WO1996035003A1 - Element electrochimique a couche autoregulatrice de diffusion gazeuse - Google Patents

Element electrochimique a couche autoregulatrice de diffusion gazeuse Download PDF

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Publication number
WO1996035003A1
WO1996035003A1 PCT/US1995/016125 US9516125W WO9635003A1 WO 1996035003 A1 WO1996035003 A1 WO 1996035003A1 US 9516125 W US9516125 W US 9516125W WO 9635003 A1 WO9635003 A1 WO 9635003A1
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Prior art keywords
electrochemical cell
electrode
cathode
diffusion layer
anode
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PCT/US1995/016125
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English (en)
Inventor
Dennie Turin Mah
Clarence Garlan Law, Jr.
John Scott Newman
Douglas John Eames
James Arthur Trainham, Iii
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E.I. Du Pont De Nemours And Company
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Priority to AU44215/96A priority Critical patent/AU4421596A/en
Publication of WO1996035003A1 publication Critical patent/WO1996035003A1/fr

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/023—Porous and characterised by the material
    • H01M8/0234—Carbonaceous material
    • 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
    • C25B15/00—Operating or servicing cells
    • C25B15/08—Supplying or removing reactants or electrolytes; Regeneration of 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
    • 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
    • C25B9/23—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms comprising ion-exchange membranes in or on which electrode material is embedded
    • 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
    • H01M8/1004—Fuel cells with solid electrolytes characterised by membrane-electrode assemblies [MEA]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0065—Solid electrolytes
    • H01M2300/0082—Organic polymers
    • 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 electro ⁇ chemical cell and process for converting essentially anhydrous hydrogen halide to essentially dry halogen gas.
  • the process of the present invention is useful for converting anhydrous hydrogen halide, in particular, hydrogen chloride, hydrogen fluoride, hydrogen bromide and hydrogen iodide, to a halogen gas, such as chlorine, fluorine, bromine, or iodine.
  • the electro ⁇ chemical cell has a mass flow field that increases the diffusion resistance of a fluid within either a cathode or an anode compartment of the cell.
  • Hydrogen chloride (HC1) or hydrochloric acid is a reaction by-product of many manufacturing processes which use chlorine.
  • chlorine is used to manufacture polyvinyl chloride, isocyanates, and chlorinated hydrocarbons/fluorinated hydrocarbons, with hydrogen chloride as a by-product of these processes.
  • supply so exceeds demand hydrogen chloride or the acid produced often cannot be sold or used, even after careful purification.
  • Shipment over long distances is not economically feasible.
  • Discharge of the acid or chloride ions into waste water streams is environmentally unsound. Recovery and feedback ' of the chlorine to the manufacturing process is the most desirable route for handling the HCl by-product.
  • the current electrochemical commercial process is known as the Uhde process.
  • aqueous HCl solution of approximately 22% is fed at 65° to 80° C to both compartments of an electrochemical cell, where exposure to a direct current in the cell results in an electrochemical reaction and a decrease in HCl concentration to 17% with the production of chlorine gas and hydrogen gas.
  • a polymeric separator divides the two compartments.
  • the process requires recycling of dilute (17%) HCl solution produced during the electrolysis step and regenerating an HCl solution of 22% for feed to the electrochemical cell.
  • the overall reaction of the Uhde process is expressed by the equation:
  • the chlorine gas produced by the Uhde process is wet, usually containing about 1% to 2% water. This wet chlorine gas must then be further processed to produce a dry, usable gas. If the concentration of HCl in the water becomes too low, it is possible for oxygen to be generated from the water present in the Uhde process. This possible side reaction of the Uhde process due to the presence of water, is expressed by the equation: 2H 2 0 ___. o 2 + 4H + + 4e ⁇
  • the presence of water in the Uhde system limits the current densities at which the cells can perform to less than 500 amps./ft. 2 , because of this side reaction.
  • the side reaction results in reduced electrical efficiency and corrosion of the cell components.
  • Balko employs an electrolytic cell having a solid polymer electrolyte membrane. Hydrogen chloride, in the form of hydrogen ions and chloride ions in aqueous solution, is introduced into an electrolytic cell. The solid polymer electrolyte membrane is bonded to the anode to permit transport from the anode surface into the membrane. In Balko, controlling and minimizing the oxygen evolution side reaction is an important consideration. Evolution of oxygen decreases cell efficiency and leads to rapid corrosion of components of the cell. The design and configuration of the anode pore size and electrode thickness employed by Balko maximizes transport of the chloride ions.
  • Limiting current density occurs when the concentration of water within the membrane reaches a value that will no longer support additional proton conduction. Therefore, limiting current density can develop when the conductivity decreases due to low water concentrations. It is important to regulate limiting current so that the components of the cell are not destroyed.
