US20180230612A1 - Method For Monitoring A Process For Powder-Bed Based Additive Manufacturing Of A Component And Such A System - Google Patents

Method For Monitoring A Process For Powder-Bed Based Additive Manufacturing Of A Component And Such A System Download PDF

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US20180230612A1
US20180230612A1 US15/751,216 US201615751216A US2018230612A1 US 20180230612 A1 US20180230612 A1 US 20180230612A1 US 201615751216 A US201615751216 A US 201615751216A US 2018230612 A1 US2018230612 A1 US 2018230612A1
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copper
layer
binder
mixture
gas diffusion
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Ralf Krause
Anna Maltenberger
Christian Reller
Bernhard Schmid
Günter Schmid
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Siemens Energy Global GmbH and Co KG
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Siemens AG
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Publication of US20180230612A1 publication Critical patent/US20180230612A1/en
Assigned to Siemens Energy Global GmbH & Co. KG reassignment Siemens Energy Global GmbH & Co. KG ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: SIEMENS AKTIENGESELLSCHAFT
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
    • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
    • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
    • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
    • C25B11/095—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds at least one of the compounds being organic
    • C25B11/0489—
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/02—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form
    • C25B11/03—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form perforated or foraminous
    • C25B11/031—Porous electrodes
    • C25B11/035—
    • C25B11/0405—
    • C25B11/0415—
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
    • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
    • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
    • C25B11/055—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material
    • C25B11/057—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material consisting of a single element or compound
    • C25B3/04—
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B3/00—Electrolytic production of organic compounds
    • C25B3/20—Processes
    • C25B3/25—Reduction

Definitions

  • the present invention relates to a gas diffusion electrode preferably comprising a copper-containing carrier and a first layer comprising at least copper and at least one binder and a second layer.
  • the (first) layer comprises hydrophilic and hydrophobic pores and/or channels.
  • the second layer comprising copper and at least one binder, wherein the second layer is present atop the carrier and the first layer atop the second layer, wherein the content of binder in the first layer is less than in the second layer.
  • the present invention also relates to a process for producing a gas diffusion electrode and to an electrolysis cell comprising a gas diffusion electrode.
  • CO 2 is converted to carbohydrates by photosynthesis. This process, which is divided up into many component steps over time and spatially at the molecular level, is reproducible on the industrial scale only with difficulty.
  • the more efficient route at present compared to pure photocatalysis is the electrochemical reduction of the CO 2 .
  • CO 2 is converted to a higher-energy product (such as CO, CH 4 , C 2 H 4 , C1-C4 alcohols etc.) with supply of electrical energy which is preferably obtained from renewable energy sources such as wind or sun.
  • the amount of energy required in this reduction corresponds ideally to the combustion energy of the fuel and should only come from renewable sources or utilize electricity that cannot be accepted from the grid at that moment.
  • metals are used as catalysts, some of which are shown by way of example in table 1, taken from Y. Hori, Electrochemical CO 2 reduction on metal electrodes, in: C. Vayenas, et al. (eds.), Modern Aspects of Electrochemistry, Springer, New York, 2008, pp. 89-189.
  • Table 1 shows the typical Faraday efficiencies (FE) over various metal cathodes.
  • FE Faraday efficiencies
  • CO 2 is reduced virtually exclusively to CO over Ag, Au, Zn, and to some degree over Pd, Ga, whereas a multitude of hydrocarbons are observed as reduction products over copper.
  • metal alloys and also mixtures of metal and co-catalytically active metal oxide are also of interest, since these can increase the selectivity for a particular hydrocarbon.
  • the prior art in this regard is not yet very developed.
  • reaction equations show, by way of example, reactions at an anode and at a cathode for reduction over a copper cathode.
  • the electrode In order to be able to provide all these crystallographic surfaces for a high efficiency of ethylene formation at high current density, the electrode must not consist of a smooth sheet, but should be micro- to nanostructured.
  • GDE gas diffusion electrodes
  • Silver/silver oxide/PTFE (polytetrafluoroethylene)-based gas diffusion electrodes have been used on the industrial scale in recent times for the production of sodium hydroxide solution in existing chloralkali electrolysis processes (oxygen-depolarized electrodes). It was possible to increase the efficiency of the chloralkali electrolysis process by 30-40% by comparison with conventional electrodes.
  • the methodology of catalyst embedding with PTFE is known from a multitude of publications and patterns.
  • said wet method 1. can have the disadvantages mentioned hereinafter, aside from the fact that examples of gas diffusion electrodes known from the literature contain the catalyst only as an additive and consist mainly of bound conductive charcoal (for high conversions the catalyst loading should be high):
  • suspensions or pastes that are usually applied by spraying or bar coating generally have long drying times, which means that continuous production with relatively large electrode areas (of industrial relevance) is not economically possible. Excessively rapid drying leads to cracking, called “mud cracking”, within the layers applied, which makes the electrode unusable.
  • the porosity of the layer applied is determined (generated) in the wet-chemical method virtually exclusively by the evaporation of the solvent.
  • This process is highly solvent- or boiling point-dependent and can lead to a high reject rate of the electrodes produced, since the evaporation cannot be assured in a homogeneous manner over the entire area.
  • a further central disadvantage is the use of surface-active substances (surfactants) or thickeners, plasticizers, which are used for stabilization of the particle suspensions since they cannot be removed without residue by the corresponding drying phases or the thermal crosslinking process.
  • Nafion® perfluorosulfonic acid, PFSA
  • PFSA perfluorosulfonic acid
  • Nafion® itself is a hydrophilic ionomer having highly acidic R—HSO 3 groups which can lead to unwanted acid corrosion or partial dissolution of the metal in the case of some catalysts.
  • Nafion®-bound layers additionally have much lower porosity than PTFE-bound layers.
  • Nafion® The purely hydrophilic properties of Nafion® can likewise be disadvantageous, since Nafion®, owing to its hydrophilic properties, is unsuitable for formation of hydrophobic channels that are advantageous for gas transport within a gas diffusion electrode.
  • Usable electrodes comprising Nafion® should therefore consist of multiple layers in order to be able to implement the essential properties of a GDE.
  • multilayer coating processes are not very attractive for economic reasons. Nafion®-based coating processes can additionally lead to unwanted formation of hydrogen.
  • the drying method 3. is based on a roll calendering process, for example of PTFE/catalyst powder.
  • the corresponding technique can be traced back to EP 0297377 A2, according to which electrodes based on Mn 2 O 3 were produced for batteries.
  • DE 3710168A1 makes the first reference to the employment of the drying process with regard to the preparation of metallic electrocatalyst electrodes.
  • the technique was additionally used in patents relating to the production of silver-based (silver(I) or silver(II) oxide) gas diffusion electrodes (oxygen-depolarized electrodes).
  • the patents EP 2444526 A2 and DE 10 2005 023615 A1 mention mixtures having a binder content of 0.5-7%.
  • the carrier used was Ag or nickel meshes having a wire diameter of 0.1-0.3 mm and a mesh size of 0.2-1.2 mm.
  • the powder is applied directly to the mesh before it is supplied to the roll calender.
