Classifications

• • C25B11/0484—
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/34—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/24—Halogens or compounds thereof
  • C25B1/26—Chlorine; Compounds thereof
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/075—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/075—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound
  • C25B11/081—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound the element being a noble metal
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/091—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
  • C25B11/093—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 noble metal or noble metal oxide and at least one non-noble metal oxide
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/04—Processes of manufacture in general
  • H01M4/0402—Methods of deposition of the material
  • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/04—Processes of manufacture in general
  • H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/88—Processes of manufacture
  • H01M4/8825—Methods for deposition of the catalytic active composition
  • H01M4/8828—Coating with slurry or ink
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/90—Selection of catalytic material
  • H01M4/9016—Oxides, hydroxides or oxygenated metallic salts
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/90—Selection of catalytic material
  • H01M4/9041—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
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/90—Selection of catalytic material
  • H01M4/92—Metals of platinum group
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/50—Fuel cells

Definitions

• the invention relates to an improved catalyst coating with electrocatalytically active components based on ruthenium oxide and titanium oxide, especially for use in chloralkali or hydrochloric acid electrolysis for production of chlorine.
• the invention further relates to a production process for the catalyst coating and to a novel electrode.
• the present invention specifically describes a process for wet-chemical deposition of mixed oxide layers composed of ruthenium oxide and titanium oxide on a metallic support and the use thereof as electrochemical catalysts in chlorine production by electrolysis.
• the invention proceeds from electrodes and electrode coatings known per se, which are typically coated onto an electrically conductive support and comprise catalytically active components including, in particular, electrocatalytically active components based on ruthenium oxide and titanium oxide.
• Chlorine is produced industrially typically by electrolysis of sodium chloride or hydrochloric acid or by gas phase oxidation of hydrogen chloride (Schmittinger, Chorine, Wiley-VCH 1999, pages 19-27). If electrolysis processes are used, chlorine is produced at the anode.
• the anode material used is usually titanium as the electrode material, on the surface of which there is an electrochemically active catalyst.
• the layer on the surface comprising the catalyst is typically also referred to as the coating.
• the task of the catalyst is to lower the overpotential and prevent evolution of oxygen at the anode (Winnacker-kuchler, Chemischetechnik, Sawe und Kunststoffmaschine [Chemical Technology, Processes and Products], 5th edition, Wiley-VCH 2005, pages 469-470).
• Electrodes for electrolysis processes are typically based on a metal which is one of the so-called valve metals.
• Valve metals are understood to mean, for example, the metals titanium, zirconium, tungsten, tantalum and niobium. These act as a diode material for electrical current because of oxide layers on the metal surface.
• an electrocatalytically active catalyst comprising a noble metal and/or metal oxide thereof is typically applied on the surface of the valve metals, in which case it is also optionally additionally possible for oxides of the valve metal to be present in the metal oxide (WO 200602843 (ELTECH), BECK, Electrochimica Acta, Vol. 34, No. 6, pages 811-822, 1989)).
• the oxide-forming noble metal is typically one of the platinum metals, for example iridium, ruthenium, rhodium, palladium, platinum or mixtures thereof.
• Such electrodes are typically referred to as DSA electrodes, DSA standing for “dimensionally stable anode”.
• a further process for producing mixed oxide layers composed of titanium oxide and ruthenium oxide on a titanium support is sol-gel synthesis.
• the catalyst coating should adhere firmly to the base metal and not be attacked chemically or electrochemically. With the catalyst coating, it should be possible to achieve a low electrolysis voltage even at low chloride concentrations.
• the above-described object is achieved in accordance with the invention by using a selected catalyst coating based on noble metal oxides, especially ruthenium oxide and/or iridium oxide, and valve metal oxides, especially titanium oxide, in which a solvent or dispersant with a significant excess of acid relative to the catalytic component is used in the production of a coating solution or coating suspension.
