Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B13/00—Diaphragms; Spacing elements
  • C25B13/04—Diaphragms; Spacing elements characterised by the material
• • 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
  • C25B1/02—Hydrogen or oxygen
  • C25B1/04—Hydrogen or oxygen by electrolysis of water
• • 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
  • C25B1/18—Alkaline earth metal compounds or magnesium compounds
  • C25B1/20—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
  • C25B1/24—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
  • 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
  • C25B9/70—Assemblies comprising two or more cells
  • C25B9/73—Assemblies comprising two or more cells of the filter-press type
• • 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
  • Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis

Definitions

• the present invention relates in general to the electrochemical production of hydrogen. More particularly, the present invention provides systems and methods for producing hydrogen through the use of an electrochemical cell in which the anolyte comprises an oxidizable substance that has a higher standard oxidation potential than water.
• Hydrogen gas is used in a variety of industrial applications. For instance, hydrogen is often used in the creation of ammonia for fertilizer, for the conversion of heavy- petroleum sources to lighter fractions through a process called hydrocracking, for the production of nickel -hydrogen batteries, and for several other applications. Hydrogen is a clean burning fuel and a source of energy for fuel cells.
• hydrogen can be produced through an assortment of techniques, including through the electrolysis of water, the reaction of a metal with an acid, the steam reformation of natural gas, the partial oxidation of hydrocarbons, and through several other methods.
• hydrogen gas is formed through the electrolysis of water.
• water or an alkaline water solution is placed in an electrolytic cell comprising an anode and a cathode. Then as an electrical current is passed between the anode and cathode, hydrogen is produced at the cathode by reduction of water and oxygen is produced at the anode by water oxidation.
• the two electrode half reactions for traditional alkaline water electrolysis are;
• the present invention provides systems and methods for producing hydrogen gas through the use of an electrochemical cell.
• the cell can comprise any suitable components, in some non-limiting instances, the cell comprises an anolyte compartment that houses an anolyte and an anode, a catholyte compartment that houses a catholyte and a cathode, and an alkali cation selective membrane that is disposed between the catholyte compartment and the anolyte compartment.
• the cell is configured to hold a hydrogen-containing reducible substance in the catholyte to produce hydrogen gas on the cathode and the anode and/or anolyte may comprise any suitable substance that oxidizes on the anode such that the cell has an open circuit cell voltage of less than about 1.23 V and an operating voltage that is typically ⁇ 1.8V at practical current densities when the cell produces hydrogen.
• references to the anode containing a suitable oxidizable substance are also applicable to the anolyte and vice versa.
• the term "anode/anolyte" is to mean the anode, the anolyte, or both.
• the oxidizable substance herein is selected to be easier to oxidize than water.
• a lower cell voltage than traditional water electrolysis is achieved by- utilizing a suitable oxidizable substance having a higher standard oxidation potential than oxygen generation reaction from water (i.e. a substance that is easier to oxidize) as the anode reaction.
• suitable oxidizable substances include, but are not limited to, an iodide ion, a sulfide ion, a manganese oxide ion, and an aluminum oxide ion.
• the oxidizable substance may be in the form of an alkali metal salt of the oxidizable substance that is added to the anolyte.
• the oxidizable substance may be in the form of the solid anode.
• suitable alkali metal salts include, without limitation, an iodide, sulfide, manganese oxide, and aluminum oxide of each of the following: sodium, lithium, and potassium.
• the oxidizable substance is a in a substantially solid form as is applied as a coating to a suitable current collector.
• the anode/anolyte may also comprise any other suitable material .
• the anolyte can comprise a non-aqueous solvent (including, without limitation, glycerol and/or anhydrous methanol), a second and different alkali metal salt, a solid-state conductive additive (e.g., graphite), an aqueous solution, an ionic liquid, and/or any other suitable material or a liquid conductive additive (e.g.Tetramethylammonium Tetrafluroborate or conductive metal particles).
• the catholyte can comprise any suitable substance that allows the cell to reduce a reducible substance in the catholyte to form hydrogen and when combined with the aforementioned anolyte, allows the cell to have an open cell voltage (OCV) of less than about 1 ,23V and an operating voltage ⁇ 1.8V at practical current densities during hydrogen production.
• suitable substances include, but are not limited to, an alkali hydroxide or carbonate (e.g., sodium hydroxide or sodium carbonate) and/or a non-aqueous methanol/alkali methoxide solution (e.g., a nonaqueous methanol/sodium methoxide solution).
• the anode/anolyte current collector may comprise any suitable material that allows the oxidizable substance in the anode/anolyte to oxidize when electrical current passes between the anode and the cathode.
• suitable anode current collector materials include, but are not limited to, variety of stainless steels, metal alloys such as KOVAR, titanium, platinum, lead dioxide, carbon-based materials (e.g., boron-doped diamond, glassy carbon, synthetic carbon, carbides, graphite etc.), metal oxides such as Dimensionally Stable Anode and other known or novel anode materials.
