TUNING OF FORMULATIONS BASED ON ANION-CONDUCTING POLYMERS (IONOMERS) FOR THE PRODUCTION OF ELECTROCHEMICALLY ACTIVE COATINGS

Description

[0001] The invention relates to a dispersion intended for the production of an electrochemically active laminated body. Furthermore, it relates to the production of an electrochemically active laminated body, within the scope of which the inventive dispersion is provided. Furthermore, it relates to an electrochemically active laminated body, which is obtained in particular by the production method, and to an electrochemical cell containing at least one such laminated body. Furthermore, the invention relates to a process for producing hydrogen and oxygen by splitting water, in which the electrochemical cell is used.

[0002] Electrochemical cells are technical devices in which electrochemical processes are carried out. They typically consist of an anode, a cathode, and a separator arranged between the anode and cathode, which divides the electrochemical cell into two compartments. Examples of electrochemical cells include batteries, fuel cells, and electrolysis cells. Electrolysis occurs in electrolysis cells, i.e., the breaking or forming of chemical bonds using electrical energy.

[0003] One important form of electrolysis is water electrolysis, in which water is split into oxygen and hydrogen. The separator in a water electrolysis cell can be designed as an ion-conducting membrane. A distinction is made between anion-conducting membranes (anion exchange membranes - AEM) and proton-conducting membranes (proton exchange membranes - PEM). Water splitting using anion-conducting membranes is often abbreviated to AEM-WE (anion exchange membrane water electrolysis) or also called alkaline membrane water electrolysis. The well-known alkaline water electrolysis with a porous diaphragm is not an AEM-WE in the modern sense because the diaphragm is fluid-conducting. The membrane of an AEM-WE, however, is fluid-tight. Anion conduction occurs at the ion level.

[0004] An excellent overview of the design and materials of the electrochemical cells currently used in AEM-WE is provided by: Miller, Hamish Andrew et al.: Green hydrogen from anion exchange membrane water electrolysis: a review of recent developments in critical materials and operating conditions. Sustainable Energy Fuels, 2020, 4, 2114 DOI: 10.1039 / c9se01240k

[0005] In electrochemical processes, material conversions occur on the surface of electrocatalysts. To create a high catalytically active surface and to enable mass transport, electrocatalysts are used in porous, electrically conductive layers. The layers are applied to other components of the electrochemical cell or used as a separate component. Generally, these are referred to as electrochemically active layered bodies, regardless of whether the layered body fulfills other functions within the cell besides catalysis.

[0006] In the field of water electrolysis cells, it is common practice to coat membranes with electrocatalytically active material, resulting in a "catalyst coated membrane" (CCM); see Miller et al., Section 5.2. Such a CCM is a first example of an electrochemically active laminate.

[0007] Another example of an electrochemically active composite body can be an electrode in which an electrically conductive substrate is coated with electrocatalytically active material, thus obtaining a "catalyst coated substrate" (CCS); see Miller et al., Section 5.1. Such a CCS is a second example of an electrochemically active composite body.

[0008] The morphology of an electrochemically active composite is determined by the catalyst particles and their arrangement within the composite. Polymeric binders are suitable for the permanent mechanical adhesion of the catalyst particles to each other and to a support material – especially those that enable ion transport in accordance with the electrochemical reaction (ion-conductive polymers, often referred to as "ionomers").

[0009] The efficiency and lifetime of electrochemically active composites are determined primarily by the selection and coordination of the individual components and their processing. The production of suitable catalyst-ionomer formulations is crucial in this regard.

[0010] Several catalyst-ionomer formulations and associated processes for the production of electrochemically active composites are already known in the scientific literature: For example, Chen et al. describe the production of CCMs for fuel cells based on the ionomer poly(fluorenyl aryl piperidinium): Chen, N., Wang, HH, Kim, SP et al. Poly(fluorenyl aryl piperidinium) membranes and ionomers for anion exchange membrane fuel cells. Nat Commun 12, 2367 (2021). DOI 10.1038 / s4 1467-021-226 12-3

[0011] Park et al. coated an anion-conductive membrane from Fumatech (FUMATECH BWT GmbH, Bietigheim-Bissingen, Germany) with a mixture of iridium oxide and platinum / carbon to obtain a CCM for a water electrolysis cell: Ji Eun Park, Sun Young Kang, Seung-Hyeon Oh, et al. High-performance anion-exchange membrane water electrolysis, Electrochimica Acta, Volume 295, 2019, Pages 99-106, DOI 10.1016 / j.electacta.2018.10.143

[0012] Park et al. used the polymer FAA-3-Br from Fumatech (FUMATECH BWT GmbH, Bietigheim-Bissingen, Germany) as the ionomer. However, Park et al. did not provide a precise specification of the ionomer FAA-3-Br.

