WO1998000582A2

WO1998000582A2 - System and process for producing hydrogen gas in an electrochemical cell and fuel cell powered by the hydrogen gas

Info

Publication number: WO1998000582A2
Application number: PCT/US1997/010871
Authority: WO
Inventors: Francisco Jose Freire; Kenneth Bernard Keating; Dennie Turin Mah; William H. Zimmerman; David Lee Reichert; Aaron Jay Becker; Clarence Garlan Law, Jr.; James Arthur Trainham
Original assignee: E.I. Du Pont De Nemours And Company
Priority date: 1996-06-28
Filing date: 1997-06-23
Publication date: 1998-01-08
Also published as: WO1998000582A3

Abstract

The present invention relates to a process and an electrochemical cell which produces hydrogen gas and a fuel cell which is powered by the hydrogen gas. The electrochemical cell converts hydrogen halide, such as anhydrous or aqueous hydrogen chloride, to either dry or wet chloride gas, respectively. The fuel cell generates energy in the form of direct current which can be used for a variety of purposes, which can include powering the electrochemical cell which produces the hydrogen gas.

Description

T ITLE

SYSTEM AND PROCESS FOR PRODUCING HYDROGEN GAS

IN AN ELECTROCHEMICAL CELL

AND FUEL CELL POWERED BY THE HYDROGEN GAS BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process and an electrochemical cell which produces hydrogen gas and a fuel cell which is powered by the hydrogen gas. 2. Description of the Related Art

Hydrogen chloride (HCl) or hydrochloric acid is a reaction by-product of many manufacturing processes which use chlorine. For example, chlorine is used to manufacture polyvinyl chloride, isocyanates, and chlorinated hydrocarbons/fluorinated hydrocarbons, with hydrogen chloride as a co-product of these processes. Because 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 use of a fuel cell which produces electrical energy in combination with an electrochemical cell which uses electrical energy to produce a chemical product is known. See, U.S. Patent Nos. 4,792,384 and 4,797,186. The electrochemical cells disclosed in these patents include a chloralkali cell, a chlorate cell and a cell used in the production of adiponitrile . In light of the availability of excess HCl, it would be desirable to design a system which converts HCl, either aqueous or anhydrous, to produce hydrogen gas and which could be used to run a fuel cell. Such a system could even be used to supplement the total power required for the electrochemical cell. SUMMARY OF THE INVENTION

The present invention solves the problems of the prior art by providing a system which converts anhydrous hydrogen halide to halogen gas and hydrogen gas, and which uses the hydrogen gas to power a fuel cell. Such a system may be used to convert either anhydrous or aqueous or liquid hydrogen halide to halogen gas. Thus, a benefit of the present invention is that it avoids environmental problems associated with disposing of HCl, or any hydrogen halide co- product .

A further benefit of the present invention is that electric power is produced without consuming fossil or nuclear fuels or atmospheric pollutants. Thus, the present invention affords a method of converting hydrogen gas to clean energy.

To achieve the foregoing solutions, and in accordance with the purposes of the invention as embodied and broadly described herein, there is provided a system and a process for producing hydrogen gas in an electrochemical cell, where the hydrogen gas is used to power a fuel cell. The electrochemical cell may be either a cell for converting anhydrous or liquid or aqueous hydrogen halide to halogen gas. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic diagram of the system according to the present invention for producing hydrogen gas in an electrochemical cell, where that hydrogen gas is used to power a fuel cell . Fig. 2 is a schematic diagram showing the details of an electrochemical cell for producing halogen gas from anhydrous hydrogen halide according to the present invention.

