US20180363151A1 - Electrochemical cell that operates efficiently with fluctuating currents - Google Patents

Electrochemical cell that operates efficiently with fluctuating currents Download PDF

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US20180363151A1
US20180363151A1 US16/061,975 US201616061975A US2018363151A1 US 20180363151 A1 US20180363151 A1 US 20180363151A1 US 201616061975 A US201616061975 A US 201616061975A US 2018363151 A1 US2018363151 A1 US 2018363151A1
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gas
electrode
cell
electrolyte
current
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Gerhard Frederick Swiegers
Paul Brendan Denis Michael BARRETT
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Aquahydrex Inc
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Assigned to AQUAHYDREX PTY LTD reassignment AQUAHYDREX PTY LTD ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: BARRETT, Paul Brendan Denis Michael, SWIEGERS, GERHARD FREDERICK
Assigned to AQUAHYDREX, INC. reassignment AQUAHYDREX, INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: AQUAHYDREX PTY LTD
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    • 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
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/02—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form
    • C25B11/03—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form perforated or foraminous
    • 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
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/02—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form
    • C25B11/03—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form perforated or foraminous
    • C25B11/031—Porous electrodes
    • 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
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
    • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
    • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
    • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
    • 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
    • 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
    • C25B15/02—Process control or regulation
    • 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
    • C25B9/06—
    • 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
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/8605—Porous electrodes
    • H01M4/8626—Porous electrodes characterised by the form
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H01M4/9016—Oxides, hydroxides or oxygenated metallic salts
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/94—Non-porous diffusion electrodes, e.g. palladium membranes, ion exchange membranes
    • 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
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04276—Arrangements for managing the electrolyte stream, e.g. heat exchange
    • 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
    • H01M8/18—Regenerative fuel cells, e.g. redox flow batteries or secondary fuel cells
    • H01M8/184—Regeneration by electrochemical means
    • H01M8/186—Regeneration by electrochemical means by electrolytic decomposition of the electrolytic solution or the formed water product
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/24—Grouping of fuel cells, e.g. stacking of fuel cells
    • 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
    • Y02E60/10—Energy storage using batteries
    • 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
    • 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/10—Process efficiency
    • Y02P20/129—Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/10—Process efficiency
    • Y02P20/133—Renewable energy sources, e.g. sunlight

Definitions

  • the present invention relates to the efficient or improved operation of electrochemical cells that involve a gas-liquid interface, particularly, but not exclusively, to the efficient or improved operation of gas-liquid electrochemical cells under conditions of intermittent and/or fluctuating currents.
  • electrochemical cells facilitate liquid-to-gas or gas-to-liquid transformations that involve the formation of, or presence of gas bubbles in liquid electrolyte solutions.
  • electrochemical cells used in the chlor-alkali process typically generate chlorine gas and hydrogen gas in the form of bubbles at the anode and cathode, respectively.
  • Bubbles in an electrochemical cell generally have the effect of increasing the electrical energy required to undertake the chemical transformation in the cell. This arises from effects that include the following:
  • One option is to entirely substitute the liquid-phase electrolyte with a suitable solid-state ion-exchange membrane that can carry an ion current between the electrodes.
  • a suitable solid-state ion-exchange membrane that can carry an ion current between the electrodes.
  • Numerous patents teach of this technique.
  • solid-state ion-exchange membranes take the form of a Proton Exchange Membrane (PEM), which allows for electrically-induced transport between opposing electrodes of H + ions, or anion exchange membranes, which provide for transport of OH ⁇ ions between opposing electrodes.
  • PEM Proton Exchange Membrane
  • Electrolyzers are devices that electrochemically convert water to hydrogen gas at the cathode and oxygen gas at the anode.
  • a common class of this cell is a conventional alkaline electrolyzer, which employs a strongly alkaline liquid-phase electrolyte (typically 6 M KOH) between the cathode and anode.
  • An ion-permeable, gas impermeable (or somewhat permeable) separator or diaphragm is typically employed between the two electrodes to prevent bubbles of hydrogen formed at the cathode from mixing with bubbles of oxygen formed at the anode. Mixtures of hydrogen and oxygen are explosive and therefore an undesired safety hazard.
  • the separator must also prevent the phenomenon of gas ‘crossover’, where hydrogen formed at the cathode passes through the separator to contaminate the oxygen formed at the anode, and oxygen formed at the anode passes through the separator to contaminate the hydrogen formed at the anode. If these contaminants approach the lower or higher explosion limits of hydrogen in oxygen, then a safety issue will have been created.
  • Crossover may occur by two mechanisms: (i) a process whereby microbubbles of one or both of the gases lodge in the pores of the separator, thereby creating a gaseous pathway between the catholyte and anolyte chambers, and (ii) the migration of dissolved gases in the liquid electrolyte between the electrodes (through the separator).
  • mechanism (i) may become a serious problem if the separator and its pores are not kept scrupulously wetted and free of gas bubbles at all times. This is particularly difficult to do at high applied pressures.
  • conventional alkaline electrolyzers typically continuously pump the 6 M KOH liquid electrolyte through the catholyte and anolyte chambers in order to sweep the gas bubbles away and keep the electrical conduction pathway between the anode and cathode as clear and void-free as possible.
  • conventional alkaline electrolyzers can typically be efficiently operated only up to current densities of ca. 300 mA/cm 2 (at potentials near 2 V), with system efficiencies near 60%. At higher current densities the losses in efficiency due to bubbles in the liquid electrolyte become too severe.
  • PEM solid state proton exchange membrane
  • PEM electrolyzers that typically operate at a current density of 1800 mA/cm 2 , with efficiencies of up to 75%.
  • Proton exchange membrane (PEM) electrolyzers are distinct from conventional alkaline electrolyzers in that they do not have a liquid phase electrolyte between the electrodes. Instead, they have a suitable solid-state ion-exchange resin, in the form of a membrane, between the electrodes and operate at relatively high temperatures, where the water is present largely in the form of vapour and resin-bound water rather than as a separate, clearly identifiable liquid phase.
  • solid state proton exchange membrane (PEM) electrolyzers avoid the difficulties noted above, arising from voidage, the bubble curtain effect and the bubble overpotential that occur when a liquid phase electrolyte is employed between the electrodes.
  • PEM solid state proton exchange membrane
  • liquid phase electrolyte between the electrodes in a gas-liquid electrochemical cell may have other highly deleterious effects.
  • gas generating liquid-filled electrochemical cells like conventional alkaline electrolyzers, cannot handle sudden and large increases in current as may occur when they are electrically driven by intermittent power sources, like wind generators or solar panels, which produce highly intermittent and/or fluctuating current supplies. Currents of this type are typically produced by renewable energy sources.
  • US20140120388 teaches of a cut-off switch for a battery during recharging where the activation of the cut-off switch is linked to the pressure of any gas that may be produced.
  • US20120181992 teaches of a cut-off switch that is linked to the voltage of a battery connected to an intermittent source of energy.
  • US20110156633 teaches of a solar power system that modulates the voltage of the incoming, intermittent current, in order to avoid damage.
  • solid state proton exchange membrane (PEM) water electrolyzers are better able to handle sudden current surges, for the reason that the water to be split into hydrogen and oxygen is present largely in the form of vapour and resin-bound water rather than as a separate, clearly identifiable liquid phase. Nevertheless, it is generally problematic to have sudden large increases in gas formation, with an accompanying increase in gas pressure at the ion-exchange membrane since gas crossover may increase and become an issue. That can be dealt with by using a thicker ion-exchange membrane.
  • electrochemical cells and methods of operation or use under conditions of intermittent and/or fluctuating currents are provided.
  • a method for operating an electrochemical cell comprising: a gas-producing electrode; a counter electrode, the gas-producing electrode and the counter electrode being separated by an electrolyte.
  • the electrochemical cell comprises: a gas-producing electrode; a counter electrode, the gas-producing electrode and the counter electrode being separated by an electrolyte.
  • the method comprises: supplying an intermittent and/or fluctuating current to at least the gas-producing electrode; and producing a gas at the gas-producing electrode as a result of an electrochemical reaction.
  • the gas is received by the one or more void volumes.
  • an electrochemical cell for producing a gas from an electrochemical reaction, comprising: a gas-producing electrode; a counter electrode; an electrolyte between the gas-producing electrode and the counter electrode; and, preferably though optionally, one or more void volumes.
  • an intermittent and/or fluctuating current is supplied to at least the gas-producing electrode.
  • the gas is produced at the gas-producing electrode and is received by the one or more void volumes.
  • the electrolyte is a liquid electrolyte or the electrolyte is a gel electrolyte. Also preferably, there are no bubbles of the gas formed or produced, or there are substantially no bubbles of the gas formed or produced, at the gas-producing electrode.
  • “substantially free of bubble formation” or “substantially bubble-free” or “substantially no bubbles” means that less than 15% of the gas produced takes the form of bubbles in the electrolyte. In another example embodiment, less than 10% of the gas produced takes the form of bubbles in the electrolyte. In other example embodiments, less than 8%, less than 5%, less than 3%, less than 2%, less than 1%, less than 0.5°), or less than 0.25%, of the gas produced takes the form of bubbles in the electrolyte.
  • the current is produced by an intermittent and/or fluctuating power source.
  • the power source is a solar-generator or a wind-generator or an ocean wave/tidal-generator of electricity.
  • the current is unconditioned.
  • the current is derived from excess electrical energy from an electrical grid.
  • ion-exchange membrane positioned between the gas-producing electrode and the counter electrode.
  • diaphragm e.g. separator
  • the gas-producing electrode is a gas diffusion electrode.
  • the counter electrode is a gas diffusion electrode.
  • the counter electrode may produce a second gas and bubbles of the second gas are not formed or produced, or are substantially not formed or produced at the counter electrode.
  • the second gas is received by separate one or more void volumes.
  • the current fluctuates by more than double the current.
  • the one or more void volumes are positioned within, partially within or adjacent to the electrolyte. In another example the one or more void volumes are positioned at or adjacent to the gas-producing electrode. In another example the one or more void volumes form a gaseous conduit to transport the gas. In another example the one or more void volumes allow the gas if formed rapidly in the electrolyte to escape from the electrochemical cell.
  • FIG. 1 schematically depicts an example liquid-gas electrochemical cell that can be utilised in present embodiments (not to scale).
  • FIG. 2 schematically depicts the options available to gas formed at or near to the liquid-gas interface in an electrochemical cell.
  • FIG. 3 illustrates an example method for operating an electrochemical cell.
  • FIG. 4 schematically depicts a first example arrangement for voids in a liquid-gas electrochemical cell.
  • FIG. 5 schematically depicts a second example arrangement for voids in a liquid-gas electrochemical cell.
  • FIG. 6 schematically depicts an example electrolyzer, including two gas diffusion electrodes and whose standard operating current is 10 mA.
  • FIG. 7 depicts an example current profile that rapidly and repeatedly fluctuates very suddenly between a current of 5 mA and a current of 250 mA.
  • FIG. 8 depicts an example variation in the voltage at each of the points marked A-D in FIG. 7 , measured at precisely the same time each day, over a period of 55 days of continuous operation.
  • the electrodes, electrochemical cells and/or methods of operation described in the above patent applications can be used in present embodiments.
  • the electrochemical cell 10 includes an electrolyte 15 , preferably a liquid electrolyte or a gel electrolyte that can be subjected to an electrolyte pressure, existing between and/or about anode 20 and cathode 30 , i.e. electrodes 20 , 30 .
  • the anode 20 can be a gas-producing electrode and/or the cathode 30 can be a gas-producing electrode.
  • Either of the anode 20 or the cathode 30 can be termed a counter electrode respective to the other electrode.
  • the electrode and catalyst layers at the anode 20 and cathode 30 are permeable to gases.
  • the electrochemical cell 10 includes a housing or container 40 for containing electrolyte 15 .
  • First gas region, channel or conduit 50 is formed as part of, adjacent or next to anode 20 , for collecting and/or transporting a first gas 70 , if any, produced at anode 20 .
  • Second gas region, channel or conduit 60 is formed as part of, adjacent or next to cathode 30 , for collecting and/or transporting a second gas 80 , if any, produced at cathode 30 .
  • First gas region, channel or conduit 50 and second gas region, channel or conduit 60 can be provided separately or together in electrochemical cell 10 .
  • first gas 70 and/or second gas 80 can be produced, and optionally transported out of electrochemical cell 10 .
  • the direction of gas exit is for illustration only and can be varied.