  • DE 10148599 A1 or EP 0115845 B1 described a similar process in which the powder mixture is first extruded to give a sheet or film which is pressed onto the mesh in a further step.
  • EP 2410079 A2 describes the one-stage process for production of a silver-based oxygen-depolarized electrode with the addition of metal oxide supplements such as TiO 2 , Fe 3 O 4 , Fe 2 O 3 , NiO 2 , Y 2 O 3 , Mn 2 O 3 , Mn 5 O 8 , WO 3 , CeO 2 and spinels such as CoAl 2 O 4 , Co(AlCr) 2 O 4 and inverse spinels such as (Co,Ni,Zn) 2 (Ti,Al)O 4 , perovskites such as LaNiO 3 , ZnFe 2 O 4 .
  • metal oxide supplements such as TiO 2 , Fe 3 O 4 , Fe 2 O 3 , NiO 2 , Y 2 O 3 , Mn 2 O 3 , Mn 5 O 8 , WO 3 , CeO 2 and spinels such as CoAl 2 O 4 , Co(AlCr) 2 O 4 and inverse spinels such as (Co,Ni,Z
  • catalysts which can be used as an alternative for oxygen-depolarized electrodes: precious metals, e.g. Pt, Rh, Ir, Re, Pd, precious metal alloys, e.g. Pt—Ru, precious metal compounds, e.g. precious metal sulfides and oxides, and Chevrel phases, e.g. Mo 4 Ru 2 Se 8 or Mo 4 Ru 2 S 8 , where these may also contain Pt, Rh, Re, Pd etc.
  • precious metals e.g. Pt, Rh, Ir, Re, Pd
  • precious metal alloys e.g. Pt—Ru
  • precious metal compounds e.g. precious metal sulfides and oxides
  • Chevrel phases e.g. Mo 4 Ru 2 Se 8 or Mo 4 Ru 2 S 8 , where these may also contain Pt, Rh, Re, Pd etc.
  • DE 101 30 441 A1 discloses a biporous pore system in a gas diffusion electrode, but no two-layer structure. For such a one-layer structure, flooding of the electrode was observed in in-house preliminary tests. A one-layer structure can also be found, for example, in DE 10 2010 031 571 A1. According to DE 101 30 441 A1, a metallic support skeleton is rolled into a catalyst film produced in that document.
  • US 2013/0280625 A1 discloses a two-layer structure of a gas diffusion electrode, but does not disclose any hydrophobic pores, and discloses only pores in the diffusion layer as hydrophilic layer.
  • a sacrificial material is used in an obligatory manner therein, and is required for formation of pores. However, in-house preliminary tests have shown that this is not appropriate to the aim.
  • cathodes for carbon dioxide electrolysis in which carbon dioxide can be converted effectively to hydrocarbons.
  • the present invention relates to a gas diffusion electrode comprising a preferably copper-containing carrier, preferably in the form of a sheetlike structure, and a first layer comprising at least copper and at least one binder, wherein the first layer comprises hydrophilic and hydrophobic pores and/or channels, further comprising a second layer comprising copper and at least one binder, wherein the second layer is present atop the carrier and the first layer atop the second layer, wherein the content of binder in the first layer is less than in the second layer.
  • the present invention relates to a process for producing a gas diffusion electrode, comprising
  • the present invention additionally relates, in yet a further aspect, to an electrolysis cell comprising the gas diffusion electrode of the invention.
  • FIG. 1 shows a schematic diagram of a gas diffusion electrode of the invention with hydrophobic and hydrophilic regions or channels.
  • FIG. 2 shows a schematic diagram of production of a gas diffusion electrode of the invention based on an illustrative PTFE-bound catalyst.
  • FIG. 3 shows a schematic of a further embodiment of a gas diffusion electrode of the invention in the form of a multilayer preparation.
  • FIGS. 4 to 6 show, in schematic form, illustrative diagrams of a possible construction of an electrolysis cell in one embodiment of the present invention.
  • FIGS. 7 and 8 show illustrative configuration forms for a gas distribution chamber downstream of a gas diffusion electrode of the invention in an electrolysis cell of the invention.
  • FIG. 9 shows the results of Faraday efficiencies of the electrolysis cell from comparative example 3.
  • FIGS. 10 and 11 show the results of Faraday efficiencies of the electrolysis cell from comparative example 4.
  • Hydrophobic in the context of the present invention is understood to mean water-repellent. According to the invention, hydrophobic pores and/or channels are those that repel water. More particularly, hydrophobic properties are associated in accordance with the invention with substances or molecules having nonpolar groups.
  • Hydrophilic by contrast, is understood to mean the ability to interact with water and other polar substances.
  • the present invention relates to
  • a gas diffusion electrode comprising a preferably copper-containing carrier, preferably in the form of a sheetlike structure, and a first layer comprising at least copper and at least one binder, wherein the (first) layer comprises hydrophilic and hydrophobic pores and/or channels, further comprising a second layer comprising copper and at least one binder, wherein the second layer is present atop the carrier and the first layer atop the second layer, wherein the content of binder in the first layer is less than in the second layer.
  • the second layer just like the first layer, may comprise hydrophilic and/or hydrophobic pores and/or channels.
  • gas diffusion electrode comprising a preferably copper-containing carrier, preferably in the form of a sheetlike structure, and
  • a first layer comprising at least copper and at least one binder, wherein the layer comprises hydrophilic and hydrophobic pores and/or channels.
  • FIG. 1 illustrates the relations between hydrophilic and hydrophobic regions of a GDE, which can achieve a good triphasic liquid/solid/gaseous relationship.
  • the electrode there are hydrophobic channels or regions 1 and hydrophilic channels or regions 2 on the electrolyte side, with catalyst sites 3 of low activity present in the hydrophilic regions 2 .
  • Particularly active catalyst sites 4 are in the triphasic liquid/solid/gaseous region.
  • An ideal GDE thus has maximum penetration of the bulk material by hydrophilic and hydrophobic channels in order to obtain a maximum number of triphasic regions for active catalyst sites.
  • the first layer comprises hydrophilic and hydrophobic pores and/or channels.
  • the carrier here is not particularly restricted, provided that it is suitable for a gas diffusion electrode and preferably contains copper.
  • the carrier is a sheetlike structure, further preferably a mesh, very preferably a copper mesh. This can assure both adequate mechanical stability and functionality as a gas diffusion electrode, for example with regard to a high electrical conductivity.
  • the carrier may also be suitable with regard to the electrical conductivity of the first layer.
  • the carrier therefore consists of copper.
  • a preferred copper-containing carrier in particular embodiments, is a copper mesh having a mesh size w of 0.3 mm ⁇ w ⁇ 2.0 mm, preferably 0.5 mm ⁇ w ⁇ 1.4 mm, and a wire diameter x of 0.05 mm ⁇ x ⁇ 0.5 mm, preferably 0.1 mm ⁇ x ⁇ 0.25 mm.
  • the first layer comprises copper
  • a preferably copper-containing mesh preferably the copper mesh which is used as carrier, has a mesh size of the carrier between 0.3 and 2.0 mm, preferably between 0.5-1.4 mm, in order to achieve good conductivity and stability.