• the anode comprises a dimensionally stable anode, which may include, but is not limited to, rhenium dioxide and titanium dioxide on a titanium substrate, and ruthenium dioxide and tantalum pentoxide on a titanium substrate.
• the cathode current collector can compri se any suitable material that allows electron transfer to the reducible substance in the catholyte to produce hydrogen gas.
• suitable cathode current collector materials include, without limitation, nickel, stainless steel, graphite, a nickel -cobalt-ferrous alloy (e.g., a KOVAR® alloy), and any other suitable cathode material that is known or novel.
• the membrane can comprise virtually any suitable alkali cation selective membrane.
• Such membranes include, but are not limited to, a NaSICON membrane, a NaSICON-type membrane, a LiSICON membrane, a LiSICON-type membrane, a KSICON membrane, a KSICON-type membrane, a sodium conducting glass, a ⁇ or P ' alumina membrane, and a solid polymeric sodium ion conductive membrane.
• Whi le the cell can function in any suitable manner, in some non-limiting instances, as an electrical current passes between the anode and the cathode, the reducible substance in the catholyte (e.g., water or methanol) is reduced to evolve hydrogen and the oxidizable substance in the anode/anolyte is oxidized to produce an oxidized product.
• the alkali metal salt of the oxidizable substance is selected from sodium iodide, sodium sulfide, sodium manganese oxide, or sodium aluminum oxide
• the oxidizable substance can be oxidized to form triodide complex ion or molecular iodine, molecular sulfur, manganese oxide, and alumina, respectively.
• the alkali cations from the alkali metal salt of the oxidizable substance are driven through the alkali cation selective membrane to allow the cations to enter the catholyte compartment where the cations can react to form an alkali hydroxide, an alkali methoxide, and/or a variety of other substances.
• the oxidizable substance in the anolyte e.g., the iodide ion or sulfide ion
• an oxidized product e.g., molecular iodine/tri -iodide or sulfur
• the oxidized product can be reacted with the alkali hydroxide from the catholyte compartment to regenerate the alkali metal salt of the oxidizable substance.
• molecular iodine or triodide complex ion is formed from the oxidation of the iodide ion and sodium hydroxide can be formed in the catholyte compartment.
• the molecular iodine or triodide complex ion and the sodium hydroxide can be reacted together to regenerate sodium iodide, which can be recycled through the ceil. This regeneration of oxidizable material ensures continuous production of hydrogen from water without the requirement to supply fresh oxidizable material.
• Another embodiment of the disclosed invention controls the pH of the catholyte compartment to a pH within the range of about 6 to 8. It has been found that an operating pH near neutral in the catholyte compartment helps lower the overall cell voltage. [0018] In some embodiments, the pH of the cathoiyte is maintained in the range of about 6 to 8 through the use of one or more buffer compounds. In one non-limiting embodiment, an alkali metal borate is added to the cathoiyte to lower and maintain the pH in a desired range.
• the described systems and methods have been found to be particularly useful for the production of hydrogen through the use of sodium iodide in the anolyte
• the described methods may be modified to produce hydrogen through the use of one or more other oxidizable substances that has a higher standard oxidation potential than oxygen evolution reaction from water.
• the described systems and methods may use any other alkali salt of a suitable oxidizable substance.
• the described systems and methods may use potassium iodide, lithium iodide, and/or a sulfide anolyte solutions or solid anode made of suifide/poiysulfide, manganese oxide, or aluminum oxide of an alkali metal selected from sodium, potassium, and lithium.
• Another embodiment of the disclosed invention regenerates the anolyte oxidizable substance.
• the sodium iodide can be regenerated in any suitable manner.
• the sodium iodide is regenerated by reacting oxidized product (iodine or triodide) from the anolyte with sodium hydroxide from the cathoiyte (or some other suitable source such as sodium methoxide). Therefore, practically all of the sodium iodide (or other alkali metal salt) can be regenerated for use in the cell.
• Figure 1 depicts a schematic diagram of a representative embodiment of an electrochemical cell that is configured to produce hydrogen
• Figure 2A depicts a flow chart showing a representative embodiment of a method for using the electrochemical cell
• Figure 2B depicts a schematic diagram of a representative embodiment of the electrochemical cell in which the cell comprises an anolyte that comprises sodium iodide, and a catholyte that comprises a sodium hydroxide solution,
• Figure 3 is a pourbaix diagram of electric potential vs. pH for the catholyte and anolyte reactions
• Figure 4 depicts a schematic diagram of aa representative embodiment of an electrochemical cell that is configured to produce hydrogen and to a companion electrochemical cell that is configured to regenerate the oxidizable substance;
• Figure 5 depicts a graph showing test results that plots current against voltage for one embodiment of the cell at a scan rate of 5 mV/s;
• Figure 6 depicts a graph showing test results that plots voltage against time for one embodiment of the cell wherein voltage is applied to the cell at about ImA/cm 2 ;
• Figure 7 depicts a graph showing test results that plots voltage against time for one embodiment of the cell wherein voltage is applied to the cell at about 25 mA/cm 2 .