  • First gas region, channel or conduit 50 provides one example form of one or more void volumes, positioned at or adjacent to electrode 20 .
  • Second gas region, channel or conduit 60 also provides one example form of a separate one or more void volumes, positioned at or adjacent to electrode 30 .
  • an electrical current having an associated current density, is applied to the electrodes 20 , 30 or a voltage can be applied across electrodes 20 , 30 using an electrical power source.
  • No bubbles, or substantially no bubbles, of first gas 70 and/or second gas 80 are formed at either the anode 20 or cathode 30 surfaces. That is, the electrochemical cell is substantially free of bubble formation, i.e. substantially bubble-free, at the anode and/or the cathode. This means that less than 15% of the gas formed or produced at the anode and/or the cathode takes the form of bubbles in the electrolyte.
  • the anode 20 and/or cathode 30 can include a porous conductive material, which can be flexible.
  • the porous conductive material is gas permeable and liquid permeable (i.e. electrolyte permeable).
  • the anode 20 and/or cathode 30 can include, or be next to, fixed to, or adjacent, a gas permeable material, which also can be flexible.
  • the gas permeable material is gas permeable and liquid impermeable (i.e. electrolyte impermeable), and thus the anode 20 and/or cathode 30 composite structure can be gas permeable and liquid impermeable (i.e. electrolyte impermeable), and optionally flexible.
  • the gas permeable material is non-conductive.
  • the anode 20 and/or cathode 30 can be Gas Diffusion Electrodes (GDEs).
  • electrolyte 15 can be pumped past the electrodes 20 , 30 using a pump.
  • less than 10% of the gas produced takes the form of bubbles in the electrolyte.
  • less than 8%, less than 5%, less than 3%, less than 2%, less than 1%, less than 0.5%, or less than 0.25%, of the gas produced takes the form of bubbles in the electrolyte.
  • gas permeable material should be read as a general reference including any form or type of gas permeable medium, article, layer, membrane, barrier, matrix, element or structure, or combination thereof.
  • references to a gas permeable material should also be read as including any medium, article, layer, membrane, barrier, matrix, element or structure that is penetrable to allow movement, transfer, penetration or transport of one or more gases through or across at least part of the material, medium, article, layer, membrane, barrier, matrix, element or structure (i.e. the gas permeable material). That is, a substance of which the gas permeable material is made may or may not be gas permeable itself, but the material, medium, article, layer, membrane, barrier, matrix, element or structure formed or made of, or at least partially formed or made of, the substance is gas permeable.
  • the gas permeable material may be porous, may be a composite of at least one non-porous material and one porous material, or may be completely non-porous.
  • the gas permeable material can also be referred to as a “breathable” material.
  • an example of a gas permeable material is a porous matrix, and an example of a substance from which the gas permeable material is made or formed is PTFE.
  • An electrode can be provided by or include a porous conductive material.
  • the porous conductive material is gas permeable and liquid permeable.
  • porous conductive material should be read as including any medium, article, layer, membrane, barrier, matrix, element or structure that is penetrable to allow movement, transfer, penetration or transport of one or more gases and/or liquids through or across at least part of the material, medium, article, layer, membrane, barrier, matrix, element or structure (i.e. the porous conductive material). That is, a substance of which the porous conductive material is made may or may not be gas and/or liquid permeable itself, but the material, medium, article, layer, membrane, barrier, matrix, element or structure formed or made of, or at least partially formed or made of, the substance is gas and/or liquid permeable.
  • the porous conductive material may be a composite material, for example composed of more than one type of conductive material, metallic material, or of a conductive or metallic material(s) and non-metallic material(s).
  • porous conductive materials include porous or permeable metals, conductors, meshes, grids, lattices, cloths, woven or non-woven structures, webs or perforated sheets.
  • the porous conductive material may also be a material that has “metal-like” properties of conduction.
  • a porous carbon cloth may be considered a porous conductive material since its conductive properties are similar to those of a metal.
  • the porous conductive material may be a composite material, for example composed of more than one type of conductive material, metallic material, or of a conductive or metallic material(s) and non-metallic material(s). Furthermore, the porous conductive material may be one or more metallic materials coated onto at least part of the gas permeable material, for example sputter coated, or coated or deposited onto at least part of a separate gas permeable material that is used in association with the gas permeable material.
  • examples of porous conductive materials include porous or permeable metals, conductors, meshes, grids, lattices, cloths, woven or non-woven structures, webs or perforated sheets.
  • the porous conductive material may be a separate material/layer attached to the gas permeable material, or may be formed on and/or as part of the gas permeable material (e.g. by coating or deposition).
  • the electrochemical cell can be provided in a “flat-sheet” (i.e. stacked) or a “spiral-wound” format.
  • Flat-sheet means the electrodes (e.g. cathodes and/or anodes) are formed of planar layers or substantially planar layers, so that a flat-sheet electrochemical cell is comprised of a plurality of planar electrodes or substantially planar electrodes.
  • a flat-sheet electrochemical cell can be stacked together with other flat-sheet electrochemical cells (one on top of another in a series or array of electrochemical cells) to form a layered stack of multiple electrochemical cells (i.e. a stacked electrochemical cell).
  • the “flat-sheet” and “spiral-wound” cells, modules or reactors typically involve gas permeable, liquid impermeable gas diffusion electrode sheets or layers stacked in two or more layers, where the electrodes, including gas-producing electrodes, are separated from one another by spacers or spacer layers, for example distinct electrolyte channel spacers (which are permeable to, and intended to guide the permeation of liquid electrolyte through the cell) and/or gas channel spacers (which are permeable to, and intended to guide the permeation of gases through the cell).
  • spacers or spacer layers for example distinct electrolyte channel spacers (which are permeable to, and intended to guide the permeation of liquid electrolyte through the cell) and/or gas channel spacers (which are permeable to, and intended to guide the permeation of gases through the cell).
  • there may be two distinct gas channels, one for a first gas e.g.
  • the resulting multi-electrode stack is tightly wound about a core element, to thereby create the spiral-wound cell or module.
  • the core element may contain some or all of the gas-liquid and electrical conduits with which to plumb and/or electrically connect the various components of the cell or module.
  • the core element may combine all of the channels for one or another particular gas in the stack into a single pipe, which is then conveniently valved for attachment to an external gas tank.
  • the core element may similarly contain an electrical arrangement which connects the anodes and cathodes of the module into only two external electrical connections on the module a positive pole and a negative pole.
  • spiral-wound cells or modules provide a high overall electrochemical surface area within a relatively small overall geometric footprint.
  • a spiral-wound electrochemical module is believed to provide for the highest possible active surface area within the smallest reasonable footprint.
  • Another advantage of spiral-wound arrangements is that round objects are easier to pressurize than other geometries which involve corners. So, the spiral design has been found to be beneficial for electrochemical cells in which the electrochemical reaction is favourably impacted by the application of a high pressure.
  • the modular reactor units may be so engineered as to be readily attached to other identical modular units, to thereby seamlessly enlarge the overall reactor to the extent required.
  • the combined modular units may themselves be housed within a second, robust housing that contains within it all of the liquid that is passed through the modular units and which serves as a second containment chamber for the gases that are present within the interconnected modules.
  • the individual modular units within the second, outer robust housing may be readily and easily removed and exchanged for other, identical modules, allowing easy replacement of defective or poorly operational modules.
  • electrochemical cells involving a liquid or gel electrolyte between the electrodes which are preferably one or more gas-producing electrodes
  • gas that may be formed or built up within the liquid electrolyte in the cell (for example, at the surface of an electrode in the cell) can do one of three things:
  • FIG. 2 illustrates, in schematic form, the three different pathways 1, 2, 3, following the above numbering, available to gas formed within a liquid electrolyte in a gas-liquid cell.
  • Pathway (1) above is generally deleterious to energy efficiency, since the presence of dissolved gases in the liquid electrolyte between the electrodes of an electrochemical cell leads to higher electrical resistance, as taught in US 20080160357. It also promotes crossover between the electrodes.
  • pathway (2) above is generally also deleterious to the efficient operation of a cell having liquid or gel electrolyte between its electrodes.
  • pathway (3) above need not be deleterious to the efficient operation of a cell having liquid or gel electrolyte between the electrodes, if the “existing bubble” (i.e. “gas region” or “one or more void volumes”), either natural or man-made, lies outside of, or substantially outside of, the conduction pathway between the electrodes.
  • the “existing bubble” i.e. “gas region” or “one or more void volumes”
  • One or more “void volumes” can be provided by one or more porous structures, which can be provided by one or more gas permeable materials.
  • the one or more porous structures, or gas permeable materials, providing one or more void volumes are preferably gas permeable and liquid impermeable, or substantially liquid impermeable.
  • the one or more porous structures, or gas permeable materials, providing one or more void volumes are also preferably non-conducting.
  • pathway (3) provides a potentially useful means of controlling and handling gas formation in a manner that ensures gas formation is not deleterious to the operation and efficiency of the cell. That is, the inventors have unexpectedly realised that instead of seeking to suppress or block bubble formation, it may be more efficacious to direct gas formation to a pre-existing bubble or gas region (i.e. one or more void volumes), either natural or man-made, that has been designed to accept and accommodate gas formation in a way that does not impinge or substantially impinge on the operation and efficiency of the cell.
  • a pre-existing bubble or gas region i.e. one or more void volumes
  • the inventors have realised that, as a consequence of the Laplace equation, it is, in fact, energetically more favourable for newly formed or dissolved gas within a liquid to join a large, pre-existing bubble or gas region, either natural or man-made, than it is for the gas to form an independent, new bubble on a surface (either within a ‘cleft’ or as a stand-alone spherical bubble).
  • a large, pre-existing bubble (which could also be considered as a gas region or a void volume) will necessarily have a larger radius and therefore a lower internal (‘Laplace’) pressure than either a newly-formed spherical bubble or a newly-formed bubble in a surface ‘cleft’.
  • the concentration of dissolved gas within a liquid electrolyte is also necessarily minimised about a pre-existing bubble, gas region or void volume, either natural or man-made, since the bubble, region or volume provides an additional interface through which excess gaseous molecules are favoured to escape the liquid phase.
  • the inventors have realised that providing one or more void volumes, e.g. a pre-existing bubble, gas region or gas pathway, either naturally occurring or man-made, that is preferably positioned outside of the electrical conduction pathway between a gas-producing electrode and its counter electrode, substantially outside of the electrical conduction pathway between a gas-producing electrode and its counter electrode, partially outside of the electrical conduction pathway between a gas-producing electrode and its counter electrode, peripheral to or adjacent to the electrical conduction pathway between a gas-producing electrode and its counter electrode, and/or having a small cross-sectional area relative to the electrical conduction pathway between a gas-producing electrode and its counter electrode, and which can be within, partially within, adjacent to or near to a liquid electrolyte, or gel electrolyte, between the gas-producing electrode and its counter electrode of a cell, has the effect of not only disfavouring pathway (2) above but also minimising pathway (1) above.
  • the counter electrode is a gas-producing counter electrode, so that both of the electrode
  • pathway (1) above may be further lessened by selecting physical conditions for the cell that diminish, reduce, or minimise the dissolution of gases and/or their diffusion in the liquid electrolyte under conditions of high, higher, or maximal electrolyte conductivity.
  • the deleterious effect of pathway (1) on the cell may be further lessened by configuring or selecting physical conditions for the cell that diminish, reduce, or minimise the effect that dissolved gases may have on the operation of the cell under conditions of high, higher, or maximal energy efficiency.
  • the physical conditions include but are not limited to, one or more of the following:
  • the inventors have found that it may be beneficial to use physical laws such as Picks' law, Henry's law, Raoults' law, the Senechov equation, the Stokes-Einstein (-Sutherland) equation, and similar expressions, to guide the setting of the above physical conditions. It may be useful to thereafter further refine the settings for the physical conditions using empirical measurement.
  • physical laws such as Picks' law, Henry's law, Raoults' law, the Senechov equation, the Stokes-Einstein (-Sutherland) equation, and similar expressions
  • the physical conditions within the cell should be configured or selected so as to:
  • (I) above is referred to as the “Conduction Factor” and given the symbol CF.
  • the physical conditions employed within the cell should be such that CF (typically, but not exclusively in units of S/cm) is increased or maximised to the greatest reasonable extent.
  • the conductance, or conductivity of the electrolyte is the reciprocal of electrical resistivity (in ⁇ cm—ohm centimeters). Therefore the Conduction Factor, or conductivity, is used as a measure the ionic conductance of the electrolyte.
