US20150292094A1 - Gas permeable electrodes and electrochemical cells - Google Patents

Gas permeable electrodes and electrochemical cells Download PDF

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US20150292094A1
US20150292094A1 US14/564,910 US201314564910A US2015292094A1 US 20150292094 A1 US20150292094 A1 US 20150292094A1 US 201314564910 A US201314564910 A US 201314564910A US 2015292094 A1 US2015292094 A1 US 2015292094A1
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gas
electrode
gas permeable
water
layer
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Gerhard Frederick Swiegers
Jun Chen
Stephen Thomas BEIRNE
Caiyun WANG
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Aquahydrex Inc
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University of Wollongong
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Publication of US20150292094A1 publication Critical patent/US20150292094A1/en
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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
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • 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
    • C25B1/10—
    • 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
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
    • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/70—Assemblies comprising two or more cells
    • C25B9/73—Assemblies comprising two or more cells of the filter-press type
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D1/00—Processes for applying liquids or other fluent materials
    • B05D1/18—Processes for applying liquids or other fluent materials performed by dipping
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C23C18/31—Coating with metals
    • C23C18/32—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis

Definitions

  • the present invention generally relates to electrochemical devices or cells, electrodes, methods of manufacture thereof, and/or methods for electrochemical or electrolytic reactions or processes.
  • the present invention relates to devices, cells, electrodes and/or methods for bringing about gas-to-liquid or liquid-to-gas transformations and, for example, to water electrolysis cells or electrodes that achieve water-splitting.
  • the present invention relates to methods of manufacturing electrodes and/or electrochemical devices or cells including the electrodes.
  • the electrolytic splitting of water into hydrogen gas and oxygen gas is generally achieved by applying a current to two, closely located electrodes, typically made of platinum, each of which are in contact with an intermediate water solution.
  • the anode water is typically oxidized according to the half-reaction given in equation (1).
  • the cathode protons (H + ) are typically reduced according to the half reaction shown in equation (2).
  • the overall reaction at the two electrodes is given in equation (3):
  • water electrolysers Numerous devices for splitting water electrolytically, known as water electrolysers, are commercially available.
  • a common problem with commercially-available water electrolysers is that they are generally inefficient in their ability to convert electrical energy into energy within the hydrogen that they generate. That is, they display low energy efficiency in the transformation of water into hydrogen.
  • Hydrogen is, of course, a fuel that could in the future supplant fossil fuels like gasoline and diesel. Moreover, it is potentially a non-polluting fuel since the only product of combusting hydrogen is water.
  • One kilogram of hydrogen contains the equivalent of 39 kWh of electrical energy within it (by its Higher Heating Value, or HHV, measure).
  • commercial electrolysers typically require substantially more electrical energy than 39 kWh to generate 1 kg of hydrogen.
  • the Stuart IMET 1000 electrolyser requires, on average, 53.4 kWh of electrical energy to generate 1 kg of hydrogen, giving it an overall energy efficiency for the conversion of water into hydrogen (HHV) of 73%. That is, approximately one quarter of the electrical energy fed into the electrolyser is wasted (largely as heat) and not harnessed to make hydrogen.
  • the Teledyne EC-750 electrolyser requires 62.3 kWh of electrical energy to make 1 kg of hydrogen (63% energy efficiency HHV).
  • the Proton Hogen 380 electrolyser requires 70.1 kWh/kg of hydrogen (56% energy efficiency, HHV), while the Norsk Hydro Atmospheric type No. 5040 (5150 AmpDC) requires 53.5 kWh/kg of hydrogen generated (73% energy efficiency, HHV).
  • the AvalenceHydrofiller 175 requires 60.5 kWh of electrical energy to generate 1 kg of hydrogen (64% energy efficiency, HHV).
  • the U.S.A. considered hydrogen to be strategically important as an alternative transportation fuel.
  • electric batteries can provide a better overall efficiency for the conversion of grid electrical energy into automotive power than is achieved by the current commercial water electrolysers combined with the use of high-efficiency fuel cells (powered by hydrogen).
  • the U.S.A. has, consequently, revised its strategic focus away from hydrogen-powered automobiles to electric-powered automobiles in the period 2009-2012.
  • the Department of Energy in the U.S.A. nevertheless, has, as one of its critical targets, the development of water electrolysers which achieve 90% overall energy efficiency, HHV.
  • a key problem with current commercial water electrolysers is that they suffer from electrical losses caused by their operation at extremely high electrical current densities (of typically 1000-8000 mA/cm 2 ). This is commercially unavoidable because the only way to achieve a low cost of production of hydrogen is to minimize the quantity of materials required in the electrolyser per kilogram of hydrogen that is generated. Many of the materials used in commercial electrolysers are exceedingly expensive—for example, the precious metal catalysts used at the anode/cathode and the proton exchange membrane diaphragm used to separate the gases. The only way to achieve a low overall price for the hydrogen produced, is therefore to generate the largest reasonable amount of hydrogen per unit area for the cost of manufacturing the electrolyser.
  • bubble overpotential An important energy loss is the so-called “bubble overpotential”, which occurs at both electrodes during the formation of gas bubbles of hydrogen (cathode) and oxygen (anode).
  • concentrations of O 2 bubbles required not only produce overpotential at the anode, but also represent a very reactive environment that challenges the long term stability of many catalysts.
  • an electrode for a water splitting device comprising a gas permeable material. Also included in the electrode, or as part of an associated electrode or anode/cathode, for example positioned adjacent the electrode, is a second material.
  • a spacer layer is positioned between the gas permeable material and the second material, the spacer layer providing a gas collection layer, for example within the electrode, between an anode-cathode pair, an anode-anode pair or a cathode-cathode pair.
  • a conducting layer is also provided as part of the electrode.
  • the second material may be part of the electrode, or an associated or adjacent electrode, cathode or anode, and in one form may also be a gas permeable material.
  • gas permeable material should be read as a general reference also including any form or type of gas permeable medium, article, layer, membrane, barrier, matrix, element or structure, or combination thereof.
  • gas permeable material should also be read as including a meaning that at least part of the material is sufficiently porous or penetrable to allow movement, transfer, penetration or transport of one or more gases through or across at least part of the gas permeable material.
  • the gas permeable material can also be referred to as a “breathable” material.
  • the conducting layer is provided adjacent to or at least partially within the gas permeable material; the conducting layer is associated with the gas permeable material; the conducting layer is deposited on the gas permeable material; the gas permeable material is deposited on the conducting layer; and/or the gas collection layer is able to transport gas internally in the electrode.
  • the gas permeable material is a gas permeable membrane.
  • the second material is a further or additional gas permeable membrane.
  • the gas collection layer is able to transport gas internally in the electrode to at least one gas exit area positioned at or near an edge or an end of the electrode.
  • the gas permeable material and the second material are separate layers of the electrode; the second material is part of an adjacent anode or cathode; the second material is a gas permeable material; and/or the second material is a gas permeable material and a second conducting layer is provided adjacent to or at least partially within the second material.
  • the spacer layer providing a gas collection layer is provided between a gas permeable layer and a second layer being a further gas permeable layer of the electrode.
  • the second material is a gas permeable material and a second conducting layer is associated with, positioned adjacent to, or deposited on the second material.
  • the electrode is formed of flexible layers; the electrode is at least partially wound in a spiral; and/or the conducting layer includes one or more catalysts.
  • the spacer layer is positioned adjacent to an inner side of gas permeable material, and the conducting layer is positioned adjacent to, on or partially within an outer side of the gas permeable material.
  • the gas permeable material is made at least partially or wholly from a polymer material, for example PTFE, polyethylene or polypropylene.
  • At least a portion of the conducting layer is between the one or more catalysts and the gas permeable material; the spacer layer is in the form of a gas channel spacer; and/or the spacer layer includes embossed structures on an inner surface of the gas permeable material and/or the second material.
  • an electrode for a water splitting device comprising: a first gas permeable material; a second gas permeable material; a spacer layer positioned between the first gas permeable material and the second gas permeable material, the spacer layer providing a gas collection layer; a first conducting layer associated with the first gas permeable material; and, a second conducting layer associated with the second gas permeable material.
  • the first conducting layer is provided adjacent to or at least partially within the first gas permeable material; the second conducting layer is provided adjacent to or at least partially within the second gas permeable material; the electrode is formed of flexible layers wound in a spiral; the electrode is formed of planar layers; the first conducting layer includes a catalyst; and/or the second conducting layer includes another catalyst.
  • a water splitting device comprising: an electrolyte; at least one electrode including: a gas permeable material; a second material; a spacer layer positioned between the gas permeable material and the second material, the spacer layer providing a gas collection layer; and, a conducting layer.
  • a water splitting device comprising: at least one cathode including: a first gas permeable material and a first conducting layer associated with the first gas permeable material; a second gas permeable material and a second conducting layer associated with the second gas permeable material; a spacer layer positioned between the first gas permeable material and the second gas permeable material, the spacer layer providing a gas collection layer; and, at least one anode including: a third gas permeable material and a third conducting layer associated with the third gas permeable material; a fourth gas permeable material and a fourth conducting layer associated with the fourth gas permeable material; a further spacer layer positioned between the third gas permeable material and the fourth gas permeable material, the further spacer layer providing a gas collection layer; wherein the at least one cathode and the at least one anode are at least partially within an electrolyte in operation.
  • the at least one electrode is a gas permeable electrode comprising two gas permeable materials having the spacer layer positioned between the materials and against an inner side of each material, and wherein each material includes a conducting layer on the outer side of each material.
  • the electrolyte is in fluid communication and connected to an electrolyte inlet and an electrolyte outlet, and the gas collection layer is in gaseous communication to a gas outlet.
  • methods for treating water comprising applying a low current density to the water splitting device, including: producing hydrogen gas and collecting the hydrogen gas via the gas collection layer; and/or pressurizing the electrolyte.
  • the low current density is less than 1000 mA/cm 2 ; the low current density is less than 100 mA/cm 2 ; the low current density is less than 20 mA/cm 2 ; producing hydrogen gas is at 75% energy efficiency HHV or greater; and/or producing hydrogen gas is at 85% energy efficiency HHV or greater.
  • a gas permeable electrode for a water splitting device comprising at least one gas permeable material and a spacer layer positioned against, adjacent or forming part of, an inner side of the material and between the material and another layer, said spacer layer defining a gas collection layer, and wherein the material includes a conducting layer.
  • the conducting layer includes or is associated with one or more catalysts, and wherein the conducting layer is on the outer side of the material.
  • a gas permeable electrode assembly for a water splitting device comprising two gas permeable materials having a spacer layer positioned between the materials and against, adjacent or forming part of, an inner side of each material, said spacer layer defining a gas collection layer and wherein each material includes a conducting layer.
  • one or both conducting layers include one or more catalysts, and wherein the conducting layer is on the outer side of each material.
  • the gas permeable material includes PTFE, polyethylene or polypropylene, or a combination thereof.
  • at least a portion of the conducting layer is disposed between the catalyst and the material.
  • the gas permeable material is gas permeable and electrolyte impermeable.
  • the gas permeable electrodes can be interleaved with water permeable spacers to produce a multi-layered water splitting cell.
  • An advantage of these electrodes is that they sandwich a gas collection layer between two gas permeable electrodes and may provide a cheap way of manufacturing a multi-layered water splitting cell.
  • a water splitting device comprising at least one cathode and at least one anode, wherein at least one of the least one cathode and at least one anode is a gas permeable electrode assembly comprising two gas permeable materials having a spacer layer positioned between or intermediate the materials and against, adjacent, or at least partially within, an inner side of each material, said spacer layer defining a gas collection layer, and wherein each material includes or is associated with a conducting layer.
  • the conducting layer includes one or more catalysts, and wherein the conducting layer is on the outer side of each material.
  • a water splitting device comprising a plurality of cathodes and anodes interleaved with water permeable spacers defining electrolyte layers, wherein the cathodes and the anodes are in the form of a gas permeable electrodes assembly comprising two gas permeable materials having a spacer layer positioned between or intermediate the materials and against, or at least partially within, an inner side of each material, said spacer layer defining a gas collection layer, and wherein each material includes a conducting layer.
  • the conducting layer includes one or more catalysts, and wherein the conducting layer is on the outer side of each material.
  • the water splitting devices may be configured into modular devices in which the footprint and gas handling infrastructure may be reduced.
  • a water splitting device comprising a spiral wound multi-layered water splitting cell.
  • the water splitting cell includes a plurality of cathodes and anodes interleaved with water permeable spacers defining electrolyte layers, and wherein the cathodes and the anodes are in the form of gas permeable electrode assemblies comprising two gas permeable materials having a spacer layer positioned between or intermediate the gas permeable materials and against, or at least partially within, an inner side of each material, said spacer layer defining a gas collection layer, and wherein each material includes a conducting layer that includes at least one catalyst, and wherein the conducting layer is on the outer side of each material, said electrolyte in fluid communication and connected to an electrolyte inlet and an electrolyte outlet, said gas collection layer between the anodes in fluid communication to an oxygen outlet and said gas collection layer between
  • the spiral wound water splitting device is a practical example way to reduce the footprint and gas handling infrastructure.
  • Spiral wound devices permit the electrolyte to permeate through electrolyte layers along the water splitting device.
  • the gases can be extracted laterally, for example oxygen in one direction to a collection channel and hydrogen in the other direction to another collection channel.
  • the example spiral wound water splitting device allows the cell to be manufactured from inexpensive and thin materials.
  • a key advantage of employing inexpensive manufacturing techniques to produce water splitting cells, is that it makes it commercially viable to build cells with large surface areas and operate them at low current densities.
  • These example water splitting cells are flexible and can be configured into a spiral wound water splitting device.
  • a multi-layered arrangement of flat-sheet materials may be rolled up into a spiral-wound arrangement.
  • the spiral wound arrangement may then be encased in a casing, which holds the spiral-wound element in place within a module whilst allowing for water to transit through the module.
  • Collection tubes may be positioned to plumb the respective gases, hydrogen and oxygen from the water splitting device.
  • the collection tubes may be attached to the water splitting device with the desired collection channels being open to the collection tube for the respective gas.
  • all of the hydrogen gas channels may be open at a matching location and communicate with the collection tube for the hydrogen gas.
  • the oxygen gas channels can be closed or sealed.
  • the oxygen gas channels may be open and communicate with the collection tube for the oxygen gas.
  • the hydrogen gas channels can be closed or sealed.
  • a water splitting device comprising a plurality of hollow fibre cathodes and a plurality of hollow fibre anodes, wherein said plurality of hollow fibre cathodes comprise a hollow fibre gas permeable material having a conducting layer that may include a catalyst, and wherein said plurality of hollow fibre anodes comprise a hollow fibre gas permeable material having a conducting layer that may include a catalyst.
  • proton exchange membranes are generally not required where gas permeable or breathable (preferably “bubble-free” or “substantially bubble-free”) electrodes are employed. Moreover, proton exchange membranes swell in aqueous media and, as a result, make it difficult to provide the packing efficiencies and modular designs desirable to produce water splitting cells having low capital expenditure requirements and low operating costs.
  • the water splitting cells allow the efficient use of space between the anode and cathode.
  • the water splitting cells permit at least 70% of the volume between the anode and the cathode to the occupied by electrolyte whilst maintaining the anode and cathode in a spaced apart relationship.
  • the water splitting cells may allow a non-electrolyte component (e.g. the spacer layer) in the electrolyte chamber to be less than 20% of the total resistance of the electrolyte chamber.
  • the water splitting cells may also permit the diffusion of both cations and anions across the electrolyte chamber without impedance, which would otherwise occur with use of a proton exchange membrane diaphragm.
  • the spacer layer or component within the electrolyte chamber may be gas permeable.
  • various example embodiments may be useful in performing other gas-to-liquid or liquid-to-gas transformations, such as fuel cells or water treatment devices.
  • Various example forms address the pressing need for electrochemical cells capable of performing gas-to-liquid or liquid-to-gas transformations with high energy efficiencies.
  • various example forms address the need for an electrolyser capable of manufacturing hydrogen from water at high energy efficiency and low cost.
  • the high energy efficiency is achieved by one or more of: (a) low current density, which minimises the electrical losses, (b) low-cost catalysts, for example Earth-abundant elements which operate highly efficiently at lower current densities, and (c) the use of gas permeable or breathable electrode or material structures, which reduce or eliminate the bubble overpotential at each electrode.
  • the low cost is achieved by one or more of the following features within the electrolyser: (i) low-cost materials as the substrate for the gas permeable or breathable anodes and/or cathodes, (ii) low-cost catalysts, for example Earth-abundant elements, as the catalysts at the anode and cathode (instead of high-cost precious metals), and (iii) low-cost reactor structures that have relatively high internal surface areas but relatively small external footprints.
  • the combination of these factors allows for relatively high overall rates of gas generation even when relatively small current densities per unit surface area are employed.
  • the anodes and cathodes may comprise hollow flat-sheets or tubes whose external surfaces are porous and either hydrophobic (in the case where the liquid used is hydrophilic—e.g. water) or hydrophilic (in the case where the liquid used is hydrophobic—e.g. petroleum ether), to thereby allow the gases but not the liquids, or other electrolyte fluids, to pass through them into the associated gas channels.
  • hydrophilic e.g. water
  • hydrophilic in the case where the liquid used is hydrophobic—e.g. petroleum ether
  • FIG. 1 graphically depicts the performance of example water electrolysers containing at each of the anode and the cathode: (a) Ni-coated flat-sheet breathable electrode in 1 M NaOH (without formation of bubbles or substantial formation of bubbles at the electrode), or (b) Pt-coated flat-sheet breathable electrodes in 1 M strong acid (without formation of bubbles or substantial formation of bubbles at the electrode), relative to (c) an electrolyser comprising of known solid Pt flat-sheet electrodes in 1 M strong acid at the anode and cathode (with formation of bubbles).
  • FIG. 2 graphically depicts the performance of example water electrolysers containing at each of the anode and the cathode: (a) Pt-coated hollow-fibre breathable electrodes (sealed at the bottom and open at the top) in 1 M strong acid (without formation of bubbles or substantial formation of bubbles at the electrode), relative to (b) an electrolyser comprising of known solid Pt wire electrodes in 1 M strong acid at the anode and cathode (with formation of bubbles).
  • FIG. 3 depicts: (a) a perspective view of the example cell used to perform the measurements in FIG. 1 ; (b) a cross-sectional schematic of the structure of the example cell.
  • FIG. 4 depicts: (a) a photograph of a water electrolysis experiment containing a known standard Pt wire at one electrode (with bubbles clearly visible) and an, example Pt-coated hollow-fibre (i.e. an example gas permeable electrode) (sealed at the bottom, open at the top) at the other electrode, with no bubbles visible; (b) a schematic explaining the fabrication of example gas permeable electrodes with Pt-coated hollow-fibres for use in an example water splitting cell.
  • a photograph of a water electrolysis experiment containing a known standard Pt wire at one electrode (with bubbles clearly visible) and an, example Pt-coated hollow-fibre (i.e. an example gas permeable electrode) (sealed at the bottom, open at the top) at the other electrode, with no bubbles visible; (b) a schematic explaining the fabrication of example gas permeable electrodes with Pt-coated hollow-fibres for use in an example water splitting cell.
  • FIG. 5 depicts electron microscope pictures of the surface of the example Pt-coated hollow-fibre electrode of FIG. 4 .
  • FIG. 6 depicts: (a) a schematic explaining the fabrication of example hollow-sheet gas permeable or breathable electrodes for an anode and cathode in an example electrolyser; (b) an electron micrograph of a dense, and robust example spacer (also referred to as a “permeate” or “gas-transport” spacer or spacer layer) that can be incorporated within a hollow space inside or between a rolled gas permeable material or gas permeable sheet materials.
  • a dense, and robust example spacer also referred to as a “permeate” or “gas-transport” spacer or spacer layer
  • FIG. 7 depicts an electron micrograph of the “flow-channel” example.
  • FIG. 8 depicts schematically an example process or method by which example electrodes can be formed for use as spiral-wound or flat electrodes in an electrolyser.
  • FIG. 9 depicts schematically: (a) an example electrolyser or cell having flat-sheet electrodes; (b) and (c) example electrolysers or cells having a spiral-wound electrode; (d) and (e) example electrical connections for a unipolar design and a bipolar design.
  • FIG. 10 depicts schematically an example process or method by which further example electrodes can be formed for use as spiral-wound or flat electrodes in an electrolyser.
  • FIG. 11 depicts schematically (a) a further example electrolyser or cell having flat-sheet electrodes; (b) and (c) further example electrolysers or cells having spiral-wound electrodes; using the example electrodes of FIG. 10 .
  • FIG. 12 depicts a cut-away view of an example electrolyser module containing hollow-fibre gas permeable or breathable materials.
  • FIG. 13 is a schematic illustration of the operation of one type of example electrolyser module involving hollow-fibre gas permeable or breathable materials.
  • FIG. 14 is a schematic illustration the operation of a second type of example electrolyser module involving hollow-fibre gas permeable or breathable materials.
  • FIG. 15 is a schematic illustration showing how separate modules of an example spiral wound electrolyser may be combined within a second, tube housing to generate a larger quantity of hydrogen from water.
  • FIG. 16 illustrates how separate tube housings containing multiple modules may be combined within a plant.
  • FIG. 17 illustrates an example circuit for converting three-phase AC electricity into DC electricity with near-100% energy efficiency, for use with example electrolysers.
  • FIG. 18 illustrates (a) in an exploded view, and (b) in an assembled view, how single, flat-sheet gas permeable or breathable material electrodes may be combined into an example ‘Plate-and-Frame’ style electrolyser.
  • FIG. 18( c )-( d ) illustrates how two such example anode-cathode cells may be combined into an example multi-layer electrolyser.
  • FIG. 19( a )-( c ) depicts typical rates of gas generation by the example ‘plate-and-frame’ style electrolyser from FIG. 18 , over three days of operation under conditions of constant switching “on” and “off”.
  • (a) depicts data for part of day 1;
  • (b) depicts data for part of day 2; and
  • (c) depicts data for part of day 3.
  • Example gas permeable or breathable electrodes may be formed by any convenient means.
  • gas permeable electrodes can be formed by depositing a conducting layer on a gas permeable material and subsequently depositing a catalyst on the conducting layer.
  • a gas permeable non-conducting material one could start with a gas permeable non-conducting material and then form the conducting layer on the material, and thereafter, deposit the catalyst.
  • a gas permeable conducting material may be formed by any convenient means.
  • gas permeable electrodes can be formed by depositing a conducting layer on a gas permeable material and subsequently depositing a catalyst on the conducting layer.
  • a gas permeable non-conducting material deposit the conducting layer on the material, and thereafter, deposit the catalyst.
  • a gas permeable or breathable electrode may be formed by holding or positioning a conductive layer, incorporating a catalyst or not, in close association with a gas permeable or breathable material.
  • a gas permeable or breathable material may be formed by holding or positioning a conductive layer, incorporating a catalyst or not, in close association with a gas permeable or breathable material.
  • the inventors have found that by simply pressing the conducting layer against a gas permeable material one is able to have a significant proportion of gas reaction products to migrate across the material and not form bubbles, or not substantially form bubbles or at least visible bubbles, in the electrolyte.
  • the conducting layer with catalyst may be chemically or physically bound to the gas permeable material.
  • the anode and cathode layers may be separated by suitable liquid-permeable, electrically-insulating spacers, which allow liquid ingress to the anodes and cathodes whilst simultaneously preventing short circuits from forming between the anodes and cathodes.
  • suitable liquid-permeable, electrically-insulating spacers which allow liquid ingress to the anodes and cathodes whilst simultaneously preventing short circuits from forming between the anodes and cathodes.
  • suitable spacers is the “feed-channel” spacers used in commercially-available reverse osmosis membrane modules.
  • the spacer is suitably robust to allow the transit of liquids but prevent the anodes and cathodes from collapsing on themselves, even under high applied pressures.
  • an electrode for a water splitting device comprising a gas permeable material and a second material, being part of the electrode, and/or an anode or a cathode adjacent to the electrode.
  • a spacer layer is positioned between the gas permeable material and the second material, the spacer layer providing a gas collection layer, i.e. within the electrode or between the electrode and an adjacent anode or cathode.
  • a conducting layer is also provided as part of the electrode and is associated with the gas permeable material.
  • the second material may be part of the electrode or an adjacent electrode (e.g.
  • the conducting layer can be provided adjacent to or at least partially within the gas permeable material, preferably on an outer side of the gas permeable material.
  • the conducting layer is associated with, positioned next to or is deposited on the gas permeable material.
  • the gas collection layer is able to transport gas internally in the electrode, preferably to an exit area or region of the electrode.
  • the gas permeable material is a gas permeable membrane and the second material is a further or additional gas permeable membrane.
  • the gas collection layer is able to transport gas internally in the electrode to at least one gas exit area positioned at or near an edge or an end of the electrode.
  • the gas permeable material and the second material are separate layers of the electrode.
  • the second material is preferably a gas permeable material or membrane.
  • the second material can be a gas permeable material and a second conducting layer can be provided adjacent to or at least partially within the second material.
  • the spacer layer providing a gas collection layer is provided or positioned between a gas permeable layer and a second layer (i.e. the second material) being a further gas permeable layer of the electrode.
  • the second material is a gas permeable material and a second conducting layer is associated with, positioned adjacent to, or deposited on the second material.
  • Spacer layers are provided to maintain the respective gas collection channels as well as the electrolyte channels. Suitable spacer layers can be selected for each channel.
  • the gas collection layer in the respective electrodes is maintained by a spacer layer which may be in the form of embossed structures on the inner surfaces of the materials or as a separate spacer device such as a gas diffusion spacer or the like.
  • the electrolyte layer between the anodes and cathodes may be maintained by the use of a spacer layer in the form of a “flow channel” spacer. Other suitable spaces may be used that allow the electrolyte to permeate the electrolyte layer and contact the respective anode and cathodes.
  • the internal vacancies, voids or spaces within the hollow sheets or fibres comprising the anodes and cathodes may be filled, or at least partially filled, with a spacer or spacer layer, preferably a robust spacer or spacer layer, that allows gases to pass through the spacer or spacer layer, but which prevents the walls of the hollow structure from collapsing on themselves, even under high applied pressures.
  • a spacer or spacer layer preferably a robust spacer or spacer layer, that allows gases to pass through the spacer or spacer layer, but which prevents the walls of the hollow structure from collapsing on themselves, even under high applied pressures.
  • a spacer or spacer layer preferably a robust spacer or spacer layer, that allows gases to pass through the spacer or spacer layer, but which prevents the walls of the hollow structure from collapsing on themselves, even under high applied pressures.
  • An example of such a spacer is the “permeate” spacer used in commercially-available reverse osmos
  • the gas permeable or breathable anodes and cathodes may be constructed by depositing electrically conductive metallic layers on an outer surface or surfaces of the gas permeable or breathable materials and then, if necessary, depositing suitable (electro)catalysts on the electrically conductive layers.
  • the electrically conductive metallic layers may serve as (electro)catalysts in their own right.
  • the catalysts may be so chosen as to facilitate and accelerate the liquid-to-gas or gas-to-liquid transformation.
  • the gas permeable or breathable electrodes may be conveniently constructed whereby the gas flux across the gas permeable material is tuned to the production rate of the reaction product that may form a gas at the electrode.
  • the gas permeable or breathable anodes and cathodes are constructed by co-assembling in close and tight-fit proximity to each other: (1) a gas permeable or breathable material with (2) a free-standing, planar, porous metallic or conductive structure coated, where necessary, with suitable catalysts.
  • the free-standing, planar, porous conductive structures may be fine metal meshes, grids, felts, or similar planar, porous conductors. Conductive structures of this type are commercially available from a wide variety of vendors.
  • the gas permeable or breathable materials maintain a well-defined liquid-gas interface at all of the anodes and cathodes in the cell during the reaction. This may be achieved by ensuring that the differential pressure across the gas permeable or breathable materials of the anodes and cathodes (from the liquid side to the gas side) is less than the capillary pressure to wet their pores. In this way, liquid is not driven into the gas channels nor gas driven into the liquid chambers, as a result of the applied pressure.
  • the reactor may be designed so that the applied pressure does not exceed the capillary pressure at which liquid is driven into the gas channels or gas driven into the liquid channels. That is, the pores of the materials are so chosen as to ensure the maintenance of a distinct liquid-gas interface at the anodes and cathodes during operation under the applied pressure.
  • Washburn's equation is used to calculate the maximum pore size required to maintain a clear liquid-gas interface at the gas permeable or breathable electrodes when a pressure is applied to either the gases or the liquids in the reactor, as described in the non-limiting case in example 5.
  • the pores should preferably have a radius or other characteristic dimension of less than 0.5 microns, more preferably less than 0.25 microns, and still more preferably about 0.1 microns or lower.
  • the pores should preferably have a radius or other characteristic dimension of less than 0.1 microns, more preferably less than 0.05 microns, and still more preferably about 0.025 microns or lower.
  • the materials used to fabricate the gas permeable or breathable anodes and cathodes in one example swell by less than 1% in water, or in the liquid employed in the device.
  • the gases associated with the anodes and cathodes are kept separate from each other by engineering the gas channels within the reactor such that the anode gases are separated at all points from the cathode gases.
  • the multi-layered structure of anodes and cathodes comprising the electrochemical cell is housed within a tight-fitting and robust casing which holds within it, all of the anodes and cathodes, as well as the gas and liquid channels.
  • the multi-layered structure of anodes and cathodes and their associated gas and liquid channels are fabricated in a modular form, which maybe readily linked to other modules to form larger overall reactor structures. Moreover, in the case of failure, they may be readily removed from and replaced in such structures by other identically constructed modules.
  • the multi-layered structures of anodes and cathodes within a single module have a relatively high internal surfaces area, but a relatively low external area or footprint.
  • a single module may have an internal structure of more than 2 square meters, but external dimensions of 1 square meter.
  • a single module could have an internal area of more than 10 square meters, but external area of less than 1 square meter.
  • a single module may have an internal area of more than 20 square meters, but an external area of less than 1 square meter.
  • the multi-layered structure of anodes within a single module may have the gas channels associated with the anode connected into a single inlet/outlet pipe.
  • the multi-layered structure of cathodes within a single module may have the gas channels associated with the cathode connected into a single inlet/outlet pipe, which is separate from the anode inlet/outlet pipe.
  • the multi-layered structure of anodes and cathodes within a single module may be configured as a multi-layered material arrangement.
  • the multi-layer spiral wound structure may comprise one or more than one cathode/anode electrode assembly pairs, and may comprise one or more leaf assemblies.
  • the modular units described above 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 as described above 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.
  • An example water splitting cell may be operated at relatively low current densities in order to achieve high energy efficiencies in the production of gases-from liquids, or liquids-from-gases.
  • the water splitting cells may be operated at a current density that accords with the highest reasonable energy efficiency under the circumstances.
  • the reactor may be operated at a current density that accords with more than 75% energy efficiency in terms of the higher heating value (HHV) of hydrogen.
  • HHV heating value
  • the water electrolyser may be operated at a current density that accords with more than 85% energy efficiency according to the higher heating value (HHV) of hydrogen; 85% energy efficiency may be achieved if the electrolyser generates 1 kg of hydrogen upon the application of 45.9 kWh of electrical energy.
  • the water splitting cell may be operated at a current density that accords with more than 90% energy efficiency according to the higher heating value (HHV) of hydrogen; 90% energy efficiency may be achieved if the electrolyser generates 1 kg of hydrogen upon the application of 43.3 kWh of electrical energy.
  • the removal of produced gas across the gas permeable material results in a device capable of, separating the gas from the reaction at the electrode.
  • Greater than 90% of the gas produced at the at least one electrode can be removed from the cell across the gas permeable material. Desirably, greater than 95% and greater than 99% of the gas produced can be removed across the gas permeable material.
  • the water splitting cell may operate to produce hydrogen gas at greater than 75% energy efficiency HHV. Desirably, the water splitting cell may produce hydrogen gas at greater than 90% energy efficiency HHV.
  • the water splitting cells may be operated efficiently by managing the pressure differential across the gas permeable materials.
  • the management of the pressure differential may prevent wetting of the materials and drives the gas reaction products across the material.
  • the selection of pressure differential will be typically dependent upon the nature of the water splitting materials and may be determined with reference to Washburn's equation as described below. Pressurizing the electrolyte may also be useful in providing a pressurised gas product in the gas collection layers.
  • a process for generating hydrogen comprising applying low current density to a water splitting cell pressurizing an electrolyte, splitting water and producing hydrogen gas and oxygen gas; and collecting the respective pressurised gases with the respective gas collection layers.
  • the water splitting cell may be operated at temperatures that are desirably less than 100° C., less than 75° C. and less than 50° C.
  • the individual electrochemical cells within the reactor may be so configured in series or parallel, as to maximize the voltage (Volts) and minimise the current (Amps) required. This is because, in general, the cost of electrical conductors increases as the current load increases, whereas the cost of AC-DC rectification equipment per unit output decreases as the output voltage increases.
  • the overall configuration of the individual cells in series or parallel within the reactor may be configured as to best match the available three-phase industrial or residential power. This is because a close match of the overall power requirements of the electrolyser and the available three-phase power generally allows for low-cost AC to DC conversion with near 100% energy efficiency, thereby minimising losses.
  • a preferred embodiment typically includes an electrochemical reactor for direct electrical transformation of water into hydrogen and oxygen, the water electrolyser preferably but not exclusively, comprising hollow gas permeable or breathable electrode structures (e.g. flat-sheets or fibres) as anodes and cathodes in multi-layered arrangements:
  • the water electrolyser preferably but not exclusively, comprising hollow gas permeable or breathable electrode structures (e.g. flat-sheets or fibres) as anodes and cathodes in multi-layered arrangements:
  • gas permeable or breathable electrodes were then tested by incorporation in bubble-free, laboratory-scale water electrolysers where their performance was compared under optimum conditions of acidity/basicity with standard, industry-best catalysts which generated bubbles. For this comparison we selected solid platinum (Pt) in 1 M strong acid as the “industry-best” catalyst. The reason for this choice was that the other alternative—namely, nickel (Ni) catalyst in strongly basic alkaline electrolysers—is generally considered less energy efficient overall than Pt in strong acid.
  • the first set of data displayed in FIG. 1 examines two “bubble-free” electrolysers incorporating flat-sheet breathable electrodes at both the cathode and anode: a Ni-catalyzed alkaline electrolyser in 1 M strong base ( FIG. 1( a )), and a Pt-catalyzed acid electrolyser in 1 M strong acid ( FIG. 1( b )).
  • the acid used was sulphuric acid.
  • the base used was sodium hydroxide.
  • the same catalysts were used at both of the anode and cathode simultaneously.
  • FIG. 1( a )-( b ) The data in FIG. 1( a )-( b ) was collected using the cell depicted in FIG. 3 .
  • the cell in FIG. 3( a ) is depicted schematically in FIG. 3( b ).
  • the cell comprises the following parts: a central water reservoir 100 has a water-free hydrogen collection chamber 110 on the left side and a water-free oxygen collection chamber 120 on the right side. Between the water reservoir 100 and the hydrogen collection chamber 110 is a gas permeable or breathable electrode 130 . Between the water reservoir 100 and the oxygen collection chamber 120 is a gas permeable or breathable electrode 140 .
  • a conductive layer containing a suitable catalyst 150 On, or close to, or partially within, the surface of the gas permeable or breathable electrodes 130 and 140 is a conductive layer containing a suitable catalyst 150 , or more than one catalysts.
  • an electrical power source 160 such as a battery
  • electrons flow along the outer circuit as shown in circuit pathways 170 . That current causes water to be split into hydrogen on the surface of the breathable electrode 130 (called the cathode) and oxygen on the surface of the breathable electrode 140 (called the anode). Instead of forming bubbles at these surfaces, the oxygen and hydrogen passes through the hydrophobic pores 180 into the oxygen and hydrogen collection chambers 120 and 110 , respectively.
  • Liquid water cannot pass through these pores since it repels the hydrophobic surfaces of the pores and the surface tension of the water prevents droplets of water from disengaging from the bulk of the water to thereby pass through the pores.
  • the electrodes 130 and 140 act as gas-permeable, water-impermeable barriers.
  • the Ni catalyst was a commercially available, thin. Ni-coated flexible textile, which is used for electromagnetic shielding. The textile was pushed and held tight against a gas permeable or breathable hydrophobic material. This worked just as well as depositing the metal directly onto the material surface as was done for the data in FIG. 1( b ), where the Pt catalyst was deposited directly on the material by vacuum metallization, a standard commercial process. In both cases, the catalysts were subjected to extended conditioning before the representative data shown in FIG. 1( a )-( b ) was collected.
  • electrolysers were left in operation in the 1 M strong acid/base conditions shown with an applied voltage (typically 2-3 V) for several hours before measuring the data.
  • the conditioning allows the systems to get to a clear steady state and ensures that the measurements are reliable.
  • both of the bubble-free electrolysers incorporating alkaline Ni-catalyzed and acid Pt-catalysed breathable cells at each of the anode and cathode convincingly beat simple electrolysers employing the industry-best catalyst, Pt, at both anode and cathode in a configuration where bubbles were generated.
  • the material-based electrolysers do not exhibit the usual jagged chronoamperogram profiles associated with bubble-formation, nor a slowly declining output until a steady-state is generated, as is found with bare Pt.
  • the second set of data in FIG. 2 compares, under optimum conditions of acidity (1 M strong acid):
  • FIG. 4( a ) depicts a photograph of an example electrolyser contrasting a known bare Pt wire for the cathode and a Pt-coated hydrophobic hollow-fibre gas permeable electrode for the anode.
  • the known bare Pt wire becomes covered in bubbles during the water electrolysis, whereas the hollow-fibre gas permeable electrode is bubble free, i.e. without bubble formation or without substantial bubble formation, at least visible bubble formation.
  • FIG. 4( b ) depicts a schematic of a method or process by which the bubble-free electrolyser in point ( 1 ) above was fabricated and how it operates.
  • Hydrophobic hollow-fibre materials 200 were obtained. These were then coated by vacuum metallization of Pt—a standard commercial process—to yield the Pt-coated hollow-fibre material 210 .
  • FIG. 5 depicts a scanning electron micrograph of the surface of 210, showing the thickness of the coating to be 20-50 nm). Two Pt-coated hollow-fibre materials are then sealed at the bottom using araldite glue and dipped into an aqueous solution of 1 M strong acid.
  • the open tops of the hollow-fibre materials are left to protrude above the surface of the liquid water. Electrical connections at their surfaces (on the conducting Pt) are connected to a power source, such as battery 220 , which is used to drive an electrical current between the two, with the electron movement shown at conducting pathway 230 .
  • a power source such as battery 220
  • water is split into hydrogen gas at the surface of the cathode and oxygen gas at the surface of the anode.
  • the gases do not form bubbles however, as they instead transit through the hydrophobic pores of the hollow fibre gas permeable materials 240 .
  • Liquid water does not pass through these pores because under the atmospheric test conditions, liquid water is not capable of wetting the hydrophobic porous surface, in this example based on Goretex® material, a porous form of polytetrafluoroethylene (PTFE) with a micro-structure characterized by nodes interconnected by fibrils.
  • PTFE polytetrafluoroethylene
  • FIG. 2( a ) The operation of the above example electrolyser yields the data shown in FIG. 2( a ).
  • a fixed current density of 2 mA/cm 2 we applied to the electrolyser and then examined how the voltage (energy efficiency) varied over time.
  • the data is illustrated in this way to demonstrate how a commercial electrolyser of this type may be operated.
  • the use of a fixed current density may be the most suitable mode of operation since it guarantees the generation of a particular quantity of hydrogen per day. (The rate of hydrogen generation is dependent on the current employed).
  • the data in FIG. 2( b ) shows comparable results with a known bare Pt wire at both the anode and cathode under otherwise identical conditions. In both cases, the catalysts were not pre-conditioned in order to demonstrate what happens during the first hour of operation of an electrolyser and to show why conditioning is necessary to obtain accurate data.
  • Electrolysers Comprising of Gas Permeable or Breathable Electrodes at Both Anode and Cathode May Achieve High Energy Efficiencies in Water Electrolysis
  • bubble-free water electrolysers i.e. that operate without substantial bubble formation, comprising of gas permeable or breathable electrodes at both the cathode and anode may achieve higher energy efficiencies than systems which generate bubbles in liquid-to-gas transformations. This is due to the reduction or elimination of the bubble overpotential, which comprises a major source of energy loss in such systems.
  • FIG. 6( a ) schematically depicts a double-sided, flat-sheet hydrophobic material 710 .
  • the material comprises of an upper and a lower hydrophobic surface with a spacer, known generically as a “permeate” spacer 740 between them.
  • the upper and lower surfaces contain hydrophobic pores which allow gases, but not liquid water to pass through unless sufficient pressure is applied and/or the water surface tension is sufficiently lowered.
  • the “permeate” spacer is typically dense but porous.
  • FIG. 6( b ) illustrates a typical microscopic structure of this spacer.
  • the microscopic structure of a “flow channel” spacer of this type is depicted in FIG. 7 . As can be seen in FIG.
  • the spacer in FIG. 6 ( b ) has a more dense structure, making it suitable for gas, but not liquid transport.
  • a conductive layer is deposited, typically using vacuum metallization.
  • the conductive layer is typically nickel (Ni). Using this technique, Ni layers of 20-50 nm may be deposited.
  • Ni-coated materials may then be subjected to dip-coating using, for example, electroless nickel plating, to thicken the conducting Ni layer on their surface.
  • a catalyst or more than one catalyst, may be deposited upon or otherwise attached to the conducting Ni surface.
  • catalysts such as Co 3 O 4 , LiCo 2 O 4 , NiCo 2 O 4 , MnO 2 , Mn 2 O 3 , and other catalysts are available.
  • the catalyst may be deposited by various means known in the art.
  • a representative example of depositing such a catalyst upon a nickel surface is given in the publication entitled: “Size-Dependent Activity of Co 3 O 4 Nanoparticle Anodes for Alkaline Water Electrolysis” by Arthur J. Esswein, Meredith J. McMurdo, Phillip N. Ross, Alexis T. Bell, and T. Don Tilley, in the Journal of Physical Chemistry C 2009, Volume 113, pages 15068-15072.
  • the anode 720 in FIG. 6( a ) may be prepared.
  • FIG. 8 illustrates one approach to making an example water electrolyser using the hollow, flat sheet cathode 730 and anode 720 , thus prepared.
  • the cathode 730 is sealed 731 at three of the four edges, with the fourth edge half sealed 731 and half left unsealed 732 as shown.
  • the sealing may be carried out by snap heating and melting the edges of the hollow flat-sheets to thereby block the movements of gases and liquids out of the edges. Laser heating may also be used to seal the edges of the cathode.
  • the anode 720 is sealed 721 at three of the four edges, with the fourth edge half sealed 721 and half left unsealed 722 as shown.
  • the sealing may be carried out by snap heating and melting the edges of the hollow flat-sheets to thereby block the movements of gases and liquids out of the edges. Laser heating may also be used to seal the edges of the anode.
  • the sealing depicted in FIGS. 8( a ) and ( b ) may be carried out before the deposition of the conducting Ni layer and deposition of the catalysts, if this is more suitable. As shown in FIG. 8( c ), the anodes and cathodes are then stacked with intervening flow-channel spacers of the type depicted in FIG. 7 .
  • the unsealed edges of the anodes all line up with each other along the back left edge, whereas the unsealed edges of the cathodes line up with each other along the front left edge. Note that the unsealed edges of the anodes and cathodes do