• the present invention provides systems and methods for producing hydrogen gas through the use of an electrochemical cell that has a cell open circuit voltage that is lower than the traditional open circuit voltage for water splitting ⁇ 1.23V and an operating voltage ⁇ 1.8V at practical current densities. Accordingly, the hydrogen production begins when the voltage of the electrochemical cell is less than the theoretical decomposition of water. In order to do this, the current systems and methods replace the water oxidation reaction from traditional water electrolysis with a different anode reaction that has a higher standard oxidation potential than oxygen evolution from water. To provide a better understanding of the described systems and methods, the electrochemical cell is described below in more detail. This description of the cell is then followed by a more detailed description of the manner in which the cell can be operated.
• the cell can comprise any suitable anode that allows it to produce hydrogen gas at practical levels at an overall ceil operating voltage that is less than about 1 .8V.
• Figure 1 shows a representative embodiment in which the electrochemical ceil 10 comprises an anoiyte compartment 15 that houses an anoiyte 20 and an anode 25; a catholyte compartment 30 that houses a catholyte 35 and cathode 40; and an alkali cation selective membrane 45.
• the two compartments can be any suitable shape and have any other suitable characteristic that allows the cell 10 to function as intended.
• the anoiyte and the catholyte compartments can be tubular, rectangular, or be any other suitable shape.
• the specific anode and cathode reactions allow the cell 10 to have an open circuit voltage that is less than about the theoretical decomposition voltage of water, or 1.23 V, when the cell 10 produces hydrogen.
• the anoiyte can comprise any suitable oxidizable substance that has a standard oxidation potential for the oxidation of the oxidizable substance that is higher than that of oxygen potential for the oxidation of water (i.e. easier to oxidize than water) and that allows the cell to function as intended.
• the anoiyte can comprise any suitable oxidizable substance that allows the open circuit cell voltage for the production of hydrogen from water to be less than a voltage selected from about 1.23 V, about 1.1V, about 0.9V, and about 0.7V or less.
• suitable oxidizable substances include, but are not limited to, an iodide ion, a sulfide ion, a manganese oxide ion, an aluminum oxide ion, and any other suitable oxidizable substance that has an oxidation potential that is higher than that of oxygen evolution from water,
• the oxidizable substance in the anolyte 20 can be added to the anolyte in any suitable manner.
• the oxidizable substance e.g., the iodide ion, sulfide ion, etc
• the oxidizable substance can be added to anolyte through the addition of an alkali metal salt of the oxidizable substance.
• suitable alkali metal salts of suitable oxidizable substances include, but are not limited to, sodium iodide, sodium sulfide, lithium iodide, lithium sulfide, potassium iodide, potassium sulfide, and/or any other suitable alkali metal salt of a suitable oxidi zable substance.
• the alkali metal salt comprises sodium iodide.
• the oxidizable substance can also be a solid in which case it is the anode.
• the solid oxidizable substance e.g., the manganese oxide, aluminum oxide, etc.
• the oxidizable substance can be made as thin film anode.
• suitable alkali metal salts of suitable oxidizable substances include, but are not limited to, sodium sulfide/poiysulfide, sodium manganese oxide, sodium aluminum oxide, lithium sulfide/poiysulfide, lithium manganese oxide, lithium aluminum oxide, potassium sulfide/poiysulfide, potassium manganese oxide, potassium aluminum oxide, and/or any other suitable alkali metal salt of a suitable oxidizable substance.
• the alkali metal salt comprises sodium sulfide/poiysulfide.
• the alkali metal salt of the oxidizable substance can react in any suitable manner.
• the salt when the alkali metal salt is added to anolyte, the salt can be ionized.
• the oxidizable substance of the alkali iodide, alkali sulfide, alkali manganese oxide, an alkali aluminum oxide, and/or another suitable alkali metal salt in the anode/anolyte can respectively be oxidized to form molecular iodine/tri iodide, molecular sulfur, manganese oxide, alumina, and/or another oxidized product in the anolyte.
• the alkali cation e.g., Na "1" , Li + , and K “f
• the alkali cation selective membrane 45 described below
• the cation can react to form an alkali hydroxide, alkali methoxide and gaseous hydrogen product.
• the anolyte 20 can comprise any other suitable component that allows the oxidizable substance to be oxidized at the anode 25 and that allows the open circuit voltage of the cell 10 to be less than about 1.23 V during hydrogen production at the cathode.
• the anolyte can also comprise any suitable: non-aqueous solvent (including, without limitation, glycerol, anhydrous methanol, and/or another suitable non-aqueous solvent), ionic liquid, and/or aqueous solvent, solid-state conductive additive (including, without limitation, graphite, metal particles and/or another suitable conductive additive), complexing agent (tetram ethyl ammonium tetraflurob orate or tetrabutyl ammonium iodide).
