WO2024083821A1 - Substrat de diffusion de gaz constitué d'un substrat métallique poreux et d'une couche de polymère perméable aux gaz, procédé pour le produire, électrode de diffusion de gaz et cellule électrochimique comprenant un substrat de diffusion de gaz - Google Patents

Substrat de diffusion de gaz constitué d'un substrat métallique poreux et d'une couche de polymère perméable aux gaz, procédé pour le produire, électrode de diffusion de gaz et cellule électrochimique comprenant un substrat de diffusion de gaz Download PDF

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WO2024083821A1
WO2024083821A1 PCT/EP2023/078828 EP2023078828W WO2024083821A1 WO 2024083821 A1 WO2024083821 A1 WO 2024083821A1 EP 2023078828 W EP2023078828 W EP 2023078828W WO 2024083821 A1 WO2024083821 A1 WO 2024083821A1
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polymer layer
gas diffusion
metal substrate
substrate
metal
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PCT/EP2023/078828
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German (de)
English (en)
Inventor
Alina Gawel
Siegmund DANIEL
Ulf-Peter APFEL
Kai JUNGE PURING
Lucas Hoof
Kevinjeorjios PELLUMBI
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Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
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Publication of WO2024083821A1 publication Critical patent/WO2024083821A1/fr

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    • 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
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/023—Porous and characterised by the material
    • H01M8/0232—Metals or alloys
    • 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
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/023—Porous and characterised by the material
    • H01M8/0239—Organic resins; Organic polymers
    • 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
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/023—Porous and characterised by the material
    • H01M8/0241—Composites
    • H01M8/0245—Composites in the form of layered or coated products

Definitions

  • Gas diffusion substrate made of a porous metal substrate and a gas-permeable polymer layer, method for its production and gas diffusion electrode and electrochemical cell with a gas diffusion substrate
  • the application relates to a gas diffusion substrate and a gas diffusion electrode for use in electrochemical cells and to a method for producing the gas diffusion substrate.
  • the gas diffusion electrode and the gas diffusion substrate have an electrocatalyst layer contacted by means of a metal substrate and a gas-permeable polymer layer.
  • the porous gas diffusion substrate also called diffusion layer
  • the diffusion layer serves to form a three-phase boundary between the electrolyte used for the electrochemical reaction, the electrocatalyst and the gas or liquid to be converted (i.e. the reactant).
  • This three-phase boundary can improve mass transport in the electrochemical process, enabling a higher conversion of the reactant.
  • efficient transport of the reactant to the catalyst layer is essential, which can usually be achieved by a hydrophobic pore structure of the gas diffusion substrate, and on the other hand, good electrical contact with the catalyst layer arranged on the diffusion layer.
  • the catalyst layer should also be in contact with the electrolyte of the electrochemical cell in order to ensure transport of the ions required for the electrochemical conversion (e.g. protons or hydroxide ions).
  • the three-phase boundary is formed within the catalyst layer or at the interface between the catalyst layer and the gas diffusion substrate. According to the state of the art, such diffusion layers can be produced using different processes.
  • electrically conductive filler materials can be sintered (and optionally compacted) with hydrophobic polymer binders and, if necessary, pore formers in the form of powder mixtures.
  • Two- or three-dimensional porous structures or lattice structures are usually used as carriers for the resulting materials.
  • the disadvantage of this is the continuous electrical conductivity in the diffusion layer, which tends to irreversible electrowetting when electrical potentials are applied, which can lead to the pore structure being flooded with electrolyte. If a salt is formed by the electrochemical reaction, this effect is further intensified.
  • flooding leads to limited mass transport of the reactant to the catalytically active layer, which is accompanied by a significant loss of performance.
  • a multi-layer structure with different proportions of the hydrophobic binder can reduce this effect, but cannot completely prevent it.
  • the disadvantage is that multilayer electrodes typically require high surface loadings of the catalyst.
  • three-dimensional porous electrically conductive materials such as carbon fiber fabrics or metal foams can be impregnated with a hydrophobic binder to produce diffusion layers.
  • Such diffusion layers have established themselves as state of the art in fuel cell applications.
  • the disadvantage here is that flooding of the pore structure can be observed due to potential-related electrowetting due to the continuous conductivity.
  • barrier layers are polymer foams or porous polymer layers (obtained from polymer binders and pore formers). Due to the lack of electrical conductivity, these are resistant to flooding caused by electrowetting and thus prevent mass transport limitations. However, since the integration of these polymer materials by lamination onto porous, catalytically active electrodes or by applying catalytically active materials directly to the polymer film, the electrodes are insulated on one side, which is why they are unsuitable for bipolar arrangements, which are common in large-scale applications.
  • the electrical contact of the diffusion electrode is then made on the electrolyte side and is conducted outwards in the electrode plane.
  • An improvement can be achieved by using metal mesh as current collectors.
  • this approach generally limits the scaling of the electrode size, as this is based on the electrical conductivity in the electrode plane.
  • the current density is distributed inhomogeneously over the electrode surface, which leads to a reduction in service life due to agglomeration of the catalytically active centers.
  • the application is therefore based on the object of specifying a gas diffusion substrate, a method for its production, a gas diffusion electrode and an electrochemical cell with such a gas diffusion substrate or such a gas diffusion electrode, with which the disadvantages of the prior art can be at least partially overcome and which are in particular flood-resistant and provide suitable three-phase boundaries.
  • a gas diffusion substrate has at least a first flat porous metal substrate with a first main surface and a second main surface opposite the first main surface and at least one flat gas-permeable polymer layer arranged on the first main surface.
  • the metal substrate is intended, among other things, for the electrical contacting of a catalyst layer.
  • a large number of three-phase boundaries for electrochemical processes are formed by the metal substrate, the polymer layer and the catalyst layer.
  • the gas diffusion substrate now has a first surface which is essentially formed by both the first main surface of the porous metal substrate and the flat polymer layer. This first main surface of the gas diffusion substrate therefore equally has regions which are formed by the first main surface of the metal substrate and regions that are formed by the flat polymer layer.
  • At least partial regions of this first main surface are designed in such a way that either a large number of closed regions of the polymer layer are present that are completely enclosed by a continuous region of the first main surface of the metal substrate, or a large number of closed regions of the first main surface of the metal substrate are present that are completely enclosed by a continuous region of the polymer layer.
  • a large number of closed regions of the polymer layer are present that are completely enclosed by a continuous region of the first main surface of the metal substrate, or a large number of closed regions of the first main surface of the metal substrate are present that are completely enclosed by a continuous region of the polymer layer.
  • the first flat polymer layer is made of a hydrophobic polymer.
  • embodiments are often realized in which, depending on the manufacturing process, both metal substrates can equally trigger a perforation of the polymer layer.
  • the metal substrate essentially serves to provide electrical conductivity, so that electrical contact with the catalyst coating or catalyst layer is possible.
  • the metal substrate typically provides mechanical stabilization, which is usually further improved by the catalyst layer in contact with it.
  • a polymer layer is understood to mean a polymer membrane with a substantially uniform thickness of less than 500 pm.
  • a polymer layer also called a polymer membrane according to the application
  • commercially available polymer films are used in particular, from which the gas diffusion substrate according to the application is then constructed. Due to the use of such films, the greatest possible flexibility is possible with regard to the required properties in relation to the pore size, the hydrophobicity and the layer thickness, while at the same time the aforementioned properties are uniform over the entire surface of the polymer film used, if one disregards the area in which compression of the metal substrate and polymer layer has taken place to produce the perforations using the method according to the application (whereby in principle a gradient of the pore size is also conceivable).
  • the uniform thickness can be achieved in particular by the fact that during the production process according to the application and the associated pressing of the polymer layer(s) and metal substrate(s) - apart from the perforation - no significant deformation of the polymer membrane occurs (provided the thickness of the polymer layer is not greater than that of the metal substrate).
