combusts the template and converts the precursor into the actual catalyst, preferably a metal oxide. The removal of the template creates interconnected pores that particularly advantageously provide a high surface area for catalytic processes.

[0037] The preferred synthesis approach is based on templates that serve as placeholders for a desired pore structure. During synthesis, the template is enclosed by the surrounding material (catalyst precursor) and, upon removal, leaves behind a defined porous material. Depending on the template size, pore structures with pore sizes ranging from a few micrometers to a few nanometers are created. Materials with an ordered pore structure and a monomodal pore size distribution can therefore preferably be synthesized using so-called templating processes. In this synthesis approach, templates serve as placeholders for the desired pore shape. By using a template, a particularly advantageous pore morphology of the catalyst layer could be provided. In particular, the catalyst layer could be designed as mesoporous, which made it possible to achieve particularly high mechanical stability.Furthermore, the use of the template was advantageous in that it enabled a specifically adjustable, reproducible pore distribution with a particularly high specific surface area of ​​the catalyst layer. This reproducibility represents a particularly significant advantage, especially with regard to technical applications.

[0038] In further preferred embodiments, the template preferably comprises surfactants, block copolymers, and / or dendritic core-shell polymers. The template leads to advantageous mesoporous structures within the catalyst layer, whereby the template can form micelles or also have other structures. In further alternatives, the template can also comprise a non-micelle-forming core-shell macromolecule, effectively a unimolecular micelle. Furthermore, block copolymers can also adopt lamellar structures.

[0039] In a preferred embodiment, templates are designed as soft templates. Soft templates are deformable structure-directing units. These can be micelles or lamellar structures made of amphiphilic polymers (often block copolymers). Typically, the micelles or lamellae form above a critical concentration of a polymer dispersed in a solvent. Soft templates also include dendritic or hyperbranched core-shell polymers, where the core and shell of the polymers exhibit different hydrophilicities and are thus also amphiphilic.

[0040] In another preferred embodiment, templates are designed as hard templates. Hard templates are rigid, structure-directing units. Nanostructured hard templates include metals, oxides, often silicon oxides (e.g., MCM group, SBA group, FDU group, KIT group, MSU group, TUD group, HMM group, FSM group), and carbons (e.g., CMK group). These hard templates can be individual nanoparticles or larger nanostructured structures.

[0041] In a preferred variant, the preferred drying process step can also be designed so that drying takes place in a very short time. For example, in a time range from the application of the suspension or solution to the metal substrate to the thermal treatment. In practice, this time range can occur, for example, as follows: removing the three-dimensional metal substrate from a container containing the solution or suspension and placing it directly in an oven for thermal treatment. Carrying out the drying process in this way leads to a particularly rapid synthesis of the catalyst layer on the dimensionally structured metal substrate.

[0042] In a further preferred embodiment of the drying process step, the time range from application of the suspension or solution to the metal substrate up to the thermal treatment can proceed as follows: withdrawal of the three-dimensional metal substrate from a container comprising the solution or suspension, drying in air (e.g. for about 5 minutes), then a thermal treatment in order to advantageously remove remaining solvent essentially completely and / or to stabilize the coating.

[0043] In a further preferred embodiment, the process is characterized in that the solution or suspension from step (c) is applied by dip coating. It was not obvious to the person skilled in the art that a three-dimensionally structured metal substrate could be provided with a homogeneous catalyst layer having a templated pore structure by dip coating. A templated pore structure preferably means the obtaining of a pore structure (structure comprising pores) using a template. A further advantage of dip coating is that, in particular, undercuts of a three-dimensionally structured metal substrate can also be coated in a simple manner.

[0044] Dip coating offers further advantages. For example, several three-dimensionally structured metal substrates can be coated simultaneously, enabling particularly cost-effective production. Furthermore, dip coating advantageously has a very short process time, as a brief immersion in the solution or suspension is already sufficient to obtain a preferred catalyst layer. Furthermore, dip coating is very resource-efficient, as there is no waste of material (the solution or suspension is in one container). Furthermore, it may be preferable for dip coating to be carried out by placing the substrate in a container, and then transporting the solution in and out of it.