• noble metal oxides especially ruthenium oxide and/or iridium oxide
• valve metal oxides especially titanium oxide
• the invention provides a process for wet-chemical production of a catalyst coating on an electrically conductive support for electrodes for chloralkali or hydrochloric acid electrolysis with electrocatalytically active components based on at least one noble metal oxide and/or noble metal of the noble metals of transition group VIIIa of the Periodic Table of the Elements, especially a noble metal selected from the group of: Ru, Rh, Pd, Os, Ir and Pt, especially ruthenium oxide and/or iridium oxide, and optionally additionally at least one valve metal oxide and/or valve metal, especially with a valve metal selected from the group of Ti, Zr, W, Ta, Nb or oxides thereof, characterized in that the catalyst coating is produced by
• a significant excess of acid relative to the catalytic component in the coating solution/dispersion is present, especially when the molar ratio of the sum of the amounts of acid (in mol) present in the solution/dispersion to the sum of the amounts of the metals from the metal-containing components present in the coating solution or dispersion (sum of the metals present in mol) is at least 2:1, preferably at least 3:1, more preferably at least 4:1.
• the acid may be either one or more organic acids or one or more inorganic acids, or a combination of one or more organic and one or more inorganic acids.
• at least one acid is an organic acid.
• An acid in the context of the invention is present especially when the pK a thereof in aqueous solution is not more than 12, preferably not more than 8 and more preferably not more than 5.
• the pK a for an acid HA is then determined to be
• c denotes the concentration of the respective species in mol/l.
• This exceptional surface morphology apparently increases the active surface area which can be utilized for electrochemical catalysis.
• the catalytic activity is improved and the noble metal content can be reduced compared to known catalyst coatings.
• a particular embodiment of the novel process is characterized in that the coating solution or dispersion according to step a) additionally comprises a precursor compound and/or a metal and/or a metal oxide of one or more doping elements from the group of: aluminium, antimony, lead, iron, germanium, indium, manganese, molybdenum, niobium, tantalum, titanium, tellurium, vanadium, zinc, tin and zirconium.
• a particular embodiment of the novel process involves applying the catalysts to an electrode structure comprising a valve metal, especially a metal from the group of titanium, zirconium, tungsten, tantalum and niobium, as follows:
• the electrode structure is mechanically pre-cleaned, especially sand-blasted, and can optionally subsequently be etched with an acid, for example a mineral acid such as hydrochloric acid or oxalic acid, for further removal of oxides on the surface.
• the surface can be coated using, for example, a coating solution or dispersion comprising a noble metal compound, at least one solvent from the group of: water, C 1 -C 6 -alcohol, preferably butanol or isopropanol, or a mixture of C 1 -C 6 -alcohol and water, and an acid and optionally a valve metal compound.
• a coating solution or dispersion comprising a noble metal compound, at least one solvent from the group of: water, C 1 -C 6 -alcohol, preferably butanol or isopropanol, or a mixture of C 1 -C 6 -alcohol and water, and an acid and optionally a valve metal compound.
• Preferred solvents or dispersants are therefore one or more from the group of: water and C 1 -C 6 -alcohol, more preferably butanol or isopropanol.
• the acids used in the coating solution may be one or more organic or inorganic acids or a combination of organic and inorganic acids. Preference is given to a particular process in which the acid used in the coating solution is a combination of organic and inorganic acid, where the molar ratio of the amount of organic acid (in mol) present in the coating solution or dispersion to the amount of mineral acid is 20:80 to 100:0, preferably 50:50 to 100:0, more preferably 80:20 to 100:0.
• the organic acids used are preferably water-soluble acids, for example alkanoic acids, alkanedioic acids, mono-, di- and trihaloalkanoic acids, preference being given to using at least one short-chain alkanoic acid such as formic acid, acetic acid or propionic acid, or a short-chain mono-, di- or trihaloalkanoic acid such as chloroacetic acid, dichloroacetic acid, trichloroacetic acid, fluoroacetic acid, difluoroacetic acid or trifluoroacetic acid, or toluenesulphonic acid.