  • the binder comprises a polymer, for example a hydrophilic and/or hydrophobic polymer, for example a hydrophobic polymer, especially PTFE.
  • a polymer for example a hydrophilic and/or hydrophobic polymer, for example a hydrophobic polymer, especially PTFE.
  • the first layer is produced using PTFE particles having a particle diameter between 5 and 95 ⁇ m, preferably between 8 and 70 ⁇ m.
  • Suitable PTFE powders include, for example, Dyneon® TF 9205 and Dyneon TF 1750.
  • Suitable binder particles, for example PTFE particles may, for example, be virtually spherical, for example spherical, and may be produced, for example, by emulsion polymerization.
  • the binder particles are free of surface-active substances.
  • the particle size can be determined here, for example, according to ISO 13321 or D4894-98a and may correspond, for example, to the manufacturer data (e.g. TF 9205: mean particle size 8 ⁇ m according to ISO 13321; TF 1750: mean particle size 25 ⁇ m according to ASTM D4894-98a).
  • the first layer comprises at least copper which may, for example, be in the form of metallic copper and/or copper oxide and which functions as catalyst site.
  • the first layer comprises metallic copper in the 0 oxidation state.
  • the first layer comprises copper oxide, especially Cu 2 O.
  • the oxide here may contribute to stabilizing the +1 oxidation states of copper and hence to maintaining the selectivity for ethylene with long-term stability. Under electrolysis conditions, it can be reduced to copper.
  • the first layer comprises at least 40 at % (atom percent), preferably at least 50 at % and further preferably at least 60 at % of copper, based on the layer. This can assure both suitable mechanical stability and suitable catalytic activity of this first layer that serves as catalyst layer (CL).
  • the copper for production of the gas diffusion electrode of the invention is provided as particles, which are defined further hereinafter.
  • the first layer may also comprise further promoters which improve the catalytic activity of the GDE in association with the copper.
  • the first layer comprises at least one metal oxide preferably having a lower reduction potential than the evolution of ethylene, preferably ZrO 2 , Al 2 O 3 , CeO 2 , Ce 2 O 3 , ZnO 2 , MgO; and/or at least one copper-rich intermetallic phase, preferably at least one Cu-rich phase selected from the group of the binary systems Cu—Al, Cu—Zr, Cu—Y, Cu—Hf, CuCe, Cu—Mg and the ternary systems Cu—Y—Al, Cu—Hf—Al, Cu—Zr—Al, Cu—Al—Mg, Cu—Al—Ce with copper contents >60 at %; and/or copper-containing perovskites and/or defect perovskites and/or perovskite-related compounds, preferably YBa 2 Cu 3 O 7- ⁇ where 0 ⁇ 1 (corresponding
  • Preferred promoters here are the metal oxides.
  • the metal oxide used is water-insoluble, in order that aqueous electrolytes can be used in an electrolysis using the gas diffusion electrode of the invention.
  • the redox potential of the metal oxide being lower than that of the evolution of ethylene, it is possible to ensure that ethylene can be prepared from CO 2 by means of the GDE of the invention.
  • the oxides are not to be reduced either in a carbon dioxide reduction. Nickel and iron, for example, are unsuitable since hydrogen forms here.
  • the metal oxides are preferably not inert, but should preferably constitute hydrophilic reaction sites that can serve for the provision of protons.
  • the promoters are able here to promote the function and production of electro-catalysts having long-term stability, in that they stabilize catalytically active copper nanostructures.
  • the structural promoters here can reduce the high surface mobilities of the copper nanostructures and hence reduce their tendency to sinter.
  • the concept originates from heterogeneous catalysis and is used successfully within high-temperature processes.
  • the catalyst has the following inventive features: by contrast with the known heterogeneous Cu/Al 2 O 3 , Cu/ZrO 2 , Cu/MgO/Al 2 O 3 catalysts used in industry, in particular embodiments, preferably only very copper-rich catalysts having a molar proportion of >60 at % Cu are used for the electrochemical reduction of CO 2 owing to the electrical conductivity required.
  • metal oxide/copper catalyst structures that are produced as follows:
  • LDHs layered double hydroxides
  • the corresponding precursors can be precipitated under pH control by co-dosage of a metal salt solution and a basic carbonate solution.
  • a particular feature of these materials is the presence of particularly fine copper crystallites having a size of 4-10 nm, which are structurally stabilized by the oxide present.
  • the metal oxide owing to its high specific surface area, can lead to better distribution of the catalyst metal; highly dispersed metal sites can be stabilized by the metal oxide; CO 2 chemisorption can be improved by the metal oxide; copper oxides can be stabilized.
  • the precipitation can be followed by drying with subsequent calcination in an O 2 /Ar gas stream.
  • the oxide precursors produced, according to the method can also subsequently be reduced directly in an H 2 /Ar gas stream, reducing solely the Cu 2 O or CuO to Cu and conserving the oxide promoter.
  • the activation step can also be effected by electrochemical means subsequently. In order to improve the electrical conductivity of the layer applied prior to the electrochemical activation, it is also possible to partly mix oxide precursors and activated precursors. In order to be able to increase the underlying conductivity, it is also possible to mix in 0-10% by weight of copper powder in a similar particle size.
  • the ready-calendered electrode is subjected to a subsequent calcination/thermal treatment before the electrochemical activation is conducted.
  • a further means of production of suitable electro-catalysts is based on the approach of the production of copper-rich intermetallic phases, for example Cu 5 Zr, Cu 10 Zr 7 , Cu 51 Zr 14 , which can be prepared from the melt. Corresponding ingots can subsequently be ground and fully or partly calcined in an O 2 /argon gas stream and converted to the oxide form.
  • Cu-rich phases of the binary systems Cu—Al, Cu—Zr, Cu—Y, Cu—Hf, CuCe, Cu—Mg and the corresponding ternary systems having Cu contents >60 at %: CuYAl, CuHfAl, CuZrAl, CuAlMg, CuAlCe.
  • Copper-rich phases are known, for example, from E. Kneller, Y. Khan, U. Gorres, The Alloy System Copper - Zirconium, Part I. Phase Diagram and Structural Relations , Zeitschrift für Metallischen 77 (1), p. 43-48, 1986 for Cu—Zr phases, from Braunovic, M.; Konchits, V. V.; Myshkin, N. K.: Electrical contacts, fundamentals, applications and technology; CRC Press 2007 for Cu—Al phases, from Petzoldt, F.; Bergmann, J.
  • the proportion of copper is preferably greater than 40 at %, further preferably greater than 50 at %, more preferably greater than 60 at %.
  • the intermetallic phases also contain nonmetal elements such as oxygen, nitrogen, sulfur, selenium and/or phosphorus, i.e. oxides, sulfides, selenides, nitrides and/or phosphides for example are present.
  • the intermetallic phases have been partly oxidized.
  • the catalyst particles comprising or consisting of copper for example copper particles, which are used for production of the GDE of the invention, have a homogeneous particle size between 5 and 80 ⁇ m, preferably 10 to 50 ⁇ m, further preferably between 30 and 50 ⁇ m.