Fig. 2A is a cut-away, top cross-sectional view of the anode and cathode mass flow fields as shown in Fig. 2. DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferred embodiments of the invention as illustrated in the accompanying drawings . In accordance with the present invention, there is provided a system for producing hydrogen gas m an electrochemical cell, where the hydrogen gas is used to power a fuel cell. The system of the present invention is shown generally at 10 in Fig. 1. The system includes an electrochemical cell which produces hydrogen gas from hydrogen halide. Such a cell is shown in Figs. 1 and 2 generally at 100. For the sake of convenience, the case where anhydrous hydrogen chloride is converted to dry chlorine gas will be described with respect to Figs. 1, 2 and 2A. However, it should be understood that the present invention may be used w th an electrochemical cell for converting an electrochemical cell for any converting hydrogen halide, i.e., hydrogen chloride, hydrogen fluoride, hydrogen bromide and hydrogen iodide, whether anhydrous or aqueous.

In the system shown in Fig. 1, an inlet line 12 brings in hydrogen halide to the anode-side of electrochemical cell 100. The electrochemical cell of the present invention comprises inlet means for supplying hydrogen halide to the cell. The inlet means comprises an anode-side inlet 102 as shown in Figs. 1 and 2 which supplies anhydrous hydrogen chloride (i.e., in vapor or molecular form) to the cell.

The electrochemical cell of the present invention comprises means for oxidizing hydrogen halide to produce protons and halogen gas. The oxidizing means comprises an electrode, or more specifically, an anode 104 as shown in Figs. 1, 2 and 2A.

The electrochemical cell of the present invention also outlet means for releasing the halogen gas. The outlet means comprises an anode-side outlet 106 as shown in Figs . 1 and 2. A portion of the hydrogen halide may be unreacted, and this unreacted portion leaves the electrochemical cell through the anode-side outlet, along with the halogen gas. The halogen gas, such as chlorine gas, leaves the cell through a line 14 as shown in Fig. 1.

The electrochemical cell of the present invention also comprises cation-transporting means for transporting the protons therethrough, wherein the oxidizing means is disposed in contact with one side of the cation-transporting means. Preferably, the cation-transporting means is a cation-transporting membrane 108, where the anode is disposed in contact with one side of the membrane as shown in Figs. 1, 2 and 2A. More specifically, membrane 108 may be a proton-conducting membrane. In the present invention, the membrane acts as the electrolyte. The membrane 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. The presence of 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 the patent literature. They include fluorinated polymers with side chains of the type —CF₂CFRS0₃H and —OCF₂CF₂CF₂SO₃H, where R is an F, Cl, CF₂C1, or a C^ to C₁₀ perfluoroalkyl radical. The membrane resin may be, for example, a copolymer of tetrafluoroethylene with CF₂=CF0CF₂CF (CF₃) 0CF₂CF₂SO₃H . Sometimes those resins may be in the form that has pendant —S0 F groups, rather than —S0₃H groups. The sulfonyl fluoride groups can be hydrolyzed with potassium hydroxide to —S0₃K groups, which then are exchanged with an acid to —S0₃H groups. Suitable perfluorinated cationic membranes, which are made of hydrated copolymers of polytetrafluoroethylene and poly-sulfonyl fluoride vinyl ether-containing pendant sulfonic acid groups, are offered DuPont under the trademark "NAFION^®" (hereinafter referred to as NAFION^®) . In particular, NAFION^® membranes containing pendant sulfonic acid groups include NAFION^® 115,

NAFION^® 117, NAFION^® 324 and NAFION^® 417. The first and second types of NAFION^® are unsupported and have 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 and NAFION^® 417 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 μ -thick membrane having an equivalent weight of 1100 g., and a 25 μm-thick membrane having an equivalent weight of 1500 g. NAFION^® 115 in particular may be used with the electrochemical cell of the present invention.

Although 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. For example, proton-conducting ceramics such as beta- alumina may be used. Beta-alumina is a class of nonstoichiometric crystalline compounds having the general structure Na₂O_x-Al₂θ₃, ^ⁿ which x ranges from 5 00 (β"-alumina) to 11 (β-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 (SrCe₀.₉₅Y ₀.₀₅°₃-α) ^anc* bar um neodymiate cerate (BaCe₀, ₉Nd₀.oι°₃-α) ^are 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.