• alkanoic acids alkanedioic acids
• mono-, di- and trihaloalkanoic acids preference being given to using at least one short-chain alkanoic acid such as formic acid, acetic acid or propionic acid, or a short-chain mono-, di- or trihaloalkanoic acid such as chloroacetic acid, dichloroacetic acid, t
• the inorganic acids used may be mineral acids, for example hydrohalic acids, preferably hydrochloric acid, sulphuric acid, sulphurous acid, phosphoric acid, phosphorous acid, nitric acid and/or nitrous acid or else phosphonic acids, sulphonic acids, blocked sulphonic acids, or blocked sulphuric and phosphoric acids. Particular preference is given to using mixtures of a mineral acid and an organic acid.
• the acid used in the coating solution in a) is hydrochloric acid and/or a C 1 -C 4 -carboxylic acid, preferably at least one acid from the group of: hydrochloric acid, formic acid, acetic acid or propionic acid. Very particular preference is given to using a mixture of acetic acid and hydrochloric acid.
• the coating solution may additionally, or else instead of one or more of the aforementioned metal compounds, comprise further solids.
• Preferred solids are polymorphs of carbon or non-noble metal oxides or mixtures thereof.
• the dispersion comprises preferably up to 20% by weight, more preferably to 10% by weight, of further solids, based on the weight of the suspension.
• the noble metal precursor compounds used in the novel process are, in particular, solvent-soluble fluorides, chlorides, iodides, bromides, nitrates, phosphates, sulphates, acetates, acetylacetonates or alkoxides of the elements: Ru, Rh, Pd, Os, Ir and Pt, preferably a noble metal chloride, more preferably a ruthenium chloride and/or iridium chloride.
• valve metal precursor compounds preferably solvent-soluble fluorides, chlorides, iodides, bromides, nitrates, phosphates, sulphates, acetates, acetylacetonates or alkoxides of the elements titanium, zirconium, tungsten, tantalum and niobium, more preferably at least one titanium alkoxide selected from the group of: titanium 2-ethylhexyloxide, titanium ethoxide, titanium isobutoxide, titanium isopropoxide titanium methoxide, titanium n-butoxide, titanium n-propoxide, titanium tert-butoxide, most preferably titanium n-butoxide and/or titanium isopropoxide.
• Noble metals usable with preference in the novel process for the suspension are one or more elements from the group of: Ru, Rh, Pd, Os, Ir and Pt.
• Noble metal oxides usable with preference in the novel process for the suspension are oxides of one or more elements from the group of: Ru, Rh, Pd, Os, Ir and Pt.
• valve metal compound used with preference for example in the case of titanium as the electrode support, is a titanium alkoxide.
• step a) it is additionally possible in step a) to add non-noble metal and/or doping element precursor compounds which, on completion of drying and/or sintering, form a non-noble metal oxide which may also be doped, in which case the proportion of doping elements is preferably up to 20 mol % based on the total content of metals in the coating solution or dispersion.
• Suitable non-noble metal precursor compounds are especially solvent-soluble fluorides, chlorides, iodides, bromides, nitrates, phosphates, acetates, acetylacetonates and/or alkoxides of the elements antimony, lead, iron, germanium, indium, manganese, molybdenum, niobium, tantalum, titanium, tellurium, vanadium, zinc, tin, and/or zirconium.
• Preferred non-noble metal compounds are, alone or in a mixture:
• titanium compounds selected from the group of: titanium fluoride, titanium chloride, titanium iodide, titanium bromide, titanium 2-ethylhexyloxide, titanium ethoxide, titanium isobutoxide, titanium isopropoxide, titanium methoxide, titanium n-butoxide, titanium n-propoxide, titanium tert-butoxide, and/or manganese compounds selected from the group of: manganese fluoride, manganese chloride, manganese iodide, manganese bromide, manganese nitrate, manganese phosphate, manganese acetate, manganese acetylacetonate, manganese methoxide, manganese ethoxide, manganese propoxide, manganese butoxide, and/or indium compounds selected from the group of: indium fluoride, indium chloride, indium iodide, indium bromide, indium nitrate, indium phosphate, indium
• non-noble metal-precursor compounds are tin chloride and/or indium chloride and/or manganese chloride.
