Electrode, zero-gap electrolyzer, use and process

Abstract

The invention relates to an electrode and a membrane electrode assembly for a zero-gap electrolyzer, a zero-gap electrolyzer, the use of a metal phthalocyanine, and a method for producing an electrode. An electrode (1, 1a, 1b) for a zero-gap electrolyzer (11) comprises a metal phthalocyanine (4). In this way, a particularly effective and cost-efficient catalyst can be provided.

Description

[0001] The invention relates to an electrode and a membrane electrode unit for a zero-gap electrolyzer, a zero-gap electrolyzer, the use of a metal phthalocyanine, and a method for producing an electrode.

[0002] The electrochemical conversion of carbon dioxide (CO2) is a promising technology for the sustainable production of fuels or chemicals, for example, using solar or wind energy. Electrochemical CO2 reduction is also known as ECR (electrochemical reduction). Alkaline low-temperature ECR is now widely used and has established itself as a benchmark process for upgrading gaseous CO2 to valuable products such as carbon monoxide (CO). It is known to use catalysts with platinum group metals (PGMs), which achieve high efficiencies of around 90%. However, such catalysts are expensive. To reduce costs, PGM-free catalysts are being developed, but these currently achieve significantly lower efficiencies.

[0003] Among the PGM-free catalysts are molecular catalysts and metal phthalocyanines. US patent 2019 0 224 660 A1 discloses the use of complexes of water-soluble porphyrins for the selective electrochemical reduction of CO2 to CO. US patent 2022 0 251 715 A1 relates to a flow-cell electrolyzer for the electrochemical reduction of reagent gas CO2 to gaseous CO. This electrolyzer comprises a molecular catalyst containing iron or cobalt and a metal porphyrin with one or more + N(C1-C4-alkyl)3 groups, metal phthalocyanine, metal phthalocyanine with one or more +N(C1-C4 alkyl)3 groups or cobalt quaterpyridine can be used in alkaline, gas-fed ECR. This allows for the formation of CO with a high selectivity of over 90%. However, the overall CO2 conversion is very low, at less than 15%. This results in a highly diluted gas product stream, leading to high separation costs.

[0004] Publication US 2021 0 123 146 A1 describes a process for the electrocatalytic conversion of CO2 into useful chemicals. The process involves the input of an aqueous carbonate or bicarbonate solution and the electrocatalytic reduction of this solution to carbon monoxide or another useful chemical. The associated electrolyzer is also known as a (direct) carbonate / bicarbonate electrolyzer (DCE). Silver is used as a catalyst for CO production, which results in high costs. Furthermore, DCE systems exhibit limited CO production efficiency of approximately 60% and low CO production rates (partial current densities). co of approximately 130 mA cm -2 on.

[0005] The invention is based on the objective of developing a further developed electrode as well as an associated membrane electrode unit, an electrolyzer, a use and a manufacturing process.

[0006] The problem is solved by the electrode according to claim 1 as well as the membrane electrode unit, the electrolyzer, the use and the manufacturing process according to the dependent claims.

[0007] To solve the problem, an electrode for a zero-gap electrolyzer is used. The electrode comprises a metal phthalocyanine, in particular as a catalyst.

[0008] The invention is based on the finding that metal phthalocyanines are particularly well-suited as catalysts for the electrochemical production of a product in a zero-gap electrolyzer. Specifically, a PGM-free metal phthalocyanine is used. In this way, a particularly cost-effective catalyst can be provided. Metal phthalocyanines are organic molecules with a metal atom at their center. These substances act as molecular catalysts.

[0009] Given the challenging reaction conditions in zero-gap electrolysis, it is surprising that metal phthalocyanines are particularly well suited here, as even Au or Ag catalysts, which perform well in classical electrochemical reduction, deliver comparatively poor results in this area.

[0010] A zero-gap electrolyzer is a gas-fed electrolyzer. A zero-gap electrolyzer can also be referred to as a (direct) carbonate / bicarbonate electrolyzer (DCE).

