DE102016013185B4 - Process for the production of catalytic layers for electrochemical systems - Google Patents

Abstract

Process for the production of catalytic layer (3) with threads on a nanometer scale as electrocatalysts for electrochemical processes, characterized by the alternating application of nanoscale threads (7) and of partially detachable metallic or organic or inorganic clusters (6) by physical vapor deposition on a carrier with or without subsequent thermal treatment to produce a highly dispersed catalytic layer.

Description

The invention relates to a method for the production of catalytic layers for electrochemical energy converters, which is characterized in that highly dispersed metal threads with different crystallization stages can be produced by suitable process management.

The invention further relates to such a catalytic layer for electrochemical systems which ensure better media transport on a support or self-stabilizing due to the high dispersion. Media can be the products or starting materials to be oxidized or reduced. The invention also relates to electrochemical systems with a number of such catalytic layers which function as electrodes.

Electrochemical systems or electrochemical energy converters are used to convert electrical energy into electricity or electricity into chemical energy. The task of the catalytic layer is to catalyze the desired reaction. Different catalysts are necessary for different reactions. The activity of a catalyst depends on the surface, crystallization state, porosity and type of metal.

Electrochemical energy converters can be fuel cells, electrolysers, flow batteries, batteries or other electrochemical syntheses.

Catalytic layers can be finely dispersed Pt catalysts for fuel cells, for example, which catalyze the conversion of oxygen and hydrogen to water. It can also be the synthesis of hydrocarbons by carbon dioxide by finely dispersed copper. Another reaction is the electrochemical splitting of water into oxygen and hydrogen by means of suitable finely dispersed oxides such as iridium oxide or ruthenium oxide or other metal oxides.

The catalytic layer, which often contains precious metals, leads to relatively high costs and a limited service life for the electrochemical systems.

Normal wet chemical manufacturing methods for the catalyst layer are complex. These processes make the layers relatively thick and the mass activity remains low.

literature

US 2009/0 068 461 A1 describes a method for producing nanoscale threads by electrospinning. The threads can have metallic, ceramic, carbon-containing or boron-containing compounds. They can be used in fuel cells, photodiodes, batteries or filtration systems.

DE102013200749A1 describes an electrode for batteries and its method of manufacturing lithium-ion batteries. The electrode consists of nanowires or long thin shapes with one end of the nanowires attached to a current collector. For production, electrochemical galvanization is carried out and the threads are scaled using lithium diffusion-inhibiting material.

WO 00/79630 A2 describes a gas diffusion electrode for fuel cells in which a relatively thin zone of catalytic material is provided in the interface between the respective electrode and the membrane. The electrically conductive carrier electrode has a first catalytically active material and at least one ion-conductive polymer. At least two different further catalytically active metals are then applied as a thin layer to this electrically conductive catalytic carrier electrode. Vacuum coating processes such as chemical vapor coating or physical vapor deposition or thermal coating are proposed for the deposition of the thin layers.

US 2012/0238440 A1 discloses a gas diffusion electrode for fuel cells in which graphite nanotubes are applied to a support formed from graphite fabric. These graphite nanotubes are then thinly coated with a catalytic material in order to form a noble metal-containing catalytic layer.

J. Kibsgaard, Y. Gorlin, Z. Chen, Th. Jaramillo: Meso-Structured Platinum Thin Films: Active and Stable Electrocatalysts for the Oxygen Reduction Reaction, in: Journal of the American Chemical Society, April 13, 2012, 7758-7765 proposes to increase the activity and the stability of the catalytic layer of a gas diffusion electrode to use mesostructured platinum thin layers by using a template.

• Journal of Power Sources, 5 December 2014, 255-260 schlagen einen mesoporösen Pt-Co Katalysator für Brennstoffzellen vor. Hierbei warden deutlich geringere Co Anteile verwendet.

G. Sievers, S. Mueller, A. Quade, F. Steffen, S. Jakubith, A. Kruth, V. Brueser: Mesoporous Pt-Co oxygen reduction reaction (ORR) catalysts for low temperature proton exchange membrane fuel cell synthesized by alternating sputtering, in:

• Journal of Power Sources, 5 December 2014, 255-260 propose a mesoporous Pt-Co catalyst for fuel cells. Significantly lower Co proportions are used here.

WO2015197812 A1 discloses a method of making a gas diffusion electrode with Pt and a non-metallic conductive particle deposited alternately to stabilize the catalyst layer. Placeholders are used that can be removed using suitable methods.

Out CN 102082277 A a method for producing a gas diffusion electrode for fuel cells is known, in which a stainless steel fiber fabric is first produced in a high-temperature vacuum sintering process. A chromium-containing layer and a graphite layer are then sequentially sputtered onto the stainless steel mesh and the coated stainless steel mesh is then sintered using polytetrafluoroethylene in a hydrophobic process. This is followed by a coating with graphite in order to obtain the metal-gas diffusion layer.