  • the polymer layer serves - as already mentioned - to transport the reactants of the electrochemical reaction to the catalytically active centers.
  • the polymer layer is gas-permeable; it therefore allows unhindered access of gases to the reaction centers; the pore structure or porosity of the polymer layer is usually designed in such a way that even low-molecular organic compounds can pass through the polymer layer (low-molecular compounds are understood to mean compounds with a molecular weight of up to 600 g/mol in particular; for a coordinated pore structure, however, polymer layers can also be used that are also made up of compounds with a molecular weight of up to 1000 g/mol can be passed through).
  • polymer membranes with pore sizes of 0.05 pm to 10 pm are used for this purpose.
  • Pore sizes of 0.05 pm to 5 pm, for example from 0.1 pm to 1 pm, are particularly suitable.
  • the specification of the pore sizes refers consistently to a measurement using capillary flow porometry in accordance with DIN 66140, which can be used to specify the maximum pore size.
  • these pore sizes are found in the gas diffusion layers in the non-perforated areas, i.e. outside the area in which compression of the metal substrate and polymer layer has taken place.
  • the pore sizes of the polymer membranes typically used are therefore at least a factor of 10 smaller than the perforations described in more detail below.
  • the pores in the size range mentioned serve (as do the thin polymer layers) for a particularly effective mass transport of the reactant.
  • a polymer layer can also be formed from two (or possibly more than two) membranes arranged on top of one another (which then together have the thickness disclosed for the polymer layer), with membranes each having different pore sizes or porosities being used.
  • the ratio of pore volume to the total volume of the membrane can also be determined (via the density of the polymer layer).
  • the porosity calculated in this way is usually between 40 and 90%, in particular between 50 and 80% and often between 60 and 75%. Below 40% there is a risk that mass transport will be made more difficult, above 80% and especially 90% the mechanical stability typically suffers, so that during the production of the gas diffusion substrate there is a risk of significant damage to the pores and the pore structure (for example by the pores being compressed).
  • the gas diffusion substrates according to the application in particular with at least a three-layer structure made up of two metal substrates and a polymer layer or of two polymer layers and a metal substrate, already have a high level of mechanical stability without the presence of a catalyst layer and are therefore free-standing.
  • This enables a broad spectrum for the application of catalyst layers.
  • processes for applying thin layers of less than 20 pm can also be carried out using galvanic, wet-chemical (application of ink formulations) or gas-phase processes (physical or chemical processes).
  • catalytically active materials in particular metallic ones, can also be applied to the existing catalyst layer or catalyst coating using galvanic, wet-chemical or gas-phase processes.
  • the properties of the catalyst layer can be adapted and its thickness can be varied from very thin ( ⁇ 1 pm) to thick (500 pm).
  • the gas diffusion substrate according to the application is excellently suited to achieving efficient electrochemical conversion of gases or organic compounds.
  • this gas diffusion substrate enables spatial decoupling of the material diffusion properties from the electrical conductivity provided by the metal substrate.
  • the gas diffusion substrate according to the application makes it possible to provide a flood-resistant system with which electrical conductivity is achieved within the plane formed by the gas diffusion substrate on the one hand and perpendicular to this plane on the other. This conductivity in several dimensions has the great advantage that a majority of the gas diffusion substrates according to the application can be integrated as layers in a bipolar cell stack.
  • the main surface of the gas diffusion substrate is formed simultaneously by the metal substrate and the polymer substrate, a large number of electrical contacting options are provided there. At the same time, a large number of hydrophobic areas are also provided, so that a network of phase boundaries is formed between electrically conductive metal on the one hand and hydrophobic polymer on the other. On the other hand, if the metal also contains the catalyst layer is arranged, a "network" of three-phase boundaries forms on the surface of the gas diffusion substrate.
  • the flooding resistance of the system is therefore based in particular on the fact that - unlike the systems of the prior art - the metal/polymer/catalyst system according to the application does not allow any potential-related electrowetting with regard to the electrolytes present (for example aqueous solutions) through the said network (or at least only allows it to a reduced extent), so that the existing pore structures do not block (or flood).
  • the gas diffusion substrate according to the application can, as an alternative to the nature of the first surface of the gas diffusion substrate explained above in two-dimensional terms, also be explained by any three-dimensional structural features of the metal substrate contained therein.
  • a gas diffusion substrate according to the application has a metal substrate with a large number of elevations that are formed at least on the first main surface of the metal substrate. These are often formed both on the first main surface of the metal substrate and on the second main surface of the metal substrate opposite it.
  • the gas diffusion substrate further comprises a first flat gas-permeable polymer layer that has a large number of perforations. The perforations are arranged in such a way that elevations of the metal substrate at least partially protrude into them, in particular a plurality of elevations, often the larger part of the elevations, for example all elevations on the first main surface.
  • a gas diffusion substrate formed in this way can then be used to make electrical contact with a catalyst layer or a catalyst coating via the elevations of the metal substrate.
  • another electrical connection (for example to another layer of the gas diffusion substrate) can also be made via these elevations;
  • the catalyst layer or catalyst coating can then optionally be arranged on the side of the metal substrate facing away from the polymer layer (in a two-layer system consisting of a metal substrate and a polymer layer).
  • the network of three-phase boundaries and the distance between the three-phase boundaries can be predefined by the choice of the metal substrate or the elevations provided thereon.
  • At least some of the maxima of the elevations on the first and possibly also the second main surface of the metal substrate protrude through the perforations of the first flat polymer layer and/or lie at least in the side of the first flat polymer layer (facing away from the first main surface of the flat metal substrate).
  • the diffusion substrates according to the application also allow for space-efficient installation. Due to the flexible polymer layers (with a thickness of up to 0.5 mm) and the thin metal substrates (for example with a thickness of less than 1 mm), very thin diffusion layers are obtained that are conductive perpendicular to the plane. Since numerous cells are stacked on top of one another in bipolar electrochemical converters, this thinner design can save on expensive material for current collectors and frame materials in particular and a more compact structure can be achieved.
  • the polymer layers which - as already mentioned - can also be referred to as polymer membranes due to their essentially uniform thickness of less than 500 pm over the entire surface, have a thickness of 10 to 250 pm (so that in particular the possibly required passage of low molecular weight compounds can be easily achieved).
  • thinner membranes are usually more suitable - provided they can be purchased with sufficient mechanical stability.
  • Polymer membranes made of fluorinated or partially fluorinated polymers with thicknesses of 10 to 125 pm are particularly suitable. Particularly good results are achieved - especially when using diatomic or triatomic gases (e.g. CO 2 ) - with membrane thicknesses of 20 to 50 pm, especially 30 to 35 pm.
  • diatomic or triatomic gases e.g. CO 2
  • the upper and lower limits must be slightly offset; in this case, thicknesses of 60 to 200 pm are particularly suitable. (particularly for PES, PP, PE and PAN). Layer thicknesses of 500 pm or more, typically even more than 250 pm, typically lead to a loss of mass transport effectiveness and to a significantly reduced conductivity across the diffusion layer; layer thicknesses of less than 10 pm are in principle feasible but, according to the application, have significantly less favorable mechanical stability.
  • membrane thicknesses of at least 20 pm, in particular at least 30 pm are particularly suitable in terms of mechanical stability.
  • the metal substrates typically have thicknesses of 50 to 4000 pm, in particular 100 to 1000 pm. Metal substrates with thicknesses of 150 to 500 pm produce particularly good results.
  • the thickness of the polymer layers or polymer membranes is always smaller than that of the metal substrates and usually no more than half as large.
  • the diekene ratio (at least for membranes made of fluorinated polymers) can be significantly different, for example greater than 4: 1 or greater than 6: 1 (the same applies to the embodiments described below with two metal substrates or with two polymer layers).
