WO1996035005A1 - Cellule electrochimique a repartiteur de courant en matiere carbonee - Google Patents

Cellule electrochimique a repartiteur de courant en matiere carbonee Download PDF

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Publication number
WO1996035005A1
WO1996035005A1 PCT/US1995/016113 US9516113W WO9635005A1 WO 1996035005 A1 WO1996035005 A1 WO 1996035005A1 US 9516113 W US9516113 W US 9516113W WO 9635005 A1 WO9635005 A1 WO 9635005A1
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WIPO (PCT)
Prior art keywords
current
anode
cathode
disposed
membrane
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PCT/US1995/016113
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English (en)
Inventor
Aaron Jay Becker
James Arthur Trainham, Iii
Clarence Garlan Law, Jr.
John Scott Newman
Douglas John Eames
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E.I. Du Pont De Nemours And Company
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Priority to AU44682/96A priority Critical patent/AU4468296A/en
Publication of WO1996035005A1 publication Critical patent/WO1996035005A1/fr

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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
    • H01M8/02—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
    • 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
    • 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 current distributor made of a conductive, non-porous carbonaceous material.
  • the current distributor is useful in a cell for converting anhydrous hydrogen halide, in particular, hydrogen chloride, hydrogen fluoride, hydrogen bromide and hydrogen iodide, to a dry halogen gas, such as chlorine, fluorine, bromine, or iodine.
  • the current distributor may be used in an electrochemical cell which converts an aqueous reactant to an aqueous product.
  • 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 HC1 by-product.
  • a number of commercial processes have been developed to convert HC1 into usable chlorine gas. See, e.g., F. R.
  • the commercial improvements to the Deacon reaction have used other catalysts in addition to or in place of the copper used in the Deacon reaction, such as rare earth compounds, various forms of nitrogen oxide, and chromium oxide, in order to improve the rate of conversion, to reduce the energy input and to reduce the corrosive effects on the processing equipment produced by harsh chemical reaction conditions.
  • other catalysts such as rare earth compounds, various forms of nitrogen oxide, and chromium oxide, in order to improve the rate of conversion, to reduce the energy input and to reduce the corrosive effects on the processing equipment produced by harsh chemical reaction conditions.
  • thermal catalytic oxidation processes are complicated because they require separating the different reaction components in order to achieve product purity. They also involve the production of highly corrosive intermediates, which necessitates expensive construction materials for the reaction systems. Moreover, these thermal catalytic oxidation processes are operated at elevated temperatures of 250° C and above.
  • the current electrochemical commercial process is known as the ⁇ hde process.
  • aqueous HC1 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 electro ⁇ chemical reaction and a decrease in HC1 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%) HC1 solution produced during the electrolysis step and regenerating an HC1 solution of 22% for feed to the electrochemical cell.
  • the overall reaction of the ⁇ hde 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 HC1 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:
  • 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 navi ⁇ g * a-s ⁇ li ⁇ 'polymer- electrolyte- ineinbta ⁇ e".”—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.
  • 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.
  • Balko The design and configuration of the anode.pore size and electrode thickness employed by Balko maximizes transport of the chloride ions. This results in effective chlorine evolution while minimizing the evolution of oxygen, since oxygen evolution tends to increase under conditions of chloride ion depletion near the anode surface. In Balko, although oxygen evolution may be minimized, it is not eliminated. As can be seen from Figs. 3 to 5 of Balko, as the overall current density is increased, the rate of oxygen evolution increases, as evidenced by the increase in the concentration of oxygen found in the chlorine produced. Balko can run at higher current densities, but is limited by the deleterious effects of oxygen evolution. If the Balko cell were to be run at high current densities, the anode would be destroyed.
  • Certain hydrogen halides such as HC1, are particularly corrosive.
  • a material which is suitable for use in an electrochemical cell which is able to withstand attack from such corrosive hydrogen halides and which can consistently conduct current.
  • Use of graphite for a current collector in a battery or in an electrolytic process is known.
  • U.S. Patent No. 4,048,394 to Ludwig discloses a sodium/sulfur secondary battery having a current collector comprising a graphite body having a coating of vitreous carbon.
  • U.S. Patent No. 4,497,882 to Mikkor is directed to a method of making a corrosion resistant current collector in a sodium-sulfur secondary battery.
  • 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 electronically conductive material.
  • the present invention solves the problems of the prior art by providing an electrochemical cell for directly producing essentially dry halogen gas from essentially anhydrous hydrogen halide where the cell has a conductive current distributor which acts as a corrosion-resistant barrier to the essentially dry halogen gas and the essentially anhydrous hydrogen halide.
  • This 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.
  • the present invention provides a material which can be used for a current distributor and which is able to withstand attack from corrosive hydrogen halides, such as hydrogen chloride, and which can consistently conduct current, whether used in an electrochemical cell for converting aqueous or anhydrous reactants.
  • the current distributor of the present invention provides an effective barrier between the current bus, and the electrodes, and in particular between the corrosive hydrogen halide and the halogen gas. This makes the process of the present invention even more practicable and economically attractive.
  • an electrochemical cell for producing a product from a reactant comprising an electrode; a membrane disposed in contact with one side of the electrode; a current bus is disposed on the other side of the electrode; and current distributing means disposed between the electrode and the current bus for distributing current by electronic conduction, wherein the current distributing means comprises a carbonaceous material which is conductive and non-porous carbonaceous material.
  • the carbonaceous material is either anode carbon, reimpregnated carbon or glassy carbon.
  • a cell for directly producing essentially essentially dry halogen gas from essentially anhydrous hydrogen halide 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 a current distributor disposed on the other side of the oxidizing means, wherein the current distributor comprises a carbonaceous material.
  • the carbonaceous material is a conductive, non-porous carbonaceous material.
  • 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. 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, 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.
  • hydrogen fluoride may be particularly corrosive when used with the present invention.
  • 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.
  • TEFLON ® PFA perfluoropolymer sold as TEFLON ® PFA (hereinafter referred to as "TEFLON ® PFA” by E. I. du Pont de Nemours and Company of Wilmington, Delaware (hereinafter referred to as "DuPont”) .
  • the electrochemical cell of the first and second embodiments also comprises a membrane.
  • the electrochemical cell of the first and second embodiments 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 S0 3 H, where R is a F, Cl, CF 2 C1, or a C x 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 0 j --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 .
  • 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.
  • 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 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 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. Electrochem. 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.
  • 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. 1A.
  • the purpose of the anode flow field and channels 29 formed therein is to get 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.
  • the purpose of the cathode flow field and channels 31 formed therein is to get 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 an oxygen-containing gas, which may contain water vapor (H 2 0(g)) as a result of humidification, from the cathode in the second embodiment.