  • the catalyst particles in particular embodiments, have a high purity without traces of extraneous metal.
  • promoters for example the metal oxides, to have a corresponding particle size in the production.
  • the above promoters can additionally achieve or improve the following properties:
  • the electrode in order to further adjust the porosity of the electrode, in particular embodiments, it is possible to add copper powder supplements having a particle diameter of 50 to 600 ⁇ m, preferably 100 to 450 ⁇ m, preferably 100-200 ⁇ m.
  • the particle diameter of these supplements in particular embodiments, is 1 ⁇ 3- 1/10 of the total layer thickness of the layer.
  • the supplement may also be an inert material such as a metal oxide. This can achieve improved formation of pores or channels.
  • a gas diffusion electrode of the invention can especially be produced by the production process of the invention as described further down.
  • the first layer comprises less than 5% by weight of, further preferably less than 1% by weight of and even further preferably no charcoal- and/or carbon black-based or -like fillers, for example conductive fillers, based on the layer.
  • methods known from the literature for GDE production generally refer, both for dry and wet application, to the addition of activated carbons, conductive blacks (such as Vulkan XC72), acetylene black or other charcoals.
  • conductive blacks such as Vulkan XC72
  • acetylene black or other charcoals.
  • the first layer does not contain any surface-active substances.
  • the first and/or second layer additionally do not contain any sacrificial material, for example a sacrificial material having a release temperature of roughly below 275° C., for example below 300° C. or below 350° C., and especially any pore former(s) which can typically remain at least partly in the electrode in the case of production of electrodes using such a material.
  • the content or proportion of binder for example PTFE, in particular embodiments, may be 3-30% by weight, preferably 3-20% by weight, further preferably 3-10% by weight, even further preferably 3-7% by weight, based on the one (first) layer.
  • the GDE of the invention further comprises a second layer comprising copper and at least one binder, wherein the second layer is present atop the carrier and the first layer atop the second layer, wherein the content of binder in the first layer is smaller than in the second layer.
  • the second layer may comprise coarser copper or inert material particles, for example having particle diameters of 50 to 700 ⁇ m, preferably 100-450 ⁇ m, in order to provide a suitable channel or pore structure.
  • the second layer comprises 3-30% by weight of binder, preferably 10-30% by weight of binder, further preferably 10-20% by weight of binder, preferably >10% by weight of binder, further preferably >10% by weight and up to 20% by weight of binder, based on the second layer
  • the first layer preferably comprises 0-10% by weight of binder, for example 0.1-10% by weight of binder, preferably 1-10% by weight of binder, further preferably 1-7% by weight of binder, even further preferably 3-7% by weight of binder, based on the first layer.
  • the binder here may be the same binder as in the first layer, for example PTFE.
  • the particles for production of the second layer may correspond to those in the first layer, but may also be different therefrom.
  • the second layer here is a metal particle layer (MPL) beneath the catalyst layer (CL).
  • MPL metal particle layer
  • CL catalyst layer
  • the second layer partly penetrates the first layer. This can be achieved, for example, by virtue of the process of the invention and enables a good transition between the layers with regard to diffusion.
  • the GDE of the invention may also have further layers, for example atop the first layer and/or on the other side of the carrier.
  • Corresponding dendritic copper may also be present in the first layer.
  • This may then be followed by further sieving application of the catalyst/PTFE mixture (CL), for example with a PTFE content of 0.1-10% by weight, and smoothing or drawdown, for example by means of a frame of thickness 1 mm, so as to obtain a total layer thickness (Hf) of 1 mm.
  • the MPL can achieve better mechanical stability, a further reduction in the penetration of the electrolyte and better conductivity, especially when meshes are used as carriers.
  • Stepwise production of the GDE by respective sieving application and rolling of each individual layer can lead to lower adhesion between the layers and is therefore less preferred.
  • the present invention relates to a process for producing a gas diffusion electrode, comprising
  • the production of the first and second mixtures or of the first mixture is not particularly restricted here and can be effected in a suitable manner, for example by stirring, dispersing, etc.
  • the first mixture may also comprise 0% by weight of binder, i.e. no binder, since binder from the second mixture can diffuse into the first layer that forms from the first mixture in the course of rolling and hence the first layer can also have a content of binder of, for example, at least 0.1% by weight, for example 0.5% by weight, as established in preliminary experiments.
  • the first mixture in the case of application of 2 or more mixtures comprises binder.
  • the binder comprises a polymer, for example a hydrophilic and/or hydrophobic polymer, for example a hydrophobic polymer, especially PTFE.
  • a polymer for example a hydrophilic and/or hydrophobic polymer, for example a hydrophobic polymer, especially PTFE.
  • PTFE particles having a particle diameter between 5 and 95 ⁇ m, preferably between 8 and 70 ⁇ m, are used.
  • Suitable PTFE powders include, for example, Dyneon® TF 9205 and Dyneon® TF 1750.
  • the copper for the production of the mixture is in the form of particles or catalyst particles, for example including dendritic copper, having a homogeneous particle size between 5 and 80 ⁇ m, preferably 10 to 50 ⁇ m, further preferably between 30 and 50 ⁇ m.
  • the catalyst particles in particular embodiments, have a high purity without traces of extraneous metal.
  • the first and/or second mixtures do not contain any sacrificial material, for example a sacrificial material having a release temperature of about below 275° C., for example below 300° C. or below 350° C., and especially no pore former(s) which can typically remain at least partly in the electrode in the case of production of electrodes using such a material.
  • a sacrificial material having a release temperature of about below 275° C., for example below 300° C. or below 350° C.
  • no pore former(s) which can typically remain at least partly in the electrode in the case of production of electrodes using such a material.
  • the first and/or second mixtures are not pasty, for example in the form of inks or pastes, but are in the form of powder mixtures.
  • first, second and further mixture(s) is not particularly restricted and can be effected, for example, by scattering application, sieving application, bar coating, etc.
  • the rolling application is likewise not particularly restricted and can be effected in a suitable manner. Rolling of the mixture or mass (particles) into the structure of the carrier, for example a mesh structure, is explicitly desirable in particular embodiments in order to assure a high mechanical stability of the electrode.
  • the pre-extruded film lies only on the mesh and has lower adhesion, and also mechanical stability.
  • the mixtures for the layers are applied individually to the carrier and are then rolled collectively, in order to achieve better adhesion between the layers.
  • the layers may at least partly penetrate one another, for example in a thickness of 1-20 ⁇ m.
  • the mechanical stress on the binder, for example of polymer particles, by the rolling process leads to crosslinking of the powder through the formation of binder channels, for example PTFE fibrils.
  • the attainment of this state is particularly important in order to guarantee suitable porosity or mechanical stability of the electrode.
  • the hydrophobicity can be adjusted via the respective content of polymer or via the physical properties of the catalyst powder.
  • a suitable binder content in the second mixture has been found to be 10-30% by weight, preferably 10-20% by weight, based on the second mixture, and a suitable proportion of binder in the first mixture to be 0-10% by weight, 0.1-10% by weight, further preferably 1-10% by weight, even further preferably 1-7% by weight, even further preferably 3-7% by weight.
