Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/10—Fuel cells with solid electrolytes
  • H01M8/1004—Fuel cells with solid electrolytes characterised by membrane-electrode assemblies [MEA]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/88—Processes of manufacture
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/88—Processes of manufacture
  • H01M4/8803—Supports for the deposition of the catalytic active composition
  • H01M4/8814—Temporary supports, e.g. decal
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/88—Processes of manufacture
  • H01M4/8825—Methods for deposition of the catalytic active composition
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/88—Processes of manufacture
  • H01M4/8875—Methods for shaping the electrode into free-standing bodies, like sheets, films or grids, e.g. moulding, hot-pressing, casting without support, extrusion without support
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2325/00—Details relating to properties of membranes
  • B01D2325/10—Catalysts being present on the surface of the membrane or in the pores
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/10—Fuel cells with solid electrolytes
  • H01M2008/1095—Fuel cells with polymeric electrolytes
• • 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
  • Y02E60/50—Fuel cells
• • 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
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

• the invention relates to a method for producing a catalyst coated on both sides of a polymer electrolyte membrane (English: “Catalyst Coated Membrane” - CCM) for electrochemical devices, such as fuel cells, electrochemical sensors or electrolysers. Furthermore, the invention relates to a method for producing a membrane electrode assembly and a catalyst-coated membrane on both sides.
• Fuel cells are energy converters that convert chemical energy into electrical energy.
• a fuel for example hydrogen
• an oxidant for example oxygen
• the structure of the cells is basically the same for all types. They generally consist of two electrodes, an anode and a cathode, where the reactions take place, and an electrolyte between the two electrodes.
• the electrolyte used is a polymer membrane which conducts ions (in particular H + ions).
• the electrolyte has three functions. It establishes the ionic contact, prevents electrical contact and also ensures the separation of the gases supplied to the electrodes.
• the electrodes are usually supplied with gases, which are reacted in the context of a redox reaction.
• the electrodes have the task of supplying the gases (for example hydrogen or methanol and oxygen or air), removing reaction products such as water or CO 2 , catalytically reacting the starting materials and removing or supplying electrons.
• the conversion of chemical to electrical energy occurs at the three phase boundary of catalytically active sites (eg, platinum), ionic conductive (eg, ion exchange polymers), electron conductors (eg, graphite), and gases (eg, H 2 and O 2 ).
• the largest possible active area is crucial.
• the core of a PEM fuel cell is a double-sided catalyst coated polymer electrolyte membrane (CCM) or a membrane electrode assembly (MEA).
• CCM catalyst coated polymer electrolyte membrane
• MEA membrane electrode assembly
• a double-walled catalyst-coated polymer electrolyte membrane is understood to mean a three-layered, catalyst-coated polymer electrolyte membrane which has an outer anode catalyst layer on one side of a membrane layer, the central membrane layer and an outer cathode catalyst layer on the anode catalyst layer.
• Set side of the membrane layer comprises.
• the membrane layer consists of proton-conducting polymer materials, which are referred to below as ionomers.
• the catalyst layers contain catalytically active components which catalytically support the respective reaction at the anode or cathode (for example oxidation of hydrogen, reduction of oxygen).
• the catalytically active components used are preferably the platinum group metals of the Periodic Table of the Elements.
• the membrane-electrode unit comprises a catalyst-coated polymer electrolyte membrane on both sides and at least one gas distributor layer (GDL).
• the gas distribution layers serve to supply gas to the catalyst layers and to divert the cell current.
• Membrane electrode units are known in the art, for example from WO 2005/006473 A2.
• the membrane-electrode assembly described therein comprises an ion-conducting membrane having front and rear surfaces, a first catalyst layer and a first gas diffusion substrate on the front side, and a second catalyst layer and a second gas diffusion substrate on the back surface, the first gas diffusion substrate having a smaller area Expansion as the ion-conducting membrane and the second gas diffusion substrate has substantially the same areal extent as the ion-conducting membrane.
• WO 00/10216 A1 relates to a membrane-electrode assembly with a polymer electrolyte membrane having a central and peripheral region.
• An electrode is disposed over the central region and a portion of the peripheral region of the polymer electrolyte membrane.
• a subgasket is disposed on the peripheral portion of the polymer electrolyte membrane so as to extend over the portion of the electrode which expands into the peripheral region of the polymer electrolyte membrane, and another seal is at least partially disposed on the subgasket.
• DE 199 10 773 A1 describes a method for applying electrode layers to a band-shaped polymer electrolyte membrane.
• the front and back of the membrane is continuously printed in the desired pattern with the electrode layers using an ink containing an electrocatalyst and dried the printed electrode layers immediately after printing at elevated temperature, the printing while maintaining a positionally accurate arrangement of the patterns of electrode layers. th of front and back to each other.
• the problem is that the Membrane material begins to swell upon contact with the solvent-containing ink and deforms.
• WO 02/039525 A1 proposes a production method in which a catalyst solution is applied to a support and the catalyst solution is dried before an ionomer solution is applied to the catalyst layer formed thereby. The layer of ionomer solution is cured. Two catalyst-ionomer composite layers thus prepared are combined to form a membrane-electrode assembly.
• the method proposed in WO 02/039525 A1 has the disadvantage that the catalyst layer, when applied to the support, tends to form a dense ionomer skin thereon, which hinders gas transport into the catalyst layer.
• EP 1 492 184 A1 describes a process for producing a catalyst-coated polymer electrolyte membrane for electrochemical devices.
• a polymer electrolyte membrane is used, which is connected on the back with a first support film.
• a second support film is applied to the front side, the first support film is removed, and then the second catalyst layer is applied to the back side.
• the membrane is connected to at least one support film at all coating stages.
• the support film prevents the swelling of the membrane during application of the catalyst coating.
• the application of the second support film and removal of the first support film makes this production process very expensive.