[0013] Leng et al. fabricated catalyst-coated electrodes for an alkaline fuel cell by spraying a Pt-containing ink onto a carbon mat. The ink contained a precursor to a Nafion ionomer. The ionomer was then cross-linked in situ on the carbon mat: Yongjun Leng, Lizhu Wang, Michael A. Hickner, et al., Alkaline membrane fuel cells with in-situ cross-linked ionomers, Electrochimica Acta, Volume 152, 2015, Pages 93–100, DOI 10.1016 / j.electacta.2014.11.055

[0014] Similarly, Faid et al. used a catalyst ink containing dissolved ionomer, catalyst, isopropanol, and water. The catalyst system used was Ni, Ni / C, and Pt / C and Ir: Alaa Y. Faid, et al.: Effect of anion exchange ionomer content on electrode performance in AEM water electrolysis, International Journal of Hydrogen Energy, Volume 45, Issue 53, 2020, Pages 28272-28284, DOI 10.1016 / j.ijhydene.2020.07.202

[0015] The production of electrochemically active laminates is known from US 2021 / 0009726 A1. More specifically, these laminates are MEAs (membrane electrode assemblies) intended for use in fuel cells. During MEA production, an ionomer is dissolved in a water / alcohol mixture, and catalyst particles are dispersed in the solution. The dispersion is applied to a substrate. This procedure requires that the ionomer is soluble in water / alcohol. Electrochemically active laminates intended for use in water electrolysis must not contain water-soluble ionomers, as these would dissolve again during cell operation.

[0016] Pandiarajan T. et al. coated an MEA with a dispersion of catalyst, ionomer, DMSO, 2-propanol, and water. Ce-doped manganese / iron spinel was used as the catalyst. Pandiarajan T., Berchmans LJ, Ravichandran S.: Fabrication of spinel ferrite-based alkaline anion exchange membrane water electrolyzers for hydrogen production. DOI: 10.1039 / c5ra01123j

[0017] WO 2021 / 013694 A1 discloses an anion-conducting polymer with structural formula (I) that can be used for the production of membranes. The production of CCMs, CCSs, and other electrochemically active layered bodies is not disclosed therein.

[0018] The preparation of ionomers with a structural formula (II) is described in European application 21152487.1, which was still unpublished at the time of this application.

[0019] The preparation of ionomers with a structural formula (III) is described in European application 21162711.2, which was still unpublished at the time of this application.

[0020] The invention was based on the object of making anion-conducting polymers usable as ionomers for the production of electrochemically active layered bodies.

[0021] This object is achieved by a dispersion according to claim 1, by a method for producing an electrochemically active layered body according to claim 8, by the electrochemically active layered body according to claims 13 and 15, by the electrochemical cells according to claim 16 and by the method for producing hydrogen and oxygen according to claim 17. Preferred embodiments of the invention are set out in the dependent claims.

[0022] All of these subject matters are based on the unified concept of dissolving an ionomer according to structural formulas (I), (II), and (III), processing it into a dispersion, and using this dispersion to produce catalytically active layered bodies for electrochemical cells. All of the subject matters disclosed here thus form a common inventive complex.

[0023] Investigations have shown that this type of polymer (ionomer), particularly in conjunction with the catalyst-ionomer formulations developed below, can be successfully processed into catalyst layers that are particularly suitable for electrochemical processes involving the transport of anions. This works particularly well in AEM-WE processes. The layered bodies produced from the dispersion described here are therefore particularly suitable for use as CCM or CCS in alkaline water electrolysis.

[0024] The common advantage of the ionomers according to structural formula (I), (II) or (III) is their good ionic conductivity, high chemical and mechanical stability in alkaline environment and low synthesis costs.

[0025] The anion-conducting polymers processed into the dispersion obey the structural formula (I) or (II) or (III).

[0026] The anion-conducting polymer according to structural formula (I) is defined as follows: wherein X represents a structural element comprising a positively charged nitrogen atom which is bonded to C 1< and C 2< and which is bonded via two bonds to one or two hydrocarbon radicals comprising 1 to 12, preferably 1 to 6, particularly preferably 1 or 5 carbon atoms and wherein Z represents a structural element comprising a carbon atom which is bonded to C 3< and C 4< and which comprises at least one aromatic six-membered ring which is bonded directly to one of the oxygen atoms, where the aromatic six-membered rings may be substituted by one or more halogen and / or one or more C 1 - to C 4 -alkyl radicals.

