Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/075—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound
  • C25B11/077—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound the compound being a non-noble metal oxide
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/02—Hydrogen or oxygen
  • C25B1/04—Hydrogen or oxygen by electrolysis of water
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/02—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form
  • C25B11/03—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form perforated or foraminous
  • C25B11/031—Porous electrodes
  • C25B11/032—Gas diffusion electrodes
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/052—Electrodes comprising one or more electrocatalytic coatings on a substrate
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/075—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
  • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms
  • C25B9/23—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms comprising ion-exchange membranes in or on which electrode material is embedded
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis

Definitions

• the present invention relates to a method for producing an electro-catalyst in the form of a HER catalyst for a water electrolyzer.
• the present invention relates to a method for producing an electrocatalyst in the form of an OER catalyst for a water electrolyzer.
• the present invention relates to an electrocatalyst in the form of a HER catalyst for a water electrolyzer.
• the present invention relates to an electrocatalyst in the form of an OER catalyst for a water electrolyzer.
• the invention relates to an electrode for an electrochemical cell, wherein a catalytically active catalyst layer is applied to the electrode, which contains an electrocatalyst or is formed by an electrocatalyst.
• the present invention relates to an ion exchange membrane for an electrochemical reactor, the ion exchange membrane having a first membrane side and a second membrane side, a catalytically active catalyst layer which contains an electrocatalyst or is applied by an electrocatalyst to the first and/or the second membrane side is formed.
• the present invention also relates to a method for producing an ion exchange membrane for an electrochemical reactor, the ion exchange membrane having a first membrane side and a second membrane side, a catalytically active catalyst layer being applied to the first and/or the second membrane side, which layer has a Elektrokata contains analyzer or is formed by an electrocatalyst.
• the present invention relates to a water electrolyzer with a first electrode, a second electrode and an ion exchange membrane arranged between the first electrode and the second electrode, with a first catalytically active catalyst layer between the first electrode and the ion exchange membrane, which layer contains a first electrocatalyst or formed by a first electrocatalyst, and wherein a second catalytically active catalyst layer containing a second electrocatalyst or formed by a second electrocatalyst is arranged between the second electrode and the ion exchange membrane.
• the present invention relates to a method for producing a catalytically active catalyst layer, which contains an electrocatalyst or is formed by an electrocatalyst, for an electrochemical reactor, the catalyst layer being applied to a substrate.
• the present invention relates to a method for producing a water electrolyzer with a first electrode, a second electrode and an ion exchange membrane arranged between the first electrode and the second electrode, with a first catalytically active catalyst layer between the first electrode and the ion exchange membrane, which first electrocatalyst contains or is formed by a first electrocatalyst, is arranged and wherein between the second electrode and the ion exchange membrane a second catalytically active catalyst layer, which contains a second electrocatalyst or is formed by a second electrocatalyst, is arranged.
• the production of hydrogen which can be used in a wide variety of areas such as energy supply, the chemical industry and mobility in particular, is becoming increasingly important.
• Hydrogen can be produced in a particularly simple manner by the electrolysis of water.
• Water electrolyzers are used to split water molecules. It is known in particular to form water electrolyzers with ion exchange membranes which separate the two half-cells of the water electrolyzer. Ion exchange membranes are used, for example, in the form of anion exchange membranes. These are designed in such a way that they allow anions to move from the cathodic half-cell to the anodic half-cell.
• OH ions migrate from the cathodic half-cell to the anodic half-cell when the water electrolyser is in operation, where they react to form water and oxygen, releasing electrons.
• water molecules are converted into hydrogen and OH ions by taking up electrons.
• Catalysts are used to enable water splitting at the lowest possible cell voltages.
• Noble metal catalysts such as platinum and iridium in particular, are highly efficient and generally have long-term stability. However, they are very expensive and not available in unlimited quantities.
• known water electrolyzers comprising an anion exchange membrane and operated with an alkaline electrolyte have the problem that the electrodes and other components such as seals can be damaged during long-term operation by the electrolyte due to its aggressiveness. This has a negative effect on the long-term stability of these water electrolysers.
• This object is achieved according to the invention in a method for producing an electrocatalyst in the form of an HER catalyst for a water electrolyzer in that the HER catalyst is synthesized from an aqueous solution of a molybdenum salt with the addition of an aromatic amine and an acid.
• the proposed production process enables the formation of a HER catalyst which is or contains molybdenum carbide in a simple manner.
• the HER catalyst can be synthesized in a simple manner if ammonium heptamolybdate is used as the molybdenum salt, if aniline is used as the aromatic amine and if hydrochloric acid is used as the acid.
• the molybdenum salt can be dissolved in water and the aromatic amine added.
• the acid can then be added, in particular dropwise.
• aniline another organic amine can also be used, for example melamine.
• the synthesized HER catalyst is washed and dried. For example, it can be washed with an alcohol, in particular ethanol, and then dried for a certain period of time, for example at temperatures in the range between 40°C and 80°C.
• the HER catalyst can be of particularly good quality if the dried HER catalyst is baked out. This can be achieved in particular at temperatures in the range from about 600° C. to about 800° C. Baking is preferably carried out under protective gas in order to prevent undesirable oxidation of the catalyst in air.
• the object set at the beginning is also achieved according to the invention in a method for producing an electrocatalyst in the form of an OER catalyst for a water electrolyzer in that the OER catalyst is made from an aqueous sodium borohydride solution by adding a mixture of an aqueous solution of a nickel salt and an aqueous solution of an iron salt is synthesized.
• the proposed method makes it possible, in particular, to synthesize OER catalysts in a simple manner, which contain nickel and iron in combination with oxygen in particular.
• the production process can be simplified in particular if nickel(II) chloride is used as the nickel salt and if iron(II) chloride is used as the iron salt.
• a particularly good reactivity and a highly efficient microscopic cal structure of the OER catalyst can be formed if the aqueous sodium borohydride solution when adding the mixture with ultrasound, heat and/or UV radiation is applied. In other words, energy is added to the sodium borohydride solution as the mixture is added.
