Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/08—Fuel cells with aqueous electrolytes
• • 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
  • C25B13/00—Diaphragms; Spacing elements
  • C25B13/04—Diaphragms; Spacing elements characterised by the material
  • C25B13/05—Diaphragms; Spacing elements characterised by the material based on inorganic materials
• • 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
  • C25B5/00—Electrogenerative processes, i.e. processes for producing compounds in which electricity is generated simultaneously
• • 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
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
  • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
  • H01M8/0289—Means for holding the electrolyte
  • H01M8/0293—Matrices for immobilising electrolyte solutions
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/10—Fuel cells with solid electrolytes
  • H01M8/1009—Fuel cells with solid electrolytes with one of the reactants being liquid, solid or liquid-charged
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/10—Fuel cells with solid electrolytes
  • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
• • 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 present invention relates to an improved electrolytic reactor.
• Electrolytic reactors are reactors in which a chemical reaction is caused to take place by electrical means, for example a liquid compound or an ion in solution has one or more electrons added or removed from it to form a product, for example in the production of sodium hydroxide and chlorine from salt.
• Another major electrolytic process is the production of aluminium from bauxite.
• cathode and anode compartments containing electrolyte there are separate cathode and anode compartments containing electrolyte.
• the cathode or anode can take an active part in the production of the desired end product, for example they can be in the form of a catalyst or they can be made from an electrical conducting material which is inert to the liquids with which it is in contact.
• the anode and cathode compartments need to be separated to prevent diffusion of liquids between the compartments with consequent loss of performance, poisoning of electrodes etc.
• an electric current must flow through the electrolyte and the production rate is a factor of the current flowing. This requirement of having an adequate current flowing through the electrolyte without there being the passage of liquid between the two compartments has been difficult to achieve in practice, and in spite of many proposals and the theoretical attractiveness of electrochemical reactions this has been one of the main reasons for the very limited applications of electrochemical processes.
• a particular widely used application of an electrochemical reactor is a fuel cell.
• each cell is divided by a membrane coated on both sides with a catalyst e.g. made of platinum and ruthenium.
• the anode compartment can hold a solution of the fuel in water, while the cathode compartment holds air as oxidising agent.
• One problem of fuel cells using an organic fuel is that the fuel can diffuse from the anode compartment to the cathode compartment and can lead to a self discharge reaction in the cathode leading to lower cell voltage and efficiency.
• Cathodes which are inactive towards the oxidation of organic fuels can adsorb organic molecules on the cathode catalyst surface, which will lead to a lowering of their oxygen reduction efficiency.
• a well known type of fuel cell uses methanol as the fuel and liquid fuel cells have well tested advantages over hydrogen fuel cells.
• Other liquid fuels have been proposed and, in theory, any oxidisable liquid can be used as the fuel.
• an electrolytic reactor comprising an anode compartment and a cathode compartment separated by a zeolite membrane and in which the anode compartment is adapted to contain a first compound in fluid form and the cathode compartment is adapted to contain a second compound in fluid form and in which an electric current can flow through the first and second compounds and the first and/or second compounds are chemically changed by the passage of the electric current.
• the anode compartment contains an oxidisable fuel and the cathode compartment is adapted to contain air or other oxidising agent, there being a catalyst able to catalyse the oxidation of the fuel.
• the electrolyte in the fuel cell can be acidic or basic, when the electrolyte is acidic the zeolite membrane should be substantially resistant to acids and when the electrolyte is basic the membrane should be substantially resistant to alkalis.
• the cathode can comprise the catalyst which can be, for example a platinum or platinum group metal complex.
• the zeolite membrane can be substantially impervious to acids by being formed from substantially acid resistant zeolites, e.g. zeolites and zeo-type materials which contain little or no aluminium or the zeolite membrane can be treated to render its surface substantially acid resistant.
• substantially acid resistant zeolites e.g. zeolites and zeo-type materials which contain little or no aluminium or the zeolite membrane can be treated to render its surface substantially acid resistant.
• Typical zeolites which can be used in the present invention include but are not limited to zeolites 3 A, 4A, 5 A, 13X, X, Y, ZSM5, MPOs, SAPOs, Silicalite, ⁇ , ⁇ , ⁇ .
• the zeolite membrane can be substantially impervious to alkalis by being formed from substantially basic resistant zeolites, e.g. zeolites and zeo-type materials which are resistant to alkalis at a pH 10 and above for long periods at elevated temperatures. See D.W. Breck " Zeolite Molecular Sieves", 1974 page 276 e.g. zeolite P.
• the electrolyte can be any known electrolyte such an alkali metal salt or hydroxide, alkaline earth metal salt or rare earth metal salt, preferably carbonate salts are used as these are carbon dioxide rejecting.