[0011] The zero-gap electrolyzer is specifically designed for low-temperature electrolysis. It contains, or is configured to operate with, a liquid electrolyte. The electrolyte is, in particular, a carbonate salt solution. The electrolyte circulates in both compartments, the anodic and cathodic compartments. The zero-gap electrolyzer includes a membrane, which is, in particular, porous. This membrane is also referred to as a solid-state electrolyte. The membrane can function as an ion exchanger. It can separate an anolyte side from a catholyte side. The membrane can be designed as a solid porous electrolyte membrane (SPE). The membrane is, in particular, positioned between the anode and the cathode of the electrolyzer.The zero-gap electrolyzer can have a gas diffusion electrode (GDE) at the cathode and / or a porous transport electrode (PTE) at the anode. The SPE membrane can be enclosed by the GDE and / or the PTE. Together, these components can form a membrane electrode assembly (MEA). The SPE membrane can be designed as an anion exchange membrane. Through ion transport to the cathode, this can create an alkaline environment at the catalyst layer of the cathode, thereby enabling selective electrochemical CO₂ reduction (CO₂RR) to CO.

[0012] In particular, the zero-gap electrolyzer contains no liquid catholyte. Specifically, it has an anode compartment, preferably with an inlet for gaseous CO2. Specifically, CO2 is generated directly in the cathode region and / or subsequently converted to the product(s) by electrochemical reduction.

[0013] Electroreduction of CO2 can occur, in which gaseous CO2 is reduced. The resulting CO2 bubbles can be reduced directly by the catalyst.

[0014] A zero-gap electrolyzer can achieve a small distance between the electrodes and therefore minimize the ohmic resistance of the entire cell. High partial current densities and high process stability can be achieved.

[0015] In particular, the zero-gap electrolyzer is designed to be powered by renewable energy.

[0016] In principle, all metal phthalocyanines are equally suitable, but the specific use depends on the desired product(s).

[0017] In one embodiment, the electrode comprises cobalt phthalocyanine as the metal phthalocyanine. Cobalt phthalocyanine (abbreviated as CoPc) has proven suitable for the intended purpose in tests, particularly for the production of products such as CO and / or H2. Furthermore, cobalt phthalocyanine is relatively inexpensive and readily available.

[0018] In one embodiment, the electrode comprises iron phthalocyanine, zinc phthalocyanine or copper phthalocyanine as a metal phthalocyanine.

[0019] The choice of specific catalyst depends primarily on the product to be manufactured. Iron phthalocyanine and zinc phthalocyanine are particularly well-suited for this purpose. Copper phthalocyanine is especially well-suited for the production of higher products, i.e., larger molecules such as ethane, methane, and / or formic acid (HCOOH).

[0020] The following Table 1 lists different suitable metal phthalocyanines and their possible products. Designation name Possible products CoPc Cobalt(II) phthalocyanine CO FePc Iron(II) phthalocyanine CO NiPc Nickel(II) phthalocyanine CO ZnPc Zinc(II) phthalocyanine CO, HCOOH CuPc copper(II) phthalocyanine CO, HCOOH, CH4, C2H4 MnPc Manganese(II) phthalocyanine CO, HCOOH MgPc Magnesium(II) phthalocyanine CO, HCOOH SNPC Tin(II) phthalocyanine HCOOH AgPc Silver(I) phthalocyanine CO

[0021] In one embodiment, the electrode is an active and / or cathodic electrode.

[0022] The cathodic electrode is designed to be supplied with a bicarbonate solution. Specifically, the electrode has an inlet for supplying bicarbonate solution and / or an outlet for removing bicarbonate solution.

[0023] The cathodic reaction is CO2 reduction. The anodic reaction is the standardized oxygen evolution reaction (OER). For this, a layer of iridium oxide can be used, for example.

[0024] It has been shown that with such a setup, a CO production efficiency of approximately 90% and a maximum partial flow density for CO (j) can be achieved. co ) of more than 300 mA cm -2This can be achieved. For example, in the case of CO or synthesis gas (CO / H2), a high-purity electricity with more than 90% product content can be generated.

[0025] In one embodiment, the metal phthalocyanine is applied to or deposited on a porous substrate. This has proven particularly effective for the functioning of the active, especially cathodic, electrode. The metal phthalocyanine is thus located on the porous substrate.

[0026] In one embodiment, the metal phthalocyanine is applied or deposited on a carbon-containing substrate. The substrate can contain more than 80% or 95% carbon. Deposition on a carbon-containing or carbon-based substrate has proven particularly effective for its catalytic activity. A particularly high electrocatalytic activity can be achieved.

[0027] In one embodiment, the metal phthalocyanine is applied or deposited onto carbon paper.