• the aforementioned compounds can also serve as a precursor compound for doping together with other compounds in the dispersion/solution.
• Suitable doping element precursor compounds are especially solvent-soluble fluorine compounds and/or fluorides, chlorides, iodides, bromides, nitrates, phosphates, sulphates, acetates, acetylacetonates and/or alkoxides of the elements aluminium, antimony, tantalum, niobium, tin, indium, manganese.
• Preferred doping element precursor compounds are one or more compounds from the group of: manganese compounds selected from the group of manganese fluoride, manganese chloride, manganese iodide, manganese bromide, manganese nitrate, manganese phosphate, manganese acetate, manganese acetylacetonate, manganese methoxide, manganese ethoxide, manganese propoxide, manganese butoxide, and/or aluminium compounds selected from the group of: aluminium fluoride, aluminium chloride, aluminium iodide, aluminium bromide, aluminium nitrate, aluminium phosphate, aluminium sulphate, aluminium acetate, aluminium acetylacetonate, aluminium ethoxide, aluminium propoxide, aluminium butoxide and/or antimony compounds selected from the group of: antimony fluoride, antimony chloride, antimony iodide, antimony bromide, antimony s
• Doping element precursor compounds suitable with particular preference are antimony chloride and/or tin chloride and/or manganese chloride.
• fluorine compounds selected from the group of: fluoroacetic acid, difluoroacetic acid, trifluoroacetic acid, hydrogen fluoride, ammonium fluoride, tetramethylammonium fluoride are additionally added to the solution/dispersion in step a).
• the coating solution or dispersion according to step a) additionally comprises a precursor compound selected from the group of the compounds of: indium, tin, antimony, niobium, tantalum, fluorine and manganese, preferably tin, indium and antimony, as precursors for a doping, in which case the proportion of doping elements is preferably up to 20 mol % based on the total content of metals in the coating solution or dispersion.
• the combination of tin compound as precursor compound with an antimony compound as dopant precursor or a combination of indium compound as precursor compound with a tin compound as dopant precursor is possible to obtain, in the end product, indium tin oxides (ITO) or tin antimony oxides (ATO) having a higher electrical conductivity than respectively undoped indium oxide or tin oxide
• the coating solution or dispersion according to step a) additionally comprises a precursor compound selected from the group of: tin(IV) chloride (SnCl 4 ), antimony(III) chloride (SbCl 3 ), indium(III) chloride (InCl 3 ) and manganese(II) chloride (MnCl 2 ).
• a precursor compound selected from the group of: tin(IV) chloride (SnCl 4 ), antimony(III) chloride (SbCl 3 ), indium(III) chloride (InCl 3 ) and manganese(II) chloride (MnCl 2 ).
• composition of the coating solution or dispersion it is possible to match the viscosity thereof to the respective application operation.
• thickeners stabilizers, wetting additives, etc.
• Preferred examples thereof are nonionic, water-soluble polyethylene oxide polymers and/or water-soluble methylcellulose and/or hydroxypropyl methylcellulose polymers, stabilizers such as polyvinyl alcohol and/or polyacrylic acid and/or polyvinylpyrrolidone, and wetting additives, for example anionic surfactants such as sodium dodecylsulphate or cationic surfactants such as dodecyltrimethylammonium chloride or nonionic surfactants such as polyethylene glycol monolaurate.
• anionic surfactants such as sodium dodecylsulphate
• cationic surfactants such as dodecyltrimethylammonium chloride
• nonionic surfactants such as polyethylene glycol monolaurate.
• the coating solution or dispersion prepared is preferably applied to the surface of the support in two or more cycles. This can be done by brushing, spraying, flowing or dipping the carrier onto or into the coating solution or dispersion. Other application processes are likewise conceivable, for example printing processes.