  • the unit of measurement used is typically, but not exclusively a Siemen per centimetre (S/cm).
  • the product of (II) multiplied by (III) above is referred to as the “Gas Dissolution and Diffusion Factor” and given the symbol GDDF.
  • the physical conditions employed within the cell should be such that GDDF (typically, but not exclusively in units of: cm 2 ⁇ mol/L ⁇ s) is reduced or minimised to the greatest reasonable extent. Where multiple gases are involved, the sum of their GDDF's should be minimised to the greatest reasonable extent.
  • the expression for GDDF derives from Ficks' law for diffusion of dissolved gases in a liquid phase, and reflects the influence that diffusing, dissolved gases may have on the chemical processes present in an electrochemical cell of the present embodiments.
  • the lower GDDF is, the less influence dissolved gases may have. That is, the lower GDDF is, the smaller is the effect of pathway (1) above, or the smaller is the influence of pathway (1) above on the chemical reactions in an electrochemical cell of the present embodiments.
  • the ratio of CF divided by GDDF is referred to as the “Electrolyte Factor” and given the symbol ER
  • the physical conditions employed within the cell should be such that EF (typically, but not exclusively in units of: Ls/ ⁇ cm 3 mol) is increased or maximised to the greatest extent reasonable.
  • the inventors have found that certain electrochemical cells operate most efficiently if the electrical conductance of the liquid electrolyte is increased or maximised whilst simultaneously the extent of gas dissolution and diffusion in the liquid electrolyte is reduced or minimised.
  • electrochemical cell design features include but are not limited to, one or more of the following:
  • the Inter-electrode Distance (typically, but not exclusively in units of: cm) is given the symbol ID, while the Current Density (typically, but not exclusively in units of: mA/cm 2 ) is given the symbol CD.
  • the inventors have found that, in general and without limitation, the features of design within the cell, namely: the Inter-electrode Distance (ID; typically, but not exclusively in units of: cm) and the Current Density (CD; typically, but not exclusively in units of: mA/cm 2 ) should be set such that the product of the square of CD (typically, but not exclusively in units of: mA/cm 2 ) multiplied by ID (typically, but not exclusively in units of: cm) and divided by CF (typically, but not exclusively in units of: S/cm), is reduced or minimized to the greatest reasonable extent.
  • ID Inter-electrode Distance
  • CD Current Density
  • this expression ((CD) 2 ⁇ ID)/CF), is referred to as the “Power Density Factor” and given the symbol PF (typically, but not exclusively in units of mA 2 ⁇ /cm 2 ).
  • PF typically, but not exclusively in units of mA 2 ⁇ /cm 2 .
  • the physical conditions employed within the cell should be such that PF is reduced or minimized to the greatest reasonable extent.
  • PF PowerDensity Factor
  • the Power Density Factor is related to the rate at which work must be done to push an electrical current between the electrodes in the electrochemical cell—i.e. the electrical power consumed per unit area of gas-producing electrode.
  • An increased energy and electrical efficiency in the cell must necessarily be accompanied by a reduction or minimization in the rate of work that must be done to drive an electric current between the electrodes in the cell.
  • the quantity PF is therefore a proxy for, and inversely related to the energy efficiency of the cell.
  • the inventors have found that it is also useful to quantify the percentage of the gases generated in an electro-synthetic cell of present embodiments, that crossover from one electrode to the other due to gas migration in the liquid electrolyte.
  • This Crossover quantity, CO is provided by the expression for Crossover (CO):
  • the inventors have found that, in general and without limitation, substantial energy efficiencies which may be greater than those achievable using other approaches, can be realised in electrochemical cells if the physical conditions in the cell and the features of cell design within the cell are set so that:
  • the inventors further realised that when the effect of a careful selection of the physical conditions and the cell design features as described above, are combined with the effect of providing an existing bubble or gas region, i.e. one or more void volumes, either natural or man-made, that lies outside of, or substantially outside of the electrical conduction pathway, or positioned to have only a small or minimal effect between the electrical conduction pathway, then significant improvements in energy efficiencies are achieved in the electrochemical cell. These energy efficiencies may be greater than those achievable using other approaches, such as the use of solid-state ion-exchange membranes between the electrodes.
  • Table 1 compares ihe ohmic voltage drop that occurs during typical operation of a conventional alkaline electrolyzer, a PEM electrolyzer and an electrolyzer of present embodiments.
  • an electrochemical cell in which gas is produced in the form of bubbles such as a conventional alkaline electrolyzer, may experience a typical voltage drop of up to 0.6 V between the electrodes under operational conditions due to the effect of bubbles in the liquid electrolyte.
  • an alkaline electrolyzer of the current embodiments having a 3 mm inter-electrode gap and operating at a typical current density of 50 mA/cm 2 at 80° C. using aqueous 6 M KOH as a liquid electrolyte.
  • Such an electrolyzer will experience a mere 0.011 V ohmic drop between the electrodes. A low voltage drop is consistent with high, or higher fundamental energy and electrical efficiency.
  • embodiments involve electrochemical cells and methods of use or operation in which one or more gas-producing electrodes operate in a manner that is bubble-free or substantially bubble-free.
  • the electrochemical cell does not have a diaphragm present between the gas-producing electrodes.
  • the electrochemical cell makes use of a particular catalyst-electrolyte system.
  • the electrochemical cell is optimised to determine the best settings for different variables of the electrochemical cell, including:
  • Electrolyte Factor EF
  • Power Density Factor PF
  • CO Crossover
  • Electrolyte Factor EF
  • PF Power Density Factor
  • CO Crossover
  • the Power Density Factor (PF) is influenced in a minor way by one component of the Electrolyte Factor (EF), namely the Electrolyte Conduction Factor (CF), whereas the Crossover (CO) is influenced in a minor way by the other component of the Electrolyte factor (EF), namely the Gas Diffusion and Dissolution Factor (GDDF).
  • EF Electrolyte Factor
  • CO Crossover
  • EF Gas Diffusion and Dissolution Factor
  • the Power Density Factor (PF) and the Crossover (CO) can be, effectively, determined or set for optimisation. In other words, one can find out where the Electrolyte Factor (EF) will peak, and then use the available control or freedom of the engineering quantities to cause the Power Density Factor (PF) and the Crossover (CO) to be simultaneously at minima (zeroed in the case of CO), or simultaneously as close to minima as possible.
  • the inventors have therefore discovered that energy savings can be realised in a liquid-gas electrochemical cell having a liquid- or gel-electrolyte between the gas-producing electrodes by:
  • the inventors have further realised that not only can the energy efficiencies realised by this approach be more substantial than those achievable using other approaches, such as the use of solid-state ion-exchange membranes between the electrodes, but the energy efficiencies can also be most amplified under circumstances where energy losses are normally at their greatest in conventional cells; that is, at higher pressures and/or current densities.
  • liquid-gas electrochemical cell having a liquid- or gel-electrolyte between the gas-producing electrodes where:
  • the one or more void volumes are directly adjacent to, next to, or positioned within the source of gas formation, in order to facilitate the migration of gas to the one or more void volumes.
  • One or more “void volumes” can be provided by one or more porous structures, which can be gas permeable materials.
  • the one or more porous structures, or gas permeable materials, providing one or more void volumes are preferably gas permeable and liquid impermeable, or substantially liquid impermeable.
  • the one or more void volumes are provided by a gas permeable material (i.e. a porous structure) that is not permeable to the electrolyte (i.e. liquid impermeable) but accommodates or allows passage of gas (i.e. gas permeable).
  • a void volume is provided by a gas permeable and liquid impermeable porous structure(s) or material(s).
  • the one or more void volumes are preferably non-conductive.
  • the one or more void volumes are preferably but not exclusively provided by a porous hydrophobic structure, such as a porous hydrophobic assembly, membrane or hollow fibre, or a collection of such structures, which remains unfilled with liquid electrolyte or gel electrolyte during the operation of the cell.
  • a porous hydrophobic structure such as a porous hydrophobic assembly, membrane or hollow fibre, or a collection of such structures, which remains unfilled with liquid electrolyte or gel electrolyte during the operation of the cell.
  • the void volume, or the one or more void volumes may be considered to be a “pre-existing bubble”, a “pre-formed bubble”, a “gas region”, “gas pathway”, a “gas void”, an “artificial bubble” or a “man-made bubble”.
  • the void volume, or the one or more void volumes lies outside of or on the periphery of the electrical conduction pathway of the cell, or occupies only a small cross-sectional area within the electrical conduction pathway.
  • the cross-sectional area of the void volume is less than the cross-sectional area of the electrical conduction pathway, relative to a perpendicular direction extending from the surface of an electrode.
  • a void volume may be provided by a natural bubble or bubbles that are statically or near-statically positioned outside of, or within a small cross-sectional area in the conduction pathway of the cell.
  • the static or near-static, natural bubble or bubbles may be contained, or mechanically trapped within an accommodating structure that is located outside of, or within a small cross-sectional area within the conduction pathway of the cell.
  • the natural, static or near-static bubble or bubbles may simply be formed or located outside of, or within a small cross-sectional area in the conduction pathway of the cell.
  • an electrochemical cell contains one or more void volumes configured to accept and accommodate migrating gas so as to thereby improve the efficiency of the cell.
  • a cell with an aqueous liquid or gel electrolyte may contain portions of a thin, highly hydrophobic sheet membrane or hollow fibre membrane that is isolated and not in gaseous contact with the environment about it. Such isolated portions of a thin, highly hydrophobic sheet membrane or hollow fibre membrane, may be placed so as to accept and accommodate gas that is slowly but inopportunely generated within the cell during operation.
  • the void volumes within the hydrophobic membranes may also be isolated from each other and, or they may be in gaseous contact with each other.
  • the hydrophobic membranes may be located at the edges of the cell outside of the electrical pathway of the cell, or they may be placed in, for example, a lengthwise location, along the electrical pathway, to thereby minimise their footprint for electrical resistance.
  • the void volume(s) may accommodate gas that is slowly but inopportunely created within a battery during overcharging, including but not limited to a Ni metal hydride, lead acid, or lithium ion battery, where the uncontrolled formation of independent gas bubbles has the potential to damage the battery or degrade its performance.
  • the void volumes may, in effect, replace or partially replace the sacrificial materials that are routinely incorporated to suppress gas formation.
  • the void volume(s) may further act as a “buffer tank” to hold amounts of gases that are formed prior to the reverse, recombination reaction that removes them during discharging.
  • the void volume(s) may accommodate gas formed during the operation of an electrophoretic or electroosmotic cell to thereby improve the operation of the cell.
  • the void volume(s) may act to halt or minimise the incidence of bubble formation in electrochemical cells with solid-state or gel electrolytes.
  • a void volume may still be capable of accepting substantial quantities of gas. This may arise because a void volume will necessarily and competitively accommodate migrating gas up to the point that the internal gas pressure within the void volume exceeds the so-called “bubble point” of the void volume. At that stage one or more bubbles will form in an uncontrolled manner at the interface between the void volume and the surrounding liquid media.
  • bubble point is used herein in the context described in the Applicant's International Patent Publication No. WO2015013764, entitled “Method and Electrochemical Cell for Managing Electrochemical Reactions ”, which is herein incorporated by reference.
  • the void volume does not merely accept and accommodate migrating gas, but instead, or additionally, forms a gaseous conduit that transports the migrated gas from/to another part of the cell, or into/out of the cell entirely, for example to a holding tank.
  • the void volume may act to allow unwanted gases formed within the electrolyte of the cell to escape from the cell.
  • the void volume(s) may transport gas from the electrolyte present between the electrodes, including gas-producing electrodes, to another portion of the cell that lies outside of, or substantially outside of the conduction pathway of the cell, or to the outside of the cell.
  • the void volume may act to continuously remove dissolved gases within the liquid- or gel-electrolyte of the cell between the electrodes, to thereby improve the electrical conductivity and hence the electrical efficiency of the cell. That is, the void volume may be used to continuously “de-gas” the electrolyte and vent dissolved gases to the air, so as to thereby improve the electrical conductivity of the electrolyte.
  • the void volume(s) may act to competitively suppress dissolution of gas within an electrolyte, so as to thereby maximise the electrical conductivity of the electrolyte.
  • the void volume(s) may act to carry a particular inert gas into the cell, so as to thereby saturate the electrolyte with a gas that is reactively inert and to thereby improve the overall efficiency of the cell.