• non-aqueous solvent including, without limitation, glycerol, anhydrous methanol, and/or another suitable non-aqueous solvent
• ionic liquid including, without limitation, graphite, metal particles and/or another suitable conductive additive
• complexing agent tetram ethyl ammonium tetraflurob orate or tetrabutyl ammonium iodide.
• the additional additives to the anolyte should not cause the prefer
• the additional additives to the anolyte do chemically react with the oxidized substance (e.g. complexation of tetrabutyl ammonium iodide with molecular iodine to form tetrabutyl ammonium tiiodide).
• the anolyte 20 comprises an alkali metal salt as an oxidizable substance that is mixed with a conductive additive (e.g., graphite) and a liquid additive/solvent, such as glycerol, to form a semi-solid paste.
• a conductive additive e.g., graphite
• a liquid additive/solvent such as glycerol
• the anolyte comprises sodium iodide or sodium sulfide, graphite, and a small amount of glycerol.
• the anolyte comprises a non-oxidizable alkali metal salt (e.g., sodium trtraflurob orate or sodium hexafluorophosphate) that is dissolved in a suitable solvent (e.g., methanol, water, and/or an ionic liquid).
• a suitable solvent e.g., methanol, water, and/or an ionic liquid.
• the anolyte comprises oxidizable sodium iodide or sodium sulfide that is dissolved in a suitable solvent (e.g., methanol, water, and/or an ionic liquid).
• the anolyte comprises sodium iodide or sodium sulfide in water.
• the catholyte can comprise any suitable substance that allows the cell 10 to reduce a reducible substance, such as water and/or methanol, in the catholyte to form hydrogen and allows the cell to have an open circuit voltage that is less than a voltage selected from about 1.23V, about 1.1V, about 0.9V, and about 0.7V or less and an operating voltage ⁇ 1.8V at practical currents when the cell produces hydrogen.
• a reducible substance such as water and/or methanol
• Suitable catholytes include, but are not limited to, an aqueous alkali hydroxide solution (e.g., an aqueous solution comprising sodium hydroxide, lithium hydroxide, and/or potassium hydroxide, an aqueous solution compri sing sodium carbonate, lithium carbonate, and/or potassium carbonate, an aqueous solution comprising acetic acid, halogen and mixtures thereof) and a non-aqueous methanol/alkali methoxide solution, wherein the alkali methoxide is selected from sodium methoxide, lithium methoxide, and potassium methoxide.
• the catholyte comprises an aqueous sodium hydroxide solution or a non-aqueous methanol/sodium methoxide solution.
• the anode and/or anode current collector can comprise any suitable characteristic or material that allows the cell 10 to oxidize the oxidizable substance in the anolyte 20 and to otherwise function as intended.
• the anode and/or anode current collector can have any suitable characteristic, including, without limitation, being; a flat plate, a flat membrane, a mesh, a tubular shape, and/or a tubular mesh.
• suitable anode and/or anode current collector materials include, but are not limited to, stainless steel, titanium, lead dioxide, carbon-based materials (e.g., boron-doped diamond, glassy carbon, synthetic carbon, etc.), platini zed titanium, ruthenium. (IV) dioxide (Ru0 2 ), dimensionally stable anode materials, and/or any other suitable anode material .
• the anode and/or anode current collector comprises a stainless steel mesh.
• the anode 25 comprises a dimensionally stable anode, which may include, but is not limited to, a rhenium dioxide and titanium dioxide on a titanium substrate, and a rhenium dioxide and tantalum pentoxide on a titanium substrate.
• the dimensionally stable anode may help the cell 10 to preferentially oxidize the oxidizable substance (e.g., the iodide ion, the sulfide ion, etc.) over some other chemicals in the anolyte.
• the cathode can comprise any suitable characteri stic or material that allows the cell 10 to reduce the reducible substance (e.g., water and/or methanol) to produce hydrogen and to otherwise allow the cell to function as intended.
• the cathode can have any suitable characteristic, including, without limitation, being: a flat plate, a flat membrane, a mesh, a tubular shape, and/or a tubular mesh.
• suitable cathode materials include, but are not limited to, nickel, stainless steel, graphite, a nickel-cobalt-ferrous alloy (e.g., a KOVAR® alloy), and/or any other suitable cathode material.
• the cathode comprises a nickel mesh cathode.
• any suitable reaction that allows the cell 10 to produce hydrogen can occur at the cathode 40.
• suitable anodic reactions when the alkali metal of the oxidizable alkali metal salt is sodium include, but are not limited to, the following:
• alkali metal of the oxidizable alkali metal salt is sodium
• suitable cathodic reactions when the alkali metal of the oxidizable alkali metal salt is sodium include, but are not limited to, the following:
• the cathoiyte 35 comprises sodium hydroxide or sodium carbonate solution
• more sodium hydroxide will form in the cathoiyte compartment 30 along with gaseous hydrogen.