[0045] In a preferred embodiment, the method is characterized in that the three-dimensionally structured metal substrate is designed as a net, foam, grid, sieve, fabric and / or mesh.

[0046] Particularly preferably, the three-dimensionally structured metal substrate is designed in the form of a mesh or grid. The preferred and particularly preferred embodiments as a mesh or grid are advantageous because such embodiments can be easily obtained from the materials described above. Furthermore, such configurations advantageously allow the metal substrates to be deformed in a simple manner.

[0047] In a preferred embodiment, the process is characterized in that the temperature T 2 is in a range between 200°C and 1000°C, preferably between 300°C and 800°C, and the calcination time t 2 is in a range between 1 minute and 1440 minutes, in particular between 10 minutes and 120 minutes, preferably between 10 minutes and 60 minutes. Especially within the described parameters, the template can advantageously burn completely, thus obtaining a nanostructured mesoporous catalyst layer.

[0048] In a further preferred embodiment, the template can also be dissolved / flushed out of the catalyst precursor using a suitable medium. It is understood that a combination of heat treatment and dissolving the templates via a medium can also be carried out sequentially. If templates are dissolved via a medium—without combustion—these template structures can preferably be further processed and / or reused.

[0049] To thermally decompose the template and convert the inorganic species into a crystalline metal oxide, the catalyst precursor is preferentially calcined.

[0050] Calcination leads to a drastic volume loss of the layer, caused by the conversion of the precursor to oxide, the combustion of the template, and the transformation of the amorphous pore wall into a crystalline material. Since the adhesion of the layer to the substrate is comparatively strong, partly due to covalent bonds between the substrate surface and the metal oxide species, the layer contracts exclusively perpendicular to the substrate without cracking.

[0051] All parameter ranges disclosed in this document, such as temperatures, forces, pressures, distances, etc., naturally include all values ​​within the specified ranges, as well as their maximum and minimum limits. It will be apparent to a person skilled in the art that these values ​​are also subject to certain fluctuations. In the present case, this involves a temperature range of approximately 200°C to 1000°C, and preferably approximately 300°C to 800°C, and a calcination time of preferably approximately 1 minute to 1440 minutes, in particular approximately 10 to 120 minutes. This can also be applied analogously to all other parameter ranges in the document.

[0052] Terms such as "substantially," "approximately," "about," "approximately," etc., preferably describe a tolerance range of less than ± 40%, preferably less than ± 20%, more preferably less than ± 10%, even more preferably less than ± 5%, and especially less than ± 1%, and always include the exact value. "Similar" preferably describes quantities that are "approximately equal." "Partially" preferably describes at least 5%, more preferably at least 10%, and especially at least 20%, in some cases at least 40%.

[0053] In a preferred embodiment, the thermal treatment takes place in heating systems. For example, a tube furnace in an air stream or a muffle furnace can be used to remove the template. Such furnaces exhibit a uniform temperature distribution, thus advantageously ensuring the repeatability of the process. Furthermore, the waste heat from the furnaces can be advantageously used for further process steps (e.g., drying), thereby saving energy.

[0054] In a further preferred embodiment, the thermal treatment can also be carried out using further methods instead of heating in a furnace. The substrate comprising catalyst precursors is preferably thermally treated using rapid thermal annealing (RTA) with the waste heat from a halogen lamp. Furthermore, the substrate comprising catalyst precursors is preferably heated using flash lamp annealing. This advantageously leads to rapid heating and exclusive heating of the surface. Furthermore, the laser annealing method is also preferred. This method leads to even faster heating of the substrate comprising catalyst precursors, achieving a very shallow penetration depth and heating only the surface. Heating a suitable substrate using an induction furnace would also be possible. This also leads to very rapid heating.It may also be preferable to heat using an infrared heater.

[0055] In a preferred embodiment, the process is characterized in that the temperature T 1 is in a range between 18°C ​​and 250°C. The drying of the layer on the three-dimensional metal substrate can take place in a temperature range from room temperature to 80°C. This advantageously requires very little energy. Furthermore, at such temperatures, the waste heat from the heating systems is sufficient as drying energy to achieve rapid drying of the suspension film. This also leads to significant economic savings in the process.

[0056] In a preferred embodiment, the process is characterized in that the suspension comprises one or more amphiphilic block copolymers.