  • the void volume may be associated with an electrode. That is, the void volume may form the gaseous side of a gas diffusion electrode, where the gaseous side of the electrode lies outside of, or substantially outside of the conduction pathway of the cell between the electrodes, and where the gaseous side of the gas diffusion electrode facilitates the movement of gas into or out of the cell.
  • the gas diffusion electrode may act to transport a gas generated at the electrode out of the cell; alternatively, the gas diffusion electrode may act to transport gas into the cell, from the outside of the cell. Examples of such cells include an ‘electrosynthetic’ or an ‘electro-energy’ cell.
  • the cell preferably but not exclusively has one or more of the following advantages:
  • the cell is operated under conditions where the “Electrolyte Factor” (EF; for example in units of: mA ⁇ mol/L ⁇ s) is increased or maximised to the greatest reasonable extent.
  • the “Electrolyte Factor” (EF; in units of: mA ⁇ mol/L ⁇ s) reflects the ratio of the conductive capacity of the liquid electrolyte to the extent of gas dissolution and diffusion in the liquid electrolyte.
  • the “Electrolyte Factor” reflects the ratio of the conductive capacity of the liquid electrolyte to the sum for all of the gases of the extent of gas dissolution and diffusion in the liquid electrolyte.
  • the physical conditions described above are set so as to increase or maximise the conductance of the liquid- or gel-electrolyte between the electrodes in the cell. Furthermore, preferably but not exclusively, the physical conditions described above are set so as to reduce or minimise the dissolution of gas in the liquid- or gel-electrolyte between the electrodes, so as to thereby increase or maximise the electrical conductance of the electrolyte. In the alternative, the physical conditions described above are, preferably but not exclusively, set to reduce or minimise the rate of diffusion of the gases that are dissolved in the liquid- or gel-electrolyte between the electrodes.
  • the physical conditions described above are, preferably but not exclusively, set to reduce or minimise either the dissolution of gases in the electrolyte, or the rate of diffusion of the gases in the electrolyte, or a suitable combination thereof, so as to increase or maximise the efficiency of the cell in operation and/or from an energy or electrical efficiency viewpoint.
  • the one or more void volumes e.g. a pre-existing bubble, gas region or gas pathway, either naturally occurring or man-made, in different examples, can be positioned:
  • the cell can be operated under conditions where the Crossover (CO; for example in %), is reduced or minimized to the greatest reasonable extent.
  • the Crossover (CO; in %) is the percentage of gases that cross from one electrode to the other due to gas migration in the liquid electrolyte.
  • the Crossover (CO) is preferably less than or equal to 40%. In example embodiments, the Crossover (CO) is less than or equal to 30%, less than or equal to 20%, less than or equal to 15%, less than or equal to 12%, less than or equal to 10%, less than or equal to 8%, less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, or less than or equal to 0.5%. In each case, the Crossover (CO) is greater than or equal to 0%. In another example, the Crossover (CO) is equal to or about 0%.
  • the inventors have discovered that the operation of an electrochemical cell, under the conditions described herein, can allow for cells that are capable of operating at higher pressures than are viable in many conventional systems. Additionally, the higher pressures are accompanied by greater energy efficiency and/or higher current densities. That is, in particular example embodiments, the inventors have discovered that the advantages of modes of operating the example electrochemical cells described herein, relative to comparable, conventional cells, are so unexpectedly amplified as to allow for economically-viable operation under hitherto unavailable or unviable conditions of pressure.
  • Increases in the applied pressure in electrochemical cells of example embodiments should not degrade the purity of the one or more gases collected at the anode and/or cathode, at least not to near the extent observed in conventional cells. Moreover, when operated in the described way, such cells are substantially more electrically and energy efficient than comparable conventional cells. Increases in current density at high pressure can also have the effect of progressively improving, and not degrading, the gas purity as is the case for conventional cells. This can be accompanied by high energy efficiency and/or high current densities. This realisation has important practical utility since it can yield new industrial electro-synthetic and electro-energy processes that operate under hitherto unavailable or unviable conditions of pressure and/or current density.
  • pressure refers to the “gas pressure” (e.g. a gaseous product(s) pressure), which is necessarily similar or close to, but somewhat below the “electrolyte pressure” (e.g. a liquid electrolyte pressure).
  • the “electrolyte pressure” should not be more than the “gas pressure” plus the “wetting pressure of a membrane” (otherwise the membrane will leak/flood).
  • the “gas pressure” is typically set to about 0.5 bar to about 1.5 bar below the “electrolyte pressure”.
  • high pressure i.e. the pressure
  • high pressure is preferably greater than or equal to 10 bar.
  • high pressure is preferably greater than or equal to 20 bar, greater than or equal to 30 bar, greater than or equal to 40 bar, greater than or equal to 50 bar, greater than or equal to 60 bar, greater than or equal to 70 bar, greater than or equal to 80 bar, greater than or equal to 90 bar, greater than or equal to 100 bar, greater than or equal to 200 bar, greater than or equal to 300 bar, greater than or equal to 400 bar, or greater than or equal to 500 bar.
  • the inventors have remarkably discovered that the problem of (i) gas crossover through the separator and the problem of (ii) gas pressure equalisation across the separator in an alkaline electrolyzer under high pressure conditions, as described in WO2013/066331 and on pages 160-161 in the book “Hydrogen Production by Electrolysis”, by A. Godula-Jopek (Wiley-VCH, 2015), can be eliminated or drastically curtailed by using appropriate gas diffusion electrodes at the anode and cathode and then removing the separator entirely.
  • the gas diffusion electrodes have a suitably high wetting pressure and the pressure differential of the liquid over the gas side of the electrodes is never allowed to exceed that wetting pressure, then it is possible to find physical conditions under which gas crossover is minimal and certainly far less than in a conventional electrochemical cell. As a result, it becomes possible to produce gases of high purity at high pressures.
  • Removing the diaphragm, separator or ion exchange membrane also avoids the difficulties involved in equalising the pressure of the catholyte and anolyte chambers as observed in, for example, the electrolyzer developed by Avalence LLC described in WO2013/066331 and on pages 160-161 in the book “Hydrogen Production by Electrolysis”, by A. Godula-Jopek (Wiley-VCH, 2015).
  • the separator is removed, the catholyte and anolyte chambers become one, so that no pressure differential can then exist between the cathode and anode, at least from the pressure applied to the electrolyte.
  • removal of the separator further eliminates crossover deriving from gas bubbles occupying the pores of the separator as observed in, for example, the aforementioned electrolyzer developed by Avalence LLC as described in WO2013/066331 and on pages 160-161 in the book “Hydrogen Production by Electrolysis”, by A. Godula-Jopek (Wiley-VCH, 2015).
  • the example electrochemical cells as described herein and in the Applicant's concurrent International Patent Applications entitled “Electrochemical cell and components thereof capable of operating at high current density” and “Electrochemical cell and components thereof capable of operating at high voltage”, filed on 14 Dec. 2016, which are incorporated herein by reference, can, unexpectedly, be used to generate high pressure gases of high purity at, optionally, a high current density and with, optionally, high electrical and energy efficiency without the need for a gas compressor. Similar principles apply to the reverse situation, namely fuel cells of the abovementioned type, which may utilize high pressure gases of high purity, at a high current density, to achieve high electrical and energy efficiency.
  • embodiments provide for an electrochemical cell that generates one or more high purity gases at high pressure from a liquid electrolyte, without a gas compressor.
  • the cell operates with high electrical and energy efficiency.
  • bubbles of the gas are not formed or produced, or are substantially not formed or produced at the gas-producing electrode.
  • the method includes selecting an Inter-electrode Distance (ID) between the electrodes and/or selecting a Current Density (CD) so that a Crossover (CO) for the electrochemical cell is less than or equal to 40%.
  • the Crossover (CO) is equal to or about 0%.
  • one or more void volumes are located at or adjacent to the gas-producing electrode.
  • An example method comprises operating the electrochemical cell at a current density greater than or equal to 50 mA/cm 2 and at a pressure greater than or equal to 10 bar.
  • high purity of a gas is preferably greater than or equal to 90%.
  • high purity of a gas is preferably greater than or equal to 95%, greater than or equal to 97%, greater than or equal to 99%, greater than or equal to 99.5%, greater than or equal to 99.9%, greater than or equal to 99.99%, greater than or equal to 99.999%, greater than or equal to 99.9999%, or greater than or equal to 99.99999%.
  • a produced gas has a purity equal to or about 100%.
  • high pressure is preferably greater than or equal to 10 bar.
  • high pressure is preferably greater than or equal to 20 bar, greater than or equal to 30 bar, greater than or equal to 40 bar, greater than or equal to 50 bar, greater than or equal to 60 bar, greater than or equal to 70 bar, greater than or equal to 80 bar, greater than or equal to 90 bar, greater than or equal to 100 bar, greater than or equal to 200 bar, greater than or equal to 300 bar, greater than or equal to 400 bar, or greater than or equal to 500 bar.
  • the electrochemical cell generates high purity gases at high pressure from a liquid electrolyte at high current density and without a gas compressor.
  • the electrochemical cell generates high purity gases at high pressure from a liquid electrolyte without a gas compressor, where the electrochemical cell combines at least one or both of a gas diffusion anode and a gas diffusion cathode, both of which have relatively high wetting pressures.
  • high wetting pressure is preferably greater than or equal to 0.2 bar. In alternative example embodiments, high wetting pressure is preferably greater than or equal to 0.4 bar, greater than or equal to 0.6 bar, greater than or equal to 0.8 bar, greater than or equal to 1 bar, greater than or equal to 1.5 bar, greater than or equal to 2 bar, greater than or equal to 2.5 bar, greater than or equal to 3 bar, greater than or equal to 4 bar, or greater than or equal to 5 bar.
  • the electrolyte replacement rate is preferably less than 1 replacement of the electrolyte in the cell volume every 1 hour. In alternative example embodiments, the electrolyte replacement rate is preferably less than 1 replacement of the electrolyte in the cell volume every 45 minutes, less than 1 replacement of the electrolyte in the cell volume every 30 minutes, less than 1 replacement of the electrolyte in the cell volume every 15 minutes, less than 1 replacement of the electrolyte in the cell volume every 10 minutes, less than 1 replacement of the electrolyte in the cell volume every 5 minutes, less than 1 replacement of the electrolyte in the cell volume every 1 minute, less than 1 replacement of the electrolyte in the cell volume every 30 seconds, less than 1 replacement of the electrolyte in the cell volume every 5 seconds, or less than 1 replacement of the electrolyte in the cell volume every 1 second.
  • electro-synthetic or electro-energy cells such as an electrochemical cell or a fuel cell, with one or more gas diffusion electrodes that are bubble-free or substantially bubble-free in operation, wherein the cell is operated at high pressure and/or high current density.
  • gas diffusion electrodes that are bubble-free or substantially bubble-free in operation, wherein the cell is operated at high pressure and/or high current density.
  • a renewable energy source like wind generators, solar panels or ocean wave/tidal generators
  • example electrochemical cells as described herein which operate most economically at low current densities, are unexpectedly able to be operated under conditions of remarkably large and sudden surges or variations in current, with no or little noticeable degradation in subsequent performance.
  • the example electrochemical cells as described herein can be operated under unexpected conditions or ranges to routinely handle current surges of at least 25-fold over their normal operating currents, for example delivered over several milliseconds. Moreover, testing has revealed that the electrochemical cells can handle surges of such scale repeatedly, without noticeable degradation in electrochemical performance, at intervals of a few seconds, applied continuously and without break, over periods exceeding six months. To the best of the inventors' knowledge, no other cell types and most especially no other liquid-containing cells, are capable of such performance.
  • an “artificial bubble”, such as the gas side or region of a gas diffusion electrode is present near to the point of formation of a gas in a liquid-containing cell, then the newly formed gas is strongly favoured to join that “artificial bubble” rather than to form a new bubble or dissolve in a supersaturated way within the liquid.
  • that “artificial bubble” has a substantial volume and a large gas-liquid interface, then it can accommodate and absorb even very large quantities of a gas that may be formed extremely suddenly in the liquid phase.
  • the “artificial bubble”, represented by the gas side of a gas diffusion electrode may act as a buffer that rapidly assimilates and removes even substantial quantities of gas formed very quickly within the liquid phase. In this way, the damage that may be caused by sudden, large-scale bubble formation may be eliminated in its entirety, or, at least, mitigated to a substantial extent.
  • the electrochemical cell comprises one or more void volumes, a gas-producing electrode, and a counter electrode.