• Suitable salts include sodium carbonate, sodium bicarbonate, and their mixtures, for example the electrolyte can be a buffered carbonate/bicarbonate solution.
• a typical pH is in the range of 10 to 11.
• the alkaline earth metal salts which can be used include caesium carbonate etc.
• the fuel cells of the present invention can be of the type which use an organic fuel and liquid water or an organic fuel and water vapour.
• the vapour can be generated in a heated container containing the fuel plus water vapour mixture and fed into the anode compartment of the fuel cell. This enables the fuel cell to operate at higher temperatures with corresponding increase in efficiency.
• Zeolite membranes which are hydrophilic can also allow water molecules and water vapour to pass through the membrane and prevent the passage of organic molecules.
• the liquid path length between the cathode and the anode is preferably reduced and this can be accomplished, for example, by having the zeolite membrane in contact with the anode or cathode or the zeolite membrane can be in substantial contact with the anode and cathode, so that a "sandwich" is formed comprising anode/zeolite membrane/cathode with the electrolyte substantially contained within the pores of the zeolite membrane.
• a separate zeo -type membrane can be used to prevent the escape of fuel vapour into the atmosphere e.g. from the anode compartment
• the membrane must be permeable to the waste products generated e.g. carbon dioxide and water, and impermeable to the fuel. This is particularly advantageous with volatile fuels such methanol and enables such fuel cells to operate at higher temperatures such as 80-90°C, without harmful gases escaping to the air or the risk of explosive mixtures being formed.
• zeolite membranes in fuel cells have technical advantages over the use of existing membranes.
• the zeolite membranes should be substantially crack free and should contain substantially no defects which will allow the passage of methanol molecules.
• Suitable zeolite membranes are described in co-pending patent applications PCT/GB 95/02221, PCT/GB 97/00635, PCT/GB 97/00928 and suitable electrodes are described in US Patent 5,470,073.
• the zeolite membranes are made by conventional gel methods as described in the above applications and their surface is treated with a silicic acid or other compound to remove defects.
• the membrane is from 0.1 ⁇ m to lOO ⁇ m thick.
• the pore cavity of the zeolite membrane is large enough to permit the passage of water molecules (2.6A°) but small enough to block the passage of the fuel molecules (3.8A°).
• a commonly proposed fuel is methanol
• other fuels can be used e.g. methanol, ethanol, formate esters such as ethyl formate, ethers such as methyl tertiary butyl ether and hydrocarbons and the pore size and/or the affinity for the electrolyte of the zeolite membrane can be adjusted accordingly to prevent passage of the fuel molecules.
• the presence of electrolyte through the pores of the membrane allows for ionic conductivity through the membrane and optionally the membrane can be treated to make it more conductive.
• the material from which the substantially acid resistant membrane can be made are preferably of low aluminium content, e.g. mordenite or chabazite or aluminium free zeo-type compounds such as silicalite, gallium phosphates, USY, EDY, FDY, NPI-5, LZ210 described in US Patent 4,711,770 and others or materials formed by selective de-alumination of aluminosilicates as described in US Patent 5,242,676, or by enriching aluminosilicates with silicon as described in US Patents 5,503,02A and 4,610,856A and EP82211A and as also described in D. W. Breck "Zeolite Molecular Sieves" 1974 page 503.
• mordenite or chabazite or aluminium free zeo-type compounds such as silicalite, gallium phosphates, USY, EDY, FDY, NPI-5, LZ210 described in US Patent 4,711,770 and others or materials formed by selective de-alumination of alum
• a membrane which is not acid resistant can be treated, for example, by passivating its surface, e.g. by forming a layer of an acid inert material on its surface, e.g. a layer of silica, yttria, zirconia, carbon, platinum, chromium, gold, or other acid resistant media.
• passivating its surface e.g. by forming a layer of an acid inert material on its surface, e.g. a layer of silica, yttria, zirconia, carbon, platinum, chromium, gold, or other acid resistant media.
• the pores of the membrane are too large, they can be "shrunk" by treatment with a sulphonic acid, e.g. a vinyl sulphonic acid or by a silicic acid or TEOS.
• a sulphonic acid e.g. a vinyl sulphonic acid or by a silicic acid or TEOS.
• the design of the fuel cells used in the present invention can be of any known design in which a membrane separates the anode and cathode compartments.
• the anodes and cathodes which can be used are any known anodes and cathodes.
• the invention relates to the replacement of the previously disclosed membrane with a zeolite membrane as described above. Preferred electrodes are described in Fuel cells Past Present and Future by A. Tseung ISBN 1861660677. Greenwich University Press 1998.