The electrochemical cell of the present invention also comprises 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 an electrode, or more specifically, a cathode 110, where cathode 110 is disposed in contact with the other side (as opposed to the side which is in contact with the anode) of membrane 108 as illustrated in Figs. 1, 2 and 2A.

When converting anhydrous hydrogen halide to dry halogen gas, the membrane of the electrochemical cell of the present invention must be kept hydrated in order to keep the conductivity of the membrane high and to increase the efficiency of proton transport through the membrane. This hydration is accomplished by supplying liquid water to the cathode-side of the membrane. Thus, in the case where anhydrous hydrogen halide is converted to dry halogen gas, the electrochemical cell of the present invention also comprises cathode-side inlet means for supplying water to the membrane. The cathode-side inlet means comprises a cathode-side inlet 112 as shown in Figs. 1 and 2. The electrochemical cell of the present invention also includes a cathode chamber disposed adjacent the reducing means. A cathode chamber is shown at 105 in Figs. 2 and 2A disposed adjacent to, meaning next to or near, the reducing means, or cathode. The cathode-side inlet is disposed in fluid communication with the cathode chamber. The cathode- side inlet is connected to a recycle line 16 as shown in Fig. 1. It should be noted that if the electrochemical cell of the present invention is used to convert aqueous hydrogen chloride to wet chlorine gas, then the electrochemical cell of the present invention does not include a cathode-side inlet or a recycle line for recycling water to the membrane. The electrochemical cell of the present invention also comprises cathode-side outlet means also disposed in fluid communication with the cathode chamber. The cathode-side outlet means comprises a cathode-side outlet 114 as shown in Fig. 1 or a cathode-side outlet 114 as shown in Fig. 2. A passage 115 as shown in Fig. 2 is formed between the anode-side inlet and the cathode-side outlet, and a similar passage 117 is shown formed between the cathode-side inlet and the anode-side outlet. These passages carry the reactants into and the products out of the cell through the anode and cathode-side inlets, and the anode and cathode-side outlets, as will be further explained below . The anode and the cathode comprise an electrochemically active material. 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. Preferably, the electrochemically active material may comprise a catalyst material such as platinum, ruthenium, osmium, rhenium, rhodium, iridium, palladium, gold, titanium, tin or zirconium and the oxides, alloys or mixtures thereof. 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 anode and the cathode may be porous, gas- diffusion electrodes. Gas diffusion electrodes provide the advantage of high specific surface area, as known to one skilled in the art. A particular type of gas diffusion electrode, known as an ELAT, may be used as the anode and the cathode. An ELAT comprises a support structure, as well as the electrochemically active material. In one preferred embodiment, an ELAT comprising a support structure of carbon cloth and electrochemically active material comprising ruthenium oxide, commercially available from E-TEK, of Natick, Massachusetts, may be used. Alternatively, an ELAT may be used which comprises a catalyst material mixed with carbon and particles of polytetrafluoroethylene, or PTFE, a tetrafluoropolymer resin which is sold under the trademark "TEFLON^®" (hereinafter referred to as "PTFE"), commercially available from DuPont . The catalyst material, carbon particles and PTFE are then sintered on a carbon cloth substrate, which is treated with a NAFION^® solution. This ELAT is held mechanically against the membrane of the cell.