  • the gas diffusion substrate has at least one second flat gas-permeable polymer layer in addition to the first flat gas-permeable polymer layer (where the first and second flat polymer layers are often made of the same material, in particular the same film was used as the starting material; however, two polymer layers with different porosities can also be used, for example, to set porosity gradients).
  • the second polymer layer is then arranged on the second main surface of the metal substrate.
  • a second surface of the gas diffusion substrate can also be realized, which is essentially formed from regions of a flat polymer layer (here the second flat polymer layer) and regions of the first flat metal substrate (here the second main surface of the first flat metal substrate).
  • the arrangement can be designed such that a large number of closed regions of the second polymer layer are surrounded by a continuous region of the second main surface of the metal substrate.
  • the (first) metal substrate there is a three-layer structure consisting of two polymer layers and the (first) metal substrate.
  • a plurality of closed regions of the second main surface of the metal substrate are surrounded by a continuous region of the second polymer layer, but usually also on the first surface of the gas diffusion substrate a plurality of closed regions of the first main surface of the metal substrate, which are surrounded by a continuous region of the first polymer layer.
  • the thickness of such a precisely three-layered gas diffusion substrate is then typically determined essentially by the thickness of the metal substrate and is typically 50 to 4000 pm, in particular 100 to 1000 pm, for example 150 to 500 pm.
  • the thickness of each of the polymer membranes is always smaller than that of the metal substrate and often at most half as large.
  • Such a three-layer gas diffusion substrate is typically more "open-pored” compared to a gas diffusion substrate made of two metal substrates and one polymer layer, since the openings of the first metal substrate are not partially “covered” by a second metal substrate. This results in more gas diffusion paths in comparison. Furthermore, this embodiment has a smoother surface, which can offer advantages for contacting in an electrochemical cell and exerts less mechanical stress on the polymer layers in a zero gap structure.
  • a gas diffusion substrate can be realized in particular, in which the two hydrophobic polymer layers adhere to one another; the first and the second polymer layer will often form a material bond at a large number of contact points.
  • Such a material bond can be realized in the production process of the gas diffusion substrate, in which, for example, in a pressing process, the pressure-temperature ratios are selected accordingly during pressing.
  • thinner polymer layers can be used than if there is only one polymer layer, but at the same time a high mechanical stability can be realized.
  • the gas diffusion substrate according to the application has at least one second flat porous metal substrate in addition to the first flat porous metal substrate.
  • the second flat porous metal substrate is then arranged on the surface of the polymer substrate that is opposite the side facing the first flat porous metal substrate.
  • a second surface of the gas diffusion substrate can be realized, which is essentially formed from regions of a flat polymer layer (here the first flat polymer layer) and regions of the second flat metal substrate (here the main surface of the second flat metal substrate that faces away from the first flat polymer substrate).
  • the first and second metal substrates can be made of the same material, but two different metal substrates, in particular two different types and sizes of fabric, can also be used, which can be used to set porosity gradients and achieve better control over the perforations.
  • the arrangement can again be designed such that a large number of closed regions of the second metal substrate are surrounded by a continuous region of a polymer layer.
  • the thickness of such a three-layer gas diffusion substrate is then typically determined essentially by the thickness of the two metal substrates (not the must correspond to the combined thickness of the two metal substrates and can therefore also be smaller) and is typically 100 to 6000 pm, in particular 200 to 1500 pm, for example 250 to 800 pm.
  • the thickness of the polymer membrane is always smaller than that of each of the metal substrates (which can also have different thicknesses) and often at most half as large as that of each of the metal substrates.
  • Such a three-layer gas diffusion substrate is typically mechanically more stable than a gas diffusion substrate made of two polymer layers and one metal substrate, since the two metal substrates have contact points for electrical contacting and therefore limit the degrees of freedom or mobility of the individual metal substrate.
  • the metal-metal contact points in this embodiment provide improved electrical contact.
  • Such a structure can be used to create a gas diffusion substrate in particular, in which the two metal substrates are connected to one another in a force-fitting manner via the polymer layer in between.
  • the metal-polymer-metal arrangement achieves a mechanically much more stable structure and in particular enables improved long-term stability, since the risk of delamination is significantly reduced.
  • the first metal substrate and/or the second metal substrate, but typically all metal substrates used are formed from a lattice structure (in particular a two-dimensional lattice structure).
  • Metallic wire mesh, expanded metal and perforated sheets are particularly suitable.
  • the first metal substrate and/or the second metal substrate, but typically all metal substrates used can be at least partially, usually but be made entirely of metal fibers or comprise a porous metal layer with metal fibers arranged directly on top of it. Materials such as a metal fleece (with disordered metal fibers) or a metal fabric, metal knit or metal knit (each with ordered metal fibers) come into consideration as metal substrates made of metal fibers.
  • made from metal fibers means in particular that the fibers consist essentially or completely of metal. Only in exceptional cases is it conceivable that non-metallic materials with a metal coating are used for the metal fibers. However, non-metallic materials with a coating are usually less suitable for reasons of mechanical stability alone.
  • the geometries of the metal fabrics are not limited to regular geometries (in which, for example, square openings are created between the parallel fibers); geometries can also be used in which other "weaving patterns" are present, for example a 5-shaft satin weave (as used in metal filters), as this allows greater flexibility with regard to the openings in the fabric, especially since these are rectangular and have different edge lengths and also allow a large range of variation in the edge length ratio.
  • a 5-shaft satin weave as used in metal filters
  • different surfaces of the metal substrates can be combined in different ways (in the 5-shaft satin weave, for example, there is a smooth and a rough surface).
  • the at least one first metal substrate (typically all metal substrates) is selected such that (before combining the various layers to form the gas diffusion substrate) the two main surfaces of the Metal substrates have a large number of openings or the metal substrate itself has continuous openings.
  • these openings should be formed in the respective main surface of the metal substrate in such a way that these openings take up an area of 25 to 80% of the main surface, in particular 30 to 60%, for example 35 to 40%.
  • these openings have an average area of 0.01 to 0.1 mm 2. The measurement can be carried out using light microscopic images.
  • such a metal substrate it is possible to ensure that sufficiently large recesses or areas remain in the surface of the gas diffusion substrate, which are occupied by the polymer layer (and in the case of a polymer-metal-polymer structure, allow the two polymer layers to be connected or adhered to one another). Furthermore, such a structure with openings also allows the use of metal fabrics, metal knits and the like and, finally, also a geometry that can be adapted to the parameters of a pressing process used, for example, to produce the gas diffusion substrate. Typically, in such metal fabrics and metal knits, the mesh size corresponds to approximately 0.5 to 5 times the diameter of the metal fibers or wires from which the metal fabrics and metal knits are constructed.
  • the metal substrate is at least twice as thick as one of the polymer layers.
  • the polymer layer should have a maximum thickness of one of the metal substrates. In arrangements with four or more layers, i.e. at least two metal substrates and at least two polymer layers, these two key values are typically used as a guide. When choosing the layer thickness, the aforementioned parameters have proven to be particularly useful in terms of manufacturing processes and mechanical stability.
  • the perforations of the first and/or second polymer layer (typically in all polymer layers contained in the gas diffusion substrate) have an average area (determined by means of a light microscope) of 0.01 to 1 mm 2 , in particular of 0.05 to 0.2 mm 2 .
  • the perforations take up a surface area of between 10 and 90% of the total surface area of the polymer layer, at least in partial areas of the first and/or second polymer layer (typically in all polymer layers contained). The total surface area is understood to be the area made up of the actual polymer layer itself and the surface area of the perforations (which, strictly speaking, no longer contain any polymer).
  • the surface area of the perforations will take up 30 to 70% and frequently correspond to between 40 and 60% of the total surface area of the polymer layer.
  • the aforementioned surface areas apply not only to partial areas of the first and/or second polymer layer or partial areas of all polymer layers, but to the entire polymer layer.