[0057] For the templating of ordered mesoporous catalyst layers, amphiphilic block copolymers containing a hydrophilic polyethylene oxide block (PEO) are preferably used

[0058] Preferred templates for the synthesis of ordered mesoporous solids are amphiphilic molecules. These advantageously form micelles through self-assembly and self-assemble into liquid-crystalline phases. These liquid crystals, with a nanostructure typically ranging from 2 nm to 50 nm, serve preferentially as endotems in the synthesis of mesoporous oxides.

[0059] In a further preferred embodiment, the three-dimensionally structured metal substrate comprising catalyst precursors is thermally treated in an inert atmosphere. Block copolymer substrates decompose even in inert atmospheres at temperatures above 300°C.

[0060] In a preferred embodiment, the process is characterized in that the amphiphilic block copolymer is selected from the group consisting of AB block copolymers (polyethylene oxide-block-polystyrene (PEO-PS), polyethylene oxide-block-polymethyl methacrylate (PEO-PMMA), poly-2-vinylpyridine-block-polyallyl methacrylate (P2VP-PAMA), polybutadiene-block-polyethylene oxide (PB-PEO), polyisoprene-block-polydimethylaminoethyl methacrylate (PI-PDMAEMA), polybutadiene-block-polydimethylaminoethyl methacrylate (PB-PDMAEMA), polyethylene-block-polyethylene oxide (PE-PEO), polyisobutylene-block-polyethylene oxide (PIB-PEO) and poly(ethylene-co-butylene)-block-poly(ethylene oxide) (PEB-PEO), polystyrene-block-poly(4-vinylpyridine) (PS-P4VP)Polyethylenoxid-block-polyglycolid (PEO-PLGA), Polyethylenoxid-block-polycaprolacton (PEO-PCL), Polyethylen-block-polyethylenglycol (PE-PEO), Polystyrol-block-polymethylmethacrlyt (PS-PMMA), Polystyrol-block-polyacrylsäure (PS-PAA), polypyrrol-block-polycaprolacton (PPy-PCL), Polysilicon-block-polyetylenoxid (PDMS-PEO), ABA-Block Copolymeren (Polyethylenoxid-block-polybutadien-block-polyethylenoxid (PEO-PB-PEO), Polyethylenoxid-block-polypropylenoxid-block-polyethylenoxid (PEO-PPO-PEO), Polypropylenoxid-block-polyethylenoxid-block-polypropylenoxid (PPO-PEO-PPO), Polyethylenoxid-block-polyisobutylen-block-polyethylenoxid (PEO-PIB-PEO), Polyethylenoxid-block-polybutadien-block-polyethylenoxid (PEO-PB-PEO)), Polylactid-block-polyethylenoxid-block-polylactidd (PLA-PEO-PLA), Polyglycolid-block-polyethylenoxid-block-polyglycolid (PGLA-PEO-PGLA), Polylactid-cocaprolacton-block-polyethylenoxid-block-polylactid-co-caprolacton (PLCL-PEO-PLCL),Polycaprolactone-block-polytetrahydrofuran-block-polycaprolactone (PCL-PTHF-PCL), Polypropylene oxide-block-polyethylene oxide-block-polypropylene oxide (PPG-PEO-PPG), Polystyrene-block-polybutadiene-block-polystyrene (PS-PB-PS), Polystyrene-block-polyethylene-ran-butylene-block-polystyrene (PS-PEB-PS), polystyrene block-polyisoprene-block-polystyrene (PS-PI-PS), ABC block copolymers (polyisoprene-block-polystyrene-block-polyethylene oxide (PI-PS-PEO), polystyrene-block-polyvinylpyrrolidone-block-polyethylene oxide (PS-PVP-PEO), Polystyrene block-poly-2-venylpyridine block-polyethylene oxide (PS-P2VP-PEO), Polystyrene-block-poly-2-vinylpyridine-block-polyethylene oxide (PS-P2VP-PEO), polystyrene-block-polyacrylic acid-polyethylene oxide (PS-PAA-PEO)), polyethylene oxide-block-polylactide-block-decane (PEO-PLA-decane), as well as other amphiphilic polymers (polyethylene oxide alkyl ethers (PEO-C xx ), e.g. Brij35, Brij56, Brij58) or mixtures thereof, preferably PEO-PB, PEO-PPO, PEO-PB-PEO, PEO-PPO-PEO.