  • the present invention solves the problems of the prior art by providing an electrochemical cell and process for directly producing essentially dry halogen gas from essentially anhydrous hydrogen halide.
  • This cell and process process allows for direct processing of anhydrous hydrogen halide which is a by-product of manufacturing processes, without first dissolving the hydrogen halide in water.
  • This direct production of essentially dry halogen gas when done, for example, for chlorine gas, is less capital intensive than processes of the prior art, which require separation of water from the chlorine gas.
  • This direct production of essentially dry halogen gas also requires lower investment costs than the electro ⁇ chemical conversions of hydrogen chloride of the prior art.
  • the present invention increases the diffusion resistance of the fluid in the electrode compartment of an electrochemical cell.
  • a self-regulating cell is established with respect to the maximum steady-state current which the cell may draw.
  • this allows an electrochemical cell to be designed in which a valuable component, such as the cation-exchange membrane, is protected from prolonged exposure to excessive current, which could deteriorate the membrane, and thus impact the membrane's and the cell's long-term performance.
  • an electrochemical cell comprising an electrode having a catalyst layer, a gas diffusion layer and an electrode compartment for containing a fluid therein; a membrane disposed in contact with one side of the electrode; a mass flow field disposed on the other side of the electrode for directing fluid to and away from the electrode; and means disposed between the electrode and the mass flow field for increasing the diffusion resistance of the fluid.
  • the means for increasing the diffusion resistance comprises an additional gas diffusion layer.
  • the electro ⁇ chemical cell comprises means for oxidizing molecules of essentially anhydrous hydrogen halide to produce essentially dry halogen gas and protons; cation- transporting means for transporting the protons therethrough, where the oxidizing means is disposed in contact with one side of the cation-transporting means; means for reducing the transported protons, wherein the reducing means is disposed in contact with the other side of the cation-transporting means and the reducing means has a compartment for containing fluid therein; a flow field disposed on the other side of the reducing meansf for directing fluid to and away from the reducing means; and means disposed between the reducing means and the flow field for increasing the diffusion resistance of the fluid.
  • Fig. 1 is an exploded cross-sectional view of an electrochemical cell for producing halogen gas from anhydrous hydrogen halide according to a first and a second embodiment of the present invention.
  • Fig. IA is a cut-away, top cross-sectional view of the anode and cathode mass flow fields as shown in Fig. 1.
  • Fig. 2 is a perspective view of an electro- chemical cell for producing, for example, halogen gas from aqueous hydrogen halide according to a third embodiment of the present invention.
  • an electrochemical cell for the direct production of essentially dry halogen gas from anhydrous hydrogen halide.
  • a cell is shown generally at 10 in Fig. 1.
  • the cell of the present invention will be described with respect to a preferred embodiment of the present invention, which directly produces essentially dry chlorine gas from anhydrous hydrogen chloride.
  • This cell may alternatively be used to produce other halogen gases, such as bromine, fluorine and iodine from a respective anhydrous hydrogen halide, such as hydrogen bromide, hydrogen fluoride and hydrogen iodide.
  • the term "direct” means that the electrochemical cell obviates the need to remove water from the halogen gas produced or the need to convert essentially anhydrous hydrogen halide to aqueous hydrogen halide before electrochemical treatment.
  • chlorine gas, as well as hydrogen is produced in this cell.
  • water, as well as chlorine gas is produced by this cell, as will be explained more fully below.
  • the electrochemical cell of the first and second embodiments comprises an electrode.
  • the electrochemical cell of the first and second embodiments may be described as comprising means for oxidizing molecules of essentially anhydrous hydrogen halide to produce essentially dry halogen gas and protons.
  • the oxidizing means is an electrode, or more specifically, an anode 12 as shown in Fig. 1.
  • electrochemical cell 10 On the anode side, electrochemical cell 10 has an anode-side inlet 14 and an anode-side outlet 16.
  • the electrochemical cell of the first and second embodiments also comprises cation-transporting means for transporting the protons therethrough, where one side of the oxidizing means is disposed in contact with one side of the cation-transporting means.
  • the cation-transporting means is a cation- transporting membrane 18 as shown in Fig.
  • membrane 18 may be a proton-conducting membrane.
  • Membrane 18 may be a commercial cationic membrane made of a fluoro- or perfluoropolymer, preferably a copolymer of two or more fluoro or perfluoromonomers, at least one of which has pendant sulfonic acid groups.
  • carboxylic groups is not desirable, because those groups tend to decrease the conductivity of the membrane when they are protonated.
  • Various suitable resin materials are available commercially or can be made according to patent literature.