  • the gas-producing electrode and the counter electrode being separated by an electrolyte.
  • the method 300 includes, at step 310 , supplying an intermittent or fluctuating current to at least the gas-producing electrode.
  • a gas is produced at the gas-producing electrode as a result of an electrochemical reaction.
  • the gas is received by the one or more void volumes.
  • the one or more void volumes do not merely accept and accommodate migrating gas, but instead, or additionally, form a gaseous conduit that transports the migrated gas from/to another part of the cell, or into/out of the cell entirely, for example to a holding tank.
  • the void volume(s) may act to allow unwanted gases formed within the electrolyte of the cell to escape from the cell.
  • the one or more void volumes can act to allow gases formed rapidly within the electrolyte of the electrochemical cell to escape from the cell into an external holding tank, or to be vented to the atmosphere.
  • the one or more void volumes can transport gas that is formed rapidly and suddenly, from the electrolyte present between the electrodes to another portion of the cell that lies outside of, or substantially outside of the conduction pathway of the cell, or to the outside of the cell.
  • the total void volume including the conduit and the holding tank, or the outside atmosphere, is large or very large relative to the gas volumes that may be created by rapid and sudden surges in the electrical current. That is, preferably, but not exclusively, the total void volume is such as to provide a capacity to readily absorb large quantities of gas or gases that may be formed rapidly and suddenly within the electrochemical cell.
  • the one or more void volumes can be positioned so as to provide a pathway for gas that is rapidly and suddenly created within the electrolyte between the electrodes in a battery during overcharging, including but not limited to a Ni metal hydride, lead acid, or lithium ion battery, where the uncontrolled formation of independent gas bubbles has the potential to damage the battery or degrade its performance.
  • the one or more void volumes can, in effect, replace or partially replace the sacrificial materials that are routinely incorporated to suppress gas formation.
  • the void volume(s) can transport the gas to a separate volume within the cell that acts as a “buffer tank” to hold amounts of gases that are formed prior to the reverse, recombination reaction that removes them during discharging.
  • the void volume(s) can transport gas formed rapidly and suddenly, from the electrolyte between the electrodes to another portion of the cell that lies outside of the conduction pathway of the cell, or to the outside of the cell, during the operation of an electrophoretic or electroosmotic cell to thereby improve the operation of the cell.
  • void volume(s) of this type can act to halt or minimise the incidence of bubble formation in electrochemical cells with solid-state or gel electrolytes.
  • the one or more void volumes can act to continuously remove dissolved gases that are rapidly and suddenly formed within the liquid-electrolyte or gel-electrolyte of the electrochemical cell between the electrodes, to thereby maintain and/or improve the electrical conductivity and hence maintain and/or improve the electrical efficiency of the cell. That is, the one or more void volumes can be used to continuously “de-gas” the electrolyte and vent dissolved gas or gases that are formed rapidly and suddenly, to a holding tank, or outside to the air, so as to thereby maintain and/or improve the electrical conductivity of the electrolyte.
  • the electrochemical cell provides a means for accommodating sudden, large increases in the current (or current density).
  • sudden, large increases in the current refer to preferably more than double the current.
  • sudden, large-scale increases in the current refers to preferably more than triple the current, more than four-fold the current, more than five-fold the current, more than six-fold the current, more than eight-fold the current, more than ten-fold the current, more than twelve-fold the current, more than fifteen-fold the current, more than twenty-fold the current, or more than twenty-five-fold the current.
  • the large increase in the current can be sudden and occur over a duration of less than a millisecond, about a millisecond, less than 10 milliseconds, less than 100 milliseconds, less than a second, less than a few seconds, less than 10 seconds, or less than a minute.
  • the current collectors, catalysts, and/or electrodes in the cell are capable of operating at high current densities, so as to thereby accommodate large and sudden increases and/or fluctuations in the applied/supplied current.
  • the current collectors, catalysts, and/or electrodes in the cell are capable of operating at high pressures, so as to thereby accommodate large and sudden increases and/or fluctuations in the gases formed.
  • the current collectors, catalysts, and/or electrodes in the cell are capable of operating at high energy efficiencies, so as to thereby accommodate large and sudden increases and/or fluctuations in the currents applied and gases generated.
  • electro-synthetic or electro-energy cells such as an electrochemical cell or a battery, containing a liquid-electrolyte or a gel-electrolyte with one or more gas diffusion electrodes, which are capable of accommodating large quantities of gases that may be formed rapidly and suddenly within the cell due to fluctuations and/or intermittency in the current.
  • an electro-synthetic or electro-energy cell such as an electrochemical cell or a battery, containing a liquid-electrolyte or gel-electrolyte with one or more gas diffusion electrodes, which are capable of accommodating or receiving large fluctuations and/or intermittency in the current that result in the rapid and sudden generation of substantial quantities of gases within the cell.
  • an electro-synthetic or electro-energy cell comprising a liquid-electrolyte or gel-electrolyte and at least one gas diffusion electrode; the one or more gas diffusion electrodes being bubble-free or substantially bubble-free, wherein in use the cell is operated with large fluctuations and/or intermittency in the current, resulting in the rapid and sudden generation of substantial quantities of gases.
  • a gas-liquid electrochemical cell capable of directly harnessing an intermittent energy source, such as a solar-powered or a wind-powered or an ocean wave/tidal powered renewable energy source, without notable modulation or conditioning of the current (which can be direct current, e.g. from a solar panel, or alternating current, e.g. from a wind turbine).
  • an intermittent energy source such as a solar-powered or a wind-powered or an ocean wave/tidal powered renewable energy source
  • the current which can be direct current, e.g. from a solar panel, or alternating current, e.g. from a wind turbine.
  • the raw output of intermittent current produced by such a generator can be directly harnessed by an example electrochemical cell as described herein. This eliminates a number of energy losses, allowing for more efficient use of renewable energy sources, such as solar-generators, wind-generators and ocean wave/tidal-generators.
  • intermittent power of this type can be practically employed in the electrochemical manufacture of a host of standard industrial products, including, but not exclusively: (a) chlorine, (b) hydrogen peroxide, ozone, (d) caustic (with or without chlorine), (e) potassium permanganate, (f) chlorate, (g) perchlorate, (h) fluorine, (i) bromine, (j) persulfate, (k) fuels from CO 2 , (l) CO 2 from methane, and others.
  • standard industrial products including, but not exclusively: (a) chlorine, (b) hydrogen peroxide, ozone, (d) caustic (with or without chlorine), (e) potassium permanganate, (f) chlorate, (g) perchlorate, (h) fluorine, (i) bromine, (j) persulfate, (k) fuels from CO 2 , (l) CO 2 from methane, and others.
  • electrochemical cells involving electrochemical processes unique to particular industries can be powered by intermittent renewable energy sources, including but not restricted to:
  • example electrochemical cells can be used to generate electrochemical energy, where the fuel for the energy may only be supplied intermittently, sporadically, or in a highly fluctuating manner.
  • fuel cell and related device applications such as hydrogen-oxygen fuel cells, including but not limited to alkaline fuel cells, where the fuel (in the form of the gases oxygen and hydrogen) is supplied in a fluctuating, intermittent or highly variable manner, can be realised.
  • example electrochemical cells can be used to facilitate improved recycling or disposal of unwanted materials, relative to what would otherwise have been the case, using intermittent energy sources, like solar-powered or wind-powered or ocean wave/tidal-powered renewable electricity and/or intermittently available feedstocks, such as air oxygen.
  • intermittent energy sources like solar-powered or wind-powered or ocean wave/tidal-powered renewable electricity and/or intermittently available feedstocks, such as air oxygen.
  • example electrochemical cells can be used to facilitate improved management of electrical grids that receive notable inputs from intermittent energy source, such as solar-powered.
  • Example methods for operating cells at high electrical and energy efficiencies may occur when an endothermic electrochemical reaction is facilitated.
  • the cells can act to minimise or, at least, noticeably decrease the intrinsic energy inefficiencies involved in electrochemical cells that facilitate liquid-gas reactions. For example, the energy sapping influence that bubbles may have in such cases, may be substantially mitigated.
  • the inventors have further recognised that, for such endothermic electrochemical reactions, there may be at least one catalyst available that is capable of sustainably catalyzing the reaction at cell voltages below or near to the so-called “thermoneutral voltage”, which represents the maximum possible energy efficiency with which the cell can operate.
  • thermaloneutral voltage represents the maximum possible energy efficiency with which the cell can operate.
  • the electrical efficiency is defined as the ratio of the total energy put into the cell relative to the total energy incorporated in the products generated by the cell over a particular time period.
  • high electrical and energy efficiency is preferably greater than or equal to 70%.
  • high electrical and energy efficiency is preferably greater than or equal to 75%, greater than or equal to 80%, greater than or equal to 85%, greater than or equal to 87%, greater than or equal to 90%, greater than or equal to 93%, greater than or equal to 95%, greater than or equal to 97%, greater than or equal to 99%, or greater than or equal to 99.9%.
  • New methods of operation of the example electrochemical cells at or near ambient (e.g. room) temperature as described herein are predicated on the fact that the cells may be operated economically-viably at low current densities. They may also be utilized to facilitate reactions which are endothermic in nature; that is, reactions which absorb heat. This is significant since, for reactions of that type, there may be catalysts available that catalyze the reaction at cell voltages below the so-called “thermoneutral” voltage at or near ambient (e.g. room) temperature but they can only do so at low current densities.
  • thermoneutral voltage at or near to ambient temperatures, where they produce only low current densities, within cells that operate viably at low current densities, offers a useful approach to the development of energy efficient liquid-gas electrochemical cells.
  • the operational voltage of such a cell may decline with an increase in temperature. That is, higher current densities at, about or near to the thermoneutral voltage may be achieved for a suitable catalyst by increasing the temperature of the cell. Provided the cell is capable of withstanding the higher temperatures without damage or impairment, it is possible to operate cells at, about, or near to the thermoneutral voltage with higher current densities at higher temperatures.
  • the inventors have understood that operating a suitable catalyst at operational voltages below, at, about or near to the thermoneutral voltage at higher temperatures, where they produce higher current densities, within cells that capable of withstanding the higher temperatures without damage or impairment, offers a useful approach to the development of energy efficient liquid-gas electrochemical cells.
  • thermal self-regulation involves allowing the operational temperature of the cell to vary in accordance with the thermal parameters and not be fixed. That is, a useful approach to thermal management involves allowing the cell to find its own optimum operating temperature in a process of “thermal self-regulation”. Optionally, this may be done with the cell wrapped in thermal insulation. This approach involves applying a particular current density as required (in the presence of suitable catalysts). If, at the temperature of the cell, the applied current density creates a higher voltage in the cell than the thermoneutral voltage, then the cell will progressively heat itself up. As the cell heats itself up, the cell voltage will typically decline.
  • the cell At the applied, fixed, current density, the cell will continue heating itself up until such time as the cell voltage has declined to be at, about, or near to the thermoneutral voltage (depending on the quality of the thermal insulation). At that point, the temperature of the cell will stabilize and cease increasing. During the entire process the cell would be operating at as close to 100% energy efficiency as the thermal insulation will allow. The reverse of the above will occur (causing a decrease in the operating temperature of the cell) if the current density that is applied causes the cell voltage to decline.
  • thermoneutral voltage is defined as that cell voltage at which the heat generated by the catalyst and associated conductors is equal to the heat consumed by the reaction. If an endothermic electrochemical reaction is carried out at the thermoneutral voltage, then the energy and electrical efficiency of the conversion of reactants into products is, by definition, 100%, since all of the energy that is put into the cell is necessarily converted into energy within the products of the reaction. That is, the total electrical and heat energy input into the cell is matched with the total energy present in the products of the reaction with no excess input energy radiated to the surroundings. However, if the reaction is carried out above the thermoneutral voltage, then excess energy is generated, usually in the form of heat. If the reaction is carried out below the thermoneutral voltage, then energy, usually heat, needs to be added in order to avoid self-cooling by the system.
  • example electrochemical cells as described herein can be operated at, below, or near to the thermoneutral potential in an economically-viable way, for example so as to avoid the need for extensive and energy-sapping electrical cooling systems.
  • This realisation has important and far-reaching implications for the heat management and energy efficiency of such cells.
  • example electrochemical cells of the type described in Applicant's concurrent International Patent Applications entitled “Electrochemical cell and components thereof capable of operating at high current density” and “Electrochemical cell and components thereof capable of operating at high voltage”, filed on 14 Dec. 2016, which are incorporated herein by reference can be operated at, below, or near to the thermoneutral potential in an economically-viable way.