Alternative arrangements of the electrochemically active material may be used for the anode and cathode of the present invention. The electrochemically active material may be disposed adjacent, meaning at or under, the surface of the cation-transporting membrane. For instance, the electrochemically active material may be deposited into the membrane, as shown in U.S. Patent No. 4,959,132 to Fedkiw. 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). If the electrodes are hot-pressed into the membrane, they have the advantage of having good contact between the catalyst and the membrane. In a hot-pressed electrode, the electrochemically active material may comprise a catalyst material on a support material. The support material may comprise particles of carbon and particles of PTFE. The electrochemically active material may be bonded by virtue of the PTFE to a support structure of carbon cloth or paper or graphite paper and hot-pressed to the cation- transporting membrane. The hydrophobic nature of PTFE 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 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/cm². Lower loadings are possible with other available methods of deposition, such as distributing them as thin films from inks onto the membranes, to form a catalyst- coated membrane, 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. 2 L28-30, 1992, where the inks contain solubilized NAFION^® to enhance the catalyst-ionomer surface contact and to act as a binder to the NAFION^® perfluorinated membrane sheet.

With such a system, loadings as low as 0.017 mg active material per cm² have been achieved.

In one embodiment, a thin film of the electrochemically active material is applied directly to the membrane to form a catalyst-coated membrane. In this preferred embodiment, the membrane is typically formed from a polymer as described above in its sulfonyl fluoride form, since it is thermoplastic in this form, and conventional techniques for making films from thermoplastic polymer can be used. The electrochemically active material is conventionally incorporated in a coating formulation, or "ink", which is applied to the membrane. The coating formulation, and consequently the anode and the cathode after the catalyst coated membrane is formed, also comprises a binder polymer for binding the particles of the electrochemically active material together. When the binder polymer is in the sulfonyl fluoride form, the solvent can be a variety of solvents, such as FLUORINERT FC-40, commercially available from 3M of St. Paul, Minnesota, which is a mixture of perfluoro (methyl-di-n-butyl) amine and perfluoro (tri-n- butylamine) . In this embodiment, a copolymer polymerized from tetrafluoroethylene and a vinyl ether which is represented by the formula

CF₂=CF-0-CF₂CF(CF₃) -0-CF₂CF₂S0₂F has been found to be a suitable binder polymer. In addition, ruthenium dioxide has been found to be a suitable catalyst. The sulfonyl fluoride form has been found to be compatible with FC-40 and to give a uniform coating of the ruthenium dioxide catalyst on the membrane.

If a catalyst-coated membrane as described above is used, the electrochemical cell must include a gas diffusion layer (not shown) disposed in contact with the anode and the cathode, respectively, (or at least in contact with the anode) , on the side of the anode or cathode opposite the side which is in contact with the membrane. The gas diffusion layer provides a porous structure that allows the hydrogen halide, and specifically, the anhydrous hydrogen halide, or the hydrogen chloride, to diffuse through to the layer of electrochemically active material of the catalyst- coated membrane. In addition, both the anode gas diffusion layer and the cathode gas diffusion layer distribute current over the electrochemically active material, or area, of the catalyst-coated membrane. The diffusion layers are preferably made of graphite paper, and are typically 15 - 20 mil thick.