  • the metal substrate of the gas diffusion substrate is made of a metal or has a coating with a metal that has a conductivity of at least 1 * 10 6 S/m (according to the application, always measured at 25°C).
  • the conductivity is at least selected so that it corresponds to or is higher than that of stainless steel (1.4 * 10 6 S/m).
  • the conductivity of the metal used plays a less important role than the accessibility of the porous metal substrates for the reactants. For cost/benefit considerations, the specific geometric design will therefore usually play a more central role in the selection of the metal substrate than the metal used.
  • the metal substrate is made of a metal means, in the context of this application, that it consists of it or contains it for the most part (> 90% by weight).
  • the polymer layer or polymer layers contained in the gas diffusion substrate it is essentially only important that they are hydrophobic so that the three-phase boundaries can form and that the reactants can be transported to the catalytically active centers.
  • the fact that the first flat polymer layer and all other flat polymer layers are made of a hydrophobic polymer means in particular that they consist of the hydrophobic polymer or contain it, in particular as a main component, for example as a component with a content of more than 80% by weight.
  • Polysulfones and fluorinated polymers have proven to be particularly suitable hydrophobic polymers.
  • suitable hydrophobic polymers are those polymers selected from the group consisting of polyethersulfone, fluorinated ethylene propylene (FEP), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), perfluoroalkoxy polymer (PFA), polyethylene tetrafluoroethylene (ETFE), polyethylene chlorotrifluoroethylene (ECTFE), perfluorinated elastomer [perfluoroelastomer] (FFPM/FFKM), fluorocarbon [chlorotrifluoroethylenevinylidene fluoride] (FPM/FKM), perfluoropolyether (PFPE), perfluorosulfonic acid (PFSA) and perfluoropolyoxethane, as well as mixtures of the polymers mentioned.
  • FEP fluorinated ethylene propylene
  • PVDF polyvinyl fluor
  • porous polymers are also suitable, in particular polyolefins such as polypropylene (PP) and polyethylene (PE), polyurethanes; PET, polyacrylates, cellulose-containing polymers, polyvinyl chloride, polycarbonates (especially PCTE), polyamides (e.g. nylon), polyacrylonitrile (PAN) and polyester. Glass fibers are also conceivable.
  • polyolefins such as polypropylene (PP) and polyethylene (PE), polyurethanes
  • PET polyacrylates, cellulose-containing polymers, polyvinyl chloride, polycarbonates (especially PCTE), polyamides (e.g. nylon), polyacrylonitrile (PAN) and polyester.
  • PCTE polyvinyl chloride
  • PCTE polycarbonates
  • polyamides e.g. nylon
  • PAN polyacrylonitrile
  • the transport of reactants to the catalytically active centers is essential for polymer layers contained in gas diffusion substrates.
  • gas permeability or the pore structure and pore properties of the polymer material also play a role.
  • the pore structure and pore properties must allow sufficient mass transport and still ensure a separation effect of the compartments. Therefore, When manufacturing gas diffusion substrates, it is important to ensure that the chemical composition and the shape and size of the pores are retained as far as possible, which can be achieved using the process described below, provided that the layer thickness ratios of the polymer layer to the metal substrate are observed. If polymer layers that are too thick were used, this would lead to undesirable compaction of the polymer membrane, even outside the perforation areas.
  • the object according to the application is also achieved by a gas diffusion electrode with a gas diffusion substrate as explained above.
  • An electrocatalyst layer or a coating with an electrocatalyst is arranged on a first flat metal substrate and at least one first flat polymer layer arranged thereon.
  • one layer is arranged on top of another means here and generally within the scope of this application that the two layers arranged on top of one another are in direct contact with one another and that no further layers are arranged in between.
  • an adhesive or bonding agent layer can be arranged between two layers arranged on top of one another (it is essential that this adhesive or bonding agent layer does not impair the conductivity perpendicular to the plane or at most only slightly).
  • the flat polymer layer is arranged on the first main surface of the first flat metal substrate and together with it forms the essential part of a surface of the gas diffusion substrate.
  • the electrocatalyst layer or the coating with an electrocatalyst can now extend over the entire surface of the gas diffusion substrate thus formed, but it can also only be present in partial areas. Usually it will be arranged in particular in the areas where direct contact with the first flat metal substrate is possible.
  • a larger proportion of the surface of the perforations can be used to improve the adhesion of the catalyst - particularly in embodiments with perforated polymer layers. This also results in improved through-plane conductivity.
  • Adhesion of the catalyst layer or the coating with the catalyst can be achieved.
  • the adhesion of the catalyst layer can also be improved by an organic binder contained in the catalyst layer or coating with the catalyst. This binder can then be selected to match the material of the polymer layer. Binders that only develop their adhesive effect during the production of the gas diffusion substrate, for example through thermal or mechanical treatment, are particularly suitable. Additives (e.g. conductive additives or pore formers) can also be introduced into the catalyst layer.
  • the object according to the application is also achieved by an electrochemical cell with at least one gas diffusion substrate or at least one gas diffusion electrode, as described above.
  • the electrochemical cell can be a structure that contains exactly one gas diffusion electrode according to the application.
  • a stack of several gas diffusion substrates or electrodes can also be used to increase the conversion.
  • the solution according to the application can make particularly good use of its advantages over the prior art, since the electrical conductivity perpendicular to the plane of the gas diffusion substrate enables a particularly simple structure of the electrochemical cell.
  • the electrochemical cell can also be a zero-gap cell, i.e. a cell in which the distance between the electrodes is minimized as much as possible (e.g. by contacting the electrodes with an ion-conducting membrane or an electrolyte-soaked porous separator) and in which there is no gap for a liquid electrolyte in the cell in particular.
  • An electrochemical cell has at least two chambers, with the gas diffusion electrode forming the interface between the liquid or gaseous reactant and the liquid or solid electrolyte.
  • the gas diffusion substrate with the catalyst layer or catalyst coating is infiltrated at least partially with the electrolyte. In this way, a three-phase boundary is formed from the substrate, electrolyte and catalyst.
  • the gas diffusion electrode usually functions as a cathode for the described applications. Reduction of CO 2 , CO, N 2 or O 2 or electroreduction of organic molecules (e.g. hydrogenation). Depending on the application, it can also be used as an anode for oxidation reactions (H 2 , N 2 or CO oxidation, oxidation of organic compounds).
  • the electrochemical cell also includes another electrode at which suitable oxidation or reduction processes can take place. In this case, both a diffusion electrode designed for a reductive process and an oxidative process can be used at the same time.
  • gas diffusion substrates The problem according to the application is finally solved by a method for producing gas diffusion substrates.
  • manufacturability of the gas diffusion substrates is not limited to the methods described in more detail below, since, for example, even the most complicated geometries and layer sequences can be realized within the framework of additive manufacturing, in particular the geometrically complex surfaces of the gas diffusion substrate, which are composed of polymer layer(s) and metal substrate(s). Rolling processes (e.g. roll-to-roll processes or calendering) are also conceivable.
  • the gas diffusion substrates according to the application can be produced by arranging the polymer layers and metal substrate layers required for the substrate to be produced between two pressing jaws of a press and then - depending on the materials used - adjusting the pressing pressure, pressing temperature and pressing time so that a material-locking or form-locking bond of the layers is formed.
  • the elevations on the main surface(s) of the metal substrate cause perforation of the polymer layer during pressing, so that the desired structure of the surface of the gas diffusion substrate is obtained.
  • the layer system to be pressed can be introduced between two silicone plates as pressing jaws of a hydraulic hot press and pressed for 10 minutes at 260 °C and a pressure of, for example, 2.5 to 12 kN/cm 2.
  • the catalyst layer arranged on the gas diffusion electrode can be pressed together with polymer layer(s) and metal substrate layer(s); however, a catalyst layer or a catalyst coating can also be applied subsequently (for example, a catalyst ink can be sprayed on or applied in another way). Which method is appropriate is known to the person skilled in the art and depends in particular on the pressure and temperature stability of the catalyst.