[0027] The anion-conducting polymer according to structural formula (II) is defined as follows: wherein X represents a structural element comprising a positively charged nitrogen atom which is bonded to C 1< and C 2< and which is bonded via two bonds to one or two hydrocarbon radicals comprising 1 to 12, preferably 1 to 6, particularly preferably 1 or 5 carbon atoms, and wherein Z represents a structural element comprising a carbon atom which is bonded to C 3< and C 4< and which comprises at least one aromatic six-membered ring which is bonded directly to one of the oxygen atoms, wherein the aromatic six-membered ring may be substituted in positions 3 and 5 with the same or different C 1 - C 4 -alkyl radicals, in particular with a methyl, isopropyl or tert-butyl group, wherein the methyl group is preferred.

[0028] The anion-conducting polymer according to structural formula (III) is defined as follows: wherein X represents a ketone or sulfone group; wherein Z represents a structural element comprising at least one tertiary carbon atom and at least one aromatic six-membered ring, wherein the aromatic six-membered ring is directly bonded to one of the two oxygen atoms; wherein Y represents a structural element comprising at least one positively charged nitrogen atom, wherein this nitrogen atom is bonded to the structural element Z.

[0029] A first subject of the invention is therefore a dispersion which contains at least the following components: a solution of an anion-conductive polymer; particles containing at least one electrocatalytically active substance; optionally at least one dispersant; wherein the anion-conductive polymer contains at least one structure selected from the group consisting of structural formulas (I), (II) and (III) as defined above.

[0030] Within the dispersion, the mass ratio of anion-conducting polymer to particles is between 1:1 and 1:20, between 1:1 and 1:5, or between 1:6 and 1:10. This means that the weight fraction of the particles containing the electrocatalytically active substance is greater than the weight fraction of the anion-conducting polymer. This achieves a high density of catalytically active centers. The composite produced from the dispersion thus achieves particularly high electrochemical activity.

[0031] These ionomers dissolve particularly well in solvents from the following group: N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), or dimethyl sulfoxide (DMSO). DMSO is preferred. The solvent can be removed by drying, leaving the ionomer as a solid in the form of a polymer film. The concentration of the anion-conductive polymer relative to the volume of the solvent should be between 10 mg / ml and 500 mg / ml or between 50 mg / ml and 100 mg / ml.

[0032] Preferably, an electrocatalytically active substance is used which contains at least one transition element. Transition elements within the meaning of the invention are Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Ac, Rf, Db, Sg, Bh, Hs, Mt, Ds, and Rg. Substances containing a transition element exhibit higher electrocatalytic activity than substances without a transition element. In addition, the comparatively good electrical conductivity of the transition metals reduces the internal resistance of the electrochemical cell.

[0033] The electrolytic activity of the composite produced from the dispersion is achieved by adding an electrocatalyst to the dispersion. The electrocatalyst is then immobilized in the final composite by the ionomer. Examples of electrocatalysts used include particles containing an electrocatalytically active substance selected from the group consisting of iridium (Ir), iridium oxide (IrOx), nickel oxide (NiOx), cobalt oxide (CoOx), nickel-iron mixed oxide (NiFeOx), nickel-cobalt mixed oxide (NiCoOx), lead-ruthenium mixed oxide (PbRuOx), and platinum on carbon (Pt / C). To achieve an effective density of the catalytically active centers in the composite, the mass ratio of anion-conducting polymer to particles in the dispersion is adjusted between 1:1 and 1:20, or between 1:1 and 1:5, or between 1:6 and 1:10.

[0034] Particularly preferably, an anion-conducting polymer is processed in the dispersion, which is described by at least one of the following structural formulas (IVa) to (IVd): where M a< and M b< represent a natural number from 1 to 500 or from 5 to 250, and where the aromatic rings may be further substituted with one or more halogens and / or with one or more C 1 - to C 4 - alkyl radicals, in particular with methyl radicals.

[0035] The dispersion does not necessarily have to contain a separate dispersant. Under certain circumstances, the solvent can also function as a dispersant. To increase the processability of the dispersion, however, at least one dispersant is preferably added. This makes the dispersion more flowable. A mixture of several dispersants can also be used. In particular, it has proven advantageous if the dispersion formulation contains two dispersants, namely water and an alcohol, with the volume ratio of water to alcohol being between 1:3 and 3:1. Preferably, water and alcohol are used in a ratio of 1:1. Suitable alcohols are ethanol, methanol, 1-propanol, or 2-propanol. Such a water / alcohol mixture evaporates easily when the dispersion dries.

