WO1996035000A1 - Element electrochimique a champ de flux massique en carbone vitreux - Google Patents

Element electrochimique a champ de flux massique en carbone vitreux Download PDF

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Publication number
WO1996035000A1
WO1996035000A1 PCT/US1995/016114 US9516114W WO9635000A1 WO 1996035000 A1 WO1996035000 A1 WO 1996035000A1 US 9516114 W US9516114 W US 9516114W WO 9635000 A1 WO9635000 A1 WO 9635000A1
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Prior art keywords
cathode
anode
flow field
mass flow
electrochemical cell
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PCT/US1995/016114
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English (en)
Inventor
Clarence Garlan Law, Jr.
James Arthur Trainham, Iii
John Scott Newman
Douglas John Eames
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E.I. Du Pont De Nemours And Company
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Application filed by E.I. Du Pont De Nemours And Company filed Critical E.I. Du Pont De Nemours And Company
Priority to AU44683/96A priority Critical patent/AU4468396A/en
Publication of WO1996035000A1 publication Critical patent/WO1996035000A1/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/42—Electrodialysis; Electro-osmosis ; Electro-ultrafiltration; Membrane capacitive deionization
    • B01D61/44—Ion-selective electrodialysis
    • 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
    • C25B1/14—Alkali metal compounds
    • C25B1/16—Hydroxides
    • 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
    • C25B1/22—Inorganic acids
    • 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
    • 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
    • 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
    • C25B9/60—Constructional parts of cells
    • C25B9/65—Means for supplying current; Electrode connections; Electric inter-cell connections
    • 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
    • H01M8/0204—Non-porous and characterised by the material
    • H01M8/0206—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
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/0204—Non-porous and characterised by the material
    • H01M8/0213—Gas-impermeable carbon-containing materials
    • 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
    • H01M8/24—Grouping of fuel cells, e.g. stacking of fuel cells
    • H01M8/2465—Details of groupings of fuel cells
    • H01M8/247—Arrangements for tightening a stack, for accommodation of a stack in a tank or for assembling different tanks
    • 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
    • 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
    • H01M8/0204—Non-porous and characterised by the material
    • H01M8/0206—Metals or alloys
    • H01M8/0208—Alloys
    • 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
    • H01M8/0204—Non-porous and characterised by the material
    • H01M8/0223—Composites
    • H01M8/0228—Composites in the form of layered or coated products
    • 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 having a mass flow field made of vitreous, or glassy, carbon.
  • This electrochemical cell is particularly useful in converting anhydrous hydrogen fluoride to dry fluorine gas, although it may also be used in converting other anhydrous halogen halides, in particular, hydrogen chloride, hydrogen bromide and hydrogen iodide, to a dry halogen gas, such as chlorine, bromine, or iodine.
  • the fluorine produced by such cells is often used in converting uranium tetrafluoride to uranium hexafluoride.
  • Uranium hexafluoride is used in the gas diffusion process for making nuclear material.
  • the price for fluorine can be quite high.
  • both hydrogen fluoride and fluorine are extremely corrosive to both the commonly used materials of construction in fluoride production processes, as well as to human skin. Any leakage, even that by slow permeation of such materials of construction, poses severe maintenance cost and personnel safety concerns.
  • Vitreous, or glassy carbon has been used for a current collector in a secondary battery.
  • a secondary battery which has a current collector comprising a graphite body having a coating of vitreous carbon. The anode and the cathode are molten reactants.
  • U.S. Patent No. 4,048,394 to Ludwig a secondary battery which has a current collector comprising a graphite body having a coating of vitreous carbon
  • Patent No. 4,497,882 to Mikkor discloses a sheet of graphite foil is coated with an amorphous pyrolytic or glassy carbon to fill any openings in and/or through the graphite foil.
  • a thin layer of aluminum metal is coated onto the graphite foil.
  • the aluminum metal coated side of the graphite foil is bonded to an aluminum surface of an electroncially conductive material.
  • neither of these patents discloses a mass flow field formed of vitreous or glassy carbon, and in particular in a ceil for making fluorine.
  • there exists a need for a less costly fluorine production process which utilizes materials which are able to withstand an attack from corrosive hydrogen fluoride and fluorine.
  • the present invention solves the problems of the prior art by allowing for direct processing of anhydrous hydrogen halide which is a by-product of manufacturing processes, without first dissolving the hydrogen halide in water, or as is the case with hydrogen fluoride, processing it from an HF-KF melt.
  • This direct production of essentially dry halogen gas when done, for example, for fluorine gas, is less capital intensive than processes of the prior art, which require separation of water from the fluorine gas.
  • This direct production of essentially dry halogen gas also requires lower investment costs than the electrochemical conversions of hydrogen halide of the prior art. This advantage can translate directly into lower power costs per pound of say, fluorine, generated than in.