• an electrocatalyst in the form of an HER catalyst for a water electrolyzer of the type described at the outset in that the HER catalyst contains at least one chemical compound which consists of a first transition metal and at least one of the elements carbon, oxygen, sulfur and phosphorus is formed and that the first transition metal is molybdenum or tungsten.
• such a HER catalyst has an excellent activity for hydrogen evolution.
• oxidation of such a catalyst in air in particular does not lead to any loss of activity.
• the chemical compound is molybdenum carbide (MoCx), molybdenum oxide (MoOx) and molybdenum sulfide (MoSx).
• MoCx molybdenum carbide
• MoOx molybdenum oxide
• MoSx molybdenum sulfide
• the chemical compound contains at least one second transition metal, if the first transition metal and the at least one second transition metal differ from one another, if the first transition metal defines a first metal component of the chemical compound, if the at least one second transition metal has a second metal component defined and when the first metal content is greater than the second metal content.
• Such an electrocatalyst is quasi "doped" with a second transition metal.
• HER catalysts with a good effect can be formed in particular when the at least one second transition metal is molybdenum, tungsten, nickel, iron, cobalt, copper or titanium.
• the chemical compound is advantageously W2 y MO 2 (iy) C, Ni2 y MO 2 (iy) C or Fe y Moi- y 03. It is particularly advantageous if the value of y is at most about 0.25. In other words, in this way a proportion of molybdenum is always significantly higher than the proportion of the second transition metal.
• the properties of the HER catalyst can be adjusted in the desired manner by the proportion of the second transition metal.
• the total metal content of the chemical compound is 100 mol% and is defined as the sum of the first metal content in mol% and the second metal content in mol% and when the second metal content has a value in a range from 0 to about 25 mol% . In this way it can be ensured that the first transition metal makes up the majority of the metal content in the chemical compound and thus determines the essential properties of the HER catalyst.
• Particularly efficient HER catalysts can be formed when a proportion of the chemical compound in the HER catalyst ranges from about 67 percent to about 85 percent by weight. In particular, it can be about 76 percent by weight.
• the HER catalyst contains molybdenum oxide.
• the proportion of molybdenum oxide can range from about 5 percent by weight to about 13 percent by weight. In particular, it can be about 9 percent by weight.
• the HER catalyst includes molybdenum, particularly in a range from about 10 percent to about 20 percent by weight. In particular, the HER catalyst may contain about 15 weight percent molybdenum.
• the HER catalyst has an acicular or substantially acicular structure.
• a high surface area of the HER catalyst can be realized and thus a high catalytic activity.
• the electrocatalyst is prepared by one of the advantageous methods described above for preparing an electrocatalyst in the form of a HER catalyst for a water electrolyzer.
• HER catalysts which have an acicular or essentially acicular structure.
• an electrocatalyst in the form of an OER catalyst for a water electrolyzer in that the OER catalyst contains nickel and iron in combination with oxygen and/or phosphorus if the nickel content of the nickel in the OER catalyst is greater is as an iron content of the iron on the OER catalyst and when a value of the sum of the nickel content and the iron content is at least about 50 mol% of a total metal content of the OER catalyst.
• Such an electrocatalyst has very good properties for supporting the oxygen evolution reaction in the anodic half-cell of a water electrolyzer.
• the main metallic components of the OER catalyst are nickel and iron.
• other metals can also be contained in the OER catalyst in order to optimize its performance.
• the OER catalyst contains cobalt, copper and/or manganese, if the sum of a proportion of cobalt, a proportion of copper and a manganese content on the OER catalyst has a value which is smaller than the iron content. Since the proportion of iron in the OER catalyst is smaller than the proportion of nickel, the proportions of cobalt, copper and/or manganese in the OER catalyst are relatively unimportant, but have a positive effect on the properties of the OER catalyst.
• the sum of the cobalt content, the copper content and the manganese content in the total metal content has a value in a range from 0 to about 20 mol %.
• the electrocatalyst is Ni x Fe y Cu z 04 or Ni x Fe y Mn z 04 and if x>y>z.
• the electrocatalysts mentioned have a good catalytic effect for the oxygen evolution reaction.
• the OER catalyst contains nickel, iron and oxygen, that a proportion of nickel is in a range from about 40 percent by weight to about 85 percent by weight, that a proportion of iron is in a range from about 1% to about 30% by weight and that a proportion of the oxygen is in a range from about 10% to about 35% by weight.
• nickel is in a range from about 40 percent by weight to about 85 percent by weight
• iron is in a range from about 1% to about 30% by weight
• a proportion of the oxygen is in a range from about 10% to about 35% by weight.
• the OER catalyst has a structure in the form of larger clusters that are covered with small nanoparticles.
• a large surface can be realized in this way, which helps to further improve an effect of the electrocatalyst.
• the OER catalyst is produced by one of the above-described advantageous methods for producing an electrocatalyst in the form of an OER catalyst for a water electrolyzer.
• the manufacturing processes described can be used to create an OER Catalyst can be realized with a structure that has larger clusters that are covered with small nanoparticles.
• the object at the outset is also achieved according to the invention with an electrode for an electrochemical cell of the type described above in that the electrocatalyst is one of the electrocatalysts described above.
• electrodes for an electrochemical cell can be formed in a simple manner, for example by applying a HER catalyst to one electrode and an OER catalyst to the other electrode, and if the electrodes are brought into contact with their catalyst layers over the entire surface with an anion exchange membrane will.
• the electrode comprises a gas diffusion layer and if the catalyst layer is applied to the gas diffusion layer.
• the electrode is designed in the form of an anode and if the electrocatalyst is an OER catalyst.
• the electrocatalyst is an OER catalyst.
• it can be one of the advantageous OER catalysts described above. In this way, an anodic half-cell of a water electrolyzer can be formed.
• the electrode is in the form of a cathode and if the electrocatalyst is an HER catalyst.