• EP 1 489 677 A2 relates to a further process for producing a membrane-electrode assembly in which a first gas diffusion layer is bonded to a membrane coated on one side with a catalyst and to a gas diffusion electrode.
• the object of the present invention is therefore to provide a simple and cost-effective production method for double-side catalyst-coated membranes or membrane-electrode assemblies for electrochemical devices.
• a continuous production (roll to roll) of both sides catalyst-coated membranes or Membrane electrode units allow.
• Another object of the present invention is, in particular, to avoid swelling of the membrane when applying the liquid catalyst solution.
• steps A) and B) can be carried out in any order or simultaneously.
• the removal of the first and second carrier from the first and second ionomer layers can also be carried out in step C) before the first is connected to the second semifinished product.
• An electrochemical device in this context is for example a fuel cell, an electrolytic cell or an electrochemical sensor.
• a first semifinished product is produced.
• the semifinished product is a composite of a first ionomer layer and an anode catalyst layer.
• a first ionomer layer is first applied to a first carrier.
• the ionomer layer preferably consists of cation-conducting polymer materials.
• a tetrafluoroethylene-fluorovinyl ether copolymer having acid functions, especially sulfonic acid groups is used.
• Such a material is used, for example, under the han- Nafion ® branded by EI DuPont.
• Examples of ionomer materials which can be used in the present invention are the following polymer materials and mixtures thereof:
• ionomer materials in particular essentially fluorine-free ones, for example sulfonated phenol-formaldehyde resins (linear or linked); sulfonated polystyrene (linear or linked); sulfonated poly-2,6-diphenyl-1,4-phenylene oxides, sulfonated polyaryl ether sulfones, sulfonated polyarylene ether sulfones, sulfonated polyaryl ether ketones, phosphonated poly-2,6-dimethyl-1,4-phenylene oxides, sulfonated polyether ketones, sulfonated polyether ether ketones, aryl ketones or polybenzimidazoles ,
• sulfonated phenol-formaldehyde resins linear or linked
• sulfonated polystyrene linear or linked
• the first carrier (and also the second carrier in step B)) is preferably a carrier film, in particular a film of polyester, polyethylene, polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), polypropylene (PP), polyvinyl chloride (PVC), polycarbonate , Polyamide, polyimide, polyurethane or comparable Folienmateri- alien.
• the carrier film preferably has a thickness between 10 and 250 ⁇ m, more preferably between 90 and 110 ⁇ m.
• first ionomer layer to the first support is carried out by methods known to those skilled in the art, for example by doctor blade, spray, casting, printing or extrusion processes.
• the application of the ionomer layer to the carrier is dispensed with in the method according to the invention, if ionomer membranes are used, which are already connected in the delivery state with a carrier.
• the first ionomer layer is coated with an anode catalyst layer using a first catalyst ink.
• the catalyst ink is a solution containing an electrocatalyst. It contains, for example, a solvent, one or more electrocatalysts and optionally further constituents, for example a polyelectrolyte.
• the catalyst ink which is optionally paste-like, is applied in the process according to the invention to the first ionomer layer for producing the anode catalyst layer by processes known to those skilled in the art, for example by printing, spraying, knife coating or rolling.
• the catalyst layers applied in accordance with the method of the invention can be applied fully or partially. In the partial application of a catalyst layer, the catalyst can be applied, for example, in the form of a geometric pattern.
• the anode catalyst layer is dried.
• Suitable drying processes are, for example, hot-air drying, infrared drying, microwave drying, plasma processes or combinations of these processes.
• the first carrier is removed. This takes place at the latest directly before joining the first semi-finished product. Thus, the production of the first semi-finished product is completed.
• step B) of the method according to the invention a second semifinished product is produced.
• the preparation is analogous to the production of the first semifinished product.
• a second ionomer layer and a cathode catalyst layer are applied.
• the cathode catalyst layer is dried and the support is subsequently removed from the second ionomer layer.
• the first and second ionomer layers may each be a single layer or be composed of a plurality of ionomer layers. They can have the same or different thicknesses.
• the anode catalyst layer and the cathode catalyst layer may each be a single catalyst layer or may be composed of a plurality of catalyst layers.
• the anode catalyst layer and the cathode catalyst layer may be the same or different.
• the two catalyst inks may contain the same or different electrocatalysts in equal or different proportions.
• the catalyst layers may each have the same or different areal expansions as the associated ionomer layer.
• step C) of the method according to the invention after the two carriers have been removed from the ionomer layers, the first semifinished product is joined to the second semifinished product by joining the first ionomer layer to the second ionomer layer becomes.
• the first ionomer layer can be bonded directly to the second ionomer layer, or indirectly via an intermediate membrane which is placed between the two ionomer layers during bonding.
• Such an intermediate membrane may, for example, have a larger area than the two ionomer layers and after the joining of the two semi-finished products project beyond the edge of the two ionomer layers.
• the thus formed lonomerrand can then serve for attachment, for example, a frame.
• this protruding intermediate membrane edge can also be sufficiently thick so that no frame is necessary and a seal can optionally be attached directly to this lonomerrand.
• the intermediate membrane may consist of a material, as already mentioned for the ionomer layers.
• the direct or indirect bonding of the ionomer layers is preferably carried out by compression using heat and / or pressure, for example using laminating rollers. Bonding may be accomplished by methods known to those skilled in the art, for example by hot pressing, laminating, lamination with additional solvent application, or ultrasonic welding. Bonding is preferably by compression using heat and / or pressure, for example using laminating rollers.
• the temperature is preferably between 60 0 C and 250 0 C and the pressure preferably between 0.1 and 100 bar.
• the process according to the invention for the preparation of membranes coated on both sides has, inter alia, the advantage that it can be carried out as a low-cost, cost-effective, continuous roll-to-roll process.