  • the sulfonyl fluoride groups can be hydrolyzed with potassium hydroxide to -S0 3 K groups, which then are exchanged with an acid to -S0 3 H groups.
  • Suitable cationic membranes which are made of hydrated, copolymers of polytetrafluoroethylene and poly-sulfonyl fluoride vinyl ether-containing pendant sulfonic acid groups, are offered by DuPont under the trademark "NAFION" (hereinafter referred to as NAFION ® ) .
  • NAFION ® membranes containing pendant sulfonic acid groups include NAFION ® 117,
  • NAFION ® 324 and NAFION ® 417 are both supported and has an equivalent weight of 1100 g., equivalent weight being defined as the amount of resin required to neutralize one liter of a 1M sodium hydroxide solution.
  • the other two types of NAFION ® are both supported on a fluorocarbon fabric, the equivalent weight of NAFION ® 417 also being 1100 g.
  • NAFION ® 324 has a two-layer structure, a 125 ⁇ m-thick membrane having an equivalent weight of 1100 g., and a 25 ⁇ m-thick membrane having an equivalent weight of 1500 g.
  • NAFION ® 117F grade is a precursor membrane having pendant -S0 2 F groups that can be converted to sulfonic acid groups.
  • NAFION ® 117F grade is a precursor membrane having pendant -S0 2 F groups that can be converted to sulfonic acid groups.
  • the present invention describes the use of a solid polymer electrolyte membrane, it is well within the scope of the invention to use other cation- transporting membranes which are not polymeric.
  • proton-conducting ceramics such as beta- alumina may be used.
  • Beta-alumina is a class of nonstoichiometric crystalline compounds having the general structure Na 2 O x *Al 2 0 3 , in which x ranges from 5 ( ⁇ "-alumina) to 11 ( ⁇ -alumina) .
  • the electrochemical cell of the first and second embodiments also comprises an electrode, or a cathode 20.
  • the electrochemical cell of the first and second embodiments may be described as comprising means for reducing the transported protons, where the reducing means is disposed in contact with the other side of the cation-transporting means.
  • the reducing means comprises a cathode 20, where cathode 20 is disposed in contact with the other side (as opposed to the side which is in contact with the anode) of membrane 18 as illustrated in Fig. 1.
  • Cathode 20 has a cathode-side inlet 24 and a cathode- side outlet 26 as shown in Fig. 1.
  • the cathode inlet and the outlet may be lined with TEFLON ® PFA.
  • cationic charges are transported through the membrane from anode to cathode, while each electrode carries out a half-cell reaction.
  • molecules of anhydrous hydrogen chloride are transported to the surface of the anode through anode- side inlet 14.
  • the molecules of the anhydrous hydrogen chloride are oxidized to produce essentially dry chlorine gas and protons.
  • the essentially dry chlorine gas exits through anode-side outlet 16 as shown in Fig. 1.
  • the protons, H + are transported through the membrane and reduced at the cathode. This is explained in more detail below.
  • the anode and the cathode may comprise porous, gas-diffusion electrodes. Such electrodes provide the advantage of high specific surface area, as known to one skilled in the art.
  • the anode and the cathode comprise an electrochemically active material disposed adjacent, meaning at or under, the surface of the cation-transporting membrane. A thin film of the electrochemically active material may be applied directly to the membrane. Alternatively, the electrochemically active material may be hot-pressed to the membrane, as shown in A. J. Appleby and E. B. Yeager, Energy, Vol. 11, 137 (1986). Alternatively, the electrochemically active material may be deposited into the membrane, as shown in U.S. Patent No. 4,959,132 to Fedkiw.
  • the electrochemically active material may comprise any type of catalytic or metallic material or metallic oxide, as long as the material can support charge transfer.
  • the electrochemically active material may comprise a catalyst material such as platinum, ruthenium, osmium, rhenium, rhodium, iridium, palladium, gold, titanium or zirconium and the oxides, alloys or mixtures thereof.
  • the oxides of these materials are not used for the cathode.
  • Other catalyst materials suitable for use with the present invention may include, but are not limited to, transition metal macro cycles in monomeric and polymeric forms and transition metal oxides, including perovskites and pyrochores.
  • the electrochemically active material may comprise a catalyst material on a support material.
  • the support material may comprise particles of carbon and particles of polytetrafluoro ⁇ ethylene, which is sold under the trademark "TEFLON” (hereinafter referred to as TEFLON ® ) , commercially available from DuPont.
  • the electrochemically active material may be bonded by virtue of the TEFLON ® to a support structure, or gas diffusion layer, of carbon paper or graphite cloth and hot-pressed to the cation- transporting membrane.