[0061] In a preferred embodiment, the process is characterized in that a metal salt or several metal salts of different metals, or their hydrates, are used as the metal precursor.

[0062] In further preferred embodiments, metal nanoparticles can also be used as metal precursors, which can be deposited as a layer using mesoporous templates using polymer templates. Metal nanoparticles can advantageously be obtained as industrial waste products and thus reused in a recycling process.

[0063] In a preferred embodiment, the process is characterized in that the metal salts are selected from the group consisting of metal nitrate, metal halide, metal sulfate, metal acetate, metal citrate, metal alkoxide or mixtures thereof.

[0064] In alternative embodiments, other salts can also be used provided they are soluble in the suitable solvent, if necessary with the addition of further complexing substances.

[0065] In a preferred embodiment, the process is characterized in that the metals contained in the metal precursor are selected from the group consisting of alkali metals, preferably lithium, sodium, potassium, rubidium, cesium, alkaline earth metals, preferably magnesium, calcium, strontium, barium, metals of the third main group of the periodic table, preferably boron, aluminum, indium, gallium, thallium, metals of the fourth main group of the periodic table, preferably tin, silicon, germanium, lead, metals of the fifth main group of the periodic table, preferably bismuth, and transition metals, preferably iridium, ruthenium, cobalt, zinc, copper, manganese, cadmium, vanadium, yttrium, zirconium, scandium, titanium.

[0066] In a preferred embodiment, the process is characterized by using ruthenium and / or iridium and / or titanium as metal precursors. In particular, the combination of the metals results in a catalyst layer with high integrity and stability. Ruthenium- and iridium-based layers demonstrate high activity in the oxygen evolution and chlorine evolution applications. The presence of titanium oxide in the layer also improves stability and adhesion to the titanium substrate.

[0067] In a preferred embodiment, the process is characterized in that mesoporous Ru- and Ir-containing catalyst layers are synthesized on three-dimensionally structured Ti substrates with different geometries.

[0068] In a preferred embodiment, the process is characterized in that water or a C1-C4 alcohol, C2-C4 ester, C2-C4 ether, formamide, acetonitrile, acetone, tetrahydrofuran, benzyl, toluene, dimethyl sulfoxide, dichloromethane, chloroform or mixtures thereof are used as solvent, preferably methanol, ethanol, formamide and / or tetrahydrofuran.

[0069] The advantages and preferred embodiments of the method according to the invention are to be transferred analogously to the electrode according to the invention, as well as the electrochemical cells according to the invention and vice versa.

[0070] In a preferred embodiment, the invention relates to an electrode for an electrochemical cell, preferably produced by the above-mentioned method, characterized in that the electrode is a three-dimensionally structured metal substrate and comprises a nanostructured mesoporous catalyst layer.

[0071] In electrochemical cells, it is common practice—especially in full-cell water splitting—for catalysts in the form of dispersed powders to be sprayed onto a Nafion membrane together with a binder and then incorporated into the electrochemical cells, preferably the electrolyzer. Therefore, extensive (inventive) considerations were required, which led to the incorporation of a three-dimensionally structured electrode with a nanostructured mesoporous catalyst layer into an electrochemical cell instead of catalyst powders.

[0072] An electrode comprising a nanostructured mesoporous catalyst layer offers significant advantages. For example, the higher mass activity of the species in a mesoporous catalyst layer has been demonstrated (see also Fig. 4 ).

[0073] Such an electrode is also advantageous because, due to its porous or open-pore design, it has a particularly large specific surface area per component volume and, in addition, has a high mechanical stability, which stabilizes the entire electrochemical cell.

[0074] A nanostructured mesoporous catalyst layer, in particular, offers significant advantages. It has been shown that mesoporous catalyst layers templated on a half-cell scale exhibit a significantly higher mass activity of the electrochemically active species than comparable conventional catalyst layers produced, for example, using an ink-based method. The preferred mesoporous configuration of the catalyst layer could advantageously be achieved by thermal treatment of the catalyst precursors using a template, preferably a soft template.