• the alkali metal salt in the cathoiyte 35 comprises a lithium methylate and methanol
• more lithium methoxide along with gaseous hydrogen will be formed in the cathoiyte compartment 30 as the cell 10 functions.
• the membrane can comprise virtually any suitable cation selective membrane that is configured to selectively- transport an alkali cation (e.g., Na " , Li “1” , or K T ) from the anoiyte compartment 15 to the cathoiyte compartment 30 under the influence of an electrical potential.
• an alkali cation e.g., Na " , Li “1” , or K T
• the membrane can prevent the anoiyte and cathoiyte from mixing, while still allowing alkali cations (shown as M + in Figure 1) to migrate to the cathoiyte compartment 30.
• the membrane allows the cell 10 to comprise a non-aqueous anoiyte and an aqueous cathoiyte, and vice versa.
• a NaSICON membrane e.g., a NaSICON-type membrane as produced by Ceramatec, Inc., Salt Lake City, Utah
• a LiSICON membrane e.g., a LiSICON-type membrane as produced by Ceramatec, Inc., Salt Lake City, Utah
• a LiSICON membrane e.g., a LiSICON-type membrane as produced by Ceramatec, Inc., Salt Lake City, Utah
• a LiSICON membrane e.g., a LiSICON-type membrane as produced by Ceramatec, Inc., Salt Lake City, Utah
• LiSICON membrane e.g., a LiSICON-type membrane as produced by Ceramatec, Inc., Salt Lake City, Utah
• a LiSICON membrane e.g., a LiSICON-type membrane as produced by Ceramatec, Inc., Salt Lake City, Utah
• a LiSICON membrane e.g., a LiSICON-type membrane as produced by Ceramatec, Inc., Salt Lake City,
• the described cell 10 can comprise any other suitable component or characteristic.
• the various compartments of the cell have one or more inlets and/or outlets to allow materials to be added to and/or to be removed from the cell.
• Figure 1 shows an embodiment in which the anolyte compartment 15 comprises an outlet 50 for removing oxidized products 55 (e.g., I 2 or Lf, S, etc.) from the anolyte compartment, and the catholyte compartment 30 comprises an outlet 60 for removing chemicals 65, including without limitation, an alkali hydroxide and/or an alkali methoxide, from the catholyte chamber (depending on whether the catholyte 35 originally comprised water and/or methanol) and hydrogen gas.
• oxidized products 55 e.g., I 2 or Lf, S, etc.
• the catholyte compartment 30 comprises an outlet 60 for removing chemicals 65, including without limitation, an alkali hydroxide and/or an alkali methoxide, from the catholyte chamber (depending on whether the catholyte 35 originally comprised water and/or methanol) and hydrogen gas.
• chemicals 65 including without limitation, an alkali hydroxide and/or an alkali me
• the cell 10 also comprises a power source (not shown).
• the power source can comprise any suitable electrolytic ceil power source.
• the power source can provide the cell with any suitable current density. Indeed, in some embodiments, the power source provides the cell with a current density as low as a current density selected from about 0.5 mA enT, about 1 mA/cm 2 , about 2.5 mA/cm 2 , and about 5 mA/cm ' .
• the power source provides the cell with a current density that is as high as a current density selected from about 15 mA/cm 2 , about 30 mA/cm 2 , about 50 mA/cm 2 , about 100 mA cm', and about 250 mA/cm 2 .
• the cell 10 optionally comprises a heating mechanism that is configured to heat the anolyte 20 and/or catholyte 35 as the cell functions.
• a heating mechanism that is configured to heat the anolyte 20 and/or catholyte 35 as the cell functions.
• the anolyte and/or catholyte are heated to a temperature that i s above a temperature selected from about 40 degrees Celsius, about 60 degrees Celsius, about 80 degrees Celsius, and about 90 degrees Celsius, Moreover, in such embodiments, the anolyte and/or catholyte are kept cooler than a temperature that is selected from about 140 degrees Celsius, about 130 degrees Celsius, about 120 degrees Celsius, and about 100 degrees Celsius.
• Figures 2 A and 2B respectively show a representative embodiment of a flow chart and a schematic diagram depicting an embodiment of a method 100 in which the cell may produce hydrogen.
• the systems and methods shown in Figures 2 A and 2B can be rearranged, added to, shortened, and/or otherwise changed in any suitable manner.
• FIG. 2A shows that a representative embodiment of the described method 100 begins by providing the electrochemical cell 10 (as discussed above).
• step 1 10 shows that the method continues as the anoiyte 20 and catholyte 35 are added to the cell .
• the described systems and methods can be implemented with any suitable anoiyte and/or catholyte (as discussed above), for the sake of simplicity, the following discussion focuses on using the cell with an anoiyte 20 comprising sodium iodide and a catholyte 35 comprising water (e.g., in the form of an aqueous solution of sodium hydroxide).
• Figure 2 A shows the method 100 continues as an electrical potential is applied between the anode 25 and the cathode 40.