• the amount of noble metal or noble metal-containing coating which is applied to the electrode surface can be adjusted through the concentration of the application solution or through the number of repeat cycles. Electrodes for chlorine production and other gas-evolving reactions usually consist of expanded metals or other open structures. The figure for the noble metal loading per unit electrode area is based hereinafter on the geometric area of the electrode surface projected onto a plane to the normal. The amount of noble metal or noble metal-containing coating is then based on a surface area which can be calculated from the external dimensions of the electrode area.
• the liquid components of the coating solution or dispersion are removed by drying. Thereafter, it is possible to commence a new application step b) or to subject the electrode, after the drying c), to a sintering operation d) at a temperature of at least 300° C. Thereafter, the coating solution or dispersion can again be applied, dried and sintered.
• the drying c) of the coating can be effected at standard pressure or else under reduced pressure, under air or optionally preferably under a mixture of oxygen with a protective gas, especially at least one gas from the group of nitrogen and noble gas, especially helium, neon, argon or krypton. This likewise applies to the sintering d) of the coating.
• the supports used for the catalyst and coated may especially be sheetlike structures with complex geometry, for example expanded metals, perforated sheets, foams, knits, meshes and nonwovens.
• the support is based on a valve metal from the group of titanium, zirconium, tungsten, tantalum and niobium, preferably titanium or alloys thereof or tantalum, more preferably on titanium or titanium alloys.
• Suitable titanium alloys which are preferably more corrosion-stable than pure titanium, comprise, for example, palladium, or nickel and palladium and ruthenium and chromium, or nickel and molybdenum, or aluminium and niobium.
• titanium-palladium (0.2% by weight Pd) and/or titanium-nickel-chromium-ruthenium-palladium (0.35 to 0.55% by weight of Ni, 0.1 to 0.2% by weight of Cr, 0.02 to 0.04% by weight of Ru and 0.01 to 0.02% by weight of Pd).
• the surface of the support before the application b) of the coating solution or dispersion to the support is mechanically pre-cleaned, especially sand-blasted and optionally subsequently etched with an acid such as hydrochloric acid or oxalic acid for further removal of oxides on the surface.
• a particularly preferred process is characterized in that the support is based on metallic titanium or tantalum, preferably on titanium.
• titanium(IV) n-butoxide Ti[OCH 2 CH 2 CH 2 CH 3 ] 4
• ruthenium(III) chloride RuCl 3
• acetic acid CH 3 CO 2 H
• Another preferred variant of the novel process is characterized in that the sintering d) of the coated support is performed at a temperature of 300° C. to 700° C., preferably of 400° C. to 600° C. and more preferably of 450° C. to 550° C.
• metal salts for example iridium(III) chloride (IrCl 3 ), tin(IV) chloride (SnCl 4 ), antimony(III) chloride (SbCl 3 ) and manganese(II) chloride (MnCl 2 ), to the coating solution in the novel process, it is also possible with preference to obtain multinary mixed oxides.
• iridium(III) chloride IrCl 3
• tin(IV) chloride SnCl 4
• antimony(III) chloride SbCl 3
• manganese(II) chloride MnCl 2
• the invention also provides a novel electrode with a novel catalyst coating, which is obtained as described above from the novel process.
• the invention further provides for the use of the novel electrode for electrochemical production of chlorine from alkali metal chloride solutions or hydrogen chloride or hydrochloric acid, especially from sodium chloride solutions.
• novel electrodes which are obtained from the novel process may, as well as the described applications in chlorine production, alternatively also be used for generation of electrical power in, for example, fuel cells and batteries, in redox capacitors, in the electrolysis of water, in the regeneration of chromium baths, and in the case of use of fluorine-containing electrolytes in hydrogen peroxide, ozone of the peroxodisulphate production.
• fuel cells and batteries in redox capacitors
• fluorine-containing electrolytes in hydrogen peroxide, ozone of the peroxodisulphate production may, as well as the described applications in chlorine production, alternatively also be used for generation of electrical power in, for example, fuel cells and batteries, in redox capacitors, in the electrolysis of water, in the regeneration of chromium baths, and in the case of use of fluorine-containing electrolytes in hydrogen peroxide, ozone of the peroxodisulphate production.