[0075] In a further preferred embodiment, the electrode is characterized in that the three-dimensionally structured metal substrate is designed as a net, foam, grid, fabric and / or mesh.

[0076] In a further preferred embodiment, the invention relates to an electrochemical cell comprising a binder-free catalyst.

[0077] In a preferred embodiment, the electrochemical cell comprises an electrode of the type mentioned above. A particular advantage of the electrode according to the invention is the presence of a binder-free catalyst with a substantially homogeneous pore structure. This leads to optimal mass transfer of reactants and products and, accordingly, to higher catalytic activity.

[0078] Preferably, an electrochemical cell is selected from the group comprising: battery, accumulator, fuel cell, electrolyzer.

[0079] The use of an electrode according to the invention is furthermore preferably possible in connection with electrolysis for the production of chlorine.

[0080] Furthermore, three-dimensionally structured substrates can be used in medical technology, whereby it is essential for such substrates to withstand the elevated temperatures of thermal treatment. Mesoporous materials can be used as drug carriers. Macromolecules are stored in the porous system and can be distributed over a longer period of time and released as an active ingredient to a suitable location. The ability to adjust the porosity and the material is an important advantage here. FIGURES

[0081] In the following, the invention will be explained in more detail with reference to figures, without being limited to these. Short description of the figures

[0082] Fig. 1Schematic flow diagram of a preferred process for producing a catalyst-coated three-dimensionally structured electrode Fig. 2 SEM image comparing titanium meshes before (A) and after (B) coating with mesoporous iridium oxide layers Fig. 3 Schematic flow diagram of a preferred process for producing a catalyst-coated three-dimensionally structured electrode in comparison with a prior art process Fig. 4 Diagram showing the electrocatalytic activity as a cyclic voltametric (CV) measurement of two catalyst systems in a water electrolyzer Fig. 5 Diagram showing increased catalytic activity of an electrode network with a mesoporous templated catalyst layer in chlorine production Detailed description of the illustrations

[0083] Fig. 1schematically illustrates the sequence of a preferred method for producing a catalyst-coated, three-dimensionally structured electrode. The method preferably comprises a template-assisted dip-coating process. In particular, a solution is generated in a first process step. The solution comprises precursors, solvents, and a template. A metal salt—e.g., Ru(OAc)3 or Ir(OAc)3—is very preferably used as the precursor. A micelle-forming block copolymer is preferably used as the template. After the solution has been prepared, a three-dimensionally structured electrode is immersed in the solution so that a film can form on the surface when the electrode is withdrawn. The solvent preferably evaporates at room temperature, so that the electrode has a catalyst precursor with integrated micelles on its surface after just a short time.Starting from the self-assembly of the micelles, an ordered nanostructure forms on the surface of the three-dimensionally structured electrode. In a final thermal treatment, the catalyst precursor is converted into a catalyst layer. The thermal treatment leads to combustion of the micelle-forming template, resulting in the formation of a nanostructured mesoporous catalyst layer. The SEM image shows a top view of a mesoporously templated RuIrTiO x layer calcined at 450 °C on a titanium mesh.

[0084] Fig. 2This image shows SEM images of titanium meshes, which can be used preferentially as gas diffusion layers. In particular, the image shows a titanium mesh before (A) and after (B) coating with mesoporous iridium oxide layers. The images above show the meshes at 50x magnification. The images below, however, show the meshes at 100,000x magnification. The coating was calcined in air at 400 °C.

[0085] Fig. 3shows a schematic flow diagram of a preferred method for producing a catalyst-coated, three-dimensionally structured electrode in comparison with a prior art method. In the prior art, an ink is produced. A dispersion comprising preferably isopropanol (i<PrOH), Nafion, water, and a catalyst powder are mixed using ultrasound to form an ink. A substrate, such as a Nafion membrane, is then coated with the ink. The substrate is preferably coated by spraying. In a final step, the membrane is introduced into the full-cell scale.