• Figure 2B shows that (i) the iodide ion (2 ⁇ ) is oxidized at the anode 25 to form molecular iodine (I 2 ), (ii) the sodium cation (2Na + ) is transported through the membrane 45, and (iii) water (H 2 0) is reduced at the cathode 40 to form hydrogen gas (H 2 ) and hydroxide ions (OH " ), which can react with the sodium cations to form sodium hydroxide (NaOH).
• the following reactions A and E show that, in at least some embodiments, the calculated open cell voltage for the cel l 10 illustrated in Figure 2B is about 0.94V, which is smaller than the .23 V over cell voltage for traditional water electrolysis.
• step 120 in Figure 2A shows that the method 100 optionally includes heating the anoiyte and/or the catholyte, as discussed above.
• step 122 in Figure 2A shows that the catholyte pH may be controlled.
• the pH of the catholyte in the catholyte compartment may be maintained at a near-neutral value.
• the catholyte pH is maintained at a value within the range of about 6 to 8.
• a buffer may be used to lower the pH of the catholyte in the catholyte compartment to a desired value.
• Step 125 further shows that as the method 100 continues, hydrogen gas ( 1 ⁇ >) is collected from the catholyte compartment 30 (also shown in Figure 2B).
• step 130 shows that the method 100 can optionally continue as the oxidizable substance in the anolyte is regenerated.
• the sodium iodide can be regenerated in any suitable manner. Indeed, in some embodiments, the sodium iodide is regenerated by reacting iodine formed during oxidation formed in the anolyte 20 with sodium hydroxide formed in the catholyte 35 (or some other suitable source). Accordingly, most, if not substantially ail, of the sodium iodide (or other al kali metal salt) can be regenerated for use in the cell 10.
• Figure 2B includes a regeneration cell 70, comprising an inlet to receive the oxidized product from the anolyte compartment and the reduced product from the catholyte compartment.
• the regeneration cell is configured to cause a chemical reaction between the oxidized product and the reduced product to regenerate the oxidizable substance.
• the regeneration reaction includes reacting iodine with sodium hydroxide to regenerate sodium iodide.
• the regenerated oxidizable substance can be introduced into the anolyte compartment 15.
• the described methods can be used to regenerate any suitable alkali salt of an oxidizable substance by combining any suitable oxidized product (e.g., molecular iodine or triiodide, molecular sulfur or higher polysulfides, manganese oxide, alumina, etc.) produced in the anolyte compartment 15 with a suitable alkali hydroxide (e.g., sodium hydroxide, potassium hydroxide, or lithium hydroxide) that is produced in the catholyte compartment 30 (or which is obtained from any other suitable source).
• any suitable oxidized product e.g., molecular iodine or triiodide, molecular sulfur or higher polysulfides, manganese oxide, alumina, etc.
• a suitable alkali hydroxide e.g., sodium hydroxide, potassium hydroxide, or lithium hydroxide
• the sodium iodide is regenerated by mixing the molecular iodine or triiodide with sodium hydroxide.
• the reaction can proceed in a variety of manners.
• reactions H and I show that in some embodiments when sodium hydroxide is reacted with iodine, sodium iodate forms.
• reaction J shows that, in other embodiments, the formation of sodium iodate can be avoided.
• the process is configured to preferentially facilitate or reaction J over reactions H and/or I
• the conversion of sodium hydroxide and iodine directly into sodium iodide, water, and oxygen can be driven in any suitable manner, including, without limitation, by adding highly concentrated sodium hydroxide (or another alkali hydroxide) to the iodine (or to another oxidized product): by increasing the reaction temperature; by reacting the sodium hydroxide (or another alkali hydroxide) with the iodine (or another oxidized product) in the presence of a catalyst, ultraviolet light, and/or ultrasonic vibrations, and/or by any other suitable conditions,
• the sodium hydroxide (or other alkyl hydroxide) can have any suitable concentration before it is added to the iodine (or other oxidized product).
• the concentration of the sodium hydroxide (or other alkyl hydroxide) that is added to the molecular iodine (or other oxidized product) is as low as a concentration selected from about 15%, about 25%, about 30%, and about 35% by weight.
• the concentration of sodium hydroxide (or another alkyl hydroxide) that is added to the molecular iodine (or another oxidized product) is as high as a concentration selected from about 35%, about 40%, about 50%, and about 65%, by weight.
• the concentration of the sodium hydroxide is between about 30% and about 50%, by weight, before the sodium hydroxide is added to the molecular iodine.
• the sodium hydroxide can be concentrated in any suitable manner.
• suitable methods for concentrating the sodium hydroxide (or other alkyl hydroxide) include, but are not limited to evaporating solvent (e.g., water) from the sodium hydroxide with heat obtained through solar energy, waste heat produced as an industrial byproduct, heat obtained through geothermal energy, Heat from joule heat generated during cell operation, and/or heat produced in any other suitable manner.
• evaporating solvent e.g., water
• heat obtained from solar energy, geothermal energy, and from industrial waste heat can be relatively inexpensive or substantially free.