  • the inventors have produced suitable example catalysts, which facilitate electrocatalytic water electrolysis.
  • the catalyst(s) is applied to at least one of, or both of, the electrodes to facilitate the endothermic electrochemical reaction at the operational voltage of the electrochemical cell.
  • the catalyst contains one or more of the following catalytic materials: (i) Precious metals, either free or supported, including but not limited to Pt black, Pt supported on carbon materials (e.g. Pt on carbon black), Pt/Pd on carbon materials (e.g.
  • Nickel including but not limited to: (a) nanoparticulate nickels, (b) sponge nickels (e.g. Raney nickel), and (c) nickel foams; (iii) Nickel alloys, including but not limited to, NiMo, NiFe, NiAl, NiCo, NiCoMo; (iv) Nickel oxides, oxyhydroxides, hydroxides, and combinations thereof, without limitation; (v) Spinels, including but not limited to NiCo 2 O 4 , Co 3 O 4 , and LiCo 2 O 4 ; (vi) Perovskites, including but not limited to La 0.8 Sr 0.2 MnO 3 , La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 , and Ba 0.5 Sr 0.5 Co 0.2 Fe 0.8 O 3 ; (vii) Iron, as well as iron compounds, including but not limited to nanoparticulate iron powders and the like; (viii) Molybden
  • the catalyst/s comprises one or more of the above catalytic materials mixed in with PTFE (e.g. in a 5% dispersion in alcohol from Sigma-Aldrich), creating a slurry.
  • PTFE e.g. in a 5% dispersion in alcohol from Sigma-Aldrich
  • the slurry is preferably, but not exclusively, coated, for example knife-coated, onto the electrode(s) and conductor(s) in a layer or coating.
  • the catalyst after drying, contains about 40% by weight PTFE, about 60% by weight of the catalytic materials.
  • carbon black may also be added to the slurry.
  • suitable ranges for the catalyst, when dry are:
  • the electrolyte is a liquid electrolyte or a gel electrolyte.
  • bubbles of the produced gas, or at least one gas are not, or are substantially not produced or formed at either of the electrodes.
  • thermoneutral potential an electrochemical cell that operates at, below, or near to the thermoneutral potential does not create substantial excess heat that needs to be removed. If an electrochemical cell can be operated near the thermoneutral potential, then there may be so little excess heat generated that it is easily lost to the surroundings without any need for a formal or dedicated cooling system. Alternatively, the excess heat can be used to maintain a particular operating temperature that is higher than ambient temperature. If an electrochemical cell can be operated at the thermoneutral potential, there is no heat exchanged with the surroundings at all. If an electrochemical cell can be operated below the thermoneutral potential, then heat must be applied to the cell/system in order to maintain the cell/system temperature and prevent it from cooling.
  • water electrolysis is an endothermic process. Of the 39 kWh theoretically required to form 1 kg of hydrogen gas, 33 kWh must be supplied in the form of electrical energy and 6 kWh must be supplied in the form of heat energy. Numerous catalysts are known to be capable of catalysing water electrolysis at voltages less than the thermoneutral cell potential for water electrolysis, which is 1.482 V at room temperature.
  • thermoneutral potential at or below the thermoneutral potential at typical ambient temperatures. Accordingly, conventional water electrolyzers, which can only be operated in an economically-feasible way at high current densities cannot harness this effect with any sort of utility. They must necessarily operate at voltages well above the thermoneutral voltage, causing the formation of excess heat, which must then be removed at a further energy penalty.
  • the cell may be sufficiently close to the thermoneutral voltage that the excess heat generated, along with additionally applied electrical heat, is such as to warm the cell up to a more optimum operating temperature and maintain it there without need for a formal or dedicated cooling system.
  • high current density is preferably greater than or equal to 50 mA/cm 2 . In other example embodiments, high current density is preferably greater than or equal to 100 mA/cm 2 , greater than or equal to 125 mA/cm 2 , greater than or equal to 150 mA/cm 2 , greater than or equal to 200 mA/cm 2 , greater than or equal to 300 mA/cm 2 , greater than or equal to 400 mA/cm 2 , greater than or equal to 500 mA/cm 2 , greater than or equal to 1000 mA/cm 2 , greater than or equal to 2000 mA/cm 2 , or greater than or equal to 3000 mA/cm 2 .
  • the aforementioned cells may operate at substantially higher energy and electrical efficiencies than are available for comparable, conventional cells. That is, the advantages of example electrochemical cells as described herein, suitably adapted, may be most strongly amplified at high current densities relative to a comparable conventional cell. This discovery has important practical utility since many industrial electro-synthetic and electro-energy cells aim to operate at the highest reasonable current densities. Substantial energy and electrical savings may therefore be realised.
  • Adaption of the example electrochemical cells as described herein may involve special designs for or modifications to the current collectors, busbars, electrical connections, power supplies/receivers, and other components.
  • selected components within the power supply of an electrosynthetic cell of the aforementioned types may be specially designed in order to handle the high current densities.
  • power supplies for facilitating the operation of cells of the above types are described in the Applicant's concurrent United States Provisional Application entitled “DC power supply systems and methods”, filed on 14 Dec.
  • novel current collectors such as asymmetric conducting meshes may be used, if required, in order to effectively distribute current at high current densities.
  • One particular adaption involves the use of series electrical connections as described in the Applicant's concurrent International Patent Application entitled “Electrochemical cell and components thereof capable of operating at high voltage”, filed on 14 Dec. 2016, which is incorporated herein by reference.
  • a spiral-wound electrochemical cell, module or reactor capable of operating at high current density, having a core element, around which one or more electrodes (e.g. at least one electrode pair provided by an anode or a cathode) may be wound in a spiral fashion.
  • the at least one electrode pair can form part of a multi-electrode array, which can be considered as being comprised of a series of flat flexible anodes and cathodes that can optionally be wound in a spiral fashion.
  • a “leaf” is comprised of one or more electrodes, for example an electrode, a pair of electrodes, a plurality of electrodes, or some other form of electrode unit.
  • a leaf may be flexible and can be repeated as a unit.
  • the electrode(s) is flexible, for example at least when being wound. After being wound, in some examples, the electrode(s) might be hardened using a hardening process.
  • a leaf can include in part, or be formed by:
  • two electrodes for example two cathodes or two anodes
  • an electrode pair for example an anode and cathode
  • a leaf in part, or be formed by, two electrode material layers (with both layers together for use as an anode or a cathode) that are positioned on opposite sides of an electrode gas channel spacer (i.e. a spacer material, layer or sheet, which for example can be made of a porous polymeric material) which provides a gas or fluid channel between the two electrodes.
  • an electrode gas channel spacer i.e. a spacer material, layer or sheet, which for example can be made of a porous polymeric material
  • Electrode array being a set of flat-sheet or spiral-wound electrodes with intervening, electrically-insulating “flow-channel” spacers between electrodes of different polarity (e.g. between an anode and a cathode) providing separated liquid channels.
  • the electrochemical cell, module or reactor may optionally also involve end caps, and one or more external elements.
  • a core element and end caps for a spiral-wound electrochemical cell capable of facilitating high current densities
  • the core element, end caps, and/or external elements comprising or containing an electrically conductive element, such as a (primary) busbar, provided as the end cap; and wherein, the conductive element is able to receive a conductive end from, or part of a conductive end from, or an electrode from, or a (secondary) busbar from an electrode, which may be a flexible electrode, where the electrode may be in a flat-sheet arrangement or may be spiral-wound about the core element.
  • the conductive element is able to provide a conductive lip to, or part of a conductive lip to, or an electrode to, or a (secondary) busbar to an electrode, which may be a flexible electrode, where the electrode is optionally able to be spiral-wound about the core element.
  • the current collectors of all anode electrodes are placed so as to overhang their electrodes on one side of the assembly of electrodes, leafs or the like, while the current collectors of all the cathode electrodes are placed so as to overhang their electrodes on the opposite side to the anode electrodes. All of the overhanging anode electrodes are then combined into a single electrical connection, while all of the overhanging cathode electrodes are separately combined into a single electrical connection. If multiple leafs are connected by the approach, this method may result in a parallel electrical connection of the leafs.
  • one method involves interdigitating metallic wedges between spiral current collectors extending off one end of the spiral-wound cell and then bringing the interdigitated wedges into electrical contact via a primary busbar with an attached connecting bus (‘Wedge method’).
  • the current collector, interdigitated wedges and ring may be bolted together, in which case the method is known as the “Bolted Wedge Method”:
  • the current collectors, wedges and ring may be welded together, in which case the method is known as the “Welded Wedge” Method.
  • the wedges may be narrowly disposed in finger-like projections off of the central ring, in which case the method is known as the “narrow wedge method”.
  • the wedges may be widely disposed, in which case the method is known as the “wide wedge method”.
  • example electrochemical cells are disclosed for operation at high voltages.
  • One example adaption involves arraying example cells in electrical series.
  • high voltage is preferably greater than or equal to 2 V. In other example embodiments, high voltage is preferably greater than or equal to 3 V, greater than or equal to 5 V, greater than or equal to 10 V, greater than or equal to 25 V, greater than or equal to 50 V, greater than or equal to 100 V, greater than or equal to 250 V, greater than or equal to 500 V, greater than or equal to 1000 V, or greater than or equal to 2000 V.
  • the series-connected cells are distinguished from spiral-wound and related, parallel-connected cells in that they allow for the use of substantially smaller and more readily connected primary busbars. Moreover, the cells allow for the use of a lower overall current but higher overall voltage than is generally utilized by related parallel-connected cells, including spiral-wound cells of the aforementioned type. This may be advantageous in that lower overall currents provide for lesser electrical resistance and therefore lesser (heat) losses, than higher overall currents. Moreover, power supplies which provide low overall current and high voltage are generally less expensive than power supplies which provide high overall current and low voltage. In example embodiments, power supplies for facilitating the operation of series-connected cells of these types, are described in the Applicant's concurrent United States Provisional Application entitled “DC power supply systems and methods”, filed on 14 Dec. 2016, which is incorporated herein by reference.
  • cells with series connections consume lower overall currents of higher overall voltage than cells with parallel connections that have the equivalent overall active electrochemical area and the same current density. In so doing, cells with series connections require smaller primary busbars than are necessary when large overall currents are required.
  • a plurality of electrochemical cells for an electrochemical reaction.
  • the plurality of electrochemical cells comprises a first electrochemical cell including a first cathode and a first anode, wherein at least one of the first cathode and the first anode is a gas diffusion electrode.
  • the plurality of electrochemical cells also comprises a second electrochemical cell including a second cathode and a second anode, wherein at least one of the second cathode and the second anode is a gas diffusion electrode.
  • the first cathode is electrically connected in series to the second anode by an electron conduction pathway.
  • the first cathode is a gas diffusion electrode.
  • the first anode is a gas diffusion electrode.
  • the second cathode is a gas diffusion electrode.
  • the second anode is a gas diffusion electrode.
  • an electrolyte is between the first cathode and the first anode.
  • the electrolyte is also between the second cathode and the second anode.
  • a first gas is produced at the first cathode, and substantially no bubbles of the first gas are formed at the first cathode, or bubbles of the first gas are not formed at the first cathode.
  • a second gas is produced at the first anode, and substantially no bubbles of the second gas are formed at the first anode, or bubbles of the second gas are not formed at the first anode.
  • the first gas is produced at the second cathode, and substantially no bubbles of the first gas are formed at the second cathode, or bubbles of the first gas are not formed at the second cathode, and, the second gas is produced at the second anode, and substantially no bubbles of the second gas are formed at the second anode, or bubbles of the second gas are not formed at the second anode.
  • the first cathode is gas permeable and liquid impermeable.
  • the first cathode includes a first electrode at least partially provided by a gas-permeable and electrolyte-permeable conductive material, and, a first gas channel at least partially provided by a gas-permeable and electrolyte-impermeable material.
  • the first gas can be transported in the first gas channel along the length of the first cathode.
  • the second anode includes a second electrode at least partially provided by a gas-permeable and electrolyte-permeable conductive material, and, a second gas channel at least partially provided by a gas-permeable and electrolyte-impermeable material. The second gas can be transported in the second gas channel along the length of the second anode.
  • the first gas channel is positioned to be facing the second gas channel. In another example, the first gas channel and the second gas channel are positioned between the first electrode and the second electrode.
  • the first cathode and the second anode can be planar.
  • the second cathode and the first anode can also be planar.