  • glassy carbon Since glassy carbon is much less gas permeable than current collectors of the prior art, its use in the electrochemical cell of the present invention decreases gas leakage potential and lessens cost and safety concerns. The decrease in gas permeability is extremely dramatic. The gas permeability of glassy carbon is 10 to 12 orders of magnitude lower than the gas permeability of common forms of graphite. This dramatic decrease in gas permeability makes the electrochemical cell and process of the present invention even more practicable and attractive.
  • an electrochemical cell comprising an electrochemical cell comprising an electrode, a membrane disposed in contact with one side of the electrode and mass flow field means disposed on the other side of the electrode for bringing fluids to and directing fluids away from the electrode, wherein the mass flow field comprises glassy carbon.
  • an electrochemical cell for directly producing essentially dry halogen gas from essentially anhydrous hydrogen halide comprising 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, wherein one side of the cation- transporting means is disposed in contact with one side of the oxidizing means; means for reducing the transported protons, wherein the other side of the cation-transporting means is disposed in contact with the reducing means; and a mass flow field disposed on at least one side of the cation-transporting means, wherein the mass flow field comprises glassy carbon.
  • BRIEF DESCRIPTION OF THE DRAWINGS 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 second embodiment of the present invention.
  • Fig. 1A 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 electrochemical cell for producing 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 fluorine gas from anhydrous hydrogen fluoride.
  • this cell may alternatively be used to produce other halogen gases, such as bromine, chlorine and iodine from a respective anhydrous hydrogen halide, such as hydrogen bromide, hydrogen chloride and hydrogen iodide.
  • halogen gases such as bromine, chlorine and iodine from a respective anhydrous hydrogen halide, such as hydrogen bromide, hydrogen chloride and hydrogen iodide.
  • 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.
  • fluorine gas, as well as hydrogen is produced in this cell.
  • water, as well as fluorine gas is produced by this ce-11, 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. Since in the preferred embodiment, anhydrous HF is carried through the inlet, and fluorine gas is carried through the outlet, the inlet and the outlet may be lined with a perfluoropolymer, sold as TEFLON ® PFA (hereinafter referred to as "TEFLON ® PFA" by ⁇ . I. du Pont de Nemours and Company of Wilmington, Delaware (hereinafter referred to as "DuPont”) .
  • TEFLON ® PFA perfluoropolymer
  • the electrochemical cell of the first and second embodiments also comprises a membrane, where one side of the electrode is disposed in contact with the membrane.
  • the electrochemical cell of the present invention may be described as comprising 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. 1. More specifically, 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.
  • Suitable resin materials are available commercially or can be made 'according to patent literature. They include fluorinated polymers with side chains of the type -CF 2 CFRS0 3 H and -OCF 2 CF 2 CF 2 SO 3 H, where R is an F, Cl, CF 2 C1, or a Ci to C 10 perfluoroalkyl radical.
  • 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.
  • the first type of NAFION ® is unsupported 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.
  • 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.
  • 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) .
  • This material and a number of solid electrolytes which are useful for the invention are described in the Fuel Cell Handbook. A. J. Appleby and F. R. Foulkes, Van Nostrand Reinhold, N.Y., 1989, pages 308-312.
  • Additional useful solid state proton conductors especially the cerates of strontium and barium, such as strontium ytterbiate cerate (SrCe 0> 95Ybfj #0 5 0 3 - ⁇ ) anci barium neodymiate cerate (BaCe ⁇ . 9 Nd 0 . 0 _C * 3 - ⁇ ) ar e described in a final report, DOE/MC/24218-2957, Jewulski, Osif and Remick, prepared for the U.S. Department of Energy, Office of Fossil Energy, Morgantown Energy Technology Center by Institute of Gas Technology, Chicago, Illinois, December, 1990.
  • strontium ytterbiate cerate SrCe 0> 95Ybfj #0 5 0 3 - ⁇
  • anci barium neodymiate cerate BaCe ⁇ . 9 Nd 0 . 0 _C * 3 - ⁇
  • 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 fluoride are transported to the surface of the anode through anode- side inlet 14.
  • the molecules of the anhydrous hydrogen fluoride are oxidized to produce essentially dry fluorine gas and protons.
  • the essentially dry fluorine gas exits through anode-side outlet 16 as shown in Fig. 1.
  • the protons 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.
  • 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).
  • 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 electro ⁇ chemically 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 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 HC1 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. Electrochem. Soc, Vol. 139, No.
  • the electrochemical cell of the first and second embodiments further comprises mass flow field measn.
  • the mass flow field means comprises an anode flow field 28 disposed in contact with the anode, or 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.
  • Anode flow field 28 includes a plurality of anode flow channels 29, and cathode flow field 30 includes a. plurality of cathode flow channels 31 as shown in Fig. 1A.
  • the purpose of the anode flow field and channels 29 is to get reactants, such as anhydrous HF in the first and second embodiments, to the anode and products, such as essentially dry fluorine gas, from the anode.
  • the purpose of the cathode flow field and channels 31 is to get reactants, 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.
  • reactants 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.
  • At least on of the anode and the cathode mass flow fields comprise glassy, or vitreous carbon.