[0028] In one embodiment, the metal phthalocyanine is anchored to carbon nanoparticles.

[0029] The metal phthalocyanine is anchored to carbon nanoparticles, for example, to carbon black (industrial carbon black). Carbon black contains or consists of carbon nanoparticles. It has been shown that this further increases the electrocatalytic activity and allows for a maximum partial current density for CO (j co ) of more than 400 mA cm -2 This can be achieved. Despite its high partial flow density, carbon black is particularly cost-effective. Carbon allotropes such as CNTs, G, and GO can also be used instead of carbon black.

[0030] Anchoring the metal phthalocyanine to carbon nanoparticles can be achieved, for example, by producing a dispersion of metal phthalocyanine powder and carbon nanoparticles, such as carbon black. Sonication, e.g., using ultrasound, can then be performed. The resulting powder can subsequently be washed, for example with water and / or ethanol, and dried.

[0031] In one embodiment, the catalyst dispersion contains carbon nanoparticles. Commercially available carbon nanoparticles such as carbon black can be used.

[0032] In one embodiment, the carbon nanoparticles are N-doped carbon nanoparticles. In other words, the metal phthalocyanine is anchored to N-doped carbon nanoparticles.

[0033] Nitrogen-doped carbon nanoparticles can be produced, for example, by treating carbon black at high temperatures, such as approximately 700°C, under a nitrogen atmosphere. Prior to this, the carbon black powder can be treated in concentrated nitrate (HNO3). For example, it can be refluxed or boiled under reflux for several hours, such as 6 hours, and / or at 70°C. The powder can then be washed, particularly with water and acetone, and dried. In one embodiment, the powder contains melamine in addition to nitrogen-doped carbon nanoparticles. For example, melamine is added before the nitrogen treatment, for example, 0.5 g per gram of carbon black.

[0034] In one embodiment, the electrode and / or the catalyst further contains polyvinylpyridine. This provides a functionalized catalyst that allows for particularly high performance.

[0035] Further aspects of the invention include a membrane electrode assembly with an electrode according to the invention, and a zero-gap electrolyzer with an electrode according to the invention. All features, properties, and advantages of the electrode described above, the use described below, and the manufacturing process also apply to the membrane electrode assembly and the zero-gap electrolyzer.

[0036] Another aspect of the invention is the use of a metal phthalocyanine as a catalyst in a zero-gap electrolyzer. All features, properties, and advantages of the electrode and manufacturing process described above also apply to this use.

[0037] In particular, it refers to a use for the conversion of CO2 and / or for the production of a product.

[0038] The product may contain or be CO. The product may contain or be H₂. The product may contain or be methane. The product may contain or be ethane. The product may contain or be formic acid (HCOOH). The product may contain or be a mixture of two or more of the substances mentioned. The product may contain one or more hydrocarbons. The product may contain one or more alcohols. The product may contain or be synthesis gas. For example, the product may contain or be a mixture of CO and H₂.

[0039] The product may be present in a proportion of more than 70%, in particular more than 80%, preferably more than 90%. In particular, the proportion shall not exceed 99.9%.

[0040] Another aspect of the invention is a method for producing an electrode for a zero-gap electrolyzer. The method comprises the production of a catalyst dispersion containing a metal phthalocyanine. All features, properties, and advantages of the electrode and its use described above also apply to the method.

[0041] An electrode can be produced in this way. In particular, a cathodic electrode is produced in this way. The catalyst dispersion can then be applied to a substrate to form a catalyst.

[0042] In one embodiment, the catalyst dispersion is deposited or applied to a carbon-containing and / or porous substrate.

[0043] In principle, the application or deposition process is not limited. Various methods can be used. In deposition, the build-up or accumulation of material from a liquid phase takes place. The advantage of the composition according to the invention is that simple and cost-effective methods can be used for application or deposition. In one embodiment, application or deposition is carried out by means of doctor blade coating and / or spray coating.

[0044] In one embodiment, the catalyst dispersion is deposited or applied to carbon paper. In other words, carbon paper is used as the cathode substrate.