  • the first cathode can be flexible, and the second anode can also be flexible.
  • each flexible leaf comprises of a sealed gas channel or channels with its associated electrode or electrodes.
  • double-sided electrode leafs are used.
  • the leafs comprise of two electrode material layers positioned on opposite sides of an electrode gas pocket, containing a gas channel spacer (i.e. a spacer material, layer or sheet, which, for example, can be made of a porous polymeric material) that provides a gas or fluid channel between the two electrodes.
  • a gas channel spacer i.e. a spacer material, layer or sheet, which, for example, can be made of a porous polymeric material
  • the resulting gas pocket within the leaf is typically equipped with a gas port.
  • the current collectors on the top-side of the double-sided electrode leafs are placed so as to overhang their electrodes on one side of the leaf, while the current collectors on the bottom-side of the leafs are placed so as to overhang their electrodes on the opposite side of the leaf.
  • electrode leafs comprise of two separate, adjoining gas pockets, each having its associated porous electrode located on its outside (i.e. on the opposite side to the adjacent gas pocket).
  • the resulting leaf which may be flexible, then comprises of a layered arrangement having an electrode on its top, with one gas pocket below it, followed by a second, separate gas pocket below that, followed by a second electrode below it, on the bottom of the leaf.
  • the gas pockets may each contain a gas-channel spacer within them to hold them up, and will typically each be equipped with a gas port.
  • the two porous electrodes at the top and bottom of the leaf are then electrically connected to each other by, for example, metallic interconnections that pass through the two gas pockets, or that pass around the sides of the two gas pockets.
  • Double-sided, double-gas pocketed leafs of this type are then stacked on top of each other with a liquid-permeable “flow-channel” spacer between them, to thereby create a multiple-leaf, series-connected “stack”.
  • the volumes between the leafs are filled with a liquid or gel electrolyte, then the resulting cell of this type is known as a “bipolar series cell”.
  • the upper-most electrode of the upper-most leaf in each of the aforementioned stacks will typically be connected along its length to a primary busbar, which will typically take the form of a metallic bar that runs along one edge of the top of the stack.
  • the lower-most electrode of the lower-most leaf will typically be separately connected along its length to a second primary busbar, which may take the form of a metallic bar that runs along one edge of the bottom of the stack.
  • the two busbars will typically form the connection points (positive and negative poles) to which an external power supply will be connected.
  • each busbar will typically contain less metal and be smaller overall than a busbar in a comparable, parallel-connected stack of the same overall electrochemical active surface area at the same current density (such as a spiral-wound cell of the aforementioned type).
  • the busbar are linear rods, they will typically also be simpler to connect to electrically using a means such as welding.
  • busbar attachment There will typically not be a need to use complex techniques for busbar attachment, such as the aforementioned ‘Wedge Method’, ‘Bolted Wedge Method’, ‘Welded Wedge Method’, ‘Narrow or Wide Wedge Method’, ‘Powder Method’, ‘Sphere Method’, ‘Solder method’, ‘Continuous Wedge Method’, or ‘Spiral Method’.
  • series-connected leaf stacks may be wound into a spiral-wound cell.
  • a “tricot” pack of porous flow-channel spacers may be constructed to accommodate a selected number of leafs, whose gas pocket/s are each equipped with a gas port, in a stack. The tricot pack and leafs are then wound about a central core element that has been adapted to connect the gas ports on each leaf to their relevant gas conduits within the core element.
  • leafs comprising double-sided electrodes enclosing a single gas pocket are used, pairwise electrical connections of upper and lower electrodes on adjacent leafs are made on opposite sides of the leaf stack following the spiral winding, to thereby produce a “side-connected series cell” having a spiral-wound architecture.
  • the resulting assembly provides a “bipolar series cell” having a spiral-wound architecture.
  • a void volume(s) is provided by a porous structure that is not permeable to an electrolyte, e.g. a liquid electrolyte, but accommodates or allows passage of gas, that is the porous structure is liquid-impermeable and gas permeable.
  • the void volume(s) is preferably but not exclusively provided by a porous hydrophobic structure, e.g. made of PTFE, such as a porous hydrophobic assembly, membrane or hollow fibre, or a collection of such structures, which remains unfilled with liquid electrolyte during the operation of the cell.
  • the void volume may be considered to be an “artificial bubble” or a “man-made bubble”.
  • the “artificial bubble” or “man-made” bubble lies outside of the electrical conduction pathway of the cell, or occupies only a small cross-sectional area or footprint within the electrical conduction pathway.
  • a void volume can be provided by a natural bubble or bubbles that are statically or near-statically positioned outside of, or within a small cross-sectional area or footprint in the conduction pathway of the cell.
  • the static or near-static, natural bubble or bubbles may be contained, or mechanically trapped within an accommodating structure that is located outside of, or within a small cross-sectional area or footprint within the conduction pathway of the cell.
  • the natural, static or near-static bubble or bubbles may simply be formed or located outside of, or within a small cross-sectional area or footprint in the conduction pathway of the cell.
  • an electrochemical cell contains one or more void volumes that are so configured as to accept and accommodate migrating gas so as to thereby improve the efficiency of the cell.
  • an electrochemical cell 100 with an aqueous liquid or gel electrolyte 105 between anode 110 and cathode 120 may include one or more sheets of membrane 130 , for example short portions of a thin, highly hydrophobic sheet membrane, or hollow fibre membrane, that is isolated and not in gaseous contact or communication with the environment about membrane 130 .
  • Membrane 130 provides one or more void volumes. Isolated portions of a thin, highly hydrophobic sheet membrane, or hollow fibre membrane, can be placed so as to accept and accommodate gas that is slowly but inopportunely generated within the cell during operation.
  • the voids within the hydrophobic membranes may also be isolated from each other and, or they may be in gaseous contact with each other.
  • the membranes 130 can be located at or near position 140 provided by the edges or walls of the cell 100 , that is, outside of, or at the periphery of, the electrical conduction pathway (e.g. conduction pathways are illustrated by area 125 in FIG. 5 ) which is between the electrodes, which are preferably gas-producing electrodes.
  • the hydrophobic membranes 130 can be placed in, for example, a lengthwise location or position 150 , which is parallel to or substantially parallel to, or along, the electrical conduction pathway, to thereby minimise the cross-sectional area or footprint of membranes 130 for reduced or minimal electrical resistance.
  • Position or location 150 of membranes 130 can also be considered as perpendicular, or substantially perpendicular, to one or more of the gas-producing electrodes, i.e. perpendicular to anode 110 and/or perpendicular to cathode 120 .
  • suitable porous structures or membranes that provide the void volume(s) may accommodate gas that is slowly but inopportunely created within a battery during overcharging, including but not limited to a Ni metal hydride, lead acid, or lithium ion battery, where the uncontrolled formation of independent gas bubbles has the potential to damage the battery or degrade its performance.
  • the void volumes may, in effect, replace or partially replace the sacrificial materials that are routinely incorporated to suppress gas formation in battery electrolytes or electrode coatings.
  • the void volume(s) may further act as a “buffer tank” to hold amounts of gases that are formed prior to the reverse, recombination reaction that removes them during discharging.
  • the void volume(s) may accommodate gas formed during the operation of an electrophoretic or electroosmotic cell to thereby improve the operation of the cell.
  • the void volume(s) may act to halt or minimise the incidence of bubble formation in electrochemical cells with solid-state or gel electrolytes.
  • the one or more void volumes are: positioned within, partially within or adjacent to the electrolyte; and/or located at or adjacent to one or more of the gas-producing electrodes.
  • a void volume(s) can still be capable of accepting substantial quantities of gas. This may arise because a void volume(s) will necessarily and competitively accommodate migrating gas up to the point that the internal gas pressure within the void volume exceeds the so-called “bubble point” of the void volume. At that stage one or more bubbles will form in an uncontrolled manner at the interface between the void volume and the surrounding liquid media.
  • a void volume(s) may be in gaseous isolation within a liquid or gel media does not prevent the void volume(s) from accepting and accommodating even substantial quantities of gas.
  • the membrane(s) providing the void volume(s) does not merely accept and accommodate migrating gas, but additionally or instead forms a gaseous conduit that transports the migrated gas from/to another part of the cell, or into/out of the cell entirely.
  • the void volume(s) can act to allow unwanted gases formed within the electrolyte of the cell to escape from the cell.
  • membrane 160 providing one or more void volume(s), can transport gas from the electrolyte 105 present between the gas-producing electrodes 110 , 120 to another portion 180 of the cell 100 that lies outside of, or substantially outside of the conduction pathway (e.g. conduction pathways are illustrated by area 125 ) of the cell 100 , or to the outside 170 of the cell 100 .
  • conduction pathway e.g. conduction pathways are illustrated by area 125
  • an electrochemical cell 100 for producing a gas from an electrochemical reaction comprising one or more void volumes 130 , 160 , a gas-producing electrode 120 , a counter electrode 110 , and an electrolyte 105 at least between the gas-producing electrode 120 and the counter electrode 110 .
  • an intermittent or fluctuating current is supplied to at least the gas-producing electrode 120 , and the gas is produced at the gas-producing electrode 120 and is received by the one or more void volumes 130 , 160 .
  • the membrane(s) 160 providing the void volume(s) can be placed so as to provide a pathway for gas that is slowly but inopportunely created within the electrolyte between the gas-producing electrodes.
  • the void volumes may, in effect, replace or partially replace the sacrificial materials that are routinely incorporated to suppress gas formation.
  • the void volume(s) may transport the gas to a volume within the cell that acts as a “buffer tank” to hold amounts of gases that are formed prior to the reverse, recombination reaction that removes them during discharging.
  • the membrane(s) 160 providing the void volume(s) can transport gas from the electrolyte 105 between the gas-producing electrodes 110 , 120 to another portion 180 of the cell 100 that lies outside of the electrical conduction pathway of the cell, or to the outside 170 of the cell.
  • void volume(s) of this type may act to halt or minimise the incidence of bubble formation in electrochemical cells with solid-state or gel electrolytes.
  • the void volume(s) can act to continuously remove dissolved gases within a liquid- or gel-electrolyte of an electrochemical cell between the gas-producing electrodes, to thereby improve the electrical conductivity and hence the electrical efficiency of the cell. That is, the void volume(s) can be used to continuously “de-gas” the electrolyte and vent dissolved gases to the air, so as to thereby improve the electrical conductivity of the electrolyte.
  • FIG. 4 and FIG. 5 provide example positions for one or more void volumes, e.g. a porous structure, a pre-existing bubble, gas region or gas pathway.
  • the one or more void volumes, provided by example membranes 130 , 160 can be positioned, at or near position 140 , outside of the electrical conduction pathway between the gas-producing electrodes (i.e. anode 110 and cathode 120 ).
  • the one or more void volumes, provided by example membranes 130 , 160 can be positioned, at or near position 140 , substantially outside of the electrical conduction pathway between the electrodes.
  • the one or more void volumes, provided by example membranes 130 , 160 can be positioned, at or near position 140 or outside position 170 , partially outside of the electrical conduction pathway between electrodes.
  • the one or more void volumes, provided by example membranes 130 , 160 can be positioned, at or near position 140 , peripheral to or adjacent to the electrical conduction pathway between electrodes.
  • the one or more void volumes, provided by example membranes 130 can be positioned, at or near position 150 , between the electrodes and within the electrical conduction pathway, but having a small cross-sectional area relative to the electrical conduction pathway between electrodes.
  • the one or more void volumes, provided by example membranes 130 can be positioned, at or near position 150 , between the electrodes and parallel to the electrical conduction pathway, so as to have a small cross-sectional area relative to the electrical conduction pathway between electrodes.
  • the one or more void volumes, provided by example membranes 130 can be positioned, at or near position 150 , between the electrodes and perpendicular to one or both of the electrodes, so as to have a small cross-sectional area relative to the electrical conduction pathway between electrodes.
  • the one or more void volumes, provided by example membranes 130 , 160 can be positioned, at or near position 140 and/or position 150 , to be within, partially within, adjacent to or near to a liquid electrolyte, or gel electrolyte of the cell.
  • the one or more void volumes, provided by example membranes 130 , 160 can be positioned, at, next to or adjacent to an electrode, and outside of the electrical conduction pathway between the electrodes, for example positioned substantially parallel to one or more of the electrodes and on the gas side of the one or more electrodes.
  • the void volume(s) can act to competitively suppress dissolution of gas within an electrolyte, so as to thereby maximise the electrical conductivity of the electrolyte.