  • a particularly suitable binder content for example PTFE content, has been found to be 3-30% by weight, preferably 3-20% by weight, further preferably 3-10% by weight and even further preferably 3-7% by weight of binder, based on the first mixture.
  • the degree of fibrillation of the binder for example PTFE (structure parameter correlates directly with the shear rate applied, since the binder, for example a polymer, behaves as a shear-thinning (pseudo-plastic) fluid in the rolling application.
  • the layer obtained, by virtue of the fibrillation has an elastic character. This change in structure is irreversible, and so this effect cannot be subsequently enhanced by further rolling; instead, the layer, by virtue of the elastic characteristics, is damaged with further action of shear forces.
  • Particularly significant fibrillation can disadvantageously lead to the electrode rolling up on the layer side, and so excessively high contents of binder should be avoided.
  • the water content in the rolling operation corresponds, for example, to the ambient humidity at most.
  • the content of water and solvents in the rolling application is less than 5% by weight, preferably less than 1% by weight and, for example, even 0% by weight.
  • the copper-containing carrier is a copper mesh having a mesh size w of 0.3 mm ⁇ w ⁇ 2.0 mm, preferably 0.5 mm ⁇ w ⁇ 1.4 mm, and a wire diameter x of 0.05 mm ⁇ x ⁇ 0.5 mm, preferably 0.1 mm ⁇ x ⁇ 0.25 mm.
  • the rolling into a mesh allows the interstices in the mesh, for example copper mesh, to be effectively bridged by the overlying (for example highly conductive) layer and enables complete 3D contact connection with the electrode. As a result, higher oxide contents are possible.
  • the production of the gas diffusion electrode of the invention is additionally based on the exclusion of charcoal- and/or carbon black-based or -like fillers, for example conductive fillers.
  • the catalyst itself or dendritic copper (formed, for example, through activation of the catalyst) or mixtures of the two serve here as charcoal replacement.
  • the method of the invention does not need any surface-active substances/surfactants or thickeners and additives (such as flow improvers) that have been identified as catalyst poisons.
  • the bed height y of the first mixture on the carrier in the application is in the range of 0.3 mm ⁇ y ⁇ 2.0 mm, preferably 0.5 mm ⁇ y ⁇ 1.0 mm.
  • each layer may have a corresponding bed height y, but the bed heights of all layers preferably do not add up to more than 2.0 mm, preferably to more than 1.5 mm, more preferably to more than 1 mm.
  • the gap width in the rolling application H 0 is the height of the carrier +40% to 50% of the total bed height Hf of the mixtures of the various layers, for example of the bed height y of the first mixture if it is the only one used.
  • the rolling application is effected by means of a calender.
  • the copper content in the mixture is at least 40 at %, preferably at least 50 at % and further preferably at least 60 at % of copper, based on the mixture.
  • At least one metal oxide having a lower reduction potential than the evolution of ethylene preferably ZrO 2 , Al 2 O 3 , CeO 2 , Ce 2 O 3 , ZnO 2 , MgO; and/or at least one copper-rich intermetallic phase, preferably at least one Cu-rich phase selected from the group of the binary systems Cu—Al, Cu—Zr, Cu—Y, Cu—Hf, CuCe, Cu—Mg and/or the ternary systems Cu—Y—Al, Cu—Hf—Al, Cu—Zr—Al, Cu—Al—Mg, Cu—Al—Ce with copper contents >60 at %; and/or at least one metal for formation of a copper-rich metallic phase, preferably Al, Zr, Y, Hf, Ce, Mg, or at least two metals for formation of ternary phases, preferably Y—Al, Hf—Al, Zr—Al, Al—Mg, Al—Ce, such that the copper content is >60 at
  • the addition of the metal for formation of a copper-rich metallic phase, preferably Al, Zr, Y, Hf, Ce, Mg, or at least two metals for formation of ternary phases, preferably Y—Al, Hf—Al, Zr—Al, Al—Mg, Al—Ce, such that the copper content is >60 at %, can be effected, for example, in such a way that, in the production of the gas diffusion electrode, intermetallic phases are formed, for example through co-melting and thermal oxidation, and can then be selectively reduced, for example by electrochemical means.
  • co-melting in the mixture is effected here before the binder is added. In such a case, there is thus a sequence in that the metal is first added and fused with copper before the binder and any further substances are added to the mixture.
  • the process of the invention can thus be effected by a calendering process as shown schematically in FIG. 2 .
  • the catalyst particles 6 and the binder particles 7 for example PTFE particles, are rolled onto the carrier 8 , here in the form of a copper mesh, with the aid of a calender 11 .
  • the rolling or calendering is conducted at a roller speed between 0.3 and 3 rpm, preferably 0.5-2 rpm.
  • the flow rate or an advance rate (of the GDE in length per unit time, for example in the case of calendering) Q is in the range from 0.04 to 0.4 m/min, preferably 0.07 to 0.3 m/min.
  • the electrode in order to further adjust the porosity of the electrode, in particular embodiments, it is possible to add copper powder supplements having a particle diameter of 50 to 600 ⁇ m, preferably 100 to 450 ⁇ m, further preferably 100 to 200 ⁇ m, especially to the second mixture in the case of application of multiple layers.
  • the particle diameter of these supplements in particular embodiments, is 1 ⁇ 3- 1/10 of the total layer thickness of the layer.
  • the supplement may also be an inert material such as a metal oxide. In this way, it is possible to achieve improved formation of pores or channels.
  • the GDE can be produced using a dry calendering method in which a mixture of a cold-flowing polymer (preferably PTFE) and the respective pre-calcined catalyst powder comprising copper and optionally a promoter is produced in an intensive mixing apparatus or laboratory scale with a knife mill (IKA).
  • the mixing procedure may, for example, follow the following procedure, but is not restricted thereto: grinding/mixing for 30 sec and pause for 15 sec for a total of 6 min, these figures being based, for example, on the knife mill with a total loading of 50 g.
  • the mixed powder attains a slightly tacky consistency, with fibrillation here, for example, of the binder, for example PTFE.
  • fibrillation here, for example, of the binder, for example PTFE.
  • the amount of powder or polymer/chain length chosen there may also be variation in the mixing time before this state is attained.
  • the powder mixture obtained is subsequently scattered or sieved onto a copper mesh having a mesh size of >0.5 mm and ⁇ 1.0 mm and a wire diameter of 0.1-0.25 mm in a bed thickness of 1 mm.
  • the powder mixture applied is then drawn down, for example, with a coating bar. This operation can be repeated more than once until a homogeneous layer is obtained.
  • the powder mixture can be pelletized during or after the mixing operation in order to obtain a pourable material, for example having an agglomerate diameter of 0.05 to 0.2 mm.
  • the reverse side of the copper mesh can be sealed with a film subject to no further restriction.
  • the prepared layer is compacted with the aid of a two-roll rolling device (calender).
  • the rolling process itself is characterized in that a reservoir of material forms upstream of the roll.
  • the speed of the roll is between 0.5-2 rpm and the gap width was adjusted to the height of the carrier +40% to 50% of the bed height Hf of the powder, or corresponds virtually to the thickness of the mesh +0.1-0.2 mm infeed.