Z. Yan, M. Wang, B. Huang, R. Liu, J. Zhao: Graphene Supported Pt-Co Alloy Nanoparticles as Cathode Catalyst for Microbial Fuel Cells, in: Int. J. Electrochem. Sci., 8 (2013) 149-158 suggests using nanoparticles made of a graphene-supported Pt-Co alloy to form the noble metal-containing catalytic layer of gas diffusion electrodes.

In A. Papandrew, R. Atkinson, G. Goenaga, S. Kocha, J. Zack, B. Pivovar, Th. Zawodzinski: Oxygen Reduction Activity of Vapor-Grown Platinum Nanotubes, in: Journal of The Electrochemical Society, 160 (8 ) F848-F852 (2013) it is proposed to embed a catalyst formed from platinum nanotubes in a composite electrode by mixing it with corrosion-resistant carbon materials in order to obtain the thickest possible catalytic layers that can be sufficiently obtained at high current densities.

In Ch-H. Wan, M-T. Lin, Q-H. Zhuang, Ch-H. Lin: Preparation and performance of novel MEA with multi catalyst layer structure for PEFC by magnetron sputter deposition technique, in: Surface & Coatings Technology 201 (2006) 214-222 describes the formation of a catalytic layer for a gas diffusion electrode from several two-dimensional active layers. Here, a Nafion graphite layer is alternately applied to an electrically conductive and gas-permeable carrier GDL and a layer containing platinum is applied in the sputtering process in order to create a three-dimensional reaction zone. The Nafion graphite layer is printed on in the form of an ink. The alternating Pt-Carbon-Nafion layers form a microporous layer MPL lying on the gas-permeable layer GDL.

H. Rabat, P. Brault: Plasma Sputtering Deposition of PEMFC Porous Carbon Platinum Electrodes, in: Fuel Cells 08, 2008, No. 2, 81-86 describes the production of gas diffusion electrodes by plasma sputtering for thin-layer coating of a porous columnar graphite film followed by coating the platinum-containing catalyst directly onto the proton-conducting membrane. Graphite and platinum are alternately applied to both sides of the membrane. This can increase the efficiency.

B. Schwanitz: Reduction of the platinum loading and imaging of aging phenomena in the polymer electrolyte fuel cell, Diss. ETH Zurich No. 20142, 2012 describes the alternating sputtering of Pt and Co for anode and cathode. Alternating sputtering of Co in Pt is proposed to increase the platinum surface. This requires the subsequent acid treatment of the electrodes in order to prevent contamination-related voltage losses through dissolved Co ²⁺ .

Based on this, the aim of this invention is a process for the production of better catalytic layers and corresponding catalytic layers on porous supports such as gas diffusion layers or activated carbon but also non-porous supports such as solid plates or self-stabilizing catalytic layers for electrochemical energy converters such as batteries, fuel cells and flow cells to accomplish. Solid plates can be metallic plates, oxidic plates, or carbon-containing plates.

The object is achieved with the method with the features of claim 1 and by the catalytic layer with the features of claim. Advantageous embodiments are described in the subclaims.

A better method of production is deposition by means of physical vapor deposition. This makes it possible to produce suitable structures that cannot be produced using wet-chemical methods. It is proposed to produce a highly dispersed catalytic layer by alternating deposition of the desired nanoscale metal threads and of suitable soluble clusters.

A “nanoscale thread” in the sense of the present invention is understood to mean a stationary catalytically active substance. The structure of the nanoscale threads is defined by the combination of the same substances with one another to form a self-stabilizing, highly dispersed layer.

Under normal circumstances, with the high proportions of leachable material, non-stabilized nano-thread goes into the solution. This can be largely prevented by heating with a metal that has a higher melting point than the metal to be used and that does not form an alloy at these temperatures. In the case of platinum, this can be achieved using molybdenum or tungsten, for example.

• 1 - Schnittansicht durch eine Membran-Elektrodenanordnung für Brennstoffzellen und Elektrolyseure mit katalytischer Schicht 3 aufgebracht auf MPL 2 und GDL 3 getrennt durch Membran 4 durch physikalischen Gasphasenabscheidungsprozess
• 2 - Schnittansicht durch eine Elektrodenanordnung für elektrochemische Synthesen und Elektrolyseure mit katalytischer Schicht 3 auf Träger 5 aufgebracht durch physikalischen Gasphasenabscheidungsprozess
• 3 - Schichtansicht durch eine katalytische Schicht 3 mit löslichen Clustern 6 und nanoskalierten Fäden 7
• 4 - Elektronenmikroskopische Aufnahme einer hoch dispergierten katalytischen Schicht 3.