[0036] To ensure good processability, the solids concentration of the dispersion is preferably between 5 mg / ml and 100 mg / ml or between 10 mg / ml and 25 mg / ml, each based on the total volume of the liquid components of the dispersion. The solids present in the dispersion correspond to the catalytically active particles. The ionomer in the solution is considered liquid.

[0037] The dispersion described here is intended to produce an electrochemically active layered body.

[0038] A further subject of the invention is therefore a method for producing an electrochemically active layered body, comprising the following steps: a) Providing a dispersion according to the invention which contains at least the following components: a dispersing agent; an organic solvent different from the dispersing agent; a solution of an anion-conductive polymer in the organic solvent; particles containing at least one electrocatalytically active substance; b) Providing a substrate; c) Applying the dispersion to the substrate; d) Drying the dispersion applied to the substrate; e) Obtaining a laminated body comprising the substrate and an at least two-phase coating applied thereto, wherein the coating comprises the anion-conductive polymer as a first phase and the particles as a second phase, and wherein the second phase is dispersed in the first phase.

[0039] The solvent and the optional dispersant evaporate during drying, so that they are not found in the laminate.

[0040] The dispersion is applied to the substrate in a known manner by doctor blade, spraying or screen printing.

[0041] One advantage of the dispersion described here is that it can be used to coat textile substrates. Electrochemically active laminates based on a textile structure have a particularly large surface area and can therefore enable high process intensity. A textile fabric is therefore preferably used as the substrate. Textile fabrics are nonwovens, felts, wovens, or knitted fabrics. The fabrics are composed of fibers, threads, or yarns. Felts or nonwovens composed of nickel fibers, carbon fibers, or steel fibers are preferably coated with the dispersion. Such substrates are inexpensive, electrically conductive, and stable in the alkaline environment of an AEM-WE process. They are therefore suitable as electrodes in CCS designs.

[0042] The dispersion described here can also be used to coat a membrane made of an anion-conducting polymer. If an anion-conducting membrane is used as the substrate, the resulting layered body is a CCM. Preferably, the membrane used as the substrate also contains ionomers of structure (I) or (II) or (III). This allows for particularly good bonding of the catalyst particles to the membrane because the ionomers are compatible.

[0043] A dispersion optimally suited for the production of electrochemically active laminates is prepared by the following procedure: i) Providing the dispersant; ii) Providing the organic solvent different from the dispersant; iii) Providing the anion-conductive polymer; iv) Providing the particles; v) Dissolving the anion-conductive polymer in the organic solvent to obtain a solution of the anion-conductive polymer; vi) Suspending the particles in the dispersant to obtain a suspension; vii) Dosing the solution into the suspension.

[0044] This procedure leads to a particularly homogeneous distribution of the electrocatalytically active particles in the anion-conducting polymer and to a stable dispersion.

[0045] Mixtures of water and alcohol are particularly suitable as dispersants, as the particles can be easily suspended in them and the water and alcohol dry quickly after application of the dispersion. The boiling point of water and alcohol is lower than, for example, that of DMSO (189°C). Consequently, the use of water / alcohol as a dispersant enables rapid layer buildup in the production of electrochemically active laminates. However, water is unsuitable as a solvent, as the anion-conducting polymers used in water electrolysis must, by design, be water-insoluble. Otherwise, the water electrolysis cell would quickly disintegrate during operation. Since alcohols also hardly dissolve the anion-conducting polymers described here, a significantly more powerful organic solvent must be used.At least one of the following substances is preferably used as the organic solvent: N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), or dimethyl sulfoxide (DMSO). DMSO is preferred. These solvents can also be removed by drying, leaving the ionomer as a solid in the form of a polymer film. However, the above-mentioned organic substances are not suitable as dispersants for all catalyst systems, as sedimentation experiments have shown. Depending on the selected catalyst system, it therefore makes sense to use different substances as solvents or dispersants.

[0046] The invention further provides an electrochemically active laminated body comprising a substrate and an at least two-phase coating applied thereto, wherein the coating comprises an anion-conductive polymer as the first phase and particles containing an electrocatalytically active substance as the second phase, and wherein the second phase is dispersed in the first phase, wherein the anion-conductive polymer contains at least one structure according to formula (I), (II) or (III). Depending on the substrate chosen, the laminated body is in particular a CCM or a CCS. In both cases, the loading based on the electrochemically active substance is preferably between 0.2 mg / cm 2 and 10 mg / cm 2 or 0.4 mg / cm 2 and 2 mg / cm 2 .