• the HER catalyst can be one of the advantageous HER catalysts described above.
• a cathodic half-cell of a water electrolyzer can thus be formed with high efficiency.
• the task at the outset is achieved with an ion exchange membrane for an electrochemical reactor of the type described at the outset.
• the electrocatalyst is one of the advantageous electrocatalysts described above.
• ion exchange membranes can be designed as independent units with the electrocatalysts described above, which simplifies the production of water electrolyzers.
• the ion exchange membrane can, for example, be coated on one or both sides with a catalyst layer, optionally with an HER catalyst and/or an OER catalyst.
• the ion exchange membrane is formed in the form of an anion exchange membrane. In particular, this allows OH ions to get from the cathodic half-cell into the anodic half-cell of a water electrolyzer.
• a first catalyst layer is applied to the first side of the membrane, if the first catalyst layer contains a first electrocatalyst or is formed by a first electrocatalyst and if the first electrocatalyst is an OER catalyst.
• the OER catalyst can be one of the advantageous OER catalysts described above. In this way, an ion exchange membrane can easily be coated with inexpensive yet highly active OER catalysts.
• a second catalyst layer is applied to the second side of the membrane, if the second catalyst layer contains a second electrocatalyst or is formed by a second electrocatalyst and if the second electrocatalyst is a HER catalyst.
• the HER catalyst can be one of the advantageous HER catalysts described above.
• the ion exchange membrane can thus be used in a simple manner to delimit a cathodic half-cell of a water electrolyzer.
• the object stated at the outset is also achieved according to the invention in a method for producing an ion exchange membrane for an electrochemical reactor in that one of the advantageous electrocatalysts described above is used as the electrocatalyst. In this way, an ion exchange membrane can easily be formed as an independent unit that can be used to form a water electrolyzer.
• the first catalyst layer applied to a first transfer support has the first membrane side and the second catalyst layer applied to a second transfer support has the second membrane side are brought into extensive contact and pressed together.
• the catalyst layers are therefore not applied directly to the ion exchange membrane, but first to a transfer support.
• the catalyst layers are then transferred from the transfer carrier, which can be in the form of a transfer substrate, by laying them flat with the respective catalyst layer on one of the membrane sides and then pressing them with the ion exchange membrane.
• the transfer carrier can then be removed, for example pulled off.
• the catalyst layers and the ion exchange membrane are heated during pressing.
• they can be heated to a temperature in a range from about 40°C to about 130°C.
• the temperature can be about 65°C during pressing.
• the pressing is carried out at a pressure in a range from about 5 bar to about 130 bar.
• Good bonding of the catalyst layers to the ion exchange membrane can be achieved in particular by pressing being carried out over a period of between approximately 1 minute and approximately 15 minutes. In particular, the time period can be about 4 minutes.
• the transfer carriers are preferably removed from the catalyst layers after pressing. If the ion exchange membranes, which are provided with catalyst layers, are used as independent units, the transfer carriers can remain in place for the time being. They can thus be used as a protective layer. For the manufacture of a water electrolyzer, the transfer supports are then stripped off before the catalyst layers are brought into contact with an electrode of the water electrolyzer.
• the object set at the outset is also achieved according to the invention in a water electrolyzer of the type described at the outset in that the first electrocatalyst and/or the second electrocatalyst is one of the advantageous electrocatalysts described above.
• first electrode and/or the second electrode is designed in the form of one of the advantageous electrodes described above. In this way, production of the water electrolyzer can be simplified if the electrodes are used in particular already coated.
• the first electrode is in the form of an anode
• the second electrode is in the form of a cathode and if the ion exchange membrane is in the form of an anion exchange membrane.
• an anion exchange membrane water electrolyzer can be easily formed.
• the first electrocatalyst is an OER catalyst and the second electrocatalyst is a HER catalyst.
• the OER catalyst is one of the OER catalysts described above.
• the HER catalyst is one of the advantageous HER catalysts described above. A water electrolyzer with a high level of efficiency can thus be designed simply and inexpensively.
• the first catalyst layer is applied to the first electrode or to the ion exchange membrane and if the second catalyst layer is applied to the second electrode or to the ion exchange membrane.
• subunits, optionally the ion exchange membrane or the electrodes, can be formed that already carry the respective catalyst layers.
• a water electrolyzer can be formed in a particularly simple manner if the first electrode with the first catalyst layer, the ion exchange membrane and the second electrode with the second catalyst layer are pressed together. In this configuration, electrodes already coated with electrocatalysts are used, which are then pressed with an uncoated ion exchange membrane. This is particularly advantageous when the ion exchange membrane is in the form of an anion exchange membrane. Anion exchange membranes are usually mechanically not very stable. It is therefore technically extremely difficult to apply the catalyst layers to these membranes. The procedure described simplifies the production of water electrolysers significantly.
• the water electrolyzer comprises an electrolyte with a pH in the range from about 7 to about 13.
• the pH of the electrolyte is preferably in the range from about 7 to about 11.
• an electrolyte with a pH close to 7 can be used, i.e. a Electrolyte, which is only weakly alkaline.
• the long-term stability of the water electrolyser in particular can be increased, since strongly alkaline electrolytes are very aggressive and there is a risk that components of the water electrolyser that come into contact with the electrolyte can be damaged, such as electrodes and seals.
• the water electrolyzer can be formed in a simple manner if the electrolyte is formed by a neutral to alkaline salt dissolved in a solvent.
• the neutral to alkaline salt has a concentration with a value in a range from 0 to about 0.4 molar, in particular it can be in a range from 0 to 0.1 molar.
• weakly alkaline electrolytes can be formed in this way.
• the neutral to alkaline salt is or contains potassium hydroxide (KOH), sodium hydroxide (NaOH), lithium hydroxide (LiOH), sodium or potassium carbonate or bicarbonate (Na2CO3, K2CO3, NaHCO3, KHCO3).
• the solvent is or contains water or alcohol.
• environmentally friendly water electrolysers can be trained.