  • the hydrophobic nature of TEFLON ® does not allow a film of water to form at the anode. A water barrier in the electrode would hamper the diffusion of HCl to the reaction sites.
  • the electrodes are preferably hot-pressed into the membrane in order to have good contact between the catalyst and the membrane.
  • the loadings of electrochemically active material may vary based on the method of application to the membrane.
  • Hot-pressed, gas-diffusion electrodes typically have loadings of 0.10 to 0.50 mg/cm 2 .
  • Lower loadings are possible with other available methods of deposition, such as distributing them as thin films from inks onto the membranes, as described in Wilson and Gottesfeld, "High Performance Catalyzed Membranes of Ultra-low Pt Loadings for Polymer Electrolyte Fuel Cells", Los Alamos National Laboratory, J. Electro- chem. Soc, Vol. 139, No.
  • the electrochemical cell of the first and second embodiments further comprises an anode flow field 28 disposed in contact with the anode and a cathode flow field 30 disposed in contact with the cathode.
  • the flow fields are electrically conductive, and act as both mass and current flow fields. More specifically, the mass flow fields may include a plurality of anode flow channels 29 and a plurality of cathode flow channels 31 as shown in Fig. IA.
  • Anode flow field and channels 29 direct reactants, such as anhydrous HCl in the first and second embodiments, to the anode and products, such as essentially dry chlorine gas from the anode.
  • Cathode flow field 30 and channels 31 direct catholyte, such as liquid water in the first embodiment, or oxygen gas in the second embodiment, to the cathode and products, such as hydrogen gas in the first embodiment, . or water vapor (H 2 0(g)) in the second embodiment, from the cathode.
  • Catholyte such as liquid water in the first embodiment, or oxygen gas in the second embodiment
  • products such as hydrogen gas in the first embodiment, . or water vapor (H 2 0(g)) in the second embodiment
  • Water vapor may be needed to keep the membrane hydrated. However, . water vapor may not be necessary in this embodiment because of the water produced by the electrochemical reaction of the oxygen (0 2 ) added as discussed below.
  • the anode and the cathode mass flow fields may comprise grooved porous graphite paper.
  • the flow fields may also be made of a porous carbon in the form of a foam, cloth or matte.
  • the electrochemical cell of the first and second embodiments may also comprise an anode mass flow manifold 32 and a cathode mass flow field manifold 34 as shown in Fig. 1.
  • the purpose of such manifolds is to bring anolyte to and products from the anode, and catholyte to and products from the cathode.
  • the manifolds form a frame around the anode mass flow field and the anode, and the cathode mass flow field and the cathode, respectively.
  • These manifolds are preferably made of a corrosion resistant material, such TEFLON ® PFA.
  • a gasket 36, 38 also contributes to forming a frame around the respective anode and cathode mass flow fields.
  • These gaskets are preferably also made of a corrosion resistant material, such as polytetrafluoroethylene, sold under the trademark TEFLON ® PTFE by DuPont.
  • molecules of essentially anhydrous hydrogen halide are fed to the inlet of the cell and are transported to the anode.
  • the molecules of the essentially anhydrous hydrogen halide are oxidized at the anode to produce essentially dry halogen gas and protons.
  • the current supplied to the cell causes the protons to be transported through the cation-transporting membrane, and the transported protons are reduced at the cathode.
  • Water, as either liquid water in the first embodiment, or an oxygen-containing gas in the second embodiment, is supplied to the membrane at the cathode and is transported by diffusion towards the anode. The transported protons drag the water in the membrane towards the cathode.
  • the amount of current required to achieve a balance between the water transported by diffusion toward the anode and dragged by the proton transport toward the cathode is controlled by adjusting the amount of water supplied to the membrane. Limiting current occurs when this balance is achieved. It is important to regulate limiting current so that the components of the cell are not destroyed.
  • the electrochemical cell of the present invention includes means for increasing the diffusion resistance of the fluid which is directed to and away from the electrode by the mass flow field.
  • the electrodes of the present invention comprise a catalyst layer.
  • the electrodes comprise a gas diffusion layer, disposed in contact with the catalyst layer on the side of the catalyst layer facing away from the membrane. Applicants have found that by increasing (or conversely decreasing) the thickness of the gas diffusion layer, the diffusion resistance of the water in the cathode compartment may be increased (or conversely decreased) .
  • the diffusion resistance means of the present invention comprises an additional gas diffusion layer 33 as shown in Fig. 1.
  • the additional diffusion layer of the present invention increases limiting current by increasing the amount of current required to achieve a balance between the water transported by diffusion toward the anode and dragged by the proton transport toward the cathode. This protects the membrane by controlling the amount of water in the membrane, internally within the cell.