As noted above, when converting anhydrous hydrogen halide to dry halogen gas in the electrochemical cell of the present invention, water is added to the electrochemical cell through the cathode-side inlet. The protons which are produced by the oxidation of the hydrogen halide are transported through the membrane and reduced at the cathode to form hydrogen gas. This hydrogen gas is evolved at the interface between the cathode and the membrane. The hydrogen gas, which is shown as H₂ in Figs. 1 and 2, exits the cell through the cathode-side outlet and through a line 18 as shown in Fig. 1. In addition, a portion of the water supplied to the cathode-side inlet is released through the cathode-side outlet, as shown as H 0 in Figs. 1 and 2, and through line 18. The hydrogen gas and the water are separated in a separator 24 as shown in Fig. 1, which returns the water through line 16 to the cathode-side inlet. In reality, not all the water may be separated from the hydrogen gas, so that the hydrogen gas may be saturated with moisture when it is sent to the fuel cell. However, for simplicity of illustration, just H₂ is shown being sent to the fuel cell in Fig. 1. The hydrogen gas is sent through a line 17 to a fuel cell. Returning again to the description of Fig. 2, the electrochemical cell of the present invention further comprises an anode flow field 116 disposed in contact with the anode and a cathode flow field 118 disposed in contact with the cathode as shown in Figs. 2 and 2A. The flow fields are electrically conductive, and act as both mass and current flow fields. Preferably, the anode and the cathode flow fields comprise porous graphite paper. Such flow fields are commercially available from Spectracorp, of Lawrence, Massachusetts. However, the flow fields may be made of any material and in any manner known to one skilled in the art. For example, the flow fields may alternatively be made of a porous carbon in the form of a foam, cloth or matte. For the purpose of acting as mass flow fields, the anode mass flow field includes a plurality of anode flow channels 120, and the cathode mass flow field includes a plurality of cathode flow channels 122 as shown in Fig. 2A, which is a cut-away, top cross-sectional view showing only the flow fields of Fig. 2. Preferably, the channels of the anode mass flow field and the channels of the cathode mass flow field are parallel to each other, and more particularly, are vertical and parallel to each other. The anode flow fields and the anode flow channels get reactants, such as anhydrous hydrogen chloride, to the anode and products, such as dry chlorine gas, as well as any unreacted hydrogen halide, such as unreacted hydrogen chloride, from the anode. The cathode flow field and the cathode flow channels get catholyte, such as liquid water to the membrane in the case where anhydrous hydrogen halide is converted and products, such as hydrogen gas and water, from the cathode.

The electrochemical cell of the present invention may also comprise an anode-side gasket 124 and a cathode-side gasket 126 as shown in Fig. 2. Gaskets 124 and 126 form a seal between the interior and the exterior of the electrochemical cell. Preferably, the anode-side gas is made of a fluoroelastomer , sold under the trademark VITON^® (hereinafter referred to as VITON^®) by DuPont Dow Elastomers L.L.C. of Wilmington, Delaware. The cathode-side gasket may be made of the terpolymer ethylene/propylene/diene (EPDM) , sold under the trademark NORDEL^® by DuPont, or it may be made of VITON^®. The electrochemical cell of the present invention also comprises an anode current bus 128 and a cathode current bus 130 as shown in Fig. 2. The current buses conduct current to and from a voltage source (not shown) . Specifically, anode current bus 128 is connected to the positive terminal of a voltage source through a line 20 as shown in Fig. 1, and cathode current bus 130 is connected to the negative terminal of the voltage source through a line 22 as shown in Fig. 1, so that when voltage is applied to the cell, current flows through all of the cell components to the right of current bus 128 as shown in Fig. 2, including current bus 130, 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 present invention may further comprise an anode current distributor 132 as shown in Fig. 2. The anode current distributor collects current from the anode current bus and distributes it to the anode by electronic conduction. The anode current distributor may comprise a fluoro- polymer which has been loaded with a conductive material. In one embodiment, the anode current distributor may be made from polyvinylidene fluoride, sold under the trademark KYNAR® (hereinafter referred to as "KYNAR®") by Elf Atochem North America, Inc. Fluoropolymers, and graphite.

The electrochemical cell of the present invention may further comprise a cathode current distributor 134 as shown in Fig. 2. The cathode current distributor collects current from the cathode and for distributing current to the cathode bus by electronic conduction. The cathode distributor also provides a barrier between the cathode current bus and the cathode and the hydrogen chloride. Like the anode current distributor, the cathode current distributor may comprise a fluoropolymer, such as KYNAR®, which has been loaded with a conductive material, such as graphite.

The electrochemical cell of the present invention also includes an anode-side stainless steel backer plate (not shown) , disposed on the outside of the cell next to the anode current distributor, and a cathode- side stainless steel backer plate (also not shown) , disposed on the outside of the cell next to the cathode current distributor. These steel backer plates have bolts extending therethrough to hold the components of the electrochemical cell together and add mechanical stability thereto.

When more than one anode-cathode pair is used, such as in manufacturing, 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. To create such a bi-polar stack, anode current distributor 132 and every element to the right of the anode current distributor as shown in Fig. 2, up to and including cathode current distributor 134, are repeated along the length of the cell, and current buses are placed on the outside of the stack.