[0045] In one embodiment, the catalyst dispersion further contains an ionomer, for example, a Nafion ionomer. The ionomer stabilizes the catalyst layer or holds it together. The ionomer allows the conduction of ions through the catalyst layer. The Nafion ionomer allows the conduction of protons. + It can be used additionally or alternatively as a sustainion ionomer and / or an ionomer that impairs the conductance of OH. - -ions are permitted. Piperlone ionomer and / or an ionomer that impairs the conductivity of HCO3 can be used additionally or alternatively. - and CO3 2- allowed.

[0046] In one embodiment, the catalyst dispersion also contains polyvinylpyridine. This substance is able to absorb CO2 and thus interact with the CoPc. Its suitability as a catalyst is therefore improved.

[0047] In one embodiment, the catalyst dispersion is applied to a substrate by spraying. It has been shown that a suitable layer of the catalyst material can be produced simply and cost-effectively in this way. Drying then takes place, resulting in a solid layer.

[0048] Another independent aspect of the invention is a method for producing a product using a zero-gap electrolyzer with an electrode according to the invention. All features, properties, and advantages of the electrode described above and the other aspects also apply to this method.

[0049] Instead of soot, carbon nanotubes and / or graphene can be used in the aforementioned electrodes and / or processes. Examples of implementation

[0050] The following starting materials were used, for example: CoPc powder (90%), IrOx nanoparticles, KHCO3, ethanol (anhydrous, 99.9%), acetone (anhydrous, 99.9%), melamine, HCl solution (HCl, 37%), HNO3 solution (HNO3, 67%), polyvinylpyridine (PV4P, 99.99%) and dimethylformamide (DMF, anhydrous, 99.9%) from Sigma-Aldrich (Merck). Carbon black nanoparticles (Vulcan XC-72), Nation 117 membrane, Nafion ionomer dispersion (ethanolic, 5 wt%), Ti fiber substrate, Toray carbon paper (5 wt% PTFE content).

[0051] In one example, nitrogen-doped carbon black (hereinafter also referred to as N-CB) was produced, for example, based on the method according to A. Öztürk and A. Bayrakceken Yurtcan, J. Solid State Chem 296 (2021) 121972 (DOI: 10.1016 / j.jssc.2021.121972). One gram of commercially available carbon black was immersed in, for example, 50 ml of concentrated HNO3 and held under reflux for, for example, 6 hours at, for example, 70°C. The powder was then purified, in particular with water and / or acetone. The powder was dried, in particular, for several hours and / or overnight, for example, at approximately 60°C. In particular, the powder was mixed with 0.5 g of melamine and / or treated at, for example, 700°C under a nitrogen atmosphere.

[0052] In one example, a metal phthalocyanine was anchored to the N-doped carbon black, for example, based on the method according to Öztürk and A. Bayrakceken Yurtcan, J. Solid State Chem 296 (2021) 121972 (DOI: 10.1016 / j.jssc.2021.121972) and / or according to H.-L. Zhu et al., J. Phys. Chem. Lett. 14 (2023) 3844-3852 (DOI: 10.1021 / acs.jpclett.3c00317). For example, CoPc powder and N-CB were dispersed in a mass ratio of 1:1, for example, in dimethylformamide. The dispersion was then left in an sonication bath for approximately 2 hours. The dispersion was also stirred for several hours and / or overnight. The powder was washed and dried, in particular with water and / or ethanol, for example in a vacuum oven, at room temperature and / or for several hours or overnight.

[0053] In one example, catalyst ink was prepared. The catalyst ink can be prepared to have a total solids content of 6% w / v. In one example, a catalyst ink containing metal phthalocyanine catalyst powder, e.g., CoPc catalyst powder, carbon particles, and Nafion ionomer was prepared. For example, the mass ratio of metal phthalocyanine, e.g., CoPc, and carbon particles is 1:1. For example, a mass of 10% Nafion ionomer is used with respect to the total solids content. For example, the solids are dispersed, particularly in ethanol. A particularly uniform dispersion can be achieved, for example, by treatment in an Ultra-Turex machine and / or an ultrasonic bath. In one example, these two steps were carried out sequentially.

[0054] In one example, IrO was used x -Ink produced. The IrO xInk can be manufactured to have a total solids content of 6% w / v. For example, IrO₂ is used. x - Nanoparticles dispersed, in particular in ethanol or an ethanolic solution. In particular, the dispersion also contains Nafion ionomer, for example, in a mass of 20% Nafion ionomer with respect to the total solids content, which is combined with the IrO x -nanoparticles are dispersed. A particularly uniform dispersion can be achieved, for example, by treatment in an Ultra-Turex machine and / or an ultrasonic bath. In one example, these two steps were carried out sequentially.