  • the additional diffusion layer is self- regulating in that, by its inclusion, the cell of the present invention will achieve this balance on its own, without having to externally adjust the amount of water supplied to the membrane.
  • Increasing the diffusion resistance of the fluid in the electrode compartment is especially important at the cathode, where all the water in the cathode compartment has to go through the diffusion layer. It is also possible to place the additional diffusion layer on the anode side, although this is not shown. However, this is not preferable in the first and second embodiments, as it could limit the access of the hydrogen halide to the catalyst.
  • the gas diffusion layer of the electrode is usually made of carbon paper or graphite cloth.
  • the additional gas diffusion layer may also be made of carbon paper or graphite paper or cloth.
  • the additional gas diffusion layer may be made of any porous conductive material. It should be noted that the use of an additional gas diffusion layer is useful with an electrochemically active material which is disposed at or under the surface of the cation- transporting membrane, which is applied directly to the membrane, or which is hot-pressed to the membrane.
  • the diffusion resistance may also be adjusted by adjusting the hydrophobicity of the gas diffusion layer of the electrode and/or of the additional gas diffusion layer.
  • the diffusion resistance may also be adjusted by changing the porosity of the gas diffusion layer of the electrode and/or of the additional gas diffusion layer.
  • the flow channels may face away from the anode or the cathode, respectively, so that the valley floor of the channel provides the additional thickness to achieve the same result. When this is done, the flow channels may be differentially spaced.
  • the electrochemical cell of the first and second embodiments also comprises an anode current bus 46 and a cathode current bus 48 as shown in Fig. 1.
  • the current buses conduct current to and from a voltage source (not shown) .
  • anode current bus 46 is connected to the positive terminal of a voltage source
  • cathode current bus 48 is connected to the negative terminal of the voltage source, so that when voltage is supplied to the cell, current flows through all of the cell components to the right of current bus 46 as shown in Fig. 1, including current bus 48, from which it returns to the voltage source.
  • the current buses are made of a conductor material, such as copper.
  • the electrochemical cell of the first and second embodiments further comprises a current distributor disposed in contact with the flow field.
  • An anode current distributor 40 is disposed in contact with anode flow field 28, and a cathode current distributor 42 is disposed in contact with cathode flow field 30.
  • the anode current distributor collects current from the anode bus and distributes it to the anode by electronic conduction.
  • the cathode current distributor collects current from the cathode and distributes it to the cathode bus.
  • the anode and the cathode current distributors preferably each comprise a non-porous layer.
  • the anode current distributor provides a barrier between the anode current bus and the anode, and the anhydrous hydrogen halide, such as hydrogen chloride, and the halogen gas, such as chlorine.
  • the cathode current distributor provides a barrier between the cathode current bus and the cathode and the hydrogen halide. This barrier is desirable, as there is some migration of hydrogen halide through the membrane.
  • the current distributors of the present invention may be made of a variety of materials, and the material used for the anode current distributor need not be the same as the material used for the cathode current distributor.
  • the anode current distributor is made of platinized tantalum
  • the cathode current distributor is made of a nickel-based alloy, such as UNS10665, sold as HASTELLOY ® B-2, by Haynes, International.
  • the electrochemical cell also comprises a conductive structural support 44 disposed in contact with anode current distributor 40.
  • the support on the anode side is preferably made of UNS31603 (316L stainless steel) .
  • a seal 45 preferably in the form of an O-ring made from a perfluoroelastomer, sold under the trademark KALREZ® by DuPont, ' is disposed between structural support 44 on the anode side and anode current distributor 40.
  • the cathode current distributor acts as a corrosion-resistant structural backer on the cathode side. This piece can be drilled and tapped to accept the TEFLON ® PFA fitting, which is used for the inlet and outlet.
  • a bipolar arrangement as familiar to one skilled in the art, is preferred.
  • the electrochemical cell of the present invention may be used in a bipolar stack.
  • current distributors 40 and 42 and all the elements disposed in between as shown in Fig. 1 are repeated along the length of the cell, and current buses are placed on the outside of the stack.
  • the anhydrous hydrogen halide may comprise hydrogen chloride, hydrogen bromide, hydrogen fluoride or hydrogen iodide.
  • hydrogen fluoride may be particularly corrosive when used with the present invention.
  • the production of bromine gas and iodine gas can be accomplished when the electrochemical cell is run at elevated temperatures (i.e., about 60 C and above for bromine and about 190° C and above for iodine) .
  • a membrane made of a material other than NAFION ® should be used.
  • anhydrous hydrogen halide is hydrogen chloride.