  • the calender can also be heated. Preference is given to temperatures in the range of 20-200° C., preferably 20-50° C.
  • the catalyst itself can be processed prior to the application in the calcined state, for example also as a metal oxide precursor, or already in the reduced state. Mixtures of the two forms are possible. This is also true in the case of the intermetallic phases or alloys described, and so these can likewise be used in the oxide form or in the metallic state. Furthermore, it is not ruled out that the calendered electrode can be calcined subsequently, for example at 300-360° C. for 5 to 15 min.
  • the gas diffusion electrode of the invention especially in the case of hydrocarbon-selective copper catalyst electrodes, to apply a copper-PTFE base layer as a second layer for better contact connection with nanoscale materials, while simultaneously maintaining a high porosity.
  • the base layer may be characterized by a very high conductivity, for example 7 mohm/cm or more, and preferably has a high porosity, for example of 50-70%, and a hydrophobic character.
  • the binder content, for example PTFE may be chosen, for example, between 3-30% by weight, for example 10-30% by weight.
  • the intermediate copper layer as the second layer may itself be catalytically active in the region of the overlap zone with the catalyst layer as the first layer, and especially serves for better areal electrical connection of the electrocatalyst and can improve the availability of CO 2 owing to the high porosity. With the aid of this method, the required amount of catalyst can be reduced by a factor of 20-30.
  • the corresponding electrocatalyst/binder (e.g. PTFE) mixture can, in a first step, be sieved out onto the reverse side of the current distributor and calendered. It is additionally also possible to apply the 2-layer variant described as a double layer.
  • the binder used, especially PTFE, in particular embodiments, should be treated beforehand in a knife mill in order to achieve fiber formation.
  • abrasive hard materials may be mixed in the range between 0-50% by weight.
  • suitable materials SiC, B 4 C, Al 2 O 3 (high-grade corundum), SiO 2 (crushed glass), preferably in a grain size of 50-150 ⁇ m.
  • the production of the gas diffusion electrode with a binder-based (e.g. PTFE-based) diffusion barrier is based on multiple layers that cannot be considered in isolation from one another, but preferably have an overlap zone of maximum breadth in the boundary regions, for example of 1-20 ⁇ m.
  • the method of two-layer construction additionally includes the option of dispensing with binder materials as the first layer within the catalyst layer, which means that it is possible to achieve better electrical conductivity. It is likewise possible to process very ductile or brittle powder particles. This is not possible in a single-layer construction. In the case of mechanically sensitive catalysts, it is possible to dispense with the process step of the knife mill, which means that the catalyst remains unchanged since mechanical stress resulting from the mixing operation can be avoided.
  • Electrode activation of the electrode obtained can optionally be conducted, for example by chemical or electrochemical activation, and is not particularly restricted.
  • An electrochemical activation procedure may lead to penetration of cations of the conductive salt of the electrolyte (e.g. KHCO 3 , K 2 SO 4 , NaHCO 3 , KBr, NaBr) into the hydrophobic GDE channels, thus creating hydrophilic regions. This effect is particularly advantageous and has not been described to date in the literature.
  • the present invention relates to an electrolysis cell comprising a gas diffusion electrode of the invention, which is preferably used as cathode.
  • the gas diffusion electrodes of the invention can be operated specifically in plate electrolyzers.
  • the further constituents of the electrolysis cell for instance the anode, optionally one or more membranes, inlet(s) and outlet(s), the voltage source etc., and further optional devices such as cooling or heating units, are not particularly restricted in accordance with the invention, nor are anolytes and/or catholytes that are used in such an electrolysis cell, and the electrolysis cell, in particular embodiments, is used on the cathode side for reduction of carbon dioxide.
  • the configuration of the anode space and the cathode space is likewise not particularly restricted.
  • FIGS. 4 to 6 Illustrative configurations for an exemplary construction of a typical electrolysis cell and possible anode and cathode spaces are shown in FIGS. 4 to 6 .
  • Electrochemical reduction of CO 2 takes place in an electrolysis cell typically consisting of an anode and a cathode space.
  • FIGS. 4 to 6 show examples of a possible cell arrangement. For each of these cell arrangements, it is possible to use a gas diffusion electrode of the invention, for example as cathode.
  • the cathode space II in FIG. 4 is configured such that a catholyte is supplied from the bottom and then leaves the cathode space II at the top.
  • the catholyte can also be supplied from the top, as in the case, for example, of falling-film electrodes.
  • the oxidation of a substance which is supplied from the bottom, for example, with an anolyte takes place in the anode space I, and the anolyte together with the oxidation product then leaves the anode space.
  • FIG. 4 it is additionally possible to convey a reaction gas, for example carbon dioxide, through the gas diffusion electrode into the cathode space II for reduction.
  • a reaction gas for example carbon dioxide
  • FIG. 4 the spaces I and II are separated by a membrane M.
  • the gas diffusion electrode K and a porous anode A directly adjoin the membrane M, by means of which the anode space I is separated from the cathode space II.
  • the construction in FIG. 6 corresponds to a mixed form of the construction from FIG. 4 and the construction from FIG. 5 , wherein a construction with the gas diffusion electrode as shown in FIG.
  • FIGS. 4 to 6 are schematic diagrams.
  • the electrolysis cells from FIGS. 4 to 6 may also be combined to form mixed variants.
  • the anode space may be configured as a PEM half-cell, as in FIG. 5
  • the cathode space consists of a half-cell containing a certain electrolyte volume between membrane and electrode, as shown in FIG. 4 .
  • the distance between electrode and membrane is very small or 0 when the membrane is porous and includes a feed of the electrolyte.
  • the membrane may also have a multilayer configuration, such that separate feeds of anolyte and catholyte are enabled.
  • the membrane may be an ion-conducting membrane, or a separator that brings about mechanical separation only and is permeable to cations and anions.
  • gas diffusion electrode of the invention makes it possible to construct a three-phase electrode.
  • a gas can be guided from behind toward the electrically active front side of the electrode in order to conduct an electrochemical reaction there.
  • there may also merely be flow along the back of the gas diffusion electrode meaning that a gas such as CO 2 is guided along the back side of the gas diffusion electrode relative to the electrolyte, in which case the gas can penetrate through the pores of the gas diffusion electrode and the product can be removed at the back.
  • the gas flow in the case of backflow is the reverse of the electrolyte flow, in order that any liquid forced through can be transported away.
  • a gap between the gas diffusion electrode and the membrane as electrolyte reservoir is advantageous.
  • one cell variant (a) enables direct active flow of a gas such as CO 2 through the GDE.
  • the products formed are removed from the electrolysis cell through the catholyte outlet and separated from the liquid electrolyte in a downstream phase separator.
  • a disadvantage of this method is the elevated mechanical stress on the GDE and partial or complete forcing of the electrolyte out of the pores. Disadvantages are likewise found to be the elevated occurrence of gas in the electrolyte space and displacement of the electrolyte.
  • a high excess of CO 2 is required for the mode of operation.