For the electrochemical cell described above, a voltage in the range of 1.0 to 2.0 volts may be applied. A current density of greater than 5.38 kA/m² (500 amps/ft²) , which is achieved in the Uhde system of the prior art) may be achieved at a voltage of 2 voltes or less. In fact, a current density in the range of 8 - 16 kA/m² or greater may be achieved, with 8 - 12 kA/m² being the average range for current density at a voltage of 1.8 to 2.0 volts. The current efficiency, that is, the amount of electrical energy consumed in converting anhydrous hydrogen halide to halogen gas, of the electrochemical cell of the present invention, is on the order of 98% - 99%. In addition, in the present invention, the electrochemical cell has a utility, that is, conversion per pass, or mole fraction of anhydrous hydrogen halide converted to essentially dry halogen gas per single pass in the range of 50% - 90%, with 70% being the average. The amount of water, in the vapor state, in the anolyte outlet due to membrane hydration is less than 400 parts per million (ppm) , and is typically in the range of 200 - 400 ppm.

The electrochemical cell of the present invention can be operated at higher temperatures at a given pressure than electrochemical cells of the prior art which convert aqueous hydrogen chloride to chlorine . This affects the kinetics of the reactions and the conductivity of the membrane. Higher temperatures result in lower cell voltages. However, limits on temperature occur because of the properties of the materials used for elements of the cell. For example, 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 approaching 150°C. Thus, a range of operating temperatures for a polymer electroylyte membrane is 40°C - 120°C. However, with a membrane made of other materials, such as ceramic material like beta-alumina, it is possible to operate a cell at temperatures about 200°C. Room temperature operation is possible, with the attendant advantage of ease of use of the cell. However, operation at elevated temperatures provides the advantages of improved kinetics and increased water activity for membrane hydration. A preferred range of temperatures is 60°C - 90°C.

It should also be noted that one is not restricted to operate the electrochemical cell of the present invention at atmospheric pressure. The cell may be run at different pressures, which change the transport characteristics of water or other components in the cell, including the membrane. A range of operating pressures is 30 - 110 psig, with 60 - 110 preferred. The system of the present invention also comprises a fuel cell connected to the outlet means of the electrochemical cell and powered by the hydrogen gas produced by the electrochemical cell . A fuel cell according to the present invention is shown generally at 200 in Fig. 1. Fuel cell 200 comprises a membrane 210, and an anode 204 and a cathode 210 disposed in contact with the membrane. The anode, cathode and membrane may be constructed as discussed above for the electrochemical cell. The fuel cell of the present invention also has a fuel-cell anode side inlet 206 for supplying the hydrogen gas to the anode of the fuel cell . The hydrogen gas is sent from the electrochemical cell to the fuel cell through a line, such as line 17 as shown in Fig. 1. The fuel cell also has a fuel cell cathode-side inlet 212 for supplying an oxygen- containing gas, or oxidant, such as oxygen or air, to the fuel cell membrane. Fuel cell 200 operates like any fuel cell known n the art, where power is produced, and water and air are produced in the fuel cell . The system of the present invention thus further includes a fuel cell cathode-side outlet 214 for releasing water and air from the fuel cell .

The hydrogen and the oxidant enter the respective inlets and penetrate the electrodes, which are porous, to contact the surface of the membrane. On the anode, or hydrogen side of the fuel cell, electrons are given up and the hydrogen ions migrate to the cathode chamber, where they combine with returning electrons in the presence of oxygen to form water. Water is formed in the cathode chamber and is carried out through outlet 214. If air is the oxidant, outlet 214 is also employed to remove nitrogen which builds up.

The fuel cell thus produces DC power. Thus, a benefit of the present invention is that electric power is produced without consuming fossil or nuclear fuels or atmospheric pollutants. In this way, the present invention affords a method of converting hydrogen gas to clean energy.