[0086] The process according to the invention, however, preferably uses dip coating. First, a suspension is generated, which comprises, for example, ethanol, a micelle-forming template, and a noble metal salt, namely Ir(OAc) 3 . Subsequently, a three-dimensional substrate is immersed in a container containing the described suspension. Removing the three-dimensional substrate from the suspension results in a layer of a catalyst precursor being deposited on the substrate. A catalyst layer is subsequently formed by thermal treatment, and in a final process step, the three-dimensional substrate is introduced into a full-cell scale.

[0087] Fig. 4shows the electrocatalytic activity of a CCG (catalyst-coated gas diffusion layer) coated with a mesoporous iridium oxide as the anode in contact with a membrane. The membrane is coated on the cathode side with a common Pt / C catalyst (single-sided coated CCM). The setup is compared with a commercially available CCM (catalyst-coated membrane) with the same Pt / C catalyst on the cathode side and a binder-containing Ir layer (double-sided coated CCM) as the reference system. The CCG system achieves a geometric current density approximately twice that of the binder-containing commercial reference.

[0088] The Fig. 5The illustrated dot plot shows increased catalytic activity of three-dimensionally structured electrodes with mesoporous templated catalyst layers in chlorine production. For comparison, a reference catalyst was used, in which a three-dimensionally structured electrode was coated using a conventional synthesis method and therefore does not contain a templated mesoporous catalyst layer.

[0089] The following boundary conditions were used for the comparison: 80°C; NaCl (300 g / l) at the anode; NaOH (400 g / l) at the cathode; chronopotentiometric measurements at 350 mA / cm 2 < ; cathode: commercial catalyst on Ni mesh; membrane: N982WX; anode: catalyst coating on Ti mesh

Claims

1. A method for producing a catalyst-coated three-dimensionally structured electrode comprising the following steps: a) Providing a three-dimensionally structured metal substrate; b) producing a suspension comprising a template, a metal precursor and a solvent; c) applying the suspension to the three-dimensionally structured metal substrate, so that a suspension film forms on the three-dimensionally structured metal substrate; d) drying of the suspension film on the three-dimensionally structured metal substrate at a temperature T1 in a range between 18° C to 250° C, so that the solvent within the suspension film evaporates and a layer of a catalyst pre-stage with integrated template structures is obtained; e) thermal treatment of the three-dimensionally structured metal substrate, comprising catalyst pre-stages, at a second temperature T2 in a range between 200° C and 1000° C and a calcinating time t2 in a range between 1 minute and 1440 minutes, so that a mesoporous catalyst coating forms.

2. The method according to claim 1 characterized in that an immersion coating technique is used to apply the suspension from step c).

3. The method according to one or several of the preceding claims characterized in that the three-dimensionally structured metal substrate is embodied as a net, foam, grid, strainer, fabric and / or mesh.

4. The method according to one or several of the preceding claims characterized in that the temperature T2 is in a range between 300° C and 800° C and that the calcinating time t2 is in a range between 10 and 120 minutes.

5. The method according to one or several of the preceding claims characterized in that the suspension comprises one or several amphiphile block copolymers.