• the carrier with the lonomer layer arranged thereon is present as a ribbon on a roll before the two semi-finished products are joined together.
• deformation of the ionomer layers by, for example, swelling upon application of the catalyst ink is avoided by bonding the ionomer layers to supports until the catalyst inks are dried.
• the catalyst ink only has to be optimized for the wetting of the ionomer layer, so that good bonding of the respective catalyst layer to the ionomer layer is achieved (for example, in contrast to a double-catalyst-coated membrane produced according to WO 02/39525).
• the catalyst-coated membrane produced by the process according to the invention is subsequently activated by treatment with acid. bar.
• the acid extracts the solvent from the membrane (the two interconnected ionomer layers) and protonates the membrane.
• Possible acids for the subsequent activation of the catalyst-coated membrane on both sides are, for example, H 2 SO 4 or HNO 3 .
• At least one of the first and second ionomer layers before carrying out step C) of the process according to the invention contains a solvent with a content of 0.5 to 35%.
• the ionomer layers contain, for example, a residual solvent such as dimethylacetamide (DMAc) or N-methyl-2-pyrrolidone (NMP), the residual solvent serving as a plasticizer and allowing the ionomer layers to be bonded in step C), for example, by a lamination process.
• the ionomer layers may also contain water as a solvent, whereby a defined water content in the membrane can be adjusted.
• a frame is connected to a protruding semifinished edge, a protruding intermediate membrane edge, a protruding ionomer layer edge or a protruding edge of the membrane.
• a membrane coated on both sides with a protruding semifinished edge is formed by joining the two semifinished products.
• the frame can be attached to this projecting edge of the semifinished product.
• the joining of the first semifinished product with the second semifinished product can take place directly or indirectly via an intermediate membrane.
• an intermediate membrane a membrane comprising the first and second ionomer layers and an intermediate membrane is formed when joining the two semifinished products.
• the intermediate membrane can terminate flush with at least one ionomer layer or form a protruding intermediate membrane edge. At this intermediate membrane edge, a one-piece or multi-part frame can be attached.
• the first and the second ionomer layer can each be covered over the full area or over a partial area with the respective catalyst layer.
• the catalyst coated membrane of the invention on both sides can have a protruding ionomer layer edge.
• a one-piece or multi-part frame can be attached. If the first and the second ionomer layer and, if appropriate, further ionomer layers as an already connected membrane overflow over the two catalyst layers, they form an overhanging membrane edge. At this membrane edge, a one-piece or multi-part frame can be attached.
• the first and the second semi-finished product have different areal expansions, so that after joining the two semi-finished products to the membrane coated on both sides, a protruding semifinished product edge remains.
• the catalyst-coated membrane constructed in this way on both sides permits improved gas-tightness in the sealing or sealing of the edge region of the catalyst-coated membrane on both sides.
• a seal and / or a reinforcing frame can be attached to the protruding semi-finished edge.
• the protruding semifinished edge may run along two or along four edges of the double-catalyst coated membrane. It is useful for better sealing and saving precious metal to attach a frame to the catalyst-coated membrane on both sides, in particular an inert plastic frame in the sealing area.
• a bead In the case of double-sided catalyst-coated membranes, which are produced by conventional processes, a bead always results from the overlapping of the membrane or the catalyst-coated membrane with the frame, for example when the reinforcement frame is inserted between two membrane halves. In the overlap region of the membrane halves with the frame, a bead is formed with a thickness that corresponds to the sum of the membrane thickness of both membrane halves and the frame thickness. By such a bead, the contacting of the active surface is difficult. By laminating two semifinished products of different sizes and laminating a plastic frame onto the projecting semifinished product edge of the larger semifinished product according to the invention, a framed membrane coated with catalyst on both sides can be produced without beads. Therefore, according to a preferred embodiment of the present invention, the protruding semifinished edge of the double-catalyst-coated membrane is connected to a frame.
• the bilaterally catalyst coated membrane in the present invention can be joined to a frame comprising two equally sized frame halves.
• the double-sided catalyst coated membrane in the present invention can be connected to a frame comprising two different sized frame halves.
• a frame comprising two different sized frame halves.
• the double-catalyst coated membrane in the present invention may be bonded to a frame which is an intermediate frame between two ionomer layer edges projecting over the anode and cathode layer. If the first and the second ionomer layers overlap over the two catalyst layers (partial coating with catalyst), they form protruding monomer layer edges.
• the intermediate frame When connecting the two semi-finished products, the intermediate frame can then be arranged such that it is at least partially located between the two ionomer layer edges and connected thereto.
• the two ionomer layer edges are deformed in an S shape, since the ionomer layers extend from the membrane between the catalyst layers, outwards along one of the two sides of the intermediate frame.
• catalyst-coated membrane may consist of any non-functionalized, gas-tight polymer, in particular polyethersulfone, polyamide, polyimide, polyether ketone, polysulfone, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene (PE) or Polypropylene (PP).
• the frame or frame halves in the present invention may be present as a ribbon on a roll prior to attachment to the double-catalyst coated membrane so that a roll-to-roll process enables high throughput.
• the frame can be equipped with an adhesive layer.
• At least one of the anode or cathode catalyst layers is connected to a gas diffusion layer.
• the gas diffusion layer can serve as a mechanical support for the electrode and ensures a good distribution of the respective gas over the catalyst layer and for the discharge of the electrons.
• a gas diffusion layer (gas distribution layer) is needed in particular for fuel cells which are operated with hydrogen on the one hand and oxygen or air on the other hand.
• the anode catalyst layer having a first gas diffusion layer and the cathode catalyst layer are connected to a second gas diffusion layer so that the first gas diffusion layer and the anode catalyst layer and the second gas diffusion layer and the cathode catalyst layer are flush with each other.
• the two gas diffusion layers according to this embodiment also have these different large area expansions and are flush with the respective catalyst layer on all sides.