• the object set at the outset is also achieved according to the invention in a method for producing a catalytically active catalyst layer of the type described at the outset in that one of the advantageous electrocatalysts described above is used as the electrocatalyst.
• electrocatalysts By using the electrocatalysts mentioned, catalytically highly effective catalyst layers can be formed.
• An electrode, a gas diffusion layer arranged on an electrode or an ion exchange membrane of the electrochemical reactor or a transfer carrier is preferably used as the substrate.
• the catalyst layers can be formed on the electrode, the gas diffusion layer, the ion exchange membrane or a transfer carrier.
• Catalyst layers can be easily formed on substrates in the form of a carbon fiber mat, a metal fiber mat or a stack of stainless steel wire mesh.
• the metal fiber mats can be designed in the form of titanium fiber mats, nickel fiber mats or stainless steel fiber mats.
• the catalyst layer applied to the transfer support is applied to the electrode, the gas diffusion layer arranged on an electrode or the ion exchange membrane of the electrochemical reactor and the transfer support is removed.
• the application of the catalyst layer can be optimized in particular if the substrate and the transfer support are pressed together, in particular at a temperature that is above room temperature. In other words, heating the transfer support and the substrate when transferring the catalyst layer is advantageous.
• Catalyst layers can be handled in a simple manner if a foil is used as the transfer carrier.
• this can be made of plastic or metal.
• the plastic can be, for example, polytetrafluoroethylene.
• Such a plastic film can be pulled off the catalyst layer in a simple manner if this has been applied to an ion exchange membrane or an electrode, for example.
• the catalyst layer can be formed in a simple manner if it is formed by applying a catalyst solution containing the electrocatalyst to the substrate. Catalyst solutions are easy to handle and can be applied to the substrate using a variety of methods.
• the substrate is heated when the catalyst solution is applied.
• it can be heated to a temperature ranging from about 50°C to about 90°C.
• the temperature can be about 65°C.
• the catalyst layer can be formed in a simple manner by applying the catalyst solution to the substrate by spraying, by screen printing, by drawing a film or by doctoring.
• Particularly efficient catalyst layers can be formed if the catalyst solution is sprayed on by spraying a plurality of layers with a spray gun from a distance of about 3 cm to about 10 cm using an inert gas flow with a volume flow in a range from about 1 l/min to about 5 l /min is formed.
• the distance between the spray gun and the substrate when spraying can be around 5 cm.
• the volume flow of the inert gas can be formed in particular by a stream of nitrogen and/or argon.
• a volume flow of the inert gas can be, in particular, 2 l/min.
• the catalyst solution applied to the substrate is dried.
• the catalyst solution is formed by dissolving the electrocatalyst in a solvent. It is particularly environmentally friendly when the solvent is water and/or alcohol.
• propanol is used as the alcohol.
• this can be 2-propanol.
• an ion exchange ionomer is added to the solution of the electrocatalyst in the solvent. It is preferably an ionomer from which the ion exchange membrane is formed.
• Nafion, Aquivion, Sustainion XB-7 and/or Fumion is used as the ion exchange ionomer.
• a mixing time can in particular be in a range from about 5 minutes to about 25 minutes. In particular, it can be about 15 minutes.
• the object stated at the outset is achieved according to the invention in that the first catalyst layer is applied to the first electrode and the first electrode and the second electrode are pressed with the ion exchange membrane arranged between them .
• Water electrolyzers can thus be formed in a simple manner, in particular with mechanically unstable ion exchange membranes.
• the contact between the ion exchange membrane and the first catalyst layer leaves be prepared in such a simple way.
• the second catalyst layer can also be applied to the second electrode before the electrodes are pressed with the ion exchange membrane arranged between them.
• one of the advantageous electrocatalysts described above is used as the first electrocatalyst and/or as the second electrocatalyst.
• the first electrocatalyst can be one of the HER catalysts described above and the second electrocatalyst can be one of the OER catalysts described above.
• the water electrolyzer can be designed in a simple manner if electrodes are used as the first electrode and as the second electrode, as are described above as advantageous embodiments.
• the water electrolyzer can be formed in a simple manner, in particular by forming the first catalyst layer and/or the second catalyst layer using one of the advantageous methods described above.
• Figure 1 a schematic representation of the production of an OER
• FIG. 2 a scanning electron micrograph of an exemplary embodiment of an OER catalyst
• Figure 3 a schematic representation of an embodiment of a
• FIG. 4a a schematic representation of the application of a catalyst solution to a substrate by spraying
• FIG. 4b a photographic representation of a catalyst layer prepared by spraying
• FIG. 5a a schematic representation of the application of a catalyst solution to a substrate by means of screen printing
• FIG. 5b a photographic representation of an exemplary embodiment of a catalyst layer prepared by screen printing
• FIG. 6a a schematic representation of the formation of a catalyst layer on a substrate by drawing a film or squeegeeing
• FIG. 6b a photographic representation of a catalyst layer formed by film drawing
• FIG. 7 a schematic exploded view of an exemplary embodiment of an electrolytic cell
• FIG. 8 a schematic sectional view of an exemplary embodiment of an electrolyzer
• FIG. 9 a schematic exploded view of a further exemplary embodiment of an electrolyzer
• FIG. 10 a comparative representation of the operating parameters of different electrolytic cells
• FIG. 11 a comparative representation of cell parameters of further electrolytic cells
• Figure 12 is a scanning electron micrograph of an embodiment of a HER catalyst
• FIG. 13 a schematic representation of a structure of an embodiment of an alkaline water electrolyzer and its mode of operation
• FIG. 14 Reaction equations for water electrolysis in an alkaline medium
• FIG. 15 shows a schematic representation of the structure of an exemplary embodiment of an ion exchange membrane coated on both sides with catalyst layers;
• FIG. 16 shows a schematic representation of an exemplary embodiment of an ion exchange membrane before pressing with two substrates, each of which has a catalytically active layer on one side;
• FIG. 17 the dependency of the current densities on the respective cathode potentials (related to the reversible hydrogen electrode RHE) of the HER catalysts of exemplary embodiments 2 to 12;
• FIG. 18 the dependency of the current densities on the respective anode potentials (related to the reversible hydrogen electrode RHE) of the OER catalysts of exemplary embodiments 13 to 20 and of iridium black;
• FIG. 19 the dependence of the cell potential on the current density in cell tests with open cells with different membranes as indicated
• FIG. 20 the dependence of the cell potential on the current density in cell tests with open cells and closed cells with different membranes
• NiFeOx/Mo2C and Ir/Pt as catalyst and the corresponding amount of recovered oxygen (electrolyte: 0.1M KOH; cell temperature: 50°C).