  • Glassy carbon has a number of very desirable characteristics, especially compared to graphite.
  • the gas permeability of glassy carbon is 10 to 12 orders * of magnitude lower than the gas permeability of common forms of graphite, which is often used as a mass flow field.
  • the density of glass carbon is slightly less than some forms of graphite, and its apparent porosity is very low compared to graphite (1-3 compared to 20- 30%) . This low porosity has important consequences for other physical properties, such as gas permeability.
  • the tight interlocking structure of glassy carbon results in low porosity, and this also results in a structure which is virtually not permeable to gases. This structure is absent in graphite, which permits significant passage of gas molecules through its structure.
  • vitreous carbon is a commercially available material, and is sold by Tokai Carbon Co., Ltd.
  • 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 products to and reactants from both the anode and the cathode, as well as to 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 as 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.
  • 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 of the present invention 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 colects 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 by electronic conduction.
  • the anode and the cathode current distributors preferably each comprise a non-porous layer.
  • the anode current distributor thus provides a barrier between the anode and the current bus, as well as between the current bus and the hydrogen halide, such as hydrogen fluoride, the halogen gas, such as fluorine.
  • the cathode current distributor provides a barrier between the cathode current bus and the and the cathode, as well as between the cathode current bus and the hydrogen halide. This is desirable because 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.
  • anode current bus 46 in Fig. 1, it is within the scope of the present invention for the structural support to be placed behind the anode current bus (i.e., to the left of bus 46 as shown in Fig. 1) and still achieve the same results.
  • 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.
  • 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.
  • a process for the direct production of essentially dry halogen gas from essentially anhydrous hydrogen halide may comprise hydrogen chloride, hydrogen bromide, hydrogen fluoride or hydrogen iodide.
  • 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) .
  • 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.
  • anode current distributor 40 collects current from the anode bus and distributes it to the anode by electronic conduction.
  • Molecules of essentially anhydrous hydrogen fluoride 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 molecules are oxidized at the anode under the potential created by the voltage source to produce essentially dry fluorine gas (F 2 (g)) at the anode, and protons (H + ) .
  • F 2 (g) essentially dry fluorine gas
  • protons H +
  • the fluorine gas (F (g)) exits through anode-side outlet 16 as shown in Fig. 1.
  • 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 48.
  • anhydrous hydrogen halide is hydrogen fluoride.
  • anode current distributor 40 collects current from the anode bus and distributes it to the anode by electronic conduction. Molecules of essentially anhydrous hydrogen fluoride 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 fluoride (HF(g)) are oxidized under the potential created by the voltage source to produce essentially dry fluorine gas at the anode, and protons (H + ) , as expressed in equation (4) above.
  • the fluorine gas (F 2 ) 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 to water, which is expressed by the equation:
  • the cathode reaction is the formation of water.
  • This cathode reaction has the advantage of more favorable thermodynamics relative to H 2 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 amount of voltage or energy required as input to the cell is reduced in this second embodiment.
  • 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 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.
  • one is not restricted to operate the electrochemical cell of either the first or the second embodiment at atmospheric pressure.
  • the cell could be run at differential pressure gradients, which change the transport characteristics of water or other components in the cell, including the membrane.
  • 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
  • the cell of the third embodiment may be 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 reactants, such as aqueous HC1 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 the cathode and product from the cathode.
  • the mass flow fields of the third embodiment include flow channels 29' and 31' for performing these functions.
  • the mass flow fields comprise glassy carbon as described above with respect to the first two embodiments.
  • 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) .
  • 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 from the voltage source through all of the elements to the right of current bus 46' as shown in Fig. 2, including current bus 48' from which it returns to the voltage source.
  • 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 distributes current to the anode by electronic conduction and allows current to flow away from the anode.
  • the cathode current distributor distributes current to the cathode by electronic conduction and allows current to flow to the cathode.
  • 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, as well as between the anode current bus and the reactant, such as aqueous hydrogen chloride and the product, such as wet gaseous chlorine.
  • the cathode current distributor provides a barrier between the cathode current bus and the cathode, as well as between the cathode current bus and 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.
  • 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'.