• the anode catalyst layer has a first gas diffusion layer and the cathode catalyst layer has a second gas diffusion layer.
• the two semi-finished products including the respective catalyst layer
• the two gas diffusion layers can nevertheless have the same size, the larger areal extent of the semi-finished corresponding flat expansions, wherein one of the gas diffusion layers then with a gas diffusion layer edge over the edge survives the smaller semi-finished product.
• the gas diffusion layer edge can then be overlapped with a frame.
• the catalyst-coated membrane on both sides is connected to a frame and on both sides each with a gas diffusion layer and further attached to at least one transition region between the catalyst-coated membrane or the frame and a Gasdiffusi- ons slaughter a seal.
• a suitable sealing material for example, silicones, polyisobutylene (PIB), rubbers (synthetic and natural), fluoroelastomers and fluorosilicones are suitable.
• a preferred embodiment of the present invention is such that at least one of the ionomer layers contains at least one additional constituent selected from the group of blend components, reinforcing fabric, microporous support film and fillers.
• blend components it is possible to use non-functionalized polymers which improve the mechanical properties of the ionomer layer, for example polyethersulfones, polysulfones, polybenzimidazole (PBI) or polyimides.
• the reinforcing fabric may be, for example, a fine polymer or glass fiber fabric that is encapsulated with functionalized polymer.
• Suitable microporous support films are known, for example, from US 5,635,041. Alternatively, microporous membranes are conceivable, in which a functionalized polymer is poured.
• Fillers serve, for example, to store water and / or to improve the mechanical stability of the ionomer layer.
• fillers for example, silicon dioxide, zirconium phosphates, zirconium phosphonates or heteropolyacids can be used.
• the filler is a catalyst, in particular a catalyst which can decompose peroxides or H 2 O 2 and / or can prevent the formation of peroxides and / or H 2 and O 2 H 2 O can implement and / or alcohols can implement. Examples of these are noble metal nanoparticles or precious metal particles fixed on carbon black.
• a preferred embodiment of the present invention is designed such that (before step C) of the method according to the invention) at least one additional layer of an additive selected from the group consisting of solvent, solution of a polyelectrolyte, dispersion of a polyelectrolyte, filler and catalyst, is brought between the two semifinished products.
• the additive forms an intermediate layer in the total ionomer layer (membrane) of the catalyst-coated membrane on both sides, which can perform various functions (for example, can serve as adhesion promoter).
• a solvent for example dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP) or dimethylsulfoxide (DMSO)
• DMAc dimethylacetamide
• NMP N-methyl-2-pyrrolidone
• DMSO dimethylsulfoxide
• Polyelectrolytes are functionalized membrane polymers (ionomers) which are useful as an additive. This can, for example, from the already for the two lo nomer füren enumerated possible ionomers are selected, for example, Nafion ® from DuPont, Flemion ® from Asahi Chemicals or fumion ® from Fumatech.
• Fillers which can be used as an additive are, for example, inorganic materials, such as silicates or sheet silicates, which serve as a barrier layer (for example for methanol).
• Catalysts which can be used as additives include, for example, elements of the platinum group which allow recombining hydrogen and oxygen to form water, thereby internally moistening the membrane and at the same time preventing the transfer of the respective gas to the other electrode.
• step C) of the method according to the invention the first is connected to the second semifinished product, wherein the first and the second semifinished product have different degrees of sulfonation of their ionomer layers.
• the degree of sulfonation determines various properties of the membrane.
• the (undesired) swelling of the membrane increases with increasing degree of sulfonation.
• the ionic conductivity of the membrane which should be as high as possible, increases with the degree of sulfonation.
• the permeability to gases or in the case of a direct methanol fuel cell - DMFC - the permeability to methanol, which should be as low as possible, increases with increasing degree of sulfonation.
• a thin ionomer layer having a low degree of sulfonation to reduce swelling and permeability may be combined with a thick ionomer layer of higher degree of sulfonation for good conductivity into a membrane become. Since the degree of sulfonation also has a positive influence on the water absorption of the membrane, the different degrees of sulfonation of the ionomer layers can also positively influence the water balance of the membrane. In particular, a higher degree of sulfonation of the first ionomer layer on the anode side is advantageous, whereby water is transported to the anode.
• the invention relates to a method for producing a membrane electrode assembly for electrochemical devices with the steps
• the gas diffusion electrode has a second ionomer layer prior to bonding in step b).
• the method according to the invention for producing a membrane electrode assembly for electrochemical devices then has the steps:
• step a) or i) The application of the first ionomer layer to the support in step a) or i) is carried out by methods known to those skilled in the art, for example by doctor blade, spray, casting, printing or extrusion processes.
• the application of the ionomer layer to the carrier is dispensed with in the process according to the invention when ionomer membranes are used which are already connected to a carrier in the as-delivered state.
• the first ionomer layer is coated with a catalyst layer using a first catalyst ink.
• the catalyst ink is a solution containing an electrocatalyst. It contains, for example, a solvent, one or more electrocatalysts and optionally further constituents, for example a polyelectrolyte.
• the catalyst ink which is optionally paste-like, is applied in the process according to the invention to the first ionomer layer for producing the catalyst layer by methods familiar to one skilled in the art, for example by printing, spraying, knife coating or rolling.
• the catalyst layer applied in accordance with the method of the invention can be applied fully or partially. In the partial application of a catalyst layer, the catalyst can be applied, for example, in the form of a geometric pattern.
• the catalyst layer is dried.
• Suitable drying methods are, for example, hot-air drying, infrared drying, microwave drying, plasma methods or combinations of these methods.
• the first carrier is removed. This completes the production of a first semi-finished product.
• a second ionomer layer is then applied to a gas diffusion electrode (step ii)). This is done by methods familiar to the person skilled in the art.