• FIG. 13 schematically shows an exemplary embodiment of a water electrolyzer 10 with an anodic half-cell 12 and a cathodic half-cell 14.
• the two half-cells 12 and 14 are separated from one another by an ion exchange membrane 16.
• the water electrolyzer 10 han delt it is a so-called alkaline water electrolyzer 10, which is operated with an alkaline electrolyte 18 wel cher.
• the electrolyte 18 thus has a pH greater than 7.
• the ion exchange membrane 16 is formed in the alkaline water electrolyzer 10 in the form of an anion exchange membrane 20 which allows anions 22 in the form of hydroxide ions 24 to be from one of the two half-cells 12 or 14 to the other half-cell 12 or 14 respectively.
• a cathode 26 is immersed in the electrolyte 18 in the cathodic half-cell 14 and an anode 28 in the anodic half-cell 12.
• the cathode 26 is at least partially coated with a cathodic catalyst layer 30, and the anode 28 is partially coated with an anodic catalyst layer 32.
• the cathodic catalyst layer 30 consists or contains an electrocatalyst 34 in the form of a HER catalyst 36, which promotes the hydrogen evolution reaction ("HER"), ie the conversion of water into hydrogen and hydroxide ions while accepting electrons.
• HER hydrogen evolution reaction
• the anodic catalyst layer 30 is formed by an electrocatalyst 38 in the form of an OER catalyst 40, which supports the oxygen evolution reaction ("OER") in the anodic half-cell 12, ie the conversion of hydroxide ions into oxygen and water with the release of electrons.
• OER oxygen evolution reaction
• the water electrolyser 10 is operated via a power source 42 whose positive pole 44 is connected to the anode 28 and whose negative pole 46 is connected to the cathode 26 .
• a minimum cell voltage is required to operate the water electrolyzer 10 in order to enable the oxygen evolution reaction in the anodic half-cell 12 on the one hand and the hydrogen evolution reaction in the cathodic half-cell 14 on the other hand.
• electrocatalysts 34 and 38 in the form of HER catalysts 36 and OER catalysts 40 are used in order to be able to operate the water electrolyzer 10 with the lowest possible cell voltage.
• platinum and iridium can be used as electrocatalysts both for the oxygen evolution reaction and for the hydrogen evolution reaction.
• these noble metals are very expensive, so that there is great interest in using cheaper but similarly efficient catalysts such as platinum and iridium.
• Below execution examples of different electrocatalysts 34 and 38 are described, which can replace platinum and iridium as electrocatalysts 10 in alkaline water electrolyzers 34, 38.
• Ammonium heptamolybdate hexahydrate (33.03g) was dissolved in water (18.2MW, 533ml) and aniline (42.7g) added. Hydrochloric acid (1M) was added dropwise to this emulsion until a white precipitate was obtained at pH ca. 4 (350 ml). The reaction solution was stirred at 50° C. for 5 h. Thereafter, the precipitate was separated, washed with ethanol and dried at 50° C. for 12 h. The balance was 36.4 g.
• Example HER catalyst - production (AB5)
• Ammonium heptamolybdate hexahydrate (2.48g) was dissolved in water (18.2MW, 40ml) and aniline (3.14g) added. Hydrochloric acid (1M) was added dropwise to this emulsion until a white precipitate was obtained at pH ca. 4 (30 ml). The reaction solution was stirred at 50° C. for 5 h. Thereafter, the precipitate was separated, washed with ethanol. The wet precipitate was slurried with ethanol solutions of nickel chloride hexahydrate (0.33 g in 100 ml) and the ethanol evaporated in a glass dish with stirring at 50°C. The weight was 2.7 g.
• Example HER catalyst - production (AB8)
• 500mg of the product was slurried with an ethanol solution of ferric chloride tetrahydrate (0.04g in 2ml) and the ethanol allowed to evaporate.
• the crude product was heated in a quartz tube, air from the reaction chamber first being released for 4 h in a stream of argon (0.4L7min).
• the crude product was heated to 500°C at a rate of 2°C/min in a stream of argon, then kept at this temperature for 5 h and finally allowed to cool.
• the final weight was 0.27 g.
• Example HER catalyst - production (AB9)
• Oxalic acid dihydrate (25.2 g) was dissolved in water (18.2 MOhm, 400 ml), and ammonium heptamolybdate hexahydrate (2.7 g) and melamine (12.6 g) were added and the mixture was stirred at 60° C. for 6 h. Thereafter, nickel chloride hexahydrate (24 g dissolved in water (18.2 MOhm, 100 ml)) was added and the mixture was stirred at room temperature (RT) for 16 h. The precipitate was separated, washed with water and dried at 70° C. for 12 h. The balance was 38 g.
• the catalytic effect of the described second embodiment ei nes HER catalyst is better compared to the first embodiment of the HER catalyst.
• Essential components of the two exemplary embodiments of HER catalysts described are molybdenum carbide.
• FIG. 3 schematically shows the sequence of the described syntheses of the two exemplary embodiments of the HER catalysts 36 in the form of molybdenum carbide (MO2C).
• MO2C molybdenum carbide
• FIG. 17 the dependency of the current densities on the respective cathode potentials (relative to the reversible hydrogen electrode RHE) of the HER catalysts of exemplary embodiments 2 to 12 is plotted. The measurements were carried out using a rotating disc electrode. The highest current density at the lowest potential was achieved for the HER catalyst according to embodiment 2.