[0055] In one example, a modified CoPc catalyst ink was prepared. For this purpose, a catalyst ink was prepared as described above. In addition to the solid components CoPc catalyst powder, carbon particles, and Nafion ionomer, polyvinylpyridine (PV4P) macromolecules were added, specifically in a CoPc:PV4P mass ratio of 8:1.

[0056] In one example, a catalyst substrate was prepared prior to catalyst layer deposition. For instance, carbon paper, such as that from Toray, was cut, for example, into square pieces and / or pieces with an area of ​​5 cm² each. 2The pieces were sonicated, for example, in distilled water and / or acetone, sequentially, and optionally dried, for example, for several hours or overnight and / or at 70°C. In one example, pieces of titanium substrate were etched, for example, in a boiling 3M HCl solution and / or for 30 minutes. The pieces were then cleaned with distilled water and dried, for example, overnight or for several hours and / or at 25°C. The titanium substrate can serve as an anode substrate.

[0057] In one example, the catalyst layer was produced. In another example, metal phthalocyanine ink, such as CoPc ink, was applied to the carbon paper, for example by spraying, such as with an automatic SonoTek spray coater with an ultrasonic spray nozzle. For example, spraying was carried out onto a heated vacuum plate at approximately 70°C and / or the coating was 1 mg / cm³. -2Metal phthalocyanine, e.g., CoPc. In one example, IrO was used. x -Ink applied to a decal transfer sheet, for example with an automatic squeegee coating device; in one example, a catalyst layer or IrO was applied. x -Layer transferred to one side of a membrane, for example made of Nafion 117, for example by hot pressing and / or at 130°C.

[0058] In one example, an electrolyzer was assembled. Specifically, a zero-gap electrolyzer made of dioxide materials with an active area of ​​5 cm² was constructed. 2 used. The cell was assembled as follows: the CoPc electrode was inserted into the cathode plate. The uncoated side of the Nafion-117 membrane was placed on the cathode plate. The IrO x The coated side of the membrane faced the anode compartment. On the IrO xA titanium fiber substrate was applied to the layer. Customized seals, primarily made of PTFE, were installed in the anodic and cathodic chambers to ensure a total compression of 5% for the membrane electrode assembly (MEA). The electrolyte containers were sealed gas-tight. Both tanks were filled with a 0.1 M aqueous KHCO3 solution.

[0059] For the electrochemical measurements, the following measures were taken, for example: The cell was connected to a potentiostat, specifically a Metrohm potentiostat, specifically with a 20A booster. The potentiostat was coupled to AUTOLAB software. Polarization curves of each MEA were generated galvanostatically. The prescribed current density was applied for 20 minutes, and the average required overvoltage was calculated. The electrolyte was circulated using pumps, such as peristaltic pumps, at a rate of 30 ml / min. -1All measurements were performed at room temperature. Carbonate / bicarbonate electrolysis (DCE) took place on the cathode side. The standardized oxygen evolution reaction (OER) occurred on the anode side. The electrochemical results from the electrolyzer are presented as measured and without iR compensation. The gas products from the anolyte chamber were passed through gas-tight tubing to a mass flow meter, a gas chromatograph (e.g., Agilent MicroGC), and a thermal conductivity detector (TCD). The cell's efficiency in CO formation from the cathodic reaction was determined using the Faraday efficiency for CO (FEc). CO ) characterized in %, which was calculated using the following formula: FECO(%)=zcv F PI RT, where z; number of electrons required to produce the product e - (2 e -for CO production), c: concentration of the product in the gas outlet stream, v: flow rate of the gas outlet stream in SSCM (standard cubic centimeters per minute), F=94685 C mol -1 , P=101325 Pa, R=8.314 J mol -1 K -1 , T = 298 K, I: Total current flowing through the cathode.

[0060] The Faraday efficiency compares the actual amount of hydrogen produced and technically usable to the theoretically maximum production amount.

[0061] In principle, alkaline solutions such as KOH can deposit atmospheric CO2 and form aqueous carbonate-bicarbonate solutions (equations 1a and 1b).