The DC power produced by the fuel cell may be used to supplement the total power required to run the electrochemical process which is occurring in cell 100. Alternatively, the DC power produced by the fuel cell may be used to run any electrochemical process, or indeed any process, which consumes electrical energy. To implement the former case, the positive terminal of the electrochemical cell may connected to the positive terminal of the fuel cell by an electronic conductor, such as a cable, wire or bus bar. The negative terminal of the electrochemical cell is connected to the negative terminal of the fuel cell by an electronic conductor, such as a cable, wire or bus bar. Th s hook-up delivers the electric power produced by the fuel cell back to the electrochemical cell, thereby providing a portion of the power necessary to run the process. The rest of the power necessary to run the process may be provided by a voltage rectifier, not shown, which converts conventionally supplied AC power to DC power, which is compatible to that produced by the fuel cell. Further in accordance with the present invention, there is provided a process for powering a fuel cell from hydrogen gas produced by the conversion of hydrogen halide produced in an electrochemical cell. This process will be described with respect to the conversion of anhydrous hydrogen chloride to dry chlorine gas, although it should be understood that it may also apply to the conversion of any hydrogen halide to halogen gas, either anhydrous or aqueous. Moreover, this process will be described with respect to the system of Fig. 1, although the process should not be limited in any way to the elements shown in Fig. 1. In operation, a voltage is applied to the anode and the cathode of an electrochemical cell, such as cell 100, so that the anode is at a higher potential than the cathode, and current flows to an anode bus, such as anode bus 132. An anode current distributor, such as distributor 128, collects current from the anode bus and distributes it, to the anode by electronic conduction. Anhydrous hydrogen chloride gas, which is in molecular or vapor form, or aqueous hydrogen chloride, is fed to an anode-side inlet, such as inlet 102, and through flow channels in an anode mass flow field, such as channels 120 in flow field 116. Hydrogen chloride is transported to the surface of anode 104. Hydrogen chloride is oxidized at the anode under the potential created by the voltage source to produce essentially dry chlorine gas at the anode, and protons (H⁺) . This reaction is given by the equation:

Electrical 2HCl(g) ^Ener9y *► 2H⁺ + Cl₂ (g) + 2e^" The chlorine gas exits through an anode-side outlet, such as outlet 106 as shown in Fig. 2 and through a line, such as line 16 as shown in Fig. 1.

The protons are transported through the membrane, which acts as an electrolyte. The transported protons are reduced at the cathode. This reaction is given by the equation:

Electrical

Energy

2H⁺ + 2e^~ H₂(g)

The membrane of the electrochemical cell must be hydrated in order to have efficient proton transport and to increase the efficiency of proton transport through the membrane. Thus, water is delivered to the cathode through a cathode-side inlet, such as inlet 112 as shown in Fig. 2 and through the channels in cathode mass flow field, such as channels 120 in cathode mass flow field 116 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 cathode and the membrane exits via cathode-side outlet, such as outlet 114 as shown in Fig. 1. The hydrogen bubbles through the water and is not affected by the electrode. A cathode current distributor, such as distributor 134 as shown in Fig. 2, collects current from the cathode and distributes it to a cathode bus, such as bus 130 as shown in Fig. 2.

The hydrogen gas and water which are released from the electrochemical cell are sent to a fuel cell, where, further in accordance with the process of the present invention, the hydrogen gas is used to power the fuel cell, which produces DC power. For this purpose, the hydrogen gas and water are sent to a fuel-cell anode side inlet, such as inlet 206. An oxygen-containing gas, or oxidant, such as oxygen or air, is supplied to the cathode-side inlet of the cell. In the fuel cell, power, as well as water and air, are produced. The water and air are released from the fuel cell through a cathode-side outlet, such as outlet 214 as shown in Fig. 1.