  • the surface of the pressing jaws can be designed in such a way that it has elevations at the points where perforations are to be formed in the polymer layer. During the pressing process, these elevations perforate the polymer layer so that the underlying metal substrate can form part of the surface of the gas diffusion substrate.
  • the temperature during the pressing process is usually chosen so that it is below the glass transition temperature of the polymer contained in the polymer layer. Higher temperatures would result in the pore structure in the polymer layer suffering from the temperature treatment and, in the worst case, the pores would completely bake together. Nevertheless, a temperature is usually chosen which is not too far below the glass transition temperature - particularly in embodiments which contain at least two polymer layers, as this makes it easier for two polymer layers to adhere to one another or to create a material-locking bond. Temperatures between 180 and 260 °C, in particular 200 to 240 °C, have proven suitable, particularly for layers made of fluorinated polymers. Typically, independently of this or simultaneously, a contact pressure of at least 2 kN rrr 2 , for example from 2.25 to 8 kN rrr 2 , is suitable.
  • the gas diffusion substrates according to the application can also be produced as an alternative or in addition to the pressing process by at least positively connecting a metal substrate and a polymer layer to one another and then grinding the side of the polymer layer facing away from the metal substrate. until perforations form in the polymer layer, allowing electrical contact to be made with the metal substrate, or until the proportion of perforations has reached an area that ensures sufficient conductivity.
  • the gas diffusion electrode according to the application and the electrochemical cell according to the application are particularly suitable for the reduction of gases. These include CO, CO 2 , N 2 , NO X (nitrogen oxides), SO X (sulfur oxides) or oxygen. In addition, they are also suitable for the reduction or oxidation of organic substances, for example the hydrogenation of multiple bonds, carboxylation or partial oxidation. However, it must be ensured that the material, in particular the material of the polymer layer, is compatible with the organic compounds and the products resulting from them. It goes without saying that the polymer layer must also be chemically stable with respect to the electrolyte.
  • the gas diffusion substrate provides systems for electrochemical processes and with the formation of three-phase boundaries from an electrolyte, catalyst and reactants, which are conductive perpendicular to the plane and yet do not exhibit any significant flooding behavior with electrolyte through electrowetting and, furthermore, are no longer electrically insulating due to the perforated porous polymer layers or polymer films and therefore allow surface scaling and bipolar assembly in electrochemical stacks.
  • These properties and the design as free-standing gas diffusion substrates enable a flexible platform for the application of catalytically active layers and thus properties tailored to the respective processes.
  • the adaptation of the catalyst layer properties is thus decoupled from the diffusion layer. Properties such as permeability, porosity, electrical conductivity or mechanical stability can be controlled by selecting the material types and morphologies.
  • the diffusion layer according to the application the electrode according to the application and the electrochemical cell as well as the process The production of the diffusion layer is described in more detail below using examples and figures.
  • Figures 1 and 2 show a schematic view of a section of the diffusion substrate according to the application in a three-layer embodiment.
  • the thicknesses of the polymer layer(s) are shown larger for the sake of clarity. In fact, as stated above, the thickness of the polymer layers is usually significantly smaller than that of the metal substrates.
  • Figure 1 shows a first polymer layer 31 and a second polymer layer 32 underneath, between which a first flat metal substrate 21 is arranged in the form of a metal grid.
  • the largest part of the metal substrate 21 is not part of the first surface 5 of the gas diffusion substrate; however, the course of the metal grid between the polymer layers 31, 32 is shown with dashed lines (the grid has very large grid windows for the sake of clarity).
  • the surface 5 of the gas diffusion substrate is formed by the side of the polymer layer 31 facing away from the metal substrate 21 (the continuous region of the first polymer layer is clearly visible) and ten closed regions 23 of the first metal substrate 21 (three of which are on the edge of the section shown).
  • a region 23 that is closed off from the main surface 5 is shown in the form of a protruding elevation 24 of the first metal substrate 21 (this is therefore part of the first main surface of the first flat metal substrate 21).
  • a perforation 34 has formed in the polymer layer 31.
  • a perforation 34 can also be seen on the right-hand cutout edge.
  • an area 37 can be seen in which, due to the manufacturing process, a material connection is formed between the two polymer layers 31, 32 (schematically shown by a partially broken line).
  • Figure 2 shows a first flat metal substrate 21 and a second flat metal substrate 22 lying underneath, between which a first polymer layer 31 is arranged.
  • first metal substrate 21 and the second metal substrate 22 are shown as metal grids (here too, with very large grid windows for the sake of clarity).
  • the largest part of the metal substrate 22 lying underneath is not part of the first surface 5 of the gas diffusion substrate; however, the course of the metal grid is shown in some areas with dashed lines (the side of this metal substrate 22 facing away from the polymer layer forms part of the second surface of the gas diffusion substrate).
  • the first surface 5 of the gas diffusion substrate is formed here by the side of the polymer layer 31 facing the metal substrate 21 and approximately eighteen closed regions 33 of the first polymer layer 31 as well as by the metal grid of the first metal substrate 21 in the form of a continuous region.
  • some elevations 25 of the second metal substrate 22 can be seen here, which have perforated the polymer layer 31 due to the manufacturing process and are therefore also part of the first surface 5.
  • elevations 24 pointing upwards are formed only at every second intersection point of the metal grid of the first 21 (these are marked by hatched lines). The same applies to the second metal substrate 22.
  • downward-pointing elevations 26 are formed (marked by dashed hatching) so that perforations (not shown here) are formed in the polymer layer 31.
  • a perforation 34 can be seen in the area of such a downward-pointing elevation.
  • the upward- or downward-pointing elevations can - as explained above - be part of a fabric made of individual metal fibers, for example (with elevations inevitably occurring at the intersection points of the longitudinal and transverse fibers); but they can also be produced specifically at individual points of a completely flat metal grid by means of additive manufacturing, for example (this applies equally to the grid in Figure 1).
  • Figures 3a and 3b show examples of the structure of electrochemical cells with the diffusion substrates and diffusion electrodes according to the application.
  • Figure 3a shows a cell for CO 2 electrolysis in zero-gap with anion exchange membrane as electrolyte with gas diffusion electrodes with a layer structure polymer layer/metal substrate/polymer layer:
  • a (bi-)polar plate with flow guide 103 is arranged on each of the two end plates 101 with an insulator layer 102 arranged thereon.
  • the actual diffusion electrode 104 (a three-layer structure is shown in Figure 3a Polymer layer/metal substrate/polymer layer) is arranged on one of the bipolar plates 103 (the electrocatalyst layer is not shown here for the sake of clarity).
  • the gas diffusion electrode 104 is followed by an anion exchange membrane 106 and an anode 107 for O2 formation.
  • the spaces between the gas diffusion electrode 104 and anion exchange membrane 106 on the one hand and the anion exchange membrane 106 and anode 107 on the other hand are sealed to the outside with a seal 106.
  • Figure 3b shows a cell for O 2 or CO 2 reduction in the flow cell with liquid catholyte with gas diffusion electrodes with a layer structure polymer layer/metal substrate/polymer layer):
  • a (bi-)polar plate with flow guide 203 is arranged on each of the two end plates 201 with an insulator layer 202 arranged thereon.
  • the actual diffusion electrode 204 (a three-layer structure of polymer layer/metal substrate/polymer layer is shown in Figure 3b) is arranged on one of the bipolar plates 203 (the electrocatalyst layer is not shown here for the sake of clarity).
  • the gas diffusion electrode 104 is followed by an electrolyte compartment 206, an anion exchange membrane 207, another electrolyte compartment 206 and an anode 208 for O 2 formation.
  • sealing is achieved by means of several seals 206.