[0062] The separation of atmospheric CO2 to form (bi-)carbonate solutions is as follows: CO 2(g) + 2KOH (aq) ⇋ K2CO3 (aq) + H2O (1) (1a) CO 2(g) + K2CO 3(aq) + H2O (1) ⇋ 2KHCO 3(aq) (1b)

[0063] A direct bicarbonate electrolyzer is typically designed to use the generated (bi)carbonate solution as the catholyte and primary CO2 source for electrochemical reduction. The (bi)carbonate ions produced during CO2 separation react with the protons (H₂). + ), which are supplied to the cathode compartment by the cation exchange membrane, and generate i-CO2 (equations 2a and 2b). Here, i-CO2 is the gaseous CO2 formed on-site above the cathode surface. H + (aq) + HCO -3 (aq) ⇋ i-CO 2(g) + H2O (1) (2a) 2H + (aq) + CO3 -2 (aq) ⇋ i-CO 2(g) + H2O (1) (2b)

[0064] The i-CO2 adsorbed at the cathode can be electrochemically reduced to products C1 and C2 (equations 3a-3e). Such a bicarbonate electrolyzer is advantageous because it could potentially eliminate the need for energy-intensive processes for the thermal desorption and pressurization of CO2 prior to its introduction into a gas-fed CO2 electrolyzer.

[0065] The electrochemical i-CO2 conversion at the cathode, which follows the previously investigated mechanism of the electrochemical reduction of gas-fed CO2, is as follows: CO: i-CO 2(g) + H2O (1) + 2e - → CO (g) + 2OH - (aq) (3a) HCOOH: i-CO 2(g) + H2O (1) +2e - → HCOO - (aq) + OH - (aq) (3b) CH4: i-CO 2(g) + 6 H2O (1) + 8e - →CH 4(g) + 8OH - (aq) (3c) C2H4: 2 i-CO 2(g)+8 H2O (1) + 12e - → C2H 4(g) + 12OH - (aq) (3d) C2H5OH: 2i-CO 2(g) + 9 H2O (1) + 12e - → C2H5O H(aq) + 12OH - (aq) (3e)

[0066] The following (bi-)carbonate equilibrium reactions were considered for the source terms: CO 2(aq) + H2O (1) ⇋ HCO 3- (aq) + H + (aq) HCO 3- (aq) ⇋ CO3 2- (aq) + H + (aq) CO 2(aq) + OH - (aq) ⇋ HCO3 - (aq) HCO3 - (aq) + OH - (aq) ⇌ H2O (1) + CO3 2- (aq) H2O (1) ⇌ H + (aq) + OH - (aq)

[0067] Further embodiments of the invention are explained in more detail below, also with reference to figures.

[0068] They show: Fig. 1: a schematic representation of a zero-gap electrolyzer; Fig. 2: a schematic representation of a zero-gap electrolysis; Fig. 3: Polarization curves of various catalysts; Fig. 4: Faraday efficiencies of a CoPc / N-CB catalyst; Fig. 5: Faraday efficiencies of a mod-CoPc / CB catalyst; Fig. 6: Faraday efficiencies of a CoPc / CB catalyst; Fig. 7: Polarization curves of various catalysts; Fig. 8: Steps of a procedure; as well as Fig. 9: a schematic diagram of an electrode.

[0069] Fig.Figure 1 schematically shows parts of a zero-gap electrolyzer 11, namely a membrane electrode assembly 10 with the electrochemical reactions taking place. Electrodes 1 are arranged on both sides of a membrane 2 (also referred to as the solid electrolyte), namely an anodic electrode 1b and a cathodic electrode 1a. The cathodic reactant 24 comprises HCO3. - and CO3 2- On the cathode side shown below, these reactants are first treated with H +Ions passing through the cathodic electrode 1a are converted to CO2, which is then converted, particularly during the electrochemical CO2 reduction CO2RR, into the gaseous and / or liquid cathodic product 27, for example, CO, H2, and H2O. If liquid products such as formic acid (HCOOH) are formed, they remain in the electrolyte. The oxygen evolution reaction (OER) takes place on the anode side shown above. The liquid anodic reactant 23 contains H2O, and gaseous O2 is produced as the anodic product 26 during the oxygen evolution reaction (OER).

[0070] Membrane 2 allows the exchange of H + -ions between the anode side and the cathode side and in particular the ion transport of e.g. OH - , CO3 2- and / or HCO3 -from the cathode side to the anode side via minimal crossover. Membrane 2 can function as an ion exchanger.