  • current flows to the anode bus and anode current distributor 40 collects current from the anode bus and distributes it to the anode by electronic conduction.
  • Molecules of essentially anhydrous hydrogen chloride gas are fed to anode-side inlet 14 and through flow channels 29 in the anode mass flow field 28 and are transported to the surface of anode 12.
  • the protons (H + ) are transported through the membrane, which acts as an electrolyte.
  • the transported protons are reduced at the cathode.
  • Water is delivered to the cathode through cathode-side inlet 24 and through the grooves in cathode flow field 30 to hydrate the membrane and thereby increase the efficiency of proton transport through the membrane.
  • the hydrogen which is evolved at the interface between the electrode and the membrane exits via cathode-side outlet 26 as shown in Fig. 1.
  • the hydrogen bubbles through the water and is not affected by the TEFLON ® in the electrode.
  • Cathode current distributor 42 collects current from cathode 20 and distributes it to cathode bus 46.
  • anhydrous hydrogen halide is hydrogen chloride.
  • current flows to the anode bus and anode current distributor 40 collects current from the anode bus and distributes it to the anode by electronic conduction.
  • Molecules of essentially anhydrous hydrogen chloride are fed to anode-side inlet 14 and are transported through grooves of anode mass flow field 28 to the surface of anode 12.
  • An oxygen- containing gas such as oxygen (0 2 (g), air or oxygen- enriched air (i.e., greater than 21 mol% oxygen in nitrogen) is introduced through cathode-side inlet 24 and through the grooves formed in cathode mass flow field 30.
  • oxygen such as oxygen (0 2 (g)
  • air or oxygen- enriched air i.e., greater than 21 mol% oxygen in nitrogen
  • This cathode feed gas may be humidified to aid in the control of moisture in the membrane.
  • Molecules of the hydrogen chloride (HCl(g)) are oxidized under the potential created by the voltage source to produce essentially dry chlorine gas at the anode, and protons (H + ) , as expressed in equation (4) above.
  • the chlorine gas (Cl ) exits through anode-side outlet 16 as shown in Fig. 1.
  • the protons (H + ) are transported through the membrane, which acts as an electrolyte. Oxygen and the transported protons are reduced at the cathode
  • the water formed exits via cathode-side outlet 26 as shown in Fig. 1, along with any nitrogen and unreacted oxygen.
  • the water also helps to maintain hydration of the membrane, as will be further explained below.
  • Cathode current distributor 42 collects current from cathode 20 and distributes it to cathode bus 48.
  • the cathode reaction is the formation of water.
  • This cathode reaction has the advantage of more favorable thermodynamics relative to H production at the cathode as in the first embodiment. This is because the overall reaction in this embodiment, which is expressed by the following equation:
  • the membrane of both the first and the second embodiments in the anhydrous case must be hydrated in order to have efficient proton transport.
  • the cathode-side of the membrane must be kept hydrated in order to increase the efficiency of proton transport through the membrane.
  • the hydration of the membrane is obtained by keeping liquid water in contact with the cathode. The liquid water passes through the gas-diffusion electrode and contacts the membrane.
  • the membrane hydration is accomplished by the production of water as expressed by equation (6) above and by the water introduced in a humidified oxygen-feed or air-feed stream. This keeps the conductivity of the membrane high.
  • the electrochemical cell of the present invention can be operated over a wide range of temperatures.
  • Room temperature operation is an advantage, due to the ease of use of the cell.
  • operation at elevated temperatures provides the advantages of improved kinetics and increased electrolyte conductivity.
  • Higher temperatures result in lower cell voltages.
  • limits on temperature occur because of the properties of the materials used for elements of the cell.
  • the properties of a NAFION ® membrane change when the cell is operated above 120° C.
  • the properties of a polymer electrolyte membrane make it difficult to operate a cell at temperatures above 150° C. With a membrane made of other materials, such as a ceramic material like beta- alumina, it is possible to operate a cell at temperatures above 200° C.
  • Fig. 2 illustrates a third embodiment of the present invention.
  • elements corresponding to the elements of the embodiment of Fig. 1 will be shown with the same reference numeral as in Fig. 1, but will be designated with a prime (').
  • An electrochemical cell of the third embodiment is shown generally at 10' in Fig. 2.
  • the electrochemical cell of the third embodiment will be described with respect to a preferred embodiment, where halogens, such as chlorine, are generated by the electrolysis of an aqueous solution of a hydrogen halide, such as hydrochloric acid.
  • halogens such as chlorine
  • hydrochloric acid such as hydrochloric acid
  • this cell could be used as a fuel cell.
  • the electrochemical cell of the third embodiment comprises an electrode, or more specifically, an anode 12'.