  • Example 1 Manufacturing of an electrode with a grid-reinforced PTFE diffusion substrate with a layer structure polymer layer/metal substrate/polymer layer
  • a galvanically silver-plated stainless steel grid (Haver & Boecker, 0.2 mm x 0.16 mm) is pressed between two ePTFE polymer layers (Fluortex Multiflon ePTFE membrane with a thickness of 30 pm and a pore size of 0.45 pm) as polymer layers for 4 x 2 min at 200 °C and 3.6 kN cm 2 .
  • ePTFE polymer layers Fluortex Multiflon ePTFE membrane with a thickness of 30 pm and a pore size of 0.45 pm
  • the gas diffusion layer is pressed onto the catalyst coating for 10 min at 260 °C and 3.6 kN cm 2 using the same press.
  • the electrodes were functionalized with an anion exchange (ionomer) layer (Dioxide Materials) by drop casting and conditioned in 1 M KOH.
  • Figures 4a to 4c and 5a to 5c show scanning electron microscope (SEM) images of a diffusion substrate with a layer structure of polymer layer/metal substrate/polymer layer at different magnifications.
  • Figures 4a to 4c show images of a stainless steel grid or fabric with an ePTFE polymer layer (Fluortex MultiFlon membrane with a thickness of 30 pm and a pore size of 0.45 pm) made from a polymer layer/metal substrate/polymer layer structure.
  • a stainless steel grid with a mesh size of 0.16 mm according to the manufacturer was used as the metal substrate.
  • the maxima or elevations of a fabric-shaped metal substrate with a fiber diameter of about 0.16 mm protruding through the perforations of the polymer layer can be clearly seen in Figures 4b and in particular 4a.
  • the perforations of the polymer layer have dimensions of approximately 0.35 to 0.55 mm long and 0.13 to 0.17 mm wide and take up an average area of about 0.05 to 0.06 mm 2 , so that the perforations in the polymer layer take up about 40-45% of the total area of the polymer layer.
  • the surface of the diffusion substrate is thus formed by the continuous area of the perforated polymer layer and the closed areas of the metal substrate visible in the perforations of the polymer layer, which are completely enclosed by the polymer layer (see Figure 4b). It can also be seen that the elevations on the main surface of the metal substrate were pressed into the polymer layer by the manufacturing process (hot pressing). Figure 4b shows an approximately diamond-shaped area between these elevations in the center of the figure, i.e.
  • Figures 5a to 5c show images of a stainless steel mesh or fabric with a polyethersulfone (PES) polymer layer made from a polymer layer/metal substrate/polymer layer structure.
  • a stainless steel mesh with a mesh size of 0.2 mm according to the manufacturer was used as the metal substrate; the polymer layer had a thickness of 140 pm and a pore diameter of 0.45 pm.
  • the holes created by the perforations in the polymer layer can also be clearly seen in Figures 5b and in particular 5a. TI protruding maxima or elevations of the fabric-shaped metal substrate with a fiber diameter of about 0.16 mm.
  • the perforations of the polymer layer have dimensions of approximately 0.35 to 0.45 mm long and 0.16 to 0.2 mm wide and take up an average area of about 0.055 to 0.065 mm 2 , so that the perforations in the polymer layer take up about 45-50% of the total area of the polymer layer.
  • the surface of the diffusion substrate is also formed here by the continuous area of the perforated polymer layer and the closed areas of the metal substrate visible in the perforations of the polymer layer, which are completely enclosed by the polymer layer (see Figure 5b). It can be seen again that the elevations on the main surface of the metal substrate were pressed into the polymer layer by the manufacturing process (hot pressing). In Figure 5c, the open-pore structure of the polymer layer, which in particular enables gas transport, can be clearly seen. Here, too, the layer thickness and the pore structure of the polymer film used to produce the gas diffusion layer have essentially been retained.
  • Figures 6a to 6c show scanning electron microscope (SEM) images of a diffusion substrate with a layer structure of polymer layer/metal substrate/polymer layer with a catalyst coating arranged on top of it at different magnifications.
  • SEM scanning electron microscope
  • FIGs 6b and especially 6a are the maxima or elevations of the fabric-shaped metal substrate protruding through the perforations of the polymer layer (these are the regular structures of ovals or perforations arranged perpendicular to one another) with a fiber diameter of approximately 0.16 to 0.25 mm.
  • the perforations of the polymer layer have dimensions of approximately 0.25 to 0.35 mm in length and 0.13 to 0.17 mm in width and cover an average area of approximately 0.035 mm 2 , so that the perforations in the polymer layer cover approximately 30% of the total area of the polymer layer.
  • Figure 6b shows that the closed areas of the metal substrate visible in the perforations of the polymer layer are completely enclosed by the polymer layer.
  • Figure 7 shows - in contrast to all other figures - a scanning electron microscope (SEM) image of a diffusion substrate with a layer structure of polymer layer/metal substrate/polymer layer with metal fibers distributed irregularly on an expanded metal mesh.
  • SEM scanning electron microscope
  • Example 2 CO 2 electrolysis with an electrode according to Example 1
  • the CO 2 electrolysis is carried out in a 3-electrode setup (RE: mini-RHE, CE: platinum-plated titanium wire) with 0.1 MK 2 SCh/1.5 M KHCO 3 as electrolyte at room temperature.
  • the CO 2 flow is 22.5 ml min -1 , mixed with 2.5 ml min -1 Ar as internal standard and 40 mbar overpressure is applied.
  • the concentration of the product gases (H 2 , CO) formed during the electrolysis is determined using online GC/MS.
  • Table 1 summarizes the results of the electrolysis for different catalyst layer compositions.
  • the influence of the catalyst layer composition on the Faraday efficiency for CO after 20 and 120 minutes respectively and the cathode potential against the reversible hydrogen electrode after 120 minutes were investigated.
  • the current density in all measurements was 50 mA cm -2 and the anion exchanger loading was 5 mg cm -2 .
  • Higher silver loadings lead to lower electrolysis voltages, but they also reduce the Faraday efficiency for CO.
  • a PTFE content of 15 Wt.% in the catalyst coating represents an optimum for the performance of the electrodes with regard to CO 2 reduction.
  • a composition of the catalyst layer of 80 wt.% carbon black (CB), 15 wt.% PTFE and 5 wt.% silver nanoparticles was selected for the following examples 3 and 4.
  • Example 3 Comparison of the electrodes according to Example 1 with commercially available electrodes
  • Example 2 To compare the electrodes according to Example 1, the electrolysis according to Example 2 was also carried out with commercially available electrodes based on hydrophobic carbon fiber fabric with a microporous coating (CeTech). The current density was (as in Example 2) 50 mA cm -2 and the anion exchanger loading was 5 mg cm -2 . Both the CO Faraday efficiency and the voltage are comparable for both types of electrode. On average, the standardized CO Faraday efficiency for the electrode according to the application is between 88 ⁇ 4 and 85 ⁇ 9% compared to 95 ⁇ 1 to 82 ⁇ 5% for the electrodes based on the carbon fiber fabric.
  • the electrode according to the application shows a much higher stability of the Faraday efficiency over the test period, while the electrode with reference material already shows a loss of 13 percentage points.
  • the lower scatter of the potential values when using an electrode in accordance with the application which ensures a high reproducibility of a stable electrolysis operation of electro- which can be covered with a grid-reinforced gas diffusion layer.
  • the high mechanical integrity of the electrodes according to the application is particularly noteworthy here, despite the usual formation of carbonate. Commercially available carbon fiber fabric gas diffusion layers, on the other hand, can break due to carbonate formation.
  • Figure 8a shows the time course of the normalized Faraday efficiency for CO and Figure 8b of the voltage (right) during a two-hour CO 2 electrolysis for the electrode according to the application (squares) and the commercially available electrode (circles).
  • the tensile strength was used as a parameter for both electrodes.