6. The method according to claim 5 characterized in that the amphiphile block copolymer is selected from the group consisting of: AB block copolymers (poly ethylene oxide block polystyrene (PEO-PS); poly ethylene oxide block polymethyl methacrylate (PEO-PMMA); poly-2-vinyl pyridine block poly allyl methacrylate ((P2VP-PAMA); poly butadiene block polyethylene oxide ((PB-PEO); poly isoprene block poly dimethyl amine ethyl methacrylate ((Pl-PDMAEMA); poly butadiene block poly dimethyl aminoethyl methacrylate (PB-PDMAEMA); poly ethylene block poly ethylene oxide ((PE-PEO); polyisobutylene block polyethylene oxide (PIB-PEO) and poly (ethylene-co-butylene) block poly (ethylene oxide) (PEB-PEO); poly styrene block poly (4 vinyl pyridine (PS-P4VP); poly isoprene block poly ethylene oxide (PI-PEO); poly dimethoxy aniline block poly styrene (PDMA-PS); polyethylene oxide block poly-n-utyl acrylate (PEO-PBA); poly butadiene-block-poly (2 vinyl pyridine (PB-P2VP)); poly ethylene oxide-block-polyactide (PEO-PLA); polyethylene oxide block polyglycolide (PEO-PLGA); polyethylene oxide block polycaprolactone (PEO-PCL); polyethylene block polyethylene glycol (PE-PEO); polystyrene block poly methyl methacrylate (PS-PMMA); polystyrene block poly acrylic acid (PS-PAA); polypyrrole block polycaprolactone (PPy-PCL); polysilicon block poly ethylene oxide (PDMS-PEO) ABA block copolymers (polyethylene oxide block poly butadiene block polyethylene oxide (PEO-PB-PEO); polyethylene oxide block poly propylene oxide block polyethylene oxide (PEO-PPO-PEO); polypropylene oxide block polyethylene oxide block polypropylene oxide (PPO-PEO-PPO); polyethylene oxide block poly isobutylene block polyethylene oxide (PEO-PIB-PEO); polyethylene oxide block polybutadiene block polyethylene oxide (PEO-PB-PEO)); polyactide block polyethylene oxide block polyactide (PLA-PEO-PLA); polyglycolide block polyethylene oxide block polyglycolide (PGLA-PEO-PGLA); polyactde-co-caprolactone block polyethylene oxide block polyactide-co-caprolactone (PLCL-PEO-PLCL); polycaprolactone block polytetrahydrofuran block polycaprolactone (PCL-PTHF-PCL); polypropylene oxide block polyethylene oxide block polypropylene oxide (PPG-PEO-PPG); polystyrene block polybutadiene block polystyrene (PS-PB-PS); polystyrene block polyethylene-ran-butylene block polystyrene (PS-PEB-PS); polystyrene block polyisoprene block polystyrene (PS-PI-PS); ABC block copolymers (polyisoprene block polyethylene oxide (PI-PS-PEO); polystyrene block polyvinyl pyrrolidone block polyethylene oxide (PS-PVP-PEO); polystyrene block poly-2-venylpiridine block polyethylene oxide (PS-P2VP-PEO); polystyrene block poly-2-venylpiridine block polyethylene oxide (PS-P2VP-PEO); polystyrene block poly acrylic acid polyethylene oxide (PS-PAA-PEO)); polyethylene oxide block polyactide block decane (PEO-PLA-decane); as well as other amphiphilic polymers (polyethylene oxide alkyl ether (PEO-Cxx), for example Brij35, Brij56, Brij58) or mixtures thereof, preferably PEO-PB, PEO-PPO, PEO-PB-PEO, PEO-PPO-PEO.

7. The method according to one or several of the preceding claims characterized in that a metal salt or several metal salts of respectively different metals, or their hydrates, are used for the metal precursor.

8. The method according to claim 7 characterized in that the metal salts are selected from the group consisting of metal nitrate, metal halogenide, metal sulfate, metal acetate, metal citrate, metal alkoxide or mixtures thereof.

9. The method according to one or several of the preceding claims, characterized in that the metals contained in the metal precursor are selected from the group consisting of alkali metals, preferably lithium, sodium, potassium, rubidium, cesium; alkaline earth metals, preferably magnesium, calcium, strontium, barium; metals of the third main group in the periodic system, preferably boron, aluminum, indium, gallium, thallium; metals of the fourth main group in the periodic system, preferably tin, silicon, germanium, lead; metals from the fifth main group of the periodic system, preferably bismuth; and transition metals, preferably iridium, ruthenium, cobalt, zinc, copper, manganese, cadmium, vanadium, yttrium, zirconium, scandium and titanium.

10. The method according to one or several of the preceding claims characterized in that the solvent used is water or a C1-C4 alcohol, C2-C4 ester, C2-C4 ether, formamide, acetone nitril, acetone, tetrahydrofuran, benzyl, toluene, dimethyl sulfoxide, dichloromethane, chloroform, or mixtures thereof, preferably methanol, ethanol, formamide and / or tetrahydrofuran.

11. An electrode for an electrochemical cell produced with a method according to one or several of the preceding claims, characterized in that the electrode is a three-dimensionally structured metal substrate and comprises a nano-structured mesoporous catalyst coating.

12. The electrode according to claim 11 characterized in that the three-dimensionally structured metal substrate is embodied in the form of a net, foam, grid, fabric and / or mesh.

13. An electrochemical cell with an electrode according to the claims 11 and / or 12.