The hydrogen and the oxidant enter the respective inlets and penetrate the electrodes, which are porous, to contact the surface of the membrane. On the anode, or hydrogen side of the fuel cell, electrons are given up and the hydrogen ions migrate to the cathode chamber, where they combine with returning electrons in the presence of oxygen to form water. The water is formed in the cathode chamber and is carried out through the cathode-side outlet. If air is the oxidant, the cathode-side outlet is also employed to remove nitrogen which builds up. The fuel cell thus produces DC power.

In accordance with the process of the present invention, the DC power produced by the fuel cell may be used to supplement the total power required by the electrochemical process which occurs in cell 100. Alternatively, the DC power produced by the fuel cell may be used to run any electrochemical process, or indeed any process, which consumes electrical energy. The use of the DC power produced by the fuel cell to supplement the total power required by the electro- chemical cell is accomplished by the configuration described above with respect to the system of the present invention.

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 and representative apparatus 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.

Claims

WHAT IS CLAIMED IS:

1. A system for producing hydrogen gas in an electrochemical cell and for using the hydrogen gas for powering a fuel cell, comprising: (a) an electrochemical cell, including:

(i) means for oxidizing hydrogen halide to produce hydrogen gas and protons,

(ii) cation-transporting means for transporting the cations therethrough, wherein one side of the cation-transporting means is disposed in contact with the oxidizing means,

(iii) reducing means for reducing the protons to produce hydrogen gas, wherein the other side of the cation-transporting means is disposed in contact with the reducing means, and

(iv) outlet means for releasing the hydrogen gas from the electrochemical cell; and (b) a fuel cell connected to the outlet means and powered by the hydrogen gas .

2. The system of Claim 1, wherein the hydrogen halide is aqueous hydrogen chloride, the wherein the oxidizing means is an anode, the cation-transporting means is a membrane, and the reducing means is a cathode.

3. The system of Claim 1, wherein the hydrogen halide is anhydrous hydrogen chloride, wherein the oxidizing means is an anode, the cation-transporting means is a membrane, and the reducing means is a cathode .

4. The system of Claim 3, further including anode-side inlet means for supplying molecular, anhydrous hydrogen chloride to the electrochemical cell.

5. The system of Claim 4, further including anode-side outlet means for releasing dry chlorine gas from the electrochemical cell.

6. The system of Claim 5, further including cathode-side inlet means for delivering water to the membrane .

7. The system of Claim 6, further including cathode-side outlet means for releasing the water and the hydrogen gas from the electrochemical cell.

8. The system of Claim 7, wherein the fuel cell comprises a membrane, and an anode and a cathode disposed in contact with the membrane.

9. The system of Claim 8, further including a fuel-cell anode-side inlet for supplying the hydrogen gas and the water to the anode of the fuel cell.

10. The system of Claim 9, further including a fuel cell cathode-side inlet for supplying an oxygen- containing gas to the cathode-side inlet of the fuel cell .

11. The system of Claim 10, further including a fuel cell cathode-side outlet for releasing water and air from the fuel cell.

12. A process for powering a fuel cell from hydrogen gas produced in an electrochemical cell, comprising the steps of:

(a) supplying hydrogen halide to the inlet of an electrochemical cell comprising a membrane and an anode and a cathode each disposed in contact with the membrane ; and

(b) applying a voltage to the electrochemical cell such that the anode is at a higher potential than the cathode, and so that: (i) the hydrogen halide is oxidized at the anode to produce halogen gas and protons ,

(ii) the protons are transported through the membrane,

(iii) the protons are reduced at the cathode to form hydrogen gas; and

(iv) the hydrogen gas is used to power a fuel cell which produces DC power.

13. The process of Claim 12, wherein the hydrogen halide is anhydrous hydrogen chloride.

14. The process of Claim 12, wherein the hydrogen halide is aqueous hydrogen chloride.

15. The process of Claim 13 or 14, wherein the DC power produced by the fuel cell is used to supplement the total power required to run the electrochemical cell .