  • the diffusion substrates according to the application have a tensile strength of 105 ⁇ 9 MPa with a tensile elongation of 27 ⁇ 6 %.
  • a tensile strength lower by a factor of 6.5 (16 ⁇ 3 MPa) with a lower tensile elongation of 13 ⁇ 1 % was observed.
  • Figure 9a shows the Faraday efficiency for CO
  • Figure 9b the cathode potential against the reversible hydrogen electrode above for 50 mA cm -2 and below for 200 mA cm -2. Even at 200 mA cm -2, a standardized CO Faraday efficiency in the range of 40 to 10% is achieved over the entire test period.
  • Example 4 O 2 reduction with an electrode according to Example 1
  • the electrochemical O 2 reduction is carried out in a 3-electrode setup (Gaskatel FlexCell, RE: Mini-RHE, CE: Pt spiral) with 1 M KOH as electrolyte at room temperature.
  • the O 2 flow is 20 ml min -1 and an overpressure of 2 to 3 mbar is applied via a water column.
  • the gas diffusion electrode according to the application was cycled 100 times between +1.2 V and +0.3 V.
  • Figure 10a shows cyclic voltammometric investigations of O 2 reduction. For selected cycles, the course of the current density can be seen as a function of the applied voltage. O 2 reduction begins between 0.7 and 0.8 V and can be recognized by the increase in the amount of current density.
  • Figure 10b shows that the amount of current density increases at a voltage of 0.3 V with increasing number of cycles and approaches a value between -40 and -50 mA cm -2 .
  • This behavior can be attributed to the increasing wetting of the hydrophobic, carbon-containing catalytic layer by the electrolyte. Flooding and the associated decrease in the activity for O 2 reduction does not occur, however, due to the high blocking effect of the diffusion layer.
  • Example 5 Manufacturing of an electrode with a grid-reinforced PTFE diffusion substrate with a layer structure of metal substrate/polymer layer/metal substrate
  • An ePTFE polymer layer (Fluortex; membrane with a thickness of 30 pm and a pore size of 0.45 pm) is pressed between two electroplated silver-plated Cu grids (Haver & Boecker, 0.5 mm x 0.25 mm) for 2 minutes at 180 °C and 2.5 kN cm -2 .
  • the design of the diffusion substrate in the form of a porous ePTFE polymer layer between two conductive grids prevents the diffusion layer from detaching from the conductive component and thus enables easier further processing.
  • a mixture of carbon black (Imerys Graphite & Carbon), nanometer PTFE (Nanoshel) and silver nanoparticles (Alfa Aesar) is suspended in 2-propanol as a catalyst ink and homogenized for 30 minutes using an ultrasonic bath.
  • the catalyst ink is applied to the mesh-reinforced diffusion substrate with a spray gun (Iwata) at 90 °C until an Ag loading of 1 mg cm -2 is reached.
  • the electrodes are functionalized with an anion exchange (ionomer) layer (Dioxide Materials) by drop casting and conditioned in 1 M KOH.
  • Figure 1 1 a shows a light micrograph (100x magnification) and 1 1 b a scanning electron microscope (SEM) image of a diffusion substrate with a layer structure of metal substrate/polymer layer/metal substrate.
  • the fabric-shaped metal substrate can be seen.
  • the fiber diameter is about 0.15 mm and the openings in the metal substrate have an area of about 0.47 mm 2 , so that the openings cover an area of more than 90% of the main surface of the metal substrate. substrate.
  • the surface of the diffusion substrate is thus also formed here by the continuous area of the first main surface of the fabric-shaped metal substrate and the closed regions of the polymer layer visible in the openings of the metal substrate, which are completely enclosed by the main surface of the metal substrate.
  • Figure 1 1 a it can be seen that the metal substrate lying beneath the polymer layer has pressed through the polymer layer as a result of the manufacturing process (hot pressing), so that perforations have been created in the polymer layer.
  • Figure 1 1 b shows a side view. The thin polymer layer winds its way through between the two metal grid/metal fabric layers.
  • Figure 12a shows a scanning electron microscope (SEM) image of a diffusion substrate with a layer structure of metal substrate/polymer layer/metal substrate.
  • a silver-plated copper grid or fabric with a mesh size of 0.565 mm and an ePTFE polymer layer (Fluortex MultiFlon membrane with a thickness of 30 pm and a pore size of 0.45 pm) were used.
  • the fiber diameter is approximately 0.15 mm.
  • the surface of the diffusion substrate is formed by the continuous area of the first main surface of the fabric-shaped metal substrate and the closed regions of the polymer layer visible in the openings of the metal substrate, which are completely enclosed by the main surface of the metal substrate.
  • the second metal substrate under the polymer membrane is arranged rotated by approximately 45° with respect to the first metal substrate. It can also be seen that openings resulting from the manufacturing process are arranged in the polymer membrane. It can also be seen that only in the area where the polymer layer was compressed by the lower (second) metal substrate, the pore structure of the polymer film used was lost (Fig. 12b).
  • Example 6 CO 2 electrolysis with an electrode according to Example 5
  • the CO 2 electrolysis was carried out in a 3-electrode setup (RE: Mini-RHE (Gaskatel), CE: Ni foam) with 1 M KHCO 3 as electrolyte at room temperature.
  • the CO 2 flow was 22.5 ml min -1 , mixed with 2.5 ml min -1 Ar as internal standard and 40 mbar overpressure was applied.
  • the concentration of the product gases (H 2 , CO) formed during the electrolysis is determined by online GC/MS.
  • Table 2 shows the Faraday efficiencies for CO of the gas diffusion electrodes according to Example 5 at a current density of 50 mA cm -2 .
  • the selectivity for CO changes depending on the catalyst layer composition.
  • a Faraday efficiency for CO of 78% is achieved at a half-cell voltage of -1.54 V vs. RHE with a catalyst layer composition of equal mass parts of Ag nanoparticles, carbon black (CB) and PTFE nanoparticles.
  • Example 7 O 2 reduction with an electrode according to Example 5
  • FIG. 13a shows cyclic voltammometric investigations of the O 2 reduction.
  • the current density curve can be seen as a function of the applied voltage.
  • Figure 13b shows the current densities achieved at 0.3 V.
  • the electrodes used show values comparable to those of Example 4 at approx. -50 mA cm -2 to -40 mA cm -2 .
  • the current density decreases. This can be attributed to oxidation of the copper grid used, as can be seen in the cyclic voltammogram at approximately +0.8 V vs. RHE.
  • Cu oxide species on the copper support grid of the diffusion layer increase contact resistances between the catalyst layer and the diffusion layer and thus cause a gradual decrease in the current density.
  • the CO 2 electrolysis is carried out galvanostatically at a current density of 100 mA cm -2 in a zero-gap setup with 0.1 M KHCO 3 as anode substrate at 40 °C cell temperature.
  • a 40 pm thick Sustainion membrane is used as anion exchange membrane. membrane is used.
  • a 1 mm thick titanium felt from Bekaert with 1 mg cm -2 lrO 2 serves as the anode.
  • the CO 2 flow is 50 ml min -1 , mixed with 5.5 ml min -1 Ar as an internal standard and 40 mbar overpressure is applied.
  • the concentration of the product gases (H 2 , CO) formed during the electrolysis is determined using online GC/MS.
  • Figure 14a shows the time course of the standardized Faraday efficiency for CO and Figure 14b that of the total cell voltage (left) during a 40-minute CO 2 electrolysis.
  • a constant CO Faraday efficiency of 13 % is achieved at a cell voltage ⁇ 4 V.
  • Example 9 Hydrogenation of 2-methyl-3-butyn-2-ol using a diffusion substrate according to Example 1
  • a diffusion substrate according to Example 1 is used, but a different catalyst layer than in Example 1 is applied to produce the electrode.