  • water vapor may be needed to keep the membrane hydrated.
  • water vapor may not be necessary in this embodiment because of the water produced by the electrochemical reaction of the oxygen (0 ) added as discussed below.
  • the flow fields and the flow channels may have a variety of configurations.
  • the flow fields may be made in any manner known to one skilled in the art.
  • the anode and the cathode flow fields comprise 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 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 further comprises anode current distributing means disposed on one side of the electrode, or the oxidizing means, for distributing current to the electrode, or the oxidizing means, by electronic conduction and for allowing current to flow away from the electrode, or the oxidizing means.
  • the anode current distributor collects current from the anode bus and distributes it to the anode by electronic conduction.
  • the anode current distributing means comprises an anode current distributor 40 as shown in Fig. 1.
  • the current distributing means may be described as means disposed on one side of the electrode or the oxidizing means for providing a barrier between the current bus and the electrode, and also between the current bus and the hydrogen halide, such as hydrogen chloride and the halogen gas, such as chlorine gas.
  • the current distributor comprises a non-porous layer.
  • the anode flow field which is disposed next to the anode current distributor as shown in Fig. 1, brings anolyte, such as anhydrous hydrogen halide in the first and second embodiments, to the anode, and takes products, such as essentially dry chlorine gas in the first and second embodiments, away from the anode.
  • Certain hydrogen halides, such as HCl are particularly corrosive.
  • the current distributor is made from a material which is corrosion resistant, electrically conductive and which possesses a high degree of impermeability to the reactants and the starting materials, whether gaseous or liquid, of the process conducted in the electrochemical cell. These criteria can be met by certain conductive polymer composite materials.
  • the anode current distributor of the present invention comprises a conductive carbonaceous material.
  • the carbonaceous material comprises a non- porous layer.
  • This material may be either anode carbon, as used in aluminum smelting, reimpregnated graphite and glassy carbon.
  • Anode carbon used in aluminum smelting referred to herein as anode carbon, is described in the Encyclopedia of Chemical Technology, Kirk-Othmer, 4th edition, volume 2, in the section on "Aluminum and Alloys", especially page 195. Kirk-Othmer, same edition, volume 4, section on “Carbon” describes reimpregnated graphite on pages 987 and 988 and glassy carbon on page 1014.
  • Ullmann's Encyclopedia of Industrial Chemistry, Fifth edition, volume A5, section on “Carbon” discusses the manufacture of these various types of carbonaceous materials on pages 103 - 115.
  • Anode carbon as used in aluminum smelting, reimpregnated graphite and glassy carbon are aricles of commerce. Anode carbon has multiple suppliers. Great Lakes carbon Corporation, New York, N.Y., is a supplier of reimpregnated graphite. Tokai Carbon Co. Limited, is a supplier of glassy carbon. The fabrication of these materials for current distributors of the present invention may be by machining, press forming and heating, or both.
  • the electrochemical cell of the present invention may further comprise cathode current distributing means disposed on one side of the reducing means, or electrode, or more specifically the cathode.
  • the cathode current distributor collects current from the cathode and distributes it to the cathode bus by electronic conduction by electronic conduction by electronic conduction.
  • the cathode current distributing means may be described as means disposed on one side of the reducing means, or cathode, for providing a barrier between the cathode current bus and the cathode, and between the cathode current bus and the hydrogen halide and the halogen gas. This barrier on the cathode side is desirable because there is some migration of hydrogen halide through the membrane.
  • the cathode current distributing means comprises a cathode current distributor 42 as shown in Fig. 1.
  • the cathode current distributor may comprise the same carbonaceous material as described above for the anode current distributor. However, it should be noted that the material used for the anode current distributor need not be the same as the material used for the cathode current distributor.
  • the electro ⁇ chemical cell also comprises a conductive structural support 44 disposed in contact with anode current distributor 40 and a support 41 disposed in contact with anode current distributor 42.
  • the support on both the anode and the cathode side is preferably made of UNS31603 (316L stainless steel) .
  • a seal 45 preferably in the form of an O-ring made from KALREZ®, is disposed between structural support 44 on the anode side and anode current distributor 40 and between structural support 41 on the cathode side and cathode current distributor 42.
  • structural supports 41 and 44 are shown inside of respective current buses 46 and 48 in Fig. 1, it is within the scope of the present invention for the structural supports to be placed outside the current buses (i.e., to the left of bus 46 and to the right of bus 48 as shown in Fig. 1) and still achieve the same results.
  • 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 electro ⁇ chemical 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 distributor 40 distributes collects current from anode current bus 46 and distributes it to anode 12 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 molecules are oxidized at the anode under the potential created by the voltage source to produce essentially dry chlorine gas (Cl 2 (g)) at the anode, and protons (H + ) . This reaction is given by the equation:
  • the protons (H + ) are transported through the membrane, which acts as an electrolyte.
  • the transported protons are reduced at the cathode.
  • anhydrous hydrogen halide is hydrogen chloride.
  • anode current distributor 40 collects current from anode current bus 46 and distributes it to anode 12. 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 (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.
  • 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 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 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 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 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. Wherever possible, 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
  • 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* and a cathode 20'.
  • 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.
  • 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.
  • 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 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, 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 the catholyte.
  • the current distributors of the third embodiment are made of the same materials as described above for the first two embodiments.
  • the cathode current distributor may comprise the same carbonaceous material as described above specifically for the anode 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 une cellule électrochimique constituée d'une anode, d'une membrane, et d'une cathode, dans laquelle un côté de l'anode est en contact avec un côté de la membrane et la cathode est en contact avec l'autre côté de la membrane. Un bus de courant est placé de l'autre côté de l'anode. Un répartiteur de courant, qui répartit le courant par conduction électronique, est placé entre le bus de courant et l'électrode, qui peut être soit l'anode soit la cathode. Le répartiteur de courant est en matière carbonée conductrice, et de préférence, en matière carbonée non poreuse choisie dans un groupe constitué de carbone anodique, de graphite réimprégné et de carbone vitreux. Le répartiteur de courant fait ainsi office de barrière entre le bus de courant et le réactif et produit de la cellule. Cela est particulièrement important dans les milieux agressifs, tel que celui du chlorure d'hydrogène. Par conséquent, le répartiteur de courant de l'invention s'avère être d'utilité dans une cellule pour convertir directement de l'halogénure d'hydrogène anhydre en gaz halogène quasiment sec, notamment la transformation du chlorure d'hydrogène anhydre en gaz chloré, ou bien on peut l'utiliser dans une cellule pour convertir des réactifs aqueux.
PCT/US1995/016113 1995-05-01 1995-12-13 Cellule electrochimique a repartiteur de courant en matiere carbonee WO1996035005A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU44682/96A AU4468296A (en) 1995-05-01 1995-12-13 Electrochemical cell having a current distributor comprising a carbonaceous material