• the gas diffusion electrode includes at least a gas diffusion layer and a catalyst layer.
• the gas diffusion electrode further includes another layer between the gas diffusion layer and the catalyst layer, particularly a microporous layer (e.g., carbon black and a hydrophobic binder (e.g., PTFE)) which serves to control the water balance.
• a microporous layer e.g., carbon black and a hydrophobic binder (e.g., PTFE) which serves to control the water balance.
• the first ionomer layer is connected to (optionally a second ionomer layer) of the gas diffusion electrode to form a membrane electrode unit.
• Bonding may be accomplished by methods known to those skilled in the art, for example by hot pressing, laminating, lamination with additional solvent application, or ultrasonic welding. Bonding is preferably by compression using heat and / or pressure, for example using laminating rollers. The temperature is preferably between 60 ° C and 250 ° C and the pressure preferably between 0.1 and 100 bar.
• the membrane-electrode assembly thus produced is supplemented by the application of a further gas diffusion layer to the catalyst layer prepared in step a) or i).
• the invention further relates to a catalyst-coated membrane on both sides for electrochemical devices, the catalysts coated on both sides
• Membrane comprises two interconnected semi-finished products, a first semi-finished a first ionomer layer connected to an anode catalyst layer and a second semifinished product comprising a second ionomer layer bonded to a cathode layer, wherein a frame is connected to a protruding semifinished edge, a protruding intermediate membrane edge, a protruding ionomer layer edge or a protruding membrane edge or as an intermediate frame between two ionomer layer edges is.
• the catalyst-coated membrane of the invention on both sides can be prepared by the process according to the invention for the preparation of catalyst-coated membranes on both sides.
• the invention relates to a double-sided catalyst-coated membrane for electrochemical devices, wherein the double-catalyst-coated membrane comprises two interconnected semi-finished products, a first semi-finished product of an anode layer connected to a first ionomer and a second semi-finished from a cathode catalyst layer connected to a second lonomer harsh, wherein the two semi-finished products have different areal expansions.
• a membrane coated on both sides with a protruding semifinished edge is formed by joining the two semifinished products.
• a frame can be attached.
• the first semi-finished product can be joined to the second semi-finished product directly or indirectly via an intermediate membrane.
• An embodiment of a catalyst-coated membrane according to the invention therefore has a membrane containing the first and second ionomer layer and an intermediate membrane.
• the intermediate membrane can be flush with at least one ionomer layer or form a protruding intermediate membrane edge.
• a one-piece or multi-part frame can be attached.
• the intermediate membrane can also be chosen so thick that no additional framework is necessary for supporting the catalyst coated membrane of the invention on both sides. Then, a seal can be attached directly to the protruding intermediate membrane edge.
• the first and the second ionomer layer of the catalyst-coated membrane of the invention on both sides can each be covered over the full area or part of the area with the respective catalyst layer.
• the catalyst coating on both sides of the invention may have a protruding ionomer layer edge. At this lonomer Anlagenrand a one-piece or multi-part frame can be attached.
• first and the second ionomer layer and, if appropriate, further ionomer layers as an already connected membrane overflow over the two catalyst layers, they form an overhanging membrane edge.
• a one-piece or multi-part frame can be attached.
• first and the second ionomer layers overlap over the two catalyst layers (partial coating with catalyst), they form overhanging ionomer layer edges.
• an intermediate frame can then be arranged such that it is at least partially located between the two ion layer edges and connected thereto.
• the two ionomer layer edges are deformed in an S-shape since the ionomer layers extend from the membrane between the catalyst layers to the outside along each of the two sides of the intermediate frame.
• the invention relates to a fuel cell which contains at least one catalyst-coated membrane according to the invention on both sides.
• a fuel cell which contains at least one catalyst-coated membrane according to the invention on both sides.
• FIG. 1 schematically shows a method according to the invention for the production of membranes coated on both sides with a catalyst, without a frame,
• FIG. 2 shows a membrane coated on both sides with a catalyst according to the invention, with a frame
• FIG. 3 shows a further catalyst-coated membrane according to the invention with a frame comprising two frame halves of different sizes
• FIG. 4 shows another membrane coated on both sides according to the invention, with a frame and gas diffusion layers of various sizes, which are flush with the respective catalyst layer
• FIG. 6 shows a further catalyst coated membrane according to the invention with a frame and gas diffusion layers of equal size
• FIG. 6 shows a further catalyst-coated membrane according to the invention with frame, gas diffusion layers and seal,
• FIG. 7 shows a further catalyst-coated membrane according to the invention with an intermediate membrane
• FIG. 8 shows a further catalyst-coated membrane according to the invention with an intermediate membrane and a frame
• FIG. 9 shows a further catalyst-coated membrane according to the invention with an intermediate membrane, a frame and gas diffusion layers,
• FIG. 10 shows a further catalyst-coated membrane according to the invention with an intermediate membrane, frame, gas diffusion layers and gasket,
• FIG. 11 shows a further catalyst-coated membrane according to the invention with a catalyst layer applied on only one side on only one side
• FIG. 12 shows a further catalyst-coated membrane according to the invention on both sides according to FIG. 11 with frame
• FIG. 13 shows a further catalyst-coated membrane according to the invention comprising two semi-finished products with a catalyst layer applied over a partial area
• FIG. 14 shows a further catalyst-coated membrane according to the invention according to FIG. 13 with a frame
• FIG. 15 shows another membrane coated on both sides according to the invention, according to FIG. 14, with gas diffusion layers,
• FIG. 16 shows a further catalyst-coated membrane according to the invention according to FIG. 15 with a seal
• FIG. 17 shows a further catalyst coated membrane according to the invention with catalyst layers, gas diffusion layers and gasket applied over part of the surface
• FIG. 18 shows a further catalyst-coated membrane according to the invention with catalyst layers applied over part of the area and a frame fastened between the ionomer layers,
• FIG. 19 shows a further membrane coated according to the invention on both sides according to FIG. 18 with gas diffusion layers
• FIG. 20 shows a further catalyst-coated membrane according to the invention according to FIG. 19 with a seal
• Figure 21 shows the current-voltage characteristics to a first example according to the invention and a first comparative example
• Example and a second comparative example are identical to Example 1 and a second comparative example.