  • the electrochemical cell of the third embodiment also comprises a membrane disposed in contact with one side of the electrode.
  • a membrane 18' is shown in Fig. 2 having one side disposed in contact with one side of anode 12* .
  • the membrane need not necessarily be a cation-transporting membrane.
  • the electrochemical cell of the third embodiment also comprises an electrode, or more specifically, a cathode 20', where cathode 20' is disposed in contact with the other side (as opposed to the side which is in contact with the anode) of membrane as illustrated in Fig. 2.
  • the electrochemical cell of the third embodiment further comprises a mass flow field disposed in contact with the electrode.
  • the mass flow field may be an anode mass flow field 28' disposed in contact with the anode, or a cathode mass flow field 30' disposed in contact with the cathode.
  • the mass flow fields act as both mass and current flow fields.
  • the purpose of the anode flow field is to get anolyte, such as aqueous HCl in the third embodiment to the anode and products, such as wet chlorine gas, from the anode.
  • the purpose of the cathode flow field is to get catholyte to and product, such as hydrogen gas, from the cathode. More specifically, the mass flow fields include flow channels 29' and 31' as shown in Fig. 2.
  • the electrochemical cell of the third embodiment also includes an additional gas diffusion layer 33' as shown in Fig. 2.
  • This additional diffusion layer increases the gas diffusion resistance of the fluid in the electrode compartment, as described above for the first two embodiments.
  • additional gas diffusion layer 33' may be disposed between the cathode and the cathode flow field, or between the anode and the anode flow field, although it is only shown on the cathode side.
  • the electrochemical cell of the third embodiment also comprises a current bus for conducting current to the electrode, where the current bus is disposed on the other side of the electrode.
  • An anode current bus 46' and a cathode current bus 48' are shown in Fig. 2.
  • the current buses conduct current from a voltage source (not shown) .
  • the current buses of the third embodiment are made of a conductor material, such as copper.
  • the electrochemical cell of the third embodiment further comprises a current distributor disposed on one side of the electrode.
  • An anode current distributor 40' is disposed on one side of anode 12', and a cathode current distributor 42' is disposed on one side of cathode 20*.
  • the anode current distributor collects current from the anode bus and distributes to the anode by electronic conduction.
  • the cathode current distributor collects current from the cathode and distributes it to the cathode bus.
  • the anode and the cathode current distributors preferably each comprise a non-porous layer.
  • the anode current distributor provides a barrier between the anode current bus and the anode, and also the reactant, such as aqueous hydrogen chloride and the produce, such as wet gaseous chlorine.
  • the cathode current distributor provides a barrier between the cathode current bus and the cathode, and also the catholyte.
  • the current distributors of third embodiment may be made of a variety of materials, and the material used for the anode current distributor need not be the same as the material used for the cathode current distributor. The choice of material would depend on the choice of anolte and catholyte.
  • cationic charges are transported through the membrane from anode to cathode, while each electrode carries out a half-cell reaction.
  • hydrochloric acid which is introduced at arrow 14', which indicates the anode-side inlet, is electrolyzed at anode 12' to produce gaseous chlorine, which exits at arrow 16', which represent the anode-side outlet, and hydrogen ions (H + ) .
  • the H + ions are transported across membrane 18', to cathode 20' along with some water and some hydrochloric acid.
  • the hydrogen ions are discharged at the cathode through a cathode-side outlet 24'.
  • the invention will be clarified by the following Examples, which are intended to be purely examplary of the invention.
  • the electrode/membrane assemblies used in the following Examples are commercially available from Giner, Inc. of Waltham, Massachusetts, as membrane and electrode assemblies containing 0.33 mg. of ruthenium oxide per cm. 2 and integrally bonded to a NAFION ® 117 membrane in the H + form.
  • EXAMPLE 1 A 315 square centimeter (i.e., 7 in. x 7 in.) electrolytic cell having a NAFION ® 117 membrane electrode assembly (MEA) was assembled with an additional gas diffusion layer having a thickness of 0.020 in.
  • the additional gas diffusion layer was made of graphite paper.
  • the MEA cathode catalyst was supported on a support structure, or layer, of graphite paper which had a thickness of 0.003 in.
  • the combined gas diffusion layer was equal to 0.023 in.
  • Anhydrous HCl was fed to the anode-side inlet of the cell while deionized water was fed to the cathode-side inlet.
  • the maximum current which could be sustained was 60 A (180 ASF) .
  • the current drawn by the electrochemical cell became self regulating. That is, when either or both the anhydrous HCl gas feedor the applied cell voltage were increased, the cell current initially rose anywhere from 75 to 105 A, and then returned to a constant current of 60 A in less than one hour without any intervention.