[0071] Fig. Figure 2 schematically shows a zero-gap electrolysis process. The membrane electrode assembly 10 is shown in the center. This assembly contains a first electrode 1 in the form of an anodic electrode 1b or anode, a second electrode 1 in the form of a cathodic electrode 1a or cathode, and a membrane 2 located between the electrodes 1.

[0072] Each electrode is connected to an electrolyte tank via a circuit, with a pump to maintain the electrolyte circuit. The cathodic electrode 1a, shown on the right, is connected to a catholyte tank 29 containing liquid or gaseous cathodic reactant 24. A pump maintains the catholyte circuit 32, ensuring a continuous supply of cathodic reactant 24 to the cathodic electrode 1a. Gaseous cathodic product 26 can escape from the catholyte circuit 32, for example, from the catholyte tank 29. The anodic electrode 1b, shown on the left, is connected to an anolyte tank 28 containing liquid or gaseous anodic reactant 23. A pump maintains the anolyte circuit 31, ensuring a continuous supply of anodic reactant 23 to the anodic electrode 1b. Gaseous anodic product 27 can escape from the anolyte circuit 31, for example from the anolyte tank 28.Gaseous products can be drawn off from the supernatant or the gas space above the liquid level. Any liquid products remain in the electrolyte and are diluted there.

[0073] In one embodiment, the Fig. The experimental setup shown in Figure 2 was used. To evaluate the efficiency of the catalysts, the polarization curves and the Faraday efficiency for CO (FE) were determined. CO ) each electrode, especially according to the common protocols.

[0074] In the first version, the catalyst contained CoPc and carbon black. In the second version, the catalyst contained an additional molecule, namely polyvinylpyridine. In a third version, designed analogously to the first version, the catalyst contained N-CoPc instead of CoPc, i.e., nitrogen-doped carbon black.

[0075] The Fig.Figures 3 to 7 show the electrochemical performance of the electrodes according to the invention in the zero-gap DCE electrolyzer. Fig. Figure 3 shows polarization curves of the different catalysts. The cell potential CP is plotted against the total current density j. The total polarization curves of the nitrogen-doped carbon black-anchored CoPc catalyst CoPc / N-CB exhibit the lowest overpotential compared to the standard catalyst ink (CoPc catalyst anchored to carbon black; CoPc / CB) and its PV4P macromolecule-modified version (Modified CoPc catalyst anchored to carbon black; mod-CoPc / CB). The CoPc / N-CB electrode requires an overpotential of 3.4 V to achieve a total current density j of 800 mA cm⁻¹. -2 to reach

[0076] Fig. Figure 4 shows the Faraday efficiency FE of the CoPc / N-CB catalyst. Fig. Figure 5 shows the Faraday efficiency FE of the mod-CoPc / CB catalyst. Fig. Figure 6 shows the Faraday efficiency FE of the CoPc / CB catalyst.

[0077] Analysis of gas products in the case of CoPc / N-CB in Fig. 4 shows that the catalyst has a CO selectivity (FE CO ) from 80% up to a current density of 200 mA cm -2 maintains, after which the FE CO at reaction rates of more than 800 mA cm -2 falls below 50%. This represents a similar performance to the CoPc / CB ( Fig. 6) The mod-CoPc / CB ( Fig. 5) holds a FE CO from 80% up to 300 mA cm -2 upright and holds the FE CO over 50% up to a total current density of 900 mA cm -2 The electrochemical ( Fig. 3) and catalytic ( Fig. 4 to 6) The power of the electrodes is determined by their polarization curves ( Fig. 7) in the form of the partial flow density for CO (j co ) further clarified. Fig. Figure 7 shows polarization curves of the different electrodes in relation to the partial current density for CO j. COThe cell potential CP is plotted against the partial flow density for CO j. CO The CoPc / CB and CoPc / N-CB electrodes achieve the same maximum j CO (350 mA cm -2 ), whereby the CoPc / N-CB electrodes require a lower cell overpotential. The mod-CoPc / CB electrode achieved the highest j CO -value of 440 mA cm -2 and thus significantly surpasses the state of the art.

[0078] Fig. Figure 8 shows steps of a process for producing an electrode. The process includes producing a catalyst dispersion 15. In particular, the process also includes producing a catalyst-containing layer 17, for example by depositing the catalyst dispersion.