Abstract

L'invention porte sur un élément électrochimique présentant une électrode, une membrane en contact avec l'un des côtés de l'électrode ainsi qu'un champ de flux massique disposé de l'autre côté de l'électrode, dirigeant le fluide vers l'électrode et inversement. Le champ de flux massique comprend du carbone vitreux. L'élément électrochimique de cette invention s'avère particulièrement utile dans un processus de conversion d'halogénure anhydre d'hydrogène, notamment du fluorure d'hydrogène, directement en un halogène gazeux sensiblement sec, tel que du fluorure d'hydrogène anhydre en gaz fluoré. L'élément peut également être utilisé pour convertir un réactif aqueux.
PCT/US1995/016114 1995-05-01 1995-12-13 Element electrochimique a champ de flux massique en carbone vitreux WO1996035000A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU44683/96A AU4468396A (en) 1995-05-01 1995-12-13 Electrochemical cell having a mass flow field made of glassy carbon

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US43160695A 1995-05-01 1995-05-01
US08/431,606 1995-05-01

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WO1996035000A1 true WO1996035000A1 (fr) 1996-11-07

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2403166A (en) * 2003-06-25 2004-12-29 Accentus Plc Electrodeionisation process

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2445861A1 (fr) * 1979-01-02 1980-08-01 Gen Electric Element collecteur de courant pour cellule electrochimique
GB2083012A (en) * 1980-08-22 1982-03-17 Carbone Corp Composite carbonaceous articles and their production
JPS58166659A (ja) * 1982-03-27 1983-10-01 Hitachi Ltd 燃料電池
JPS62133674A (ja) * 1985-12-06 1987-06-16 Tokai Carbon Co Ltd 燃料電池用リブ付セパレ−タ−の製造方法

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2445861A1 (fr) * 1979-01-02 1980-08-01 Gen Electric Element collecteur de courant pour cellule electrochimique
GB2083012A (en) * 1980-08-22 1982-03-17 Carbone Corp Composite carbonaceous articles and their production
JPS58166659A (ja) * 1982-03-27 1983-10-01 Hitachi Ltd 燃料電池
JPS62133674A (ja) * 1985-12-06 1987-06-16 Tokai Carbon Co Ltd 燃料電池用リブ付セパレ−タ−の製造方法

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 007, no. 292 (E - 219) 27 December 1983 (1983-12-27) *
PATENT ABSTRACTS OF JAPAN vol. 011, no. 359 (E - 559) 21 November 1987 (1987-11-21) *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2403166A (en) * 2003-06-25 2004-12-29 Accentus Plc Electrodeionisation process
GB2403166B (en) * 2003-06-25 2006-11-01 Ipsolutions Electrodeionisation process

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