• heat sources are also environmentally friendly.
• the sodium hydroxide is concentrated through an evaporative process employing one or more such heat sources.
• the reaction can be heated to any suitable temperature.
• the temperature should be below the boiling point of the reactants.
• the reaction is heated to a temperature that is as high as a temperature selected from about 1 10 degrees Celsius, about 120 degrees Celsius, about 130 degrees Celsius, and about 140 degrees Celsius.
• the reaction may be kept below a temperature as low as a temperature selected from about 100 degrees Cel sius, about 90 degrees Celsius, about 70 degrees Celsius, and about 60 degrees Celsius.
• the reaction is heated to a temperature between about 70 and about 140 degrees Celsius.
• the regeneration reaction is driven by heating the reaction
• the reaction can be heated in any suitable manner.
• the reaction can be heated with heat obtained from solar energy, geothermal energy, industrial waste heat, and/or any other suitable heat source.
• the catalyst can comprise any suitable catalyst, including, without limitation, a carbon catalyst and/or a metal-oxide catalyst.
• a suitable catalyst includes, but i s not limited to, a catalyst comprising copper oxide (CuO) and manganese dioxide (Mn0 2 ).
• the reaction may be exposed to any suitable wavelength of ultraviolet light, from any suitable source, including, without limitation, the sun, an ultraviolet lamp, etc.
• the regeneration of the alkali metal salt e.g., reaction J
• the reaction can be exposed to ultrasonic vibrations having any suitable frequency and amplitude.
• the iodate ion ( ⁇ 0 3 ' ) can be converted to the iodide ion ( ⁇ ) in any suitable manner, in some embodiments, the conversion of the iodate ion is possible when the ion is reduced in acidic conditions in the presence of a glassy carbon electrode modified by molybdenum oxides as shown in the following reaction N:
• Catholyte pH can affect the reaction potential of the reaction occurring in the cathoiyte compartment.
• Fig. 3 is a pourbaix diagram of potential vs. pH for the catholyte reduction reaction, reaction "a”, which produces hydrogen and hydroxide ions, the anolyte oxidation reaction, which produces iodine, and the water oxidation reaction "b", which produces oxygen. From Fig. 3, the reaction potential for the two water dissociation reactions is affected by pH. In contrast, the reaction potential for the anolyte oxidation reaction which produces iodine is not affected by pH.
• the pH of the catholyte in the catholyte compartment is maintained at a near-neutral value.
• the cathoiyte pH is maintained at a value within the range of about 6 to 8.
• a buffer may be used to lower the pH of the catholyte in the catholyte compartment to a desired value.
• a borax buffer sodium borate
• FIG. 4 illustrates another apparatus and method for the electrochemical production of hydrogen and for the regeneration of the anolyte.
• Two electrochemical cells 410, 415 are shown in Fig. 4.
• Electrochemical cell 410 is configured similar to the cells shown in Figs. 1 and 2B in which an oxidizable substance in the anolyte is oxidized to form an oxidized product and a reducible substance in the catholyte is reduced to form hydrogen and a reduced product. While iodide is shown as the oxidizable substance and water is shown as the reducible substance, these substances are only illustrative and other oxidizable and reducible substances may be used as disclosed herein.
• Electrochemical cell 415 operates to regenerate the oxidizable substance. This may be accomplished by introducing the oxidized product (iodine) into the catholyte compartment of cell 415. Catholyte solution containing the reduced product (hydroxyl ions in the form of NaOH) is withdrawn from the catholyte compartment of cell 410 and passed through a concentrator/dehydrator in which water is removed causing the sodium hydroxide concentration to be greatly increased. The concentrated sodium hydroxide solution is introduced into the anolyte compartment of electrochemical cell 4 5. The two electrode half reactions illustrated in cell 415 are:
• the operating voltage of cell 415 is reduced as the anolyte pH is increased. Therefore, the anolyte preferably has a pH greater than 11 and more preferably a pH from 12 to 14.
• the water produced at the anode of cell 415 can be recovered and recycled to the catholyte compartment of cell 410.
• the Nal produced in the catholyte compartment of ceil 415 is the regenerated oxidizable substance and is introduced into the anolyte compartment of cell 410.
• the catholyte compartment of ceil 410 is operated at a pH of about 8 and maintained at this lower pFI through use of a buffer, such as borax (sodium borate).
• a buffer such as borax (sodium borate).
• the catholyte removed from cell 410 necessarily contains the sodium borate buffer in addition to the sodium hydroxide. As the sodium hydroxide is concentrated and the pH increases in the concentrator/dehydrator, the sodium borate precipitates and is recovered and recycled for further use in the catholyte compartment of cell 410.
• Additional operational efficiency may be obtained by operating the anolyte compartment of cell 415 at a low temperature and at low current. Further operational efficiency may be obtained by operating the catholyte compartment of cell 410 at high temperature and high current.