• the size of the anode in the laboratory cell used was 10 cm ⁇ 10 cm; the anode support material contained titanium and had the form of an expanded metal, characterized by the mesh size of 8 mm, land width 2 mm and land thickness 2 mm. Between the anode space and cathode space, a DuPont Nafion 982 ion exchange membrane was used.
• the cathode used was a standard nickel cathode from Denora for NaCl electrolysis, which had been equipped with a ruthenium-containing coating. The electrode separation was 3 mm.
• a coating solution comprising 2.00 g of ruthenium(III) chloride hydrate (Ru content 40.5% by weight), 9.95 g of n-butanol, 0.94 g of conc. hydrochloric acid (37% by weight), 5.93 g of tetra-n-butyl titanate (Ti—(O-Bu) 4 ) is made up. This is applied by brush to a sand-blasted expanded titanium metal with the same geometry as in Example 1 as a support. In the coating solution, the concentration of mineral acid is 27.3 mol % and the acid concentration thus totals 27.3 mol %. The ratio of the sum of the amounts of acid to the sum of the amounts of metal in the coating solution is 0.375.
• the expanded metal is dried at 80° C. for 10 min and then sintered at 470° C. for 10 min.
• the application operation is repeated three times more, as are the drying and sintering.
• the last sintering operation is effected at 520° C. for 60 min.
• the areal ruthenium loading was determined from the consumption of the coating solution to be 20.8 g/m 2 , with a composition of 31.5 mol % of RuO 2 and 68.5 mol % of TiO 2 .
• This anode thus treated was used in a cell as in Example 1 in sodium chloride electrolysis with a commercial standard cathode.
• the chlorine concentration of the gas escaping from the anode chamber was 97.6% by volume.
• the electrolysis voltage was 3.06 V.
• Titanium sheets having a diameter of 15 mm (thickness 2 mm) were sand-blasted to clean and to roughen the surface and then etched in 10% oxalic acid at 80° C. (30 min), then cleaned with isopropanol.
• the concentration of organic acid is 34.3 mol %, the concentration of mineral acid 52.8 mol %, and the total acid concentration 87.0 mol %.
• the sum of the concentration of the metals is 13 mol %.
• the ratio of the sum of the amounts of acid to the sum of the amounts of metal in the coating solution is 6.71.
• the coating solution was four times applied dropwise to titanium platelets or brushed onto expanded titanium metal.
• the areal ruthenium loading was determined from the increase in weight of the platelet to be 13.01 g/m 2 , with a composition of 29.85 mol % of RuO 2 and 70.15 mol % of TiO 2 .
• Titanium sheets having a diameter of 15 mm (thickness 2 mm) were sand-blasted to clean and to roughen the surface and then etched in 10% oxalic acid at 80° C. (30 min), then cleaned with isopropanol.
• the concentration of organic acid is 88.9 mol %, the concentration of mineral acid 1.8 mol %, and the total acid concentration 90.7 mol %.
• the ratio of the sum of the amounts of acid to the sum of the amounts of metal in the coating solution is 9.75.
• the coating solution was four times applied dropwise to titanium platelets or brushed onto expanded titanium metal.
• the areal ruthenium loading was determined from the increase in weight of the platelet to be 15.47 g/m 2 , with a composition of 30.01 mol % of RuO 2 , 62.85 mol % of TiO 2 , 6.94 mol % of SnO 2 and 0.20 mol % of Sb 2 O 5 .
• Titanium sheets having a diameter of 15 mm (thickness 2 mm) were sand-blasted to clean and to roughen the surface and then etched in 10% oxalic acid at 80° C. (30 min), then cleaned with isopropanol. Expanded titanium metal was sand-blasted to clean and to roughen the surface and then cleaned with isopropanol.
• the coating solution was four times applied dropwise to titanium platelets or, in parallel, brushed onto expanded titanium metal.