[0047] Particularly preferably, the electrochemically active layered body contains an anion-conducting polymer which is described by at least one of the following structural formulas (IVa) to (IVd): where M a< and M b< represent a natural number from 1 to 500, preferably from 5 to 250 and where the aromatic rings may be further substituted with one or more halogens and / or with one or more C 1 - to C 4 - alkyl radicals, in particular with methyl radicals.

[0048] Such ionomers exhibit good ionic conductivity, high chemical and mechanical stability in alkaline environments, and low synthesis costs. Furthermore, they immobilize the catalyst particles well on the substrate and are excellently processable in dispersion.

[0049] Depending on the chosen dispersion formulation, the selected application method, and the time / temperature regime of the drying process, the coating on the substrate, or more precisely its first dispersed phase consisting of the anion-conducting polymer, acquires a special structure that improves the accessibility of the catalytically active centers of the particles in the coating to the electrolyte. An electrochemically active laminate obtained by the coating process according to the invention is therefore also a subject of the invention.

[0050] The electrochemically active composite produced from the dispersion is ideal for use in an electrochemical cell, such as a CCM or CCS. In addition to the composite, the electrochemical cell can also include other components, such as other electrodes or separators, or fluid conductors or contact plates.

[0051] Due to the particular stability of the ionomer and the catalytic activity of the particles processed in the dispersion and found in the laminated body, the electrochemical cell containing the laminated body is preferably used to carry out a process for producing hydrogen and oxygen by electrochemically splitting water, in which an aqueous electrolyte with a pH of 7 to 15 is filled into the electrochemical cell. Such an AEM-WE process is also a subject of the invention.

[0052] The invention will now be explained in more detail using exemplary embodiments. They show: Figure 1: Structure of the electrochemical cell; Figure 2: Test bench for the electrochemical cell; Figure 3: Graphical representation of the current-voltage curves.

[0053] The basis for producing formulations with the polymers (ionomers) described above is the preparation of an ionomer solution. Suitable solvents include N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), or dimethyl sulfoxide (DMSO). DMSO is preferred because it is classified as a non-hazardous substance. The polymer content is between 10 mg / ml and 500 mg / ml or between 25 mg / ml and 200 mg / ml.

[0054] The mass ratio of ionomer to catalytically active substance is between 1:1 and 1:20 or between 1:3 and 1:5 for catalysts based on, for example, platinum supported on carbon (Pt / C), iridium (Ir), iridium oxide (IrOx), nickel oxide (NiOx), cobalt oxide (CoOx), nickel-iron mixed oxide (NiFeOx), nickel-cobalt mixed oxide (NiCoOx) or lead-ruthenium mixed oxide (PbRuOx).

[0055] Catalyst and ionomer solution can be applied either after dispersion (for example using a ULTRA-TURRAX ®< dispersing device from IKA, Staufen, DE or a three-roll mill, for example from EXAKT, Norderstedt, DE - under shearing action both cause the particle size to be adjusted (d 50 in the range between 0.1 µm and 50 µm) or after dispersion (for example using screen printing or a doctor blade process).Secondly, aqueous dispersions can be produced, particularly for application in spray processes, in which a catalyst is first dispersed in a solution of water and lower alcohols (preferably ethanol, 1-propanol, or 2-propanol) under the action of ultrasound or a disperser (for example, with an ULTRA-TURRAX®< dispersing device from IKA, Staufen, Germany, with additional adjustment of the particle size: d 50 in the range between 0.1 µm and 50 µm). The ionomer solution (preferably 50 mg / ml) is then added, followed by further dispersion under ultrasound. The solids concentration here is between 5 mg / ml and 100 mg / ml, preferably between 10 mg / ml and 25 mg / ml. The unit mg / ml of the ionomer solution refers to mass of polymer / volume of solvent or of the dispersion to mass of catalyst / volume of liquid components.

[0056] Particularly suitable substrates for the application of the prepared formulations are nonwovens made of carbon or nonwovens made of metal (nickel, stainless steel, titanium) as well as ion-conducting, polymeric membranes.

[0057] The loading of the substrate relative to the catalyst is between 0.2 mg / cm 2< and 10 mg / cm 2< or 0.4 mg / cm 2< and 2 mg / cm 2< .

[0058] Table 1 shows the composition of some dispersions according to the invention with which catalyst layers could be applied to substrates.

[0059] The ionomer used is a substance prepared as described in Example 3 of WO 2021 / 013694 A1.