• Figure 1 shows schematically the preparation of double-sided catalyst coated membranes with frame according to a method of the invention.
• a first roll 1 contains a first semifinished product 2 on a first carrier 3.
• the first semifinished product 2 comprises a first ionomer layer 4 and an anode catalyst layer 5.
• the first ionomer layer 4 is connected to the anode catalyst layer 5.
• a second roller 6 contains a second semifinished product 7 on a second carrier 8.
• the second semifinished product 7 comprises a second ionomer layer 9 and a cathode catalyst layer 10.
• the second ionomer layer 9 is connected to the cathode catalyst layer 10.
• the cathode catalyst layer 10 can be used both over the entire area and over part of the area, e.g. be applied in the form of uniform geometric pattern.
• the first and second rollers 1, 6 are rotated in the unwinding direction 12.
• the first and second carriers 3, 8 are removed from the first and second ionomer layers 4, 9 and wound on in the winding direction 13 rotating first and second carrier rollers 14 and 15, respectively.
• the first semifinished product 2 with the second semifinished product 7 by connecting the first ionomer layer 4 with the second ionomer layer 9 connected. This takes place under the action of pressure and temperature with the aid of two laminating rollers 16, 17, which rotate in the rolling direction 18.
• the generated on both sides catalyst-coated membrane 11 is then provided with a support film. This is a provided on the film roll 19 support sheet 20 which is connected to the catalyst-coated membrane 11 on both sides.
• the supported, double-catalyst-coated membrane 21 produced in this way is wound onto a supply roll 22. From the supply roll 22 pieces can now be separated and framed as needed, which then come as a framed on both sides catalyst-coated membranes in electrochemical devices, in particular in polymer electrolyte membrane fuel cells are used.
• FIG. 2 shows a membrane coated on both sides with a frame according to the invention.
• the catalyst-coated membrane 23 shown on both sides in FIG. 2 was preferably produced by the process according to the invention. It consists of two semi-finished products 24, 25 each having an ionomer layer 26 or 27 and an anode or cathode catalyst layer 28 or 29.
• the anode catalyst layer 28 terminates flush with the first ionomer layer 26 and the cathode catalyst layer 29 terminates flush with the second ionomer layer 27.
• the first semi-finished product 24 and the second semi-finished product 25 have different areal expansions, so that the membrane-coated membrane 23 produced on both sides by the two semi-finished products 24, 25 has a protruding semi-finished edge 30. At the protruding semi-finished edge 30, a frame 31 is attached.
• FIG. 3 shows a further catalyst-coated membrane according to the invention with a frame comprising two frame halves of different sizes.
• the catalyst-coated membrane shown in FIG. 3 largely corresponds to that shown in FIG. 2, with the difference that it is connected to a frame 31 which comprises two frame halves 32, 33 of different sizes.
• the first frame half is larger with respect to its surface and surrounds the smaller first semifinished product 24 and the second frame half 33 is smaller with respect to its surface and surrounds the larger second semifinished product 25.
• the outer edges 34 of the frame halves 32, 33 are flush.
• FIG. 4 shows a further catalyst-coated membrane according to the invention with frames and gas diffusion layers of different sizes.
• the catalyst coated membrane 23 shown on both sides in FIG. 4 is largely constructed as in FIG. 3, in particular the frame 31 is composed of two frame halves 32, 33.
• Two different sized gas diffusion layers 35, 36 are connected to the catalyst-coated membrane 23 on both sides.
• the areal extent of the respective gas diffusion layer 35 or 36 corresponds to the areal extent of the semifinished product 24 or 25 connected therewith.
• the first gas diffusion layer 35 with the anode catalyst layer 28 and the second gas diffusion layer 36 with the cathode catalyst layer 29 each terminate flush ,
• FIG. 5 shows a further catalyst-coated membrane according to the invention with a frame and gas diffusion layers of equal size.
• the catalyst-coated membrane 23 shown on both sides in FIG. 5 is largely constructed as in FIG. 3; in particular, the frame 31 is composed of two frame halves 32, 33. Two gas diffusion layers 35, 36 of equal size are connected to the catalyst-coated membrane 23 on both sides. In this case, the areal extent of both gas diffusion layers 35, 36 corresponds to the areal extent of the second semifinished product 25. In this way, the second gas diffusion layer 36 is flush with the cathode catalyst layer 29.
• the first gas diffusion layer 35 communicates with a gas diffusion layer edge 37 via the (with respect to the area smaller) anode catalyst layer 28 via. Thereby, the gas diffusion layer edge 37 is arranged overlapping with a part of the first frame half 32.
• FIG. 6 shows a further catalyst-coated membrane according to the invention with frames, gas diffusion layers and seals.
• FIG. 7 shows a further catalyst-coated membrane according to the invention having two catalyst layers which are applied over the entire surface of the ionomer layers and an intermediate membrane.
• the catalyst coated membrane 23 shown on both sides in FIG. 7 consists of two semi-finished products 24, 25 each having an ionomer layer 26 and 27, respectively, and an anode or cathode catalyst layer mounted on the entire surface thereof. Layer 28 and 29, respectively.
• the anode catalyst layer 28 terminates flush with the first ionomer layer 26 and the cathode catalyst layer 29 terminates flush with the second ionomer layer 27.
• the first semifinished product 24 and the second semifinished product 25 have the same large area expansions.