• the areal ruthenium loading was determined from the increase in weight of the platelet to be 15.47 g/m 2 , with a composition of 29.9 mol % of RuO 2 , 70.1 mol % of TiO 2 .
• Titanium sheets having a diameter of 15 mm (thickness 2 mm) were sand-blasted to clean and to roughen the surface and then etched in 10% oxalic acid at 80° C. (30 min), then cleaned with isopropanol.
• Solution 1 1.59 g of tetra-n-butyl titanate were added dropwise to an initial charge of 4.77 g of acetic acid while cooling in an ice bath with vigorous stirring, with at least 1 min of stirring time between two drops. The clear solution formed was then stirred while cooling for a further 12 h.
• Solution 2 0.96 g of crenox TR-HP-2 from crenox GmbH (BET surface area 5-7 m 2 /g; density 4.2 g/cm 3 ; TiO2-rutile 99.5% purity, density 4.2 g/cm 3 , mean particle size 206 nm (determined from electron micrograph as the average from 38 particles) was dispersed by means of ultrasound in a solution of 0.52 g of ruthenium(III) chloride hydrate (Ru content 40.35% by weight), 216 mg of tin(IV) chloride pentahydrate and 9 mg of antimony(III) chloride in 26.11 g of demineralized water for 1 h.
• Solution 2 was added dropwise to solution 1, in the course of which solution 1 was cooled in an ice bath and stirred vigorously. Thereafter, the product was stirred for a further 96 h.
• the concentration of organic acid is 80.2 mol %
• the sum of the concentration of the metal compounds is 19.8 mol %.
• the ratio of the sum of the amount of acid to the sum of the amounts of metal in the coating solution is 4.05.
• the coating solution was added dropwise to titanium platelets four times.
• the areal ruthenium loading was determined from the increase in weight of the platelets to be 4.85 g/m 2 , with a composition of 86.0 mol % of TiO 2 , 10.7 mol % of RuO 2 , 3.2 mol % of SnO 2 and 0.1 mol % of Sb 2 O 5 .
• Titanium sheets having a diameter of 15 mm (thickness 2 mm) were sand-blasted to clean and to roughen the surface and then etched in 10% oxalic acid at 80° C. (30 min), then cleaned with isopropanol.
• the concentration of organic acid is 65.4 mol %
• the concentration of mineral acid 10.0 mol % is 64.6 mol %
• the ratio of the sum of the amounts of acid to the sum of the amounts of metal in the coating solution is 3.06.
• the coating solution was four times applied dropwise to titanium platelets or brushed onto expanded titanium metal.
• the areal ruthenium loading was determined from the increase in weight of the platelet to be 13.01 g/m 2 , with a composition of 29.85 mol % of RuO 2 and 70.15 mol % of TiO 2 .
• Electrochemical activity for chlorine evolution was measured on a laboratory scale for samples from Examples 3 to 7 on titanium electrodes (diameter 15 mm, thickness 2 mm) by recording polarization curves.
• the potential, determined in each case at a current density of 4 kA/m 2 , of the sample from Example 3 was 1.415 V; the sample from Example 4: 1.370 V; the sample from Example 5: 1.412 V; the sample from Example 6: 1.388 V and the sample from Example 7: 1.364 V.
• the coating on expanded metal from Example 5 was used in a cell as in Example 1 in sodium chloride electrolysis with a commercial standard cathode.
• the electrolysis voltage after 3 days was 2.96 V, then the current density was increased to 6 kA/m 2 and the NaCl concentration was lowered to 180 g/l. After being 3.26 V initially, the electrolysis voltage fell somewhat, to 3.23 V after 10 days at 6 kA/m 2 . The mean electrolysis voltage over the next 92 days was then 3.21 V.
• the chlorine concentration of the gas escaping from the anode chamber was 98.0% by volume after 3 days at 6 kA/m 2 , and 97.0% after 102 days at 6 kA/m 2 . Subsequently, the system was set back to the current density of 4 kA/m 2 at a brine concentration of 210 g/l and the electrolysis voltage was 2.92 V.

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