[0060] The ionomer was first dissolved in dimethyl sulfoxide with stirring and at 60 °C for 16 h. The catalysts were then dispersed in the dispersant, consisting of equal volumes of water and ethanol, either using ultrasound (BRANSONIC™ B-1200 E2 from Branson Ultrasonics Corporation, Brookfield, CT, US) for 30 min in an ice bath at a power of 30 W or using an ULTRA-TURRAX®< T10 basic disperser (IKA, Staufen, DE) for 3 min at level 3. After addition of the ionomer solution, further dispersion was carried out using ultrasound in an ice bath for 1 min at a power of 30 W and dispersion was carried out using a shaker (MS1 Minishaker from IKA, Staufen, DE) for 10 s at 2500 rpm. The proportions were selected according to Table 1.

[0061] The dispersions according to the invention were sprayed onto the substrates using a PRISM 400 ultrasonic spray coater (Ultrasonic Systems, Inc., Haverhill, MA, US). The formulation was continuously stirred during the process. These substrates were kept at a temperature of 60°C, which continuously evaporated the dispersant, thus producing the laminated bodies according to the invention.

[0062] The resulting composites could be used as electrodes for the production of hydrogen and / or oxygen in alkaline membrane water electrolysis (AEM-WE). The electrochemical cell according to Figure 1It essentially consisted of two electrically active laminates (A, A') (at least one of which was produced by the process according to the invention) separated by an anion-conducting membrane (B). The electrolyte supply (1M KOH, 60 °C) was provided via a flow and current distributor (C), each of which was electrically insulated by seals (D).

[0063] The function of the produced composite bodies could be tested in the cell mentioned in a test stand ( Figure 2 ) using typical current-voltage curves (galvanostatic: 0.02 - 1.50 A / cm 2< ), which the diagrams in Figure 3 and Figure 4 show.

[0064] In principle, the catalyst layers produced on the basis of the described catalyst ionomer formulations (dispersions) can also be used in electrochemical processes other than alkaline membrane water electrolysis (AEM-WE) - examples include an alkaline fuel cell or the electrolysis (reduction) of carbon dioxide. Table 1 Composition of dispersions Example Ionomer solution Mass ratio Dispersants catalytically active substance solid Dispersing Substrat Electrochemically active substance on substrate # Concentration of ionomer in DMSO [mg / ml] particles ionomer Percentage of water Percentage of ethanol Designation Concentration [mg / ml] technology Designation Loading [mg / cm 2 ] 1 50 3 1 1 1 Pt / C 11 Ultrasonic Fleece: Carbon 0,6 2 50 4 1 1 1 Ir 11 Ultrasonic Fleece: stainless steel 1,0 3 50 4 1 1 1 IrOx 11 Ultrasonic Fleece: Carbon 1,1 4 50 3 1 1 1 Ir 11 Ultrasonic Fleece: stainless steel 0,9 5 50 6 1 1 1 Ir 11 Ultrasonic Fleece: stainless steel 1,0 6 50 9 1 1 1 Ir 11 Ultrasonic Fleece: stainless steel 1,0 7 50 4 1 1 1 PbRuOx 11 Ultrasonic Fleece: stainless steel 1,0 8 50 4 1 1 1 NiOx 11 Ultrasonic Fleece: stainless steel 0,9 9 50 4 1 1 1 CoOx 11 Ultrasonic Fleece: stainless steel 0,9 10 27,5 13 1 1 1 Pt / C 27 Ultrasonic Fleece: Carbon 0,2 11 27,5 13 1 1 1 IrOx 27 Ultrasonic Fleece: Carbon 1,6 12 50 3 1 1 1 Pt / C 11 Ultrasonic membrane 0,6 13 50 4 1 1 1 Ir 11 Ultrasonic membrane 1,0 14 50 3 1 1 1 Pt / C 11 ULTRA-TURRAX ®< Fleece: Carbon 0,7 15 50 4 1 1 1 Ir 11 ULTRA-TURRAX ®< Fleece: stainless steel 1,0 Sedimentation tests

[0065] Sedimentation experiments will be used to investigate the stability of the dispersions. Four different compositions are available, each with and without ionomers. Either platinum / carbon or nickel oxide is used as the catalyst. Implementation:

[0066] The dispersions are prepared in a snap-cap jar: Dispersion 1: 11 mg / ml Pt / C in DMSO Dispersion 2: 11 mg / ml Pt / C in ethanol:water Dispersion 3: 11 mg / ml NiO in DMSO Dispersion 4: 11 mg / ml NiO in ethanol:water

[0067] Dispersions 1 to 4 are placed in the ultrasonic bath for 30 minutes and then shaken. Sedimentation is observed and documented.