• the described systems and methods may have several beneficial characteristics, hi one example, the described methods are able to produce hydrogen through a method that uses less electrical energy (lower voltage) than does the production of hydrogen through some traditional methods for producing hydrogen gas through the electrolysis of water. Accordingly, some embodiments of the described systems and methods may more efficient and/or less expensive than some conventional methods of water electrolysis.
• the described systems and methods include an alkali cation selective membrane
• the described systems advantageously allow the cell 10 to keep the contents of the anolyte 15 and catholyte 30 compartments separate. In this manner, the described systems and methods can allow the cell to function while the anolyte 20 and the catholyte 35 comprise different materials.
• the alkali metal salt can be regenerated by mixing the oxidized product from the anolyte compartment 15 with the alkali hydroxide produced in the catholyte compartment 30, in some embodiments, most, if not all of the alkali metal salt can be regenerated and be recycled through the cell 10 to produce more hydrogen. In this manner, the described systems and methods may be more efficient and less costly than they would otherwise be if the alkali metal salt could not be regenerated,
• FIG. 5 shows how the described systems and methods may function.
• a standard electrochemical cyclic voltammetry (CV) method was used to study oxidation of near neutral pH sodium iodide solution.
• the test setup includes three platinum electrodes (one reference, one counter and one working) immersed in an aqueous solution of 0.2M NaLO. lM I 2 .
• the test was conducted at ambient temperature.
• the cell voltage is gradually increased and decreased versus the cell open circuit voltage and the working electrode potential is measured using the reference electrode. Also measured is the cell current generated by the reactions at the working and counter electrodes.
• Figure 5 shows the different processes (represented by increased current) occurring during the working electrode potential scan versus the reference.
• the positive anodic (oxidation) scan the first process to occur is the oxidation of iodide to triiodide according to reaction O:
• the described cell 10 was used with an anolyte consisting of a 1 : 1 weight ratio of sodium iodide (Nal) to 20 ⁇ graphite, with a small amount of glycerol to bind the mixture.
• anolyte consisting of a 1 : 1 weight ratio of sodium iodide (Nal) to 20 ⁇ graphite, with a small amount of glycerol to bind the mixture.
• the independent variables were temperature and current density.
• the cell 10 was operated at 65 degrees Celsius and 100 degrees Celsius as well as with a current density of 1 and 25 mA/cm 2 and the cell underwent 4 separate runs, [00100] To provide a better understanding of the described experimental results, a brief description of the experimental setup is provided below.
• the sodium iodide used was 99.9% Nal (metals basis). Furthermore, the glycerol used for mixing the sodium iodide with the graphite was a conventional 99% glycerol.
• the catholyte used in all tests was a 15 wt% NaOH solution.
• a stainless steel mesh anode was found to provide a lower overall cell voltage than did platinum and titanium mesh anodes, a stainless steel mesh was used as the anode current collector 25 for the majority of tests.
• a nickel mesh was used as the cathode current collector 40 in all of the experiments.
• a NaSICON solid electrolyte membrane having an area and thickness of about 3.24 cm "' and about 0.5mm, respectively, was used as the membrane 45 to separate the anolyte 15 and the catholyte 30 compartments.
• high-temperature- rated polytetrafluoroethylene (TEFLON®) tubing and tube fittings were used to pump the 1 5 wt% NaOH in and out of the cell.
• the electrode current col lectors 25 and 40 were each positioned approximately 1 mm from the membrane 45 (e.g., the thickness of a conventional gasket).
• the anode/anolyte paste was placed directly on an exposed part of the membrane 45, in the center of a gasket (not shown).
• the anode 25, in turn, was then placed over the anolyte paste and onto the gasket, followed by an additional layer of sodium iodide/graphite paste on the outside part of the anode 25.
• the membrane 45 and electrodes 25 and 40 were then sealed in a scaffold (not shown).
• the cell and cell solutions were allowed to heat up to the desired temperature (e.g., 65 or 100 degrees Celsius). At that point, the solutions were then al lowed to circulate along with an applied voltage, A SOLARTRON® 1255B Frequency Response Analyzer with SI1287 Electrochemical Interface or a BK PRECISION® 1786B was used to provide the constant current to the cell.
• the desired temperature e.g., 65 or 100 degrees Celsius.
• Figures 6 and 7 show the voltage vs. time plots for the tests run at I and 25 mA per sq.cm. of membrane area, respectively.
• Figure 7 shows the voltage behavior when a current density of 25mA/cm 2 was applied to the cell at 65 degrees Celsius.
• the cell voltage increased from initial value of 0.86V to 1 .4V during the span of the 10 min test. It is possible that the higher voltage is representative of reaction P.
• This preliminary result again confirms that it is possible to achieve lower voltages using sodium iodide/iodine reaction compared to oxygen evolution reaction by water splitting even at practical current densities.

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• 2017
  • 2017-03-02 EP EP17711462.6A patent/EP3423612A1/de not_active Withdrawn

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