  • the void volume(s) can act to carry a particular inert gas into the cell, so as to thereby saturate the electrolyte with a gas that is reactively inert and to thereby improve the overall efficiency of the cell.
  • an electrochemical cell having an electrolyte between gas-producing electrodes of the electrochemical cell, wherein the electrolyte is a liquid-electrolyte or a gel-electrolyte.
  • the electrochemical cell comprises one or more void volumes to receive a gas produced by the electrochemical cell, and wherein dissolution of the gas in the electrolyte is reduced or avoided by the one or more void volumes.
  • bubbles of the gas are not produced at the gas-producing electrodes.
  • the one or more void volumes can be positioned within, partially within or adjacent to the electrolyte in example forms.
  • the one or more void volumes facilitate migration of the gas to the one or more void volumes so that:
  • Electrolyte Factor (EF) is increased/maximized
  • PF Power Density Factor
  • the one or more void volumes transport gas from the electrolyte to another portion of the cell that lies outside of the conduction pathway of the cell. In another example, the one or more void volumes transport gas from the electrolyte to outside of the cell. In another example, the one or more void volumes transport an inert gas into the cell.
  • the one or more void volumes are provided by a porous structure that is permeable to the gas and impermeable to the electrolyte. In another example, the one or more void volumes are provided by a porous structure that is gas-permeable and liquid-impermeable. In another example, the one or more void volumes are provided by a porous hydrophobic structure which remains unfilled with electrolyte during operation of the cell.
  • the one or more void volumes are a pre-existing bubble, a gas region or a gas pathway. In another example, the one or more void volumes are provided by at least one natural bubble that is statically positioned by an accommodating structure.
  • the one or more void volumes are positioned outside of the electrical conduction pathway between the electrodes. In another example, the one or more void volumes are positioned partially outside of the electrical conduction pathway between the electrodes. In another example, the one or more void volumes are positioned peripheral to the electrical conduction pathway between the electrodes. In another example, the one or more void volumes are positioned between the electrodes and parallel to the electrical conduction pathway between the electrodes. In another example, the one or more void volumes are positioned between the electrodes and perpendicular to one or both of the electrodes.
  • the one or more void volumes are integrally formed as part of at least one electrode. In another example, the one or more void volumes are positioned at or adjacent to at least one electrode. In another example, the one or more void volumes at least partially form a gaseous side of a gas diffusion electrode.
  • At least one electrode of the electrochemical cell comprises a non-conductive gas permeable material that is substantially impermeable to the electrolyte and provided on a gas side of the at least one electrode, and a porous conductive material provided on an electrolyte side of the at least one electrode.
  • Example 2 Applying Large and Fluctuating Currents to a Water Electrolysis Cell
  • the void volume may be associated with an electrode. That is, the void volume may form the gaseous side of a gas diffusion electrode, where the gaseous side of the electrode lies outside of, or substantially outside of the conduction pathway of the cell between the electrodes, and where the gaseous side of the gas diffusion electrode facilitates the movement of gas into or out of the cell.
  • the gas diffusion electrode may act to transport a gas generated rapidly and suddenly at the electrode out of the cell. Examples of such cells include an electrosynthetic or an electro-energy cell.
  • Example electrochemical cells as described herein, and including but not limited to cells of the types described in WO2013/185170, WO2015/013764, WO2015/013765, WO2015/013766, WO2015/013767, WO2015/085369, all of which are incorporated herein by reference, can be modified to operate at high current density as described in the Applicant's concurrent International Patent Application entitled “Electrochemical cell and components thereof capable of operating at high current density”, filed on 14 Dec. 2016, which is incorporated herein by reference.
  • the electrochemical cell accommodates random, sudden or rapid and large increases in the current or the current density.
  • a large increase in the current is preferably more than double the existing, base, stable or previous operating current.
  • a large increase in the current is preferably more than triple the current, more than four-fold the current, more than five-fold the current, more than six-fold the current, more than eight-fold the current, more than ten-fold the current, more than twelve-fold the current, more than fifteen-fold the current, more than twenty-fold the current, or more than twenty-five-fold the current.
  • FIG. 6 schematically depicts an example embodiment for a water electrolyzer, containing two gas diffusion electrodes, being an anode and a cathode.
  • the standard operating current for the electrolyzer is 10 mA (or expressed as a current density is: 10 mA/cm 2 ).
  • the cell is an alkaline electrolyser; that is, the cell facilitates electrochemical water-splitting, with half reactions as shown below, in alkaline solution, containing aqueous potassium hydroxide, aq. KOH, as electrolyte. (An acid or a neutral electrolyte could alternatively be used, with suitable catalysts).
  • the electrochemical cell 1000 in FIG. 6 comprises the following parts: a central water reservoir 1100 has a water-free hydrogen collection chamber 1110 on the left side and a water-free oxygen collection chamber 1120 on the right side. Between the water reservoir 1100 and the hydrogen collection chamber 1110 is a gas diffusion electrode 1130 . Between the water reservoir 1100 and the oxygen collection chamber 1120 is a gas diffusion electrode 1140 . On or close to the surface of the gas diffusion electrodes 1130 and 1140 is a conductive layer containing a suitable catalyst 1150 . In one example, the catalyst 1150 is a mixture of nickel nano- and microparticles (90% by weight) with PTFE (10%).
  • An electrochemical cell of the type shown in FIG. 6 was subjected to a highly fluctuating applied current, supplied to the electrodes, having the profile depicted in FIG. 7 .
  • the current profile rapidly and repeatedly fluctuates very suddenly between a current of 5 mA (which in the present example system corresponds to an equivalent current density of 5 mA/cm 2 ) and a current of 250 mA (which in the present example system corresponds to an equivalent current density of 250 mA/cm 2 ).
  • the profile was applied repeatedly and continuously to the electrochemical cell of FIG. 6 for a total of 55 days.
  • FIG. 8 depicts the resulting data over the 55 days of measurement.
  • the liquid containing electrolysis cell handled the gases generated and the changes in current very well indeed.
  • the data indicates excellent stability in the electrochemical cell over the extended testing period
  • the normal operating current for the electrochemical cell was 10 mA.
  • the data at point B (250 mA) in FIG. 7 represents a 25-fold larger current than the normal operating current.
  • This example demonstrates an electrochemical cell and a method for operating the electrochemical cell, wherein the electrochemical cell comprises a gas-producing electrode, a counter electrode, and where the gas-producing electrode and the counter electrode are separated by the electrolyte. Also provided is one or more void volumes, in this case at or adjacent to the electrodes.
  • the method comprises supplying the fluctuating current to at least the gas-producing electrode, and producing a gas (H 2 or O 2 ) at the gas-producing electrode as a result of the electrochemical reaction.
  • the gas is received by the one or more void volumes.
  • gas-liquid electrochemical cells capable of handling large and sudden fluctuations and intermittency in current have important practical applications in, for example, directly harnessing intermittent energy sources, like solar-powered or wind-powered or ocean wave/tidal-powered renewable electricity, without notable modulation or conditioning of the current (direct or alternating depending on the energy source).
  • intermittent energy sources like solar-powered or wind-powered or ocean wave/tidal-powered renewable electricity
  • the raw output of intermittent current produced by such a generator can be directly harnessed by or supplied to an electrochemical cell of the present embodiments. This potentially eliminates a number of energy losses, allowing for more efficient use of renewable energy streams, such as solar-generators or wind-generators or ocean wave/tidal-generators.
  • intermittent power of this type can be practically employed in the electrochemical manufacture of a host of standard industrial products, including, but not exclusively: (a) chlorine, (b) hydrogen peroxide, (c) ozone, (d) caustic (with or without chlorine), (e) potassium permanganate, (f) chlorate, (g) perchlorate, (h) fluorine, (i) bromine, (j) persulfate, (k) fuels from CO 2 , (1) CO 2 from methane, and others.
  • standard industrial products including, but not exclusively: (a) chlorine, (b) hydrogen peroxide, (c) ozone, (d) caustic (with or without chlorine), (e) potassium permanganate, (f) chlorate, (g) perchlorate, (h) fluorine, (i) bromine, (j) persulfate, (k) fuels from CO 2 , (1) CO 2 from methane, and others.
  • electrochemical cells involving electrochemical processes unique to particular industries can be powered by intermittent renewable energy sources, including but not restricted to:
  • electrochemical cells can be used to generate electrochemical energy, where the fuel for the energy may only be supplied intermittently, sporadically, or in a highly fluctuating manner.
  • fuel cell and related device applications such as hydrogen-oxygen fuel cells, including but not limited to alkaline fuel cells, where the fuel (in the form of the gases oxygen and hydrogen) is supplied in a fluctuating, intermittent or highly variable manner, can be realised.
  • half fuel cells where, for example, only one of the electrodes is a gas diffusion electrode
  • the gas diffusion electrode may be an air electrode, which utilizes the oxygen in air.
  • present embodiments can enable the electrochemical cell to nevertheless operate efficiently.
  • Example 5 Applications to Electrochemical Recycling or Disposal
  • electrochemical cells of present embodiments can be used to facilitate improved recycling or disposal of unwanted materials.
  • the joint venture company UhdeNora have developed an electrochemical technique for recycling the hydrochloric acid waste product that often derives from the industrial use of chlorine, Cl 2 , hack into usable chlorine Cl 2 .
  • the UhdeNora cell comprises a gas diffusion cathode combined with a standard solid-state (dimensionally-stable) chlorine-generating anode.
  • the UhdeNora cell routinely operates at 1.4 V and 500 mA/cm 2 , giving an energy requirement of 1.06 kWh per kg of chlorine produced.
  • the UhdeNora cell could not operate efficiently (or likely without damage) using a highly intermittent and fluctuating power source, like a solar-generator or wind-generator, directly connected to the cell.
  • an electrochemical cell of a present embodiment can be employed instead, the cell having two gas diffusion electrodes, an anode and a cathode.
  • the anode produces chlorine gas.
  • the cell is operated with hydrogen (H 2 ) generated at the cathode.
  • the cathode (a gas diffusion electrode) has O 2 (including, potentially, air O 2 ) introduced into the cathode, causing the cathode to act as an oxygen-depolarized cathode.
  • the half actions in the former process are:
  • the cell voltage is 1.36 V in the former case and a mere 0.13 V in the latter case. In both of these cases, the cell voltage is substantially less than the conventional chlor-alkali process.
  • An electrochemical cell of present embodiments could carry out either of the above transformations using current directly from an intermittent and/or fluctuating power source, such as a solar-generator or a wind-generator, and where the current can be unconditioned. This not only enables a more efficient use of renewable energy sources, but also enables their on-site use in a way that has not been previously viable.
  • an intermittent and/or fluctuating power source such as a solar-generator or a wind-generator
  • Electrochemical cells of present embodiments can also be used to facilitate improved management of electrical grids that receive notable inputs from one or more intermittent energy sources, such as solar-powered or wind-powered or ocean wave/tidal-powered renewable electricity. Because of the fluctuating nature and intermittency of such energy sources, electrical grids containing large inputs from renewables may generate excesses, including large excesses, of unwanted electrical power, at specific times. These times can be sporadic or short. These times may, alternatively, be long-lived. On occasion, this may result in the cost of the energy becoming negative, that is, the electrical utility may have so much unwanted energy that it will pay for a user to consume the electricity.
  • intermittent energy sources such as solar-powered or wind-powered or ocean wave/tidal-powered renewable electricity.
  • electrochemical cells can be used that may, for example, manufacture useful materials that can be sold separately and thereby make good use of the excess energy. Such electrochemical cells would necessarily have to be able to effectively harness fluctuations and intermittency in the supplied power.
  • the present example electrochemical cells are able to achieve this result. Accordingly, electrochemical cells of present embodiments can be used to make good use of fluctuating and intermittent unwanted excesses of electrical energy that may become available on an electric grid and that would otherwise be wasted so as to thereby help balance and stabilize the grid.
  • Other potential applications include intermittent power generation to compensate for intermittency elsewhere in the grid or in user profiles.
  • Optional embodiments may also be said to broadly consist in the parts, elements and features referred to or indicated herein, individually or collectively, in any or all combinations of two or more of the parts, elements or features, and wherein specific integers are mentioned herein which have known equivalents in the art to which the invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

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WO2017100842A1 (fr) 2017-06-22
AU2016371238A1 (en) 2018-07-26
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CN108701801A (zh) 2018-10-23
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US20180371630A1 (en) 2018-12-27
EP3391434A4 (fr) 2019-08-21

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