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US43158895A 1995-05-01 1995-05-01
US08/431,588 1995-05-01

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WO1996035005A1 true WO1996035005A1 (fr) 1996-11-07

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2157277A (en) * 1984-04-10 1985-10-23 Kureha Chemical Ind Co Ltd Reinforced flexible graphite sheet
EP0186611A2 (fr) * 1984-12-24 1986-07-02 United Technologies Corporation Plaque séparatrice contenant du coke pour cellules électrochimiques
US5292600A (en) * 1992-08-13 1994-03-08 H-Power Corp. Hydrogen power cell
WO1995014797A1 (fr) * 1993-11-22 1995-06-01 E.I. Du Pont De Nemours And Company Anode utile pour la conversion electrochimique d'un halogenure d'hydrogene anhydre en halogene gazeux

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2157277A (en) * 1984-04-10 1985-10-23 Kureha Chemical Ind Co Ltd Reinforced flexible graphite sheet
EP0186611A2 (fr) * 1984-12-24 1986-07-02 United Technologies Corporation Plaque séparatrice contenant du coke pour cellules électrochimiques
US5292600A (en) * 1992-08-13 1994-03-08 H-Power Corp. Hydrogen power cell
WO1995014797A1 (fr) * 1993-11-22 1995-06-01 E.I. Du Pont De Nemours And Company Anode utile pour la conversion electrochimique d'un halogenure d'hydrogene anhydre en halogene gazeux

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AU4468296A (en) 1996-11-21

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