[0068] After about 30 minutes, ionomer is added: Dispersion 1 and 2: + 3.7 mg / ml ionomer Dispersion 3 and 4: + 2.8 mg / ml ionomer

[0069] The dispersions are placed in the ultrasonic bath for one minute, shaken and the sedimentation is observed. Observation:

[0070] A dispersion with Pt / C in DMSO + ionomer sediments after 15 minutes, forming two phases: the upper phase is transparent and the lower phase is black. Dispersions with nickel oxide in ethanol and water, with and without ionomer, also form a two-phase separation. Without ionomer, this separation develops after approximately 3 minutes. Here, a black layer settles at the bottom and a dark gray layer at the top. In the dispersion with ionomer, a slight separation into light and dark phases is also visible after 3 minutes, but this becomes more visible after 15 minutes. The upper phase is milky and the lower phase is black.

[0071] The dispersions Pt / C in ethanol and water with and without ionomer, as well as nickel oxide in DMSO with and without ionomer and Pt / C in DMSO show no abnormalities during the test period.

Claims

1. Dispersion comprising at least the following components: • a solution of an anion-conductive polymer; • particles comprising at least one electrocatalytically active substance; • optionally at least one dispersant; wherein the anion-conductive polymer comprises at least one structure selected from the group consisting of the structural formulae (I), (II) and (III): wherein, in (I), X is a structural element comprising a positively charged nitrogen atom bonded to C1 and C2 and which is bonded via two bonds to one or two hydrocarbon radicals comprising 1 to 12, preferably 1 to 6, particularly preferably 1 or 5 carbon atoms and wherein, in (I), Z is a structural element which comprises a carbon atom bonded to C3 and C4 and which comprises at least one aromatic six-membered ring which is bonded directly to one of the oxygen atoms, wherein the aromatic six-membered rings may be substituted by one or more halogen and / or one or more C1- to C4-alkyl radicals; wherein, in (II), X is a structural element comprising a positively charged nitrogen atom bonded to C1 and C2 and which is bonded via two bonds to one or two hydrocarbon radicals comprising 1 to 12, preferably 1 to 6, particularly preferably 1 or 5 carbon atoms, and wherein, in (II), Z is a structural element which comprises a carbon atom bonded to C3 and C4 and which comprises at least one aromatic six-membered ring which is bonded directly to one of the oxygen atoms, wherein the aromatic six-membered ring may be substituted in positions 3 and 5 by the same or different C1- to C4-alkyl radicals, in particular by a methyl, isopropyl or tert-butyl group, the methyl group being preferred; wherein, in (III), X is a ketone or sulfone group; wherein, in (III), Z is a structural element which comprises at least one tertiary carbon atom and at least one aromatic six-membered ring, where the aromatic six-membered ring is bonded directly to one of the two oxygen atoms; and wherein, in (III), Y is a structural element which comprises at least one nitrogen atom having positive charge, where this nitrogen atom is bonded to the structural element Z; characterized in that the ratio by mass of anion-conducting polymer to particles in the dispersion is between 1:1 and 1:20 or between 1:1 and 1:5 or between 1:6 and 1:10.

2. Dispersion according to Claim 1, characterized in that the solution of the anion-conductive polymer comprises at least one solvent selected from the group consisting of N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC) or dimethyl sulfoxide (DMSO), and in that the concentration of the anion-conductive polymer, based on the volume of the solvent, is between 10 mg / ml and 500 mg / ml or between 50 mg / ml and 100 mg / ml.

3. Dispersion according to Claim 1 or 2, characterized in that the electrocatalytically active substance comprises at least one transition element.

4. Dispersion according to Claim 1 or 2 or 3, characterized in that the particles comprise at least one electrocatalytically active substance selected from the group consisting of iridium (Ir), iridium oxide (IrOx), nickel oxide (NiOx), cobalt oxide (CoOx), nickel-iron mixed oxide (NiFeOx), nickel-cobalt mixed oxide (NiCoOx), lead-ruthenium mixed oxide (PbRuOx), platinum on carbon (Pt / C) and that the ratio by mass of anion-conducting polymer to particles in the dispersion is between 1:1 and 1:20 or between 1:1 and 1:5 or between 1:6 and 1:10.

5. Dispersion according to Claim 4, characterized in that the anion-conducting polymer is described by at least one of the following structural formulae (IVa) to (IVd): wherein Ma and Mb are a natural number from 1 to 500 or from 5 to 250, and wherein the aromatic rings may be further substituted by one or more halogens and / or by one or more C1- to C4-alkyl radicals, especially by methyl radicals.