• Nickel(II) chloride hexahydrate (9.745 g) was dissolved in water (18.2 MW, 133 mL) as was ferrous chloride tetrahydrate (2,823 g) in water (18.2 MW, 133 mL ) solved. Both solutions were mixed.
• the production was carried out according to example 13, with 10% of the Ni being replaced by copper (Cu) during the synthesis.
• Nickel (II) chloride hexahydrate (8.528 g) and ferrous chloride tetrahydrate (2.744 g) were dissolved in water (18.2 MW, 89 ml each).
• copper (II) chloride dihydrate (0.940 g) was dissolved in water (18.2 MW, 89 ml). The solutions were mixed.
• the production was carried out according to example 13, with 10% of the Ni being replaced by manganese (Mn) during the synthesis.
• Nickel (II) chloride hexahydrate (8.528 g) and ferrous chloride tetrahydrate (2.744 g) were dissolved in water (18.2 MW, 89 ml each).
• manganese (II) chloride tetrahydrate (1.092 g) was dissolved in water (18.2 MW, 89 mL). The solutions were mixed.
• Nickel (II) chloride hexahydrate (11.694 g) was dissolved in water (18.2 MW, 133 mL), also ferrous chloride tetrahydrate (1.133 g) was dissolved in water (18.2 MW, 133 mL). . Both solutions were mixed.
• the production was carried out according to example 13, the ratio of Ni and Fe being varied during the synthesis.
• Nickel(II) chloride hexahydrate (10.72 g) was dissolved in water (18.2 MW, 133 mL) as was ferrous chloride tetrahydrate (1.976 g) in water (18.2 MW, 133 mL ) solved. Both solutions were mixed.
• Nickel (II) chloride hexahydrate (8.77 g) was dissolved in water (18.2 MW, 133 mL) as was ferrous chloride tetrahydrate (3.670 g) in water (18.2 MW, 133 mL). solved. Both solutions were mixed.
• Production took place in accordance with exemplary embodiment 13, with the product being tempered at 250° C. after the synthesis.
• Nickel(II) chloride hexahydrate (9.745 g) was dissolved in water (18.2 MW, 133 mL) as was ferrous chloride tetrahydrate (2,823 g) in water (18.2 MW, 133 mL ) solved. Both solutions were mixed.
• a reaction flask was placed under nitrogen and sodium borohydride (10.44 g) dissolved in water (18.2 MW, 533 mL) therein. This solution was placed under ultrasound (160W, 35kHz) and the nickel/iron solution was added dropwise over 10 minutes. Thereafter, the reaction solution was stirred for 30 minutes. The reaction product was separated, washed with water and ethanol and dried at 50° C. for 12 h. Weight 5.45 g.
• reaction product 200 mg were heated in a porcelain boat at 250° C. in an air atmosphere for one hour in a tube furnace.
• Exemplary OER catalyst - production (AB21) Production took place in accordance with exemplary embodiment 13, with the product being tempered at 300° C. after the synthesis.
• Nickel(II) chloride hexahydrate (9.745 g) was dissolved in water (18.2 MW, 133 mL) as was ferrous chloride tetrahydrate (2,823 g) in water (18.2 MW, 133 mL ) solved. Both solutions were mixed.
• a reaction flask was placed under nitrogen and sodium borohydride (10.44 g) dissolved in water (18.2 MW, 533 mL) therein. This solution was placed under ultrasound (160W, 35kHz) and the nickel/iron solution was added dropwise over 10 minutes. Thereafter, the reaction solution was stirred for 30 minutes. The reaction product was separated, washed with water and ethanol and dried at 50° C. for 12 h. The final weight was 5.45 g.
• reaction product 200 mg were heated in a porcelain boat at 300° C. in an air atmosphere for one hour in a tube furnace.
• FIG. 18 the dependency of the current densities on the respective anode potentials (relative to the reversible hydrogen electrode RHE) of the OER catalysts of exemplary embodiments 13 to 21 is plotted.
• the measurements were carried out using a rotating disc electrode.
• the highest current density at the lowest potential was achieved for the OER catalysts according to exemplary embodiments 13, 20 and 21.
• the dependency of the current density on the anode potential for iridium black is plotted as a reference.
• FIG. 1 shows schematically the syntheses described according to the above-described embodiments of the electrocatalyst 38 in the form of the OER catalyst 40.
• FIG. 2 shows a scanning electron microscope image of the OER catalyst nickel-iron oxide (NiFeOx). The examined sample is amorphous.
• the described exemplary embodiments 1 to 4 are purely exemplary.
• the synthesis routes described are basically based on the synthesis of oxides, sulfides, carbides and phosphides and a mixture of metals from the fourth period of the periodic table, in particular zinc, manganese, copper, iron, nickel, chromium and cobalt, and the metals from the fifth period of the periodic table, namely molybdenum and silver.
• Figures 7 and 8 show the schematic structure of an electrolytic cell 48 of a water electrolyzer.
• An ion exchange membrane 16 in the form of an anion exchange membrane 20 is arranged between a plate-shaped anode 28 and a plate-shaped cathode 26 .
• the sheet-like ion exchange membrane 16 has a first membrane side 50, which points in the direction of the anode 28, and a second membrane side 52, pointing in the opposite direction, which points in the direction of the cathode 26.
• the first side of the membrane is in surface contact with an anodic catalyst layer 32, which contains the OER catalyst 40 or is made of this be.
• the second membrane side 52 is in planar contact with the cathodic catalyst layer 30, which consists of the HER catalyst 36 or contains it.
• An anodic gas diffusion layer 54 is arranged between the anode 28 and the anodic catalyst layer 32 and is in contact with the anode 28 on the one hand and the anodic catalyst layer 32 on the other.
• a cathodic gas diffusion layer 56 is arranged between the cathodic catalyst layer 30 and the cathode 26, which on the one hand is flat with the cathodic catalyst layer 30 and on the other hand with the anode 26 is in con tact.