  • a catalyst ink consisting of a Fe 3 Ni 6 S 8 catalyst or a Pd catalyst and polyvinyl lyl idene fluoride (PVDF) in MeOH is sprayed onto the grid-supported PTFE diffusion substrate up to a catalyst loading of 5 mg cm -2 using an Iwata SBS spray gun.
  • PVDF polyvinyl lyl idene fluoride
  • the electrochemical hydrogenation is carried out in a 3-electrode setup (working electrode: diffusion electrode as registered, reference: Hydroflex Mini-RHE, counter electrode: Ni foam).
  • the diffusion electrode forms the boundary between a cathode chamber and a compartment for the organic substrate 2-methyl-3-butyn-2-ol.
  • a 2 M potassium hydroxide solution serves as the electrolyte on the anode and cathode sides. Both the substrate and the electrolytes are passed through the cell at 10 ml min 1 each.
  • the electrolysis was carried out at 100 mA cm -2 over a period of 60 min.
  • the hydrogenation products were quantified via 1 H-NMR analysis using potassium hydrogen phthalate as an internal standard.
  • Table 3 shows the hydrogenation results for the Fe 3 Ni 6 S 8 catalyst and the Pd catalyst, respectively.
  • a hydrogenation to the alkene (2-methyl-3-buten-2-ol, MBE) of a total Faraday efficiency of 31% (Fe 3 Ni 6 S 8 ) and 19% (Pd) was observed.
  • a total Faraday efficiency of 12% was observed.
  • a transfer of the products of about 50% of the yield was observed.
  • the cathode voltages were 4.5 (Fe 3 Ni 6 S 8 ) and 1.5 V vs. RHE (Pd). Comparative experiments with a carbon cloth as a diffusion layer failed due to the high penetration of the substrate into the catholyte and show the advantage of the electrodes according to the application.
  • Example 10 Measurement of electrical conductivity perpendicular to the electrode surface
  • a test specimen (40 mm diameter) is clamped between two gold-plated copper blocks (5x5 cm2) and pressed with a pneumatic piston at different surface pressures.
  • a carbon fleece is placed above and below the test specimen. The voltage loss across the test specimen is determined from the difference between the voltage loss of the test measurement and a blank measurement with two carbon fleeces. The measurements are carried out at current densities of 200 mA cm -2 and the resistance is determined from a linear representation of the voltage loss as a function of the current density.
  • the carbon fiber fabric from CeTech and a porous PTFE polymer layer were measured as reference materials.
  • Table 4 shows that the porous PTFE polymer layer cannot be measured due to the high electrical resistance in the measuring setup and the limited maximum voltage of the test bench (0-1 V) and therefore does not have any significant electrical conductivity perpendicular to the electrode plane.
  • the diffusion substrates according to the application show a significant electrical conductivity. The electrical resistance only shows a significant dependence of the Surface resistance depends on the surface pressure.
  • Example 1 Use of metal substrates with two different surfaces in a layer structure metal substrate/polymer layer/metal substrate
  • An ePTFE polymer layer (Fluortex; membrane with a thickness of 30 pm and a pore size of 0.45 pm) is pressed between two metal meshes with a 5-shaft satin weave (different meshes from GKD - Gebr. Kufferath AG) for 2 minutes at 200 °C and 3 kN cm -2 .
  • the surfaces of the metal substrate can be combined in different ways (depending on how the smooth and rough surfaces are aligned). By choosing such metal meshes, rectangular openings can be created in the metal substrates. It can be seen that the mechanical stability of the gas diffusion layer can suffer depending on the mesh size and geometry as well as the alignment of the smooth or rough surface. Table 5 shows the results. Table 5:
  • Example 12 Relevance of the pressing parameters in the production of diffusion substrates Polymer layer/metal substrate A fabric-shaped metal substrate made of copper mesh (Haver & Boecker, 0.5 mm x 0.25 mm) was pressed onto a Bola PTFE polymer layer (0.2 mm thick; pore size 0.45
  • Table 6 shows that the gas diffusion substrates produced using the process according to the application initially show a clear conductivity perpendicular to the layer (as is clear from the comparison with the pure PTFE starting material / Table 6, line 2) and have a similar or better conductivity than the reference material carbon cloth (Table 6, line 1) at both 180 °C and 200 °C during the production of the substrates, with the conductivity increasing for higher contact pressures - see lines 4 to 19.
  • Table 6 shows that the gas diffusion substrates produced using the process according to the application initially show a clear conductivity perpendicular to the layer (as is clear from the comparison with the pure PTFE starting material / Table 6, line 2) and have a similar or better conductivity than the reference material carbon cloth (Table 6, line 1) at both 180 °C and 200 °C during the production of the substrates, with the conductivity increasing for higher contact pressures - see lines 4 to 19.
  • With a constant contact pressure and increasing contact temperature it can be seen that the surface resistance decreases with increasing contact temperatures (up to around 220 /
  • the sheet resistance decreases and thus the conductivity can be maximized without a destructive influence on the polymer layer if the contact pressure during the production of the gas diffusion layers is increased and the temperatures are increased moderately.

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Abstract

L'invention concerne un substrat de diffusion de gaz destiné à être utilisé dans une cellule électrochimique, comprenant au moins un premier substrat métallique poreux plat avec une première et une seconde surface principale et au moins une première couche polymère plate perméable aux gaz disposée dessus. Le substrat métallique est pourvu d'une couche de catalyseur à des fins de mise en contact électrique. La première couche polymère plate, qui est constituée d'un polymère hydrophobe, est disposée sur la première surface principale du substrat métallique. Dans le procédé, une première surface du substrat de diffusion de gaz est formée essentiellement à partir de la première couche polymère plate et de la première surface principale du premier substrat métallique plat. Au moins des sous-régions de ladite surface sont pourvues soit d'une pluralité de zones fermées du premier substrat métallique, qui sont entourées par une région continue de la première couche polymère, soit d'une pluralité de zones fermées de la couche polymère, qui sont entourées par une région continue de la première surface principale du premier substrat métallique plat. L'invention concerne en outre une électrode de diffusion de gaz, une cellule électrochimique comprenant un tel substrat de diffusion de gaz, et un procédé pour la produire.
PCT/EP2023/078828 2022-10-17 2023-10-17 Substrat de diffusion de gaz constitué d'un substrat métallique poreux et d'une couche de polymère perméable aux gaz, procédé pour le produire, électrode de diffusion de gaz et cellule électrochimique comprenant un substrat de diffusion de gaz WO2024083821A1 (fr)

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DE102022127150.1A DE102022127150A1 (de) 2022-10-17 2022-10-17 Gasdiffusionssubstrat aus einem porösen Metallsubstrat und einer gasdurchlässigen Polymerschicht, Verfahren zu dessen Herstellung sowie Gasdiffusionselektrode und elektrochemische Zelle mit einem Gasdiffusionssubstrat
DE102022127150.1 2022-10-17

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1253385A (zh) * 1998-11-07 2000-05-17 孙法炯 一种空气电极及用这种空气电极制成的金属空气电池
EP2800180B1 (fr) * 2011-12-26 2018-03-07 Toray Industries, Inc. Substrat d'électrode à diffusion de gaz pour pile à combustible, ensemble membrane électrode et pile à combustible

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB9903320D0 (en) 1999-02-15 1999-04-07 Johnson Matthey Plc Substrates
DE102018205571A1 (de) 2018-03-29 2019-10-02 Siemens Aktiengesellschaft Gasdiffusionselektrode, eine Elektrolyseanordnung sowie ein Verfahren zum Betreiben einer Elektrolyseanlage

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1253385A (zh) * 1998-11-07 2000-05-17 孙法炯 一种空气电极及用这种空气电极制成的金属空气电池
EP2800180B1 (fr) * 2011-12-26 2018-03-07 Toray Industries, Inc. Substrat d'électrode à diffusion de gaz pour pile à combustible, ensemble membrane électrode et pile à combustible

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