6. Dispersion according to Claim 5, comprising two dispersants, namely water and an alcohol, wherein the ratio by volume of the water to the alcohol is between 1:3 and 3:1.

7. Dispersion according to any of Claims 2 to 6, characterized by a solids concentration of 5 mg / ml to 100 mg / ml or between 10 mg / ml and 25 mg / ml, based in each case on the total volume of the liquid constituents of the dispersion.

8. Process for producing an electrochemically active layer structure, comprising the following steps: a) providing a dispersion according to any of Claims 1 to 7 comprising at least the following components: • a dispersant; • an organic solvent different from the dispersant; • a solution of an anion-conductive polymer in the organic solvent; • particles comprising at least one electrocatalytically active substance; b) providing a substrate; c) applying the dispersion to the substrate; d) drying the dispersion applied to the substrate; e) obtaining a layer structure comprising the substrate and an at least two-phase coating applied thereto, wherein the coating comprises the anion-conductive polymer as first phase and the particles as second phase and wherein the second phase is dispersed in the first phase.

9. Process according to Claim 8, characterized in that the application is carried out by bar coating, by spraying or by screenprinting.

10. Process according to Claim 8 or 9, characterized in that the substrate is a textile fabric composed of fibres of nickel, carbon or steel.

11. Process according to Claim 8 or 9, characterized in that the substrate is a membrane composed of an anion-conducting polymer.

12. Process according to any of Claims 8 to 11, characterized in that the dispersion is provided as follows: i) providing the dispersant; ii) providing the organic solvent different from the dispersant; iii) providing the anion-conductive polymer; iv) providing the particles; v) dissolving the anion-conductive polymer in the organic solvent so that a solution of the anion-conductive polymer is obtained; vi) suspending the particles in the dispersant so that a suspension is obtained; vii) adding the solution to the suspension.

13. Electrochemically active layer structure, obtained by a process according to any of Claims 8, 9 or 10, comprising a substrate and an at least two-phase coating applied thereto, wherein the coating comprises an anion-conductive polymer as first phase and particles comprising an electrocatalytically active substance as second phase, and wherein the second phase is dispersed in the first phase, characterized in that the anion-conductive polymer comprises at least one structure selected from the group consisting of the structural formulae (I), (II) and (III): wherein, in (I), X is a structural element comprising a positively charged nitrogen atom bonded to C1 and C2 and which is bonded via two bonds to one or two hydrocarbon radicals comprising 1 to 12, preferably 1 to 6, particularly preferably 1 or 5 carbon atoms and wherein, in (I), Z is a structural element which comprises a carbon atom bonded to C3 and C4 and which comprises at least one aromatic six-membered ring which is bonded directly to one of the oxygen atoms, wherein the aromatic six-membered rings may be substituted by one or more halogen and / or one or more C1- to C4-alkyl radicals; wherein, in (II), X is a structural element comprising a positively charged nitrogen atom bonded to C1 and C2 and which is bonded via two bonds to one or two hydrocarbon radicals comprising 1 to 12, preferably 1 to 6, particularly preferably 1 or 5 carbon atoms, and wherein, in (II), Z is a structural element which comprises a carbon atom bonded to C3 and C4 and which comprises at least one aromatic six-membered ring which is bonded directly to one of the oxygen atoms, wherein the aromatic six-membered ring may be substituted in positions 3 and 5 by the same or different C1- to C4-alkyl radicals, in particular by a methyl, isopropyl or tert-butyl group, the methyl group being preferred; wherein, in (III), X is a ketone or sulfone group; wherein, in (III), Z is a structural element which comprises at least one tertiary carbon atom and at least one aromatic six-membered ring, where the aromatic six-membered ring is bonded directly to one of the two oxygen atoms; and wherein, in (III), Y is a structural element which comprises at least one nitrogen atom having positive charge, where this nitrogen atom is bonded to the structural element Z.

14. Electrochemically active layer structure according to Claim 13, characterized in that the anion-conducting polymer is described by at least one of the following structural formulae (IVa) to (IVd): wherein Ma and Mb are a natural number from 1 to 500, preferably from 5 to 250, and wherein the aromatic rings may be further substituted by one or more halogens and / or by one or more C1- to C4-alkyl radicals, especially by methyl radicals.

15. Electrochemical cell comprising at least one electrochemically active layer structure according to Claim 13 or 14.

16. Process for producing hydrogen and oxygen by electrochemical cleavage of water, in which an aqueous electrolyte having a pH of 7 to 15 is filled into an electrochemical cell according to Claim 15.