• FIG. 8 shows a further catalyst-coated membrane according to the invention with a frame comprising two frame halves.
• the double-catalyst-coated membrane 23 shown in FIG. 8 largely corresponds to that shown in FIG. 7, with the difference that it is connected to a frame 31 which comprises two frame halves 32, 33 of equal size.
• the two frame halves 32, 33 are attached to the intermediate membrane edge 41.
• the outer edges 34 of the frame halves 32, 33 are flush.
• FIG. 9 shows a further catalyst-coated membrane according to the invention with frames and gas diffusion layers.
• the catalyst coated membrane 23 shown on both sides in FIG. 9 is largely constructed as in FIG. 8, with two gas diffusion layers 35, 36 being connected to the membrane 23 coated on both sides with catalyst.
• the planar extent of the gas diffusion layers 35, 36 is greater than the areal extent of the two semi-finished products 24, 25 and partially overlaps with the frame halves 32, 33.
• the two gas diffusion layers 35, 36 are the same size.
• FIG. 10 shows a further catalyst-coated membrane according to the invention with an intermediate membrane, frames, gas diffusion layers and gaskets.
• FIG. 11 shows a further catalyst-coated membrane according to the invention having a full-area catalyst layer and a partially applied catalyst layer.
• the catalyst coated membrane 23 shown in FIG. 11 consists of two semi-finished products 24, 25 each having an ionomer layer 26 or 27 and an anode or cathode catalyst layer 28 or 29.
• the cathode catalyst layer 29 is applied over the entire area to the second ionomer layer 27 and is flush with it .
• the anode catalyst layer 28 is partially applied to the first ionomer layer 26 so that an ionomer layer edge 42 projects beyond the anode catalyst layer 28. Since both catalyst layers 28, 29 have the same areal extent, the lonomer fürrand 42 is also in the case of the catalyst-coated membrane 23 on both sides.
• FIG. 12 shows a further catalyst coated membrane according to the invention with a one-part frame.
• the double-catalyst-coated membrane shown in FIG. 12 largely corresponds to that shown in FIG. 11, with the difference that it is connected to a one-piece frame 31.
• the frame 31 is attached to the protruding lonomer fürrand 42. This concludes flush with the ionomer layer edge 42.
• FIG. 13 shows a further catalyst-coated membrane according to the invention with anode and cathode catalyst layers applied over part of the area.
• the catalyst coated membrane 23 shown in FIG. 13 consists of two semi-finished products 24, 25 each having an ionomer layer 26 or 27 and an anode or cathode catalyst layer 28 or 29.
• the two catalyst layers 28, 29 are applied only partially to the ionomer layers 26, 27, so that in each case one lonomer layer edge 43, 44 projects beyond the catalyst layers 28, 29 of the ionomer layers 26, 27.
• these two ionomer layer edges 43, 44 form a membrane edge 45 projecting over the two catalyst layers 28, 29 of equal size.
• FIG. 14 shows a further catalyst-coated membrane according to the invention with a frame of two frame halves attached to a membrane edge.
• the catalyst-coated membrane shown on both sides in FIG. 14 is largely constructed as in FIG. 13, wherein in addition a frame fastened to the membrane edge 45 is provided.
• menu 31 is present.
• the frame 31 consists of two equal frame halves 32, 33, each flush with the membrane edge 45.
• the two frame halves 32, 33 can be connected to the membrane edge 45 in the production of this catalyst-coated membrane 23 according to the invention either after joining the two semi-finished products 24, 25, or in each case one frame half 32, 33 connected to one lonomer Mrs 26, 27 after this ionomer layer 26, 27 has been applied to the respective carrier and before the respective catalyst layer 28, 29 is applied to the ionomer layer 26, 27.
• a roll-to-roll process in which the catalyst layers are applied to the ionomer layers after the frame has been applied to produce the respective semifinished product, it is possible to apply e.g. An ionomer layer is first applied to the respective carrier film, then a frame film is bonded to the ionomer layer, and then the respective catalyst layer is applied to the ionomer layer in the window formed by the frame film, e.g. by doctoring or printing the catalyst ink.
• FIG. 15 shows a further catalyst-coated membrane according to the invention with frames and gas diffusion layers.
• the catalyst-coated membrane 23 shown on both sides in FIG. 15 is largely constructed as in FIG. 14, wherein in addition two gas diffusion layers 35, 36 are connected to the membrane 23 coated with catalysts on both sides.
• the gas diffusion layers 35, 36 have a larger areal extent than the catalyst layers 28, 29 and partially overlap with the two frame halves 32, 33.
• FIG. 16 shows a further catalyst-coated membrane according to the invention with frames, gas diffusion layers and seals.
• FIG. 17 shows a further catalyst-coated membrane according to the invention with gas diffusion layers and gaskets.
• the catalyst coated membrane 23 shown in FIG. 17 has two gas diffusion layers 35, 36 in addition to the structure shown in FIG which protrude beyond the respectively adjacent catalyst layer 28, 29 and form protruding gas diffusion layer edges 46, 47. These gas diffusion layer edges 46, 47 are encapsulated together with the still projecting membrane edge 45 by seals 38, 39. The seals 38, 39 are flush with the membrane edge 45 from.
• FIG. 18 shows a further catalyst-coated membrane according to the invention with catalyst layers applied over part of the area and a frame fastened between nanolayer-layered frame.
• the catalyst coated membrane 23 shown on both sides in FIG. 18 consists of two semi-finished products 24, 25 each having an ionomer layer 26 or 27 and an anode or cathode catalyst layer 28 or 29.
• the two ionomer layers 26, 27 are only partially coated with the catalyst layers 28, 29, so that they form a first ionomer layer edge 43 and a second ionomer layer edge 44, which project beyond the catalyst layers 28, 29.
• a one-piece intermediate frame 48 is attached.