• Another type of fuel cell is a rechargeable fuel cell based on the dehydrogenation of a compound at the anode with diffusion of the hydrogen through a membrane to the cathode where it is oxidised electrochemically. On the charging cycle the process is reversed; this is in effect a method of storing hydrogen.
• the process has been proposed using cyclohexane which is reduced to benzene, however the membrane which was tried was silver-palladium membrane which was expensive and rendered the process impractical.
• the hydrogen can diffuse through the membrane without either cyclohexane or benzene diffusing through to the other compartment.
• the invention also provides a rechargeable fuel cell which comprises an anode compartment and a cathode compartment separated by a zeolite membrane and in which the anode compartment is adapted to contain a first compound in fluid form which is able to be dehydrogenated at the anode to generate an electric current which dehydrogenation reaction can be reversed by passing a current through the cell in the opposite direction to reform the first compound.
• the cathode can be an air electrode and, when the first compound is cyclohexane which is dehydrogenated to benzene, the zeolite membrane will prevent diffusion of the cyclohexane and benzene into the cathode compartment where they would poison the electrode, whilst still allowing the diffusion of hydrogen through the membrane.
• Another reaction which can be carried out by the use of the electrochemical reactor of the invention is the reduction of carbon dioxide to formic acid and methanol, the use of the zeolite membrane prevents the organic compounds from diffusing through to the anode compartment and oxidising the anode.
• anode (1) and cathode (2) are in contact with the acid electrolyte solution (3).
• Methanol or other fuel is in the anode compartment (4).
• Air (oxygen) is fed to the cathode compartment (5).
• the acid solution (6) is contained within the pores of the membrane (7).
• the reactions shown in the drawing take place.
• the use of the zeolite membranes of the invention prevent the passage of methanol or methanol vapour to the cathode whilst allowing conduction through the membranes by a salt bridge through the membrane..
• the apparatus of fig. 2 In order to test the acid resistance and ionic conductivity of zeolitic membranes the apparatus of fig. 2 was set up this comprises two glass chambers (11) and (12) between which is a zeolite membrane (15) sealed in place by silicone sealant (6) so that there is a passage between the two chambers only through membrane (15).
• a platinum counter electrode (17) In compartment (11) is a platinum counter electrode (17) and in chamber (12) is Teflon (RTM) PT/C cathode (14) and the chambers can be filled with electrolyte.
• RTM Teflon
• the apparatus was filled with 1 molar sulphuric acid at room temperature.
• the cathode gave 70 mA/cm 2 at 0.5V at 500mN vs RHE.
• the cathode performance decreased to 10 mA/cm 2 , indicating severe poisoning of oxygen reduction activity by methanol and ethyl formate.
• the test was repeated with a buffered Na2CO 3 /NaHCO electrolyte.
• the membrane was prepared as in Example 3 of PCT/GB95/02221 and was 20 microns thick, the membrane was soaked in the electrolyte solution and its properties measured.
• the anode was teflon bonded with a thin layer of Nafion dispersion and the distance of the Luggin tip to the working electrode was ⁇ 2mm.
• the cathode was teflon bonded and with no zeolite membrane and in the absence of CH 3 OH gave 0.7 V 20mA cm “2 in still air, lMCH 3 OH was added and the performance dropped to 0.3V 20mA cm " due to the poisoning of the of the oxygen reduction reaction and the short circuit current generation between the Pt and C sites for the oxidation of methanol.
• the membrane was prepared by depositing the zeolite membrane onto the cathode and pasting the anode catalyst and nickel screen on the zeolite membrane surface, the full cell performance gave 0.25V at 20mA/cm2 and the performance was stable over a test of 3 hours at 60°C.
• Fig. 3 shows plot of current density on the air cathode against time with and without methanol in which :-

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Electrochemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Sustainable Energy (AREA)
• Sustainable Development (AREA)
• Manufacturing & Machinery (AREA)
• Life Sciences & Earth Sciences (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Fuel Cell (AREA)
• Inert Electrodes (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)

Applications Claiming Priority (5)

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• 1998
  • 1998-05-14 KR KR1019997010480A patent/KR20010012525A/ko not_active Withdrawn
  • 1998-05-14 AU AU74399/98A patent/AU741520B2/en not_active Ceased
  • 1998-05-14 EP EP98921610A patent/EP0986832A1/de not_active Ceased
  • 1998-05-14 CN CN98804972A patent/CN1255248A/zh active Pending
  • 1998-05-14 JP JP54893098A patent/JP2002500806A/ja active Pending
  • 1998-05-14 WO PCT/GB1998/001380 patent/WO1998052243A1/en not_active Ceased
  • 1998-05-14 CA CA002289607A patent/CA2289607A1/en not_active Abandoned

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