  • the second cell variant describes a mode of operation in which the CO 2 flows within the rear region of the GDE by virtue of an adjusted gas pressure.
  • the gas pressure here should be chosen such that it is equal to the hydrostatic pressure of the electrolyte in the cell, such that no electrolyte is forced through.
  • An essential advantage of the cell variant is a higher conversion of the reaction gas used, for example CO 2 , compared to the flow variant.
  • the gas diffusion electrode In order still to prevent passage of electrolyte through the gas diffusion electrode, it is possible to apply a film on the side of the gas diffusion electrode remote from the electrolyte, i.e. on the carrier, for example a mesh, in order to prevent the electrolyte from passing through to the gas.
  • the film here may be provided suitably and is hydrophobic for example.
  • the electrolysis cell has a membrane which separates the cathode space and the anode space of the electrolysis cell in order to prevent mixing of the electrolytes.
  • the membrane here is not particularly restricted, provided that it separates the cathode space and the anode space. More particularly, it essentially prevents passage of the gases that form at the cathode and/or anode through to the anode or cathode space.
  • a preferred membrane is an ion exchange membrane, for example in polymer-based form.
  • a preferred material for an ion exchange membrane is a sulfonated tetrafluoroethylene polymer such as Nafion®, for example Nafion® 115.
  • ceramic membranes for example the polymers that are mentioned in EP 1685892 A1 and/or are laden with zirconia, for example polysulfones.
  • the material for the anode is likewise not particularly restricted and depends primarily on the reaction desired.
  • Illustrative anode materials include platinum or platinum alloys, palladium or palladium alloys and glassy carbon. Further anode materials are also conductive oxides such as doped or undoped TiO 2 , indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), iridium oxide, etc.
  • these catalytically active compounds can also be applied merely superficially in thin-film methodology, for example on a titanium carrier.
  • the anode space can be configured as a proton exchange membrane (PEM) half-cell, while the cathode space consists of a half-cell containing a certain electrolyte volume between membrane and electrode.
  • PEM proton exchange membrane
  • the distance between electrode and membrane is very small or 0 when the membrane is porous and includes a feed of the electrolyte.
  • the membrane may also have a multilayer configuration, such that separate feeds of anolyte and catholyte are enabled. Separation effects are achieved in the case of aqueous electrolytes, for example, through the hydrophobicity of interlayers. Conductivity can nevertheless be assured if conductive groups are integrated into separation layers of this kind.
  • the membrane may be an ion-conducting membrane, or a separator that brings about mechanical separation only.
  • various gas distribution chambers may be provided, of which two illustrative gas distribution chambers are shown in FIGS. 7 and 8 . These may be provided in order to further increase the residence time of a reaction gas such as CO 2 and the associated conversion.
  • the gas distributors especially in the case of a gas diffusion electrode with backflow, can contribute to enhanced mass transfer across the entire electrode area.
  • FIG. 1 Further aspects of the present invention relate to an electrolysis system comprising an electrode of the invention or an electrolysis cell of the invention, and the use of the gas diffusion electrode of the invention in an electrolysis cell or electrolysis system.
  • the further constituents of the electrolysis system are not restricted any further and can be provided suitably.
  • the pressure in the comparative examples and examples was likewise not varied, but left at room pressure (about 1.013 bar).
  • a multilayer gas diffusion electrode was produced according to the instructions of R. Cook (J. Electrochem. Soc. 1990, 137, 2).
  • the hydrophobic gas transport layer was produced according to the publication:
  • Electrochemical characterization was accomplished using a test setup that corresponds essentially to that of the above-described electrolysis system from FIG. 6 with flow cells for electrolysis.
  • the cathode used was the particular gas diffusion electrode (GDE) with an active area of 3.3 cm 2 , the gas feed rate of carbon dioxide on the cathode side was 50 mL/min, and the electrolyte flow rate on both sides was 130 mL/min.
  • the anode was iridium oxide on a titanium carrier with an active area of 10 cm 2 .
  • the catholyte was a 1 M KHCO 3 solution with KHCO 3 in a 1 M concentration, and the anolyte was 1 M KHCO 3 , each in deionized water (18 MS)), each in an amount of 100 mL, and the temperature was 25° C.
  • 0.5 M K 2 SO 4 was also tried as catholyte, and 2.5 M KOH as anolyte.
  • the substrate used in comparative example 3.1 was a commercially available carbon cloth for gas diffusion electrodes (Flat® LT1400W, NuVant) in the form of a microporous layer.
  • a Nafion® D521 dispersion was applied to this gas diffusion layer as electrocatalyst, which was produced as follows: 0.87 g of Cu(OAc) 2 .H 2 O was dissolved in about 1 mL of H 2 O. In addition, 1.36 g of Vulkan XC 72 were mixed with 15 mL of ethylene glycol and the dissolved Cu(OAc) 2 was added and dispersed for 1 h. Thereafter, 1.5 g of the Nafion® D521 suspension were added and stirred with a glass rod. Thereafter, the mixture was applied to the hydrophobic gas diffusion layer, and dried under air and then in a drying cabinet at 120° C. for 2 h. This was followed by calcining in an oven at 250° C. with a slope of 10 K/min in an atmosphere of 10% by volume of H 2 in argon, and the calcining was continued under isothermal conditions for a total of 240 min.
  • the electrode thus obtained was subsequently characterized in terms of its electrochemical properties with a test setup that, apart from the GDE, corresponded to the one from comparative example 1.
  • the copper catalyst was provided by reduction of Cu(OAc) 2 .H 2 O.
  • a multilayer gas diffusion electrode was produced as in comparative example 3.1, using a Cu/ZrO 2 catalyst that had been obtained from Cu 8 Zr 3 as catalyst.
  • the GDE was additionally reduced prior to the measurement, 4.3 relates to an electrochemically activated electrode and 4.4 relates to a hydrogen-activated electrode.
  • the amounts used and results obtained in comparative examples 4.1-4.4 are shown in table 4, with the results additionally shown in FIGS. 10 and 11 for comparative example 4.3.
  • FIG. 10 shows a current series
  • FIG. 11 a measurement at constant current.
  • charcoal-based GDEs in comparative examples 1-4 showed elevated Faraday efficiencies for hydrogen. It was concluded from this that carbon in the form of conductive blacks or activated carbons is less suitable for the production of ethylene-selective gas diffusion electrodes.
  • the material used was the following:
  • PTFE suspension TF5035R, 58% by weight (DyneonTM), Surfactant: Triton-100 (Fluka Chemie AG)
  • Thickener hydroxyethyl methylcellulose (WalocelMKX 70000 PP 01, Wolff Cellulosics GmbH & Co. KG).
  • a solution that contained 97% by weight of Cu and 3% by weight of PTFE was produced as follows: 150 g of thickener solution (1% by weight of methylcellulose in H 2 O), 90.0 g of copper powder, 53.7 g of H 2 O and 1.5 g of surfactant were dispersed with an Ultra-Turrax T25 disperser at 13 500 rpm for 5 min (wait for 2 min after dispersing for 1 min).
  • a further GDE was produced on the basis of 0.5% by weight of PTFE by the same procedure.