• the intermediate frame 48 projects beyond the two ionomer layer edges 43, 44.
• FIG. 19 shows a further catalyst-coated membrane according to the invention with frames and gas diffusion layers.
• the catalyst-coated membrane 23 shown on both sides in FIG. 19 is largely constructed as in FIG. 18, but in addition two gas diffusion layers 35, 36 are connected to the membrane 23 coated with catalysts on both sides.
• the gas diffusion layers 35, 36 terminate flush with the two ionomer layer edges 43, 44.
• FIG. 20 shows a further catalyst-coated membrane according to the invention with intermediate frames, gas diffusion layers and gaskets.
• FIG. 21 shows the current-voltage characteristics for a first example according to the invention and for a first comparison example.
• the voltage U in mV is plotted on the Y-axis and the current density I / A in mA / cm 2 on the X-axis.
• the solid curve refers to the example according to the invention and the dashed curve to the comparative example. The examples are explained in more detail below.
• Two membranes of the type GK1065-049d (blend membrane of sPEEK and Ultrason E, non-hydrated) with a residual solvent content of> 22% NMP and a dry layer thickness of 22 ⁇ m, each on a 100 ⁇ m thick PET film provided as support, become one-sided with a catalyst ink containing a supported sprayed on carbon black catalyst with approximately 50% Pt content and Nafion ® ionomer (EW1100 5%, Sigma Aldrich) to an anode side and a kathodenseiti- saturated semifinished product with approximately 0.15 or 0, 4 mg / cm 2 Pt loading produce. The carrier is removed.
• the halves are bonded with a film laminator (Ibico IL 12 HR) between two boxes at a roll temperature of 120 ° C. and at speed 2 to a membrane coated on both sides with a catalyst. Subsequently, the composite is treated for 2 hours at 80 ° C in 1 N H 2 SO 4 and then washed thoroughly at room temperature with demineralized water.
• the resulting bilaterally catalyst-coated membrane becomes a membrane electrode assembly (MEA) having an active area of 32.5 cm 2 with two gas diffusion layers (SGL Carbon, 21 BC) for 10 minutes at 90 ° C and a force of 20 kN pressed.
• the MEA thus obtained is in a 25 cm 2 test cell, for example, the company. Electro Chem at 75 0 C, 1 bar, 100% rel.
• the measured current-voltage curve is shown in FIG. 21 as a solid line.
• the high-frequency resistance of the system determined by means of impedance spectroscopy is 2.8 m ⁇ .
• a membrane of type GK1065-049b (blend membrane of sPEEK and Ultrason E, 2 hours at 80 ° C in 1 m H 2 SO 4 hydrated) with a dry film thickness of 43 microns and a residual solvent content of ⁇ 0.5% NMP is on both sides with a Catalyst ink containing a supported on soot catalyst with about 50% Pt content and Nafion ® lonomerates (EW1100 5%, Sigma Aldrich) sprayed to herz an anode side and a cathode side loading of 0.15 and 0.4 mg / cm 2 Pt - put.
• the bilaterally catalyst-coated membrane thus obtained is treated with two Gas diffusion layers (SGL Carbon, 21 BC) for 10 minutes at 90 0 C and a force of 20 kN to a membrane electrode assembly (MEA) with an active area of 32.5 cm 2 pressed.
• the MEA thus obtained is in a 25 cm 2 test cell, for example, the company.
• the current-voltage curve is also shown in FIG. 21 as a dashed line.
• the high frequency resistance of this system determined by impedance spectroscopy is 3 m ⁇ .
• FIG. 22 shows the current-voltage characteristics for a second example according to the invention and for a second comparative example.
• the voltage U in mV is plotted on the Y-axis and the current density I / A in mA / cm 2 on the X-axis.
• the solid curve refers to the example according to the invention and the dashed curve to the comparative example. The examples are explained in more detail below.
• a membrane of the type GK1130-051 (blend membrane of sPEEK and Ultrason E, non-hydrated) with a residual solvent content of> 22% NMP and a dry film thickness of 35 ⁇ m is unilaterally coated with a catalyst ink containing a catalyst supported on carbon black with about 70% Pt. Solvent and Nafion TM ionomer solution (EW1100 10%, Sigma Aldrich) sprayed to produce a cathode side semi-finished product at about 2 mg / cm 2 Pt loading.
• a membrane of the same type is sprayed on one side with a catalyst ink containing a supported on carbon black catalyst with about 80% PtRu content and sPEEK lonomerates to produce an anode-side semifinished product with about 3 mg / cm 2 PtRu loading.
• the semi-finished products are bonded to a CCM between 2 PET films at a roller temperature of approx. 130 ° C and speed 1 using a film laminator (Ibico IL 12 HR).
• the composite is then treated at 60 ° C. in 1N HNO 3 for 2 hours and then thoroughly washed with demineralized water at room temperature.
• the measured current-voltage curve is shown in Fig. 22 (solid line).
• the impedance of the system determined by impedance spectroscopy is high. 12.2 m ⁇ . Comparative Example 2
• a membrane of the type GK1065-53 (blend membrane of sPEEK and Ultrason E, 2 hours at 80 ° C in 1M H 2 SO 4 hydrated) with a dry film thickness of 61 microns and a residual solvent content of ⁇ 0.5% NMP is containing a catalyst ink sprayed a soot-supported catalyst containing about 70% Pt and Nafion TM ionomer solution (EW1100 10%, Sigma Aldrich) to produce a cathode-side loading of 2 mg / cm 2 Pt and a catalyst ink containing a supported on carbon black catalyst about 80% PtRu content and sPEEK lonomerates sprayed to produce an anode-side loading of 3 mg / cm 2 PtRu.
• the current-voltage curve is also shown in Fig. 22 (dashed line).
• the impedance of the system determined by impedance spectroscopy is 10.6 m ⁇ .

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