• the anodic gas diffusion layer 54 and the cathodic gas diffusion layer 54 are divided schematically in Figure 8 into two regions 58 and 60, with region 60, which is each connected to one of the electrodes 62 or 64, which are on the one hand the cathode 26 and on the other hand the anode 28 , has a greater porosity than the region 58 which is positioned between the region 60 and the respective catalyst layer 30 or 32.
• This design of the gas diffusion layers 54 and 56 allows the reaction gases hydrogen from the cathodic half-cell 14 and oxygen from the anodic half-cell 12 to be optimally discharged.
• the OER catalyst in the arrangements described in FIGS. 7 and 8 can contain, in particular, nickel-iron oxide or iridium.
• the HER catalyst is or includes molybdenum carbide or platinum on the cathode 26, which is formed of stainless steel.
• the electrodes 62 and 64 are in the form of stainless steel current collector end plates.
• the areas 58 with lower porosity are in the form of fiber mats, in particular in the form of carbon fiber mats or titanium fiber mats. They have a thickness of about 250 ⁇ m. When these fiber mats are used, the region 60 is formed from a stainless steel wire mesh staple having a thickness of about 4mm.
• FIG. 9 shows a further exemplary embodiment of a schematic structure of an electrolytic cell 48.
• the reference symbols already used above are used to describe electrolytic cells 48.
• the ion exchange membrane 16 is surrounded by a seal 68 and is in full contact with the membrane sides 52 and 50, on the one hand, with the cathodic catalyst layer 30 and, on the other hand, with the anodic catalyst layer 32.
• the catalyst layers 30 and 32 are each applied to a substrate 70 and 72, respectively, which is in the form of a fiber mat. Carbon fiber mats and titanium fiber mats can be used here.
• the substrates 70 and 72 form the areas 58 described above.
• the current collectors 74 and 76 are also surrounded by a gasket 78.
• Connection contacts 80 and 82, respectively, are provided on the current collectors 74 and 76 for connection to a power source.
• the current collectors 74 and 76 are each connected to an end plate 84 and 86 by a seal 88, respectively.
• the end plates 84 and 86 are screwed together in a manner not shown and press the elements arranged between them together.
• the areas 58 in the arrangement in Figure 8 each form a substrate 70 or 72 for the cathodic catalyst layer 30 or the anodic catalyst layer 32.
• the catalyst layers 30 and 32 can either be applied to the membrane sides 50 or 52 of the ion exchange membrane 16, as shown schematically in FIG.
• Gas diffusion layers 56 and 54 in the form of stainless steel wire mesh stacks are additionally applied to the catalyst layers 30 and 32 .
• the catalyst layers 30 and 32 are applied to the substrates 70 and 72.
• these are in the form of fiber mats, in particular carbon fiber mats, stainless steel fiber mats, titanium fiber mats or nickel fiber mats.
• an additional gas diffusion layer 54 or 56 in the form of a stainless steel wire mesh stack is applied to the sides of the substrates 70 and 72 facing away from the catalyst layers 30 and 32, in order to enable optimal transport of the electrolysis gases .
• the anodic catalyst layer 32 may be applied to the ion exchange membrane 16 while the cathodic catalyst layer is applied to the substrate 70, or vice versa.
• the catalyst layers 30 and 32 optionally also contain ionomer from which the ion exchange membrane 16 is formed.
• ionomer from which the ion exchange membrane 16 is formed.
• an optimal connection of the catalyst layers 30 and 32 with the ion exchange membrane 16 can be produced and at the same time a high ionic conductivity in the catalyst layer can be ensured, even if the catalyst layers 30 and 32 are initially on substrates 70 and 72, as can be seen. matically shown in FIG. 16, applied and then brought into contact over the entire surface with the uncoated ion exchange membrane 60 and pressed.
• FIG. 11 shows an example of the result of cell tests, with an aqueous 0.1 M potassium hydroxide solution being used as the electrolyte in each case.
• the indication “CCS” means that the respective catalyst layer 30 or 32 was applied to a substrate 70 or 72, respectively.
• CCM means that the catalyst layer 30 or 32 was applied directly to the ion exchange membrane 16 or transferred from a transfer support.
• the cell was either immersed directly in the electrolyte in an open setup (open cell) or alternatively in a closed cell setup (closed cell), the electrolyte was drained from two separate annealed reservoirs through the anode and cathode sides of the cell pumped at about 10 to 100 ml/min. In the case of the closed cell, it was also possible to determine the amount of gases evolved.
• FIG. 11 clearly shows that the best cell properties can be achieved if carbon fiber materials are used as substrates 70 and 72, to which the catalyst layers 30 and 32, respectively, are applied.
• FIG. 10 shows, also in the case of the open cell, in particular that the tested cell configurations in which the catalyst layers 30 and 32 were applied to a substrate 70 and 72, respectively, show a good function while the application of the catalyst layers 30 or 32 on the ion exchange membrane 16 provides poorer results. What is striking here is the deviation for substrates 70 and 72 in the form of titanium fiber mats, with which poorer results were achieved despite coating the same and not the ion exchange membrane 16 .
• FIG. 10 shows, by way of example, the results of further cell tests with open cells using the catalysts specified in FIG. If 0.1 molar potassium hydroxide solution is used as the electrolyte, the results are best when using platinum as the HER catalyst and iridium as the OER catalyst.
• the catalysts molybdenum carbide (HER catalyst) and nickel-iron oxide (OER catalyst) described above are only slightly worse.
• the tested electrolytic cells 48 show relatively poor results, regardless of the catalysts used.
• FIG. 20 shows the comparison between open and closed cell when using nickel-iron-oxide/molybdenum carbide and iridium/platinum-coated substrates (CCS) and sustainion membrane in 0.1M KOH and 50°.
• CCS nickel-iron-oxide/molybdenum carbide and iridium/platinum-coated substrates
• the stability was also examined in the closed cell (FIG. 21).