The invention is explained in more detail with reference to the accompanying drawings:

• 1 - Sectional view through a membrane electrode arrangement for fuel cells and electrolyzers with a catalytic layer 3 applied to MPL 2 and GDL 3 separated by a membrane 4th through physical vapor deposition process
• 2 - Sectional view through an electrode arrangement for electrochemical syntheses and electrolysers with a catalytic layer 3 on carrier 5 applied by physical vapor deposition process
• 3 - Layer view through a catalytic layer 3 with soluble clusters 6th and nanoscale threads 7
• 4th - Electron microscope image of a highly dispersed catalytic layer 3 .

1 shows a sketch of a layer structure of a membrane electrode arrangement for fuel cells. Two gas diffusion electrodes GDE are arranged opposite one another and separated from one another by a membrane. The gas diffusion electrode consists of a gas diffusion layer (GDL) and the microporous layer (MPL). The catalytic layer can either be applied directly to the MPL of the GDL or to a carrier material such as Teflon-containing plastic and then applied to the membrane using a printing process.

2 shows a sketch of a layer structure of a catalytic layer deposited on a carrier. This support can be a conductive metallic or carbon-containing substrate or it can be used as a separable material to produce a self-stabilizing catalytic layer.

3 shows the cross section of a catalytic layer with nanoscale threads and soluble clusters. The nanoscale threads can be interconnected and result in a self-supporting structure or they can be present in a high dispersion that is stabilized by the binding to the carrier 5 given is.

Claims (11)

Process for the production of catalytic layer (3) with threads on a nanometer scale as electrocatalysts for electrochemical processes, characterized by the alternating application of nanoscale threads (7) and of partially detachable metallic or organic or inorganic clusters (6) by physical vapor deposition on a carrier with or without subsequent thermal treatment to produce a highly dispersed catalytic layer. Procedure according to Claim 1 , characterized by physical vapor deposition of nano-scaled amorphous or crystalline threads the elements platinum, palladium, iridium, ruthenium, copper, iron, nickel, molybdenum, chromium, tungsten, tin, zinc, aluminum, niobium, gadolinium, yttrium, tantalum, zirconium, cobalt , Carbon, antimony, germanium, silver, gold and / or their oxides and of removable metallic clusters with copper, iron, nickel, molybdenum, chromium, tungsten, tin, zinc, titanium, magnesium, vanadium, aluminum, niobium, gadolinium, Yttrium, tantalum, zirconium, cobalt, carbon, antimony, germanium, silver and gold alternate to form a highly dispersed catalytic layer (3). Procedure according to Claim 1 characterized in that the carrier is a gas diffusion electrode, a separable or a conductive material, wherein the separable material can be plastic film, fluorine-containing plastic, Kapton or easily combustible carbon film. Procedure according to Claim 2 characterized in that the metallic nanoscale threads under a protective metallic or oxidic platinum, iridium, ruthenium, palladium, copper, iron, nickel, molybdenum, chromium, tungsten, tin, zinc, aluminum, niobium, gadolinium, yttrium, tantalum, zirconium, Cobalt, carbon, antimony, germanium, silver layer have insoluble or sparingly soluble clusters of removable metals or metal oxides. Procedure according to Claim 1 characterized in that the deposited nanoscale threads have a diameter of less than 10 nm per application. Procedure according to Claim 1 characterized in that the detachable metal clusters deposited have a diameter of more than 50 nm to 300 nm per application. Method according to one of the Claims 1 to 6th , characterized in that the alternating application of metal-containing nanoscale metal threads and partially detachable metallic or organic clusters by vapor deposition, electron beam vaporization, laser beam vaporization, electric arc vaporization, molecular beam epitaxy, sputtering, magnetron sputtering, ion plating or ionized cluster beam deposition (ICBD) he follows. Procedure according to Claim 2 characterized in that the catalytic layer before and after the dissolving out of the soluble clusters by thermal treatment with higher melting fractions of the soluble substance can achieve better crosslinking and thus higher dispersion and stability. Procedure according to Claim 1 characterized in that the soluble clusters can be dissolved out by combustion or acid or base or potential-controlled electrochemical processes. Catalytic layer for electrochemical processes, characterized in that metallic nanoscale threads are platinum, palladium, copper, iron, nickel, molybdenum, chromium, tungsten, tin, zinc, aluminum, niobium, gadolinium, yttrium, tantalum, zirconium, cobalt, carbon, antimony , Germanium, silver, gold and / or their oxides and the layer has a highly dispersed structure due to the dissolution of metallic clusters. Catalytic layer after Claim 10 characterized in that the nanoscale threads can have the catalytic properties of solids.

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