  • EXAMPLE 2 In a control example, when a similar electro ⁇ chemical cell was assembled having only a cathode catalyst support layer, or structure, of 0.010 in. and no additional cathode graphite paper gas diffusion layer, the electrochemical cell drew up to 300 A (900 ASF) at 2.25 VDC and an anhydrous HCl feed rate equal to or in excess of the stoichiometric amount.
  • 300 A 900 ASF
  • anhydrous HCl feed rate equal to or in excess of the stoichiometric amount.
  • an electrochemical cell may be designed in which a valuable component such as the cation-exchange membrane is protected from prolonged exposure to excessive current, which could deteriorate the membrane and impact the membrane, and thus the cell's, long term performance. Additional advantages and modifications will readily occur to those skilled in the art.
  • the invention in its broader aspects, is, therefore, not limited to the specific details, representative apparatus and illustrative Examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

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Abstract

L'invention porte sur un élément électrochimique présentant une couche de catalyseur et une couche de diffusion de gaz ainsi qu'un champ d'écoulement massique (30) dirigeant le fluide vers l'électrode ou l'en éloignant. Un couche additionnelle de diffusion de gaz (33) située entre la couche de diffusion de gaz (20) et le champ d'écoulement (30) accroît la résistance du fluide à la diffusion. L'élément électrochimique objet de cette invention s'avère particulièrement utile dans un processus de conversion électrochimique d'halogénure anhydre d'hydrogène en un halogène gazeux sensiblement sec lorsqu'il est nécessaire de réguler et d'accroître le courant limiteur. Il est également possible de recourir à une couche additionnelle de diffusion de gaz dans un élément électrochimique à processus aqueux.
PCT/US1995/016125 1995-05-01 1995-12-13 Element electrochimique a couche autoregulatrice de diffusion gazeuse WO1996035003A1 (fr)

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US08/432,388 1995-05-01

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998045503A1 (fr) * 1997-04-07 1998-10-15 The Dow Chemical Company Electrolyse de saumures d'halogenures de metaux alcalins effectuee au moyen de systemes cathodiques comprenant de l'oxygene
WO2001078174A1 (fr) * 2000-04-05 2001-10-18 Forschungszentrum Jülich GmbH Pile a combustible a couche de diffusion
GB2403166A (en) * 2003-06-25 2004-12-29 Accentus Plc Electrodeionisation process
CN113981479A (zh) * 2020-07-09 2022-01-28 中国科学院大连化学物理研究所 一种具有内部气水分离功能的水电解双极板

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4247376A (en) * 1979-01-02 1981-01-27 General Electric Company Current collecting/flow distributing, separator plate for chloride electrolysis cells utilizing ion transporting barrier membranes
GB2073251A (en) * 1980-04-02 1981-10-14 Gen Electric Anode for reducing oxygen generation in the electrolysis of hydrogen chloride
AT389020B (de) * 1986-08-08 1989-10-10 Peter Dipl Ing Dr Schuetz Brennstoffzelle
US5399184A (en) * 1992-05-01 1995-03-21 Chlorine Engineers Corp., Ltd. Method for fabricating gas diffusion electrode assembly for fuel cells

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4247376A (en) * 1979-01-02 1981-01-27 General Electric Company Current collecting/flow distributing, separator plate for chloride electrolysis cells utilizing ion transporting barrier membranes
GB2073251A (en) * 1980-04-02 1981-10-14 Gen Electric Anode for reducing oxygen generation in the electrolysis of hydrogen chloride
AT389020B (de) * 1986-08-08 1989-10-10 Peter Dipl Ing Dr Schuetz Brennstoffzelle
US5399184A (en) * 1992-05-01 1995-03-21 Chlorine Engineers Corp., Ltd. Method for fabricating gas diffusion electrode assembly for fuel cells

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998045503A1 (fr) * 1997-04-07 1998-10-15 The Dow Chemical Company Electrolyse de saumures d'halogenures de metaux alcalins effectuee au moyen de systemes cathodiques comprenant de l'oxygene
WO2001078174A1 (fr) * 2000-04-05 2001-10-18 Forschungszentrum Jülich GmbH Pile a combustible a couche de diffusion
GB2403166A (en) * 2003-06-25 2004-12-29 Accentus Plc Electrodeionisation process
GB2403166B (en) * 2003-06-25 2006-11-01 Ipsolutions Electrodeionisation process
CN113981479A (zh) * 2020-07-09 2022-01-28 中国科学院大连化学物理研究所 一种具有内部气水分离功能的水电解双极板
CN113981479B (zh) * 2020-07-09 2022-12-02 中国科学院大连化学物理研究所 一种水电解装置

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