• water was continuously split at a current density of 1A/cm2 over a period of 150 to 230 hours and the required cell potential and the oxygen formed were measured.
• the electrolysis efficiency (calculated from the amount of oxygen obtained in relation to the amount of oxygen expected for a reaction with 100% faradaic efficiency) was 72% for molybdenum carbide and nickel-iron oxide.
• the degradation after 200 hours was 0.4 mV /H.
• Membranes were produced according to the example below.
• the layered double hydroxide (LDH) used to make the PVA-LDH membrane was synthesized as follows. Magnesium nitrate hexahydrate (7.62 g) and aluminum nitrate nonahydrate (3.72 g) were dissolved in 160 mL of water. A sodium carbonate solution (17.16 g in 540 ml of water) was added dropwise over the course of 30 minutes with vigorous stirring. During the addition, the pH was kept at 11 by adding 1M NaOH solution. The reaction solution was then stirred at 60° C. for 6 h. The precipitate was separated, washed with water and ethanol, slurried in ethanol and oven dried at 55°C. The final weight was 3.13 g.
• catalyst solutions are produced in the form of so-called inks, which are applied using different application methods, as described below, either to the substrates 70 or 72 or to the membrane sides 52 or 54 of the ion exchange membrane 16 can be applied.
• MO2C and 2 mg carbon powder were mixed with 600 ml water (18.2 MW), 150 ml ethanol and 64.5 ml Nafion D-520 (5 wt% in a mixture of water and 2-propanol) within mixed under ultrasound for 15 minutes.
• 4 mg NiFeOx was mixed with 400 ml water, 413 ml 2-propanol and 10.24 ml Aquivion D98 (6% by weight in water) within 15 minutes under ultrasound.
• NiFeOx 50 mg NiFeOx was mixed with 200mL water, 175 mg FAA-3 (5% in ethanol) added and mixed under ultrasound within 15 minutes. An area of 2x2 cm can be coated with this ink.
• the 25th exemplary embodiment for forming a catalyst solution was used to coat the substrates 70 and 72 with the catalyst layers 30 and 32, respectively.
• the catalyst solutions were prepared according to the 26th exemplary embodiment and cell measurements were carried out. It should be noted here that the catalyst solution according to the 26th embodiment was used to form the catalyst layer 32 by screen printing. To coat the substrates 70 and 72, the catalyst solution according to exemplary embodiments 24, 25 and 26, as shown schematically in FIG. 4a, was sprayed onto the substrate 70 or 72 using a spray gun in the form of an airbrush gun 90. Carbon fiber mats, nickel fiber mats, titanium fiber mats and stainless steel fiber mats served as substrates 70 and 72, respectively.
• the substrates 70 and 72 were heated during spraying with the catalyst solution 92, for example to 60° C., and the catalyst solution 92 was evenly distributed in several layers from a distance of about 5 cm by means of an inert gas flow, for example nitrogen, of about 2 l/min applied.
• an inert gas flow for example nitrogen
• the substrates 70, 72 in alternative exemplary embodiments were pressed in a hot press at 125° C. for 5 minutes with a pressure of 10 to 50 bar.
• FIG. 4b shows the result of a catalyst layer sprayed on in this way.
• the catalyst solution according to the 26th exemplary embodiment is printed with a screen printing machine 96 on a moist FAA-3-30 membrane conditioned in 0.1 M KOH solution.
• the printed area was 2.1 by 2.1 cm.
• the screen used for this screen print is specified as FL-190, 16.7 pm.
• the ion exchange membrane 16 was placed in 0.1 M KOH solution.
• FIG. 5a shows the screen printing of the catalyst solution 92 or ink.
• Figure 5b shows the printed catalyst layer 30 or 32.
• FIG. 6a shows schematically how the catalyst solution according to the 26th exemplary embodiment is applied with a doctor blade 98 to form the catalyst layer 30 or 32 onto a substrate 70 or 72 respectively.
• a transfer substrate 94 can also be used.
• the catalyst solution 92 is also applied with the airbrush gun 90 in this so-called "decal transfer process".
• the transfer substrate 94 is also heated to about 65° C. and the catalyst solution 92 is evenly applied in several layers from a distance of about 5 cm by means of a nitrogen stream of about 2 l/min. A Teflon film served as the transfer substrate 94 .
• the ion exchange membrane 16 In order to coat the ion exchange membrane 16 with the catalyst layers 30 and 32, it is placed in a dry state between two transfer substrates 94 each coated to an area of 2.1 by 2.1 cm.
• the transfer substrates 94 are coated on the one hand with a HER catalyst and on the other hand with an OER catalyst. These are in particular in the form of the molybdenum carbide and nickel-iron oxide catalysts described above.
• the catalyst layers 30 and 32 face the ion exchange membrane 16 and rest against the first membrane side 50 on the one hand and the second membrane side 52 on the other.
• the assembly of ion exchange membrane 16 sandwiched between the catalyst layers 30 and 32, respectively, disposed on the transfer substrates 94 are then placed in a hot press.
• the catalyst layers 30 and 32 are transferred to the ion exchange membrane 16 within 10 minutes at a temperature of about 65° C. and a pressure of about 90 bar. Thereafter, the transfer substrates 94 can be peeled off will. In this way, the ion exchange membrane 16 is coated on both sides with the catalyst layers 30 and 32 .
• the exemplary embodiments described for the production of electrolytic cells can be combined with a wide variety of catalysts.
• a significant advantage of the methods described for forming the catalyst layers 30 and 32 is in particular that they can ultimately be applied directly to substrates 70 and 72 as part of the respective electrodes 62 and 64, respectively. In this way it is possible to assemble the electrolytic cell simply by bracing the components described.
• the HER catalysts and OER catalysts described are excellent alternatives to the expensive precious metals platinum and iridium. They are significantly cheaper and have almost the same performance. This enables water electrolyzers 10 to be manufactured and operated economically on a large scale. This is an important step, especially in view of the forthcoming energy transition, i.e. the move away from fossil fuels towards regenerative energy sources.

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