[0079] Fig.Figure 9 schematically shows the structure of an electrode 1 or part of an electrode 1, in particular a cathodic electrode. A catalyst 3 is located on a substrate 5, for example, carbon paper, particularly within a layer. The catalyst 3 contains a metal phthalocyanine 4. For example, the catalyst 3 contains a metal phthalocyanine 4 which is anchored to carbon nanoparticles. The carbon nanoparticles can be nitrogen-doped. Reference symbol list 1 electrode 1a Cathodic electrode 1b Anodic electrode 2 Membran 3 Catalyst 4 Metal phthalocyanine 5 Substrat 10 Membrane Electrode Unit 11 Zero-Gap Electrolyzer 15 Preparation of a catalyst dispersion 17. Production of a catalyst-containing layer 23 Anodic reactant 24 Cathodic reactant 26 Anodic product 27 Cathodic product 28 anolyte tank 29 Catholyte tank 31 Anolyte circulation 32 Catholyte circulation OER Oxygen Evolution Reaction CO2RR Electrochemical CO2 Reduction CoPc / CB CoPc catalyst anchored to soot mod-CoPc / CB Modified CoPc catalyst for soot CoPc / N-CB CoPc catalyst on N-doped carbon black j Total current density j CO Partial flow density for CO CP cell potential FE Faraday efficiency FE CO Faraday efficiency for CO QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 2019 0 224 660 A1

[0003] US 2022 0 251 715 A1

[0003] US 2021 0 123 146 A1

[0004] Cited non-patent literature

[0000] A. Öztürk and A. Bayrakceken Yurtcan, J. Solid State Chem 296 (2021) 121972 (DOI: 10.1016 / j.jssc.2021.121972

[0051] Öztürk and A. Bayrakceken Yurtcan, J. Solid State Chem 296 (2021) 121972 (DOI: 10.1016 / j.jssc.2021.121972

[0052] H.-L. Zhu et al., J. Phys. Chem. Lett. 14 (2023) 3844-3852 (DOI: 10.1021 / acs.jpclett.3c00317

[0052]

Claims

[1] Electrode (1, 1a, 1b) for a zero-gap electrolyzer (11) comprising a metal phthalocyanine (4). [2] Electrode (1, 1a, 1b) according to claim 1, wherein the electrode (1, 1a, 1b) comprises metal phthalocyanine (4) iron phthalocyanine, zinc phthalocyanine or copper phthalocyanine. [3] Electrode (1, 1a, 1b) according to any of the preceding claims, wherein the electrode (1, 1a, 1b) is an active cathodic electrode (1a). [4] Electrode (1, 1a, 1b) according to one of the preceding claims, wherein the metal phthalocyanine (4) is applied to a porous substrate (5). [5] Electrode (1, 1a, 1b) according to one of the preceding claims, wherein the metal phthalocyanine (4) is applied to a carbon-containing substrate (5). [6] Electrode (1, 1a, 1b) according to one of the preceding claims, wherein the metal phthalocyanine (4) is anchored on carbon nanoparticles. [7] Electrode (1, 1a, 1b) according to the preceding claim, wherein the carbon nanoparticles are N-doped carbon nanoparticles. [8] Membrane electrode assembly (10) for a zero-gap electrolyzer (11) comprising an electrode (1, 1a, 1b) according to any one of claims 1 to 7. [9] Zero-gap electrolyzer (11) comprising an electrode (1, 1a, 1b) according to any one of claims 1 to 7. [10] Use of a metal phthalocyanine (4) as a catalyst (3) in a zero-gap electrolyzer (11). [11] Method for producing an electrode (1, 1a, 1b) for a zero-gap electrolyzer (11), comprising producing a catalyst dispersion (15) containing a metal phthalocyanine (4). [12] Method according to the previous claim, characterized by , that the catalyst dispersion is applied to a carbon-containing and / or porous substrate (5). [13] Method according to one of the two preceding claims, characterized bythat the catalyst dispersion is applied to carbon paper. [14] Method according to any one of the three preceding claims, characterized by that the catalyst dispersion further contains Nafion ionomer and / or polyvinylpyridine. [15] Method according to any one of the four preceding claims, characterized by , that the catalyst dispersion is applied to a substrate (5) by spraying.

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