  • the gas diffusion electrodes produced had very poor wettabilities and, in the case of the 0.5% PTFE content, poor porosities, as determined visually and by microscopy.
  • the GDEs contained considerable proportions of the surfactant used, which was identified as a catalyst poison in a controlled experiment. It was likewise not possible to drive out the corresponding catalyst poison Triton X 100 ((p-tert-octyl-phenoxy)polyethoxyethanol) without residue at temperatures of >340° C., as confirmed by scanning electron microscopy.
  • hydrotalcite precursor of the composition [Cu 0.6 Al 0.4 (OH) 2 ](CO 3 ) 0.4 .mH 2 O (unknown water content for the freshly precipitated hydrotalcite) is prepared by a coprecipitation. Simultaneously added are a 0.41 M metal salt solution (A) composed of Cu(NO 3 ) 2 .3H 2 O (0.246 mol) and Al(NO 3 ) 3 .9H 2 O (0.164 M) and a hydroxide/carbonate solution (B) composed of 0.3 M NaOH (12 g), 0.045 M (NH 4 ) 2 CO 3 (4.32 g), such that the pH is between pH 8 and 8.5.
  • A 0.41 M metal salt solution
  • B hydroxide/carbonate solution
  • a catalyst powder is prepared by coprecipitation of Cu(NO 3 ) 2 .3H 2 O and ZrO(NO 3 ) 2 .xH 2 O according to reference example 1 with the respective molar amounts (mol).
  • the mixing procedure follows the following procedure: grinding/mixing for 30 sec and wait for 15 sec for a total of 6 min.
  • the mixed powder attains a slightly tacky consistency after the mixing operation.
  • the mixing time before this state is attained may also vary according to the amount of powder or the polymer chosen or the chain length.
  • the powder mixture obtained is subsequently applied by scattering or sieving to a copper mesh having a mesh size of >0.5 mm and ⁇ 1.0 mm and a wire diameter of 0.1-0.25 mm in a bed thickness of 1 mm.
  • the reverse side of the copper mesh can be sealed with a film subject to no further restriction.
  • the prepared layer is compacted with the aid of a two-roll rolling device (calender).
  • the rolling process itself is characterized in that a reservoir of material forms upstream of the roll.
  • the speed of the roll is between 0.5-2 rpm and the gap width was adjusted to the height of the carrier +40% to 50% of the bed height Hf of the powder, or corresponds virtually to the thickness of the mesh +0.1-0.2 mm infeed.
  • the gas diffusion electrode obtained is activated in an electrolysis bath in a 1 M KHCO 3 solution at a current density of 15 mA/cm 2 for 6 h.
  • Dendritic copper powder (45 g; particle size ⁇ 45 ⁇ m, determined by sieving with appropriate mesh size (45 ⁇ m)) is mixed with 5 g of PTFE in an IKA knife mill by the procedure described in comparative example 6, and processed under the same conditions to give a GDE. After activation, the GDE described gave a Faraday efficiency of 16% at 170 mA/cm 2 , which remained constant over the measurement time of about 90 min.
  • the oxide precursor prepared, prior to use, is ground in a planetary ball mill (Pulverisette) for 3 min and subsequently sieved (particle size ⁇ 75 ⁇ m). 45 g of the catalyst obtained are mixed with 5 g of PTFE in an IKA knife mill by the procedure described in comparative example 6 and processed under the same conditions to give a GDE.
  • the GDEs from comparative examples 6 to 8 can be used in an electrolysis cell as described above or hereinafter, for example as cathode with which CO 2 can be reduced.
  • Copper powder with a particle diameter of 100-200 ⁇ m and PTFE TF 1750 Dyneon were mixed in an IKA A10 knife mill for 6 min (grinding for 15 sec, wait for 30 sec).
  • the powder layer was then sieved off and graded by means of a template of thickness 0.5 mm to form a base layer. This was followed by extrusion with a 2-roll calender with a roll separation of 0.5 mm.
  • a catalyst layer was applied by sieving application, for example in each case analogously to comparative examples 6 to 8, through a 0.2 mm frame, and extrusion was again effected with a 2-roll calender with a roll separation of 0.35 mm.
  • the result was a highly porous base layer with a porosity of >70%, good mechanical stability and very good conductivity at 5 mohm/cm. It was possible to use catalysts with a copper content of 40% by weight.
  • the catalysts had a purity above the commercially available materials or quality standards, as in the example as well. This was detectable by means of (surface-sensitive) XPS. SEM/EDX mapping analyses likewise did not indicate any impurities at all in the hydrophobic base layer.
  • FIGS. 4 to 6 show examples of a possible cell arrangement. The concept presented hereinafter is applicable to each of these cell arrangements.
  • the electrolysis cells from FIGS. 4 to 6 can also be joined to form mixed variants.
  • the anode space can be executed as a proton exchange membrane (PEM) half-cell, while the cathode space consists of a half-cell containing a certain electrolyte volume between membrane and electrode.
  • PEM proton exchange membrane
  • the distance between electrode and membrane is very small or 0 when the membrane is porous and includes a feed of the electrolyte.
  • the membrane may also have a multilayer configuration, such that separate feeds of anolyte and catholyte are enabled. Separation effects are achieved in the case of aqueous electrolytes, for example, through the hydrophobicity of interlayers. Conductivity can nevertheless be assured if conductive groups are integrated into separation layers of this kind.
  • the membrane may be an ion-conducting membrane, or a separator that brings about mechanical separation only.
  • the present invention provides the possibility of producing ethylene-selective, dimensionally stable gas diffusion electrodes based on catalyst powder.
  • This technique constitutes the basis for the production of electrodes on a larger scale, which can achieve current densities of >170 mA/cm 2 according to the mode of operation. All the methods known to date for production of ethylene-selective copper electrodes are unsuitable for scaleup or are not dimensionally stable.
  • Gas diffusion electrodes of the invention by contrast, can be obtained by suitable adjustment of a rolling process, especially a calendering process.
  • the production of the gas diffusion electrode of the invention is additionally based on the exclusion of conductive fillers based on charcoals or carbon blacks.
  • the charcoal substitute used here is the catalyst itself or dendritic copper or mixtures of the two.
  • the method of the invention in particular embodiments, does not need surface-active substances/surfactants or thickeners and additives (such as flow improvers) which have been identified as catalyst poisons.

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US11846031B2 (en) 2017-11-16 2023-12-19 Siemens Energy Global GmbH & Co. KG Hydrocarbon-selective electrode
US11299811B2 (en) * 2018-01-29 2022-04-12 Board Of Regents, The University Of Texas System Continuous flow reactor and hybrid electro-catalyst for high selectivity production of C2H4 from CO2 and water via electrolysis
US20210207276A1 (en) * 2018-06-27 2021-07-08 Siemens Aktiengesellschaft Gas diffusion electrode for carbon dioxide utilization, method for producing same, and electrolytic cell having a gas diffusion electrode
CN109695048A (zh) * 2019-02-28 2019-04-30 武汉大学 自支撑碳基体表面原位电化学生长纳米碳化物基电催化膜层的方法及应用

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PL3307924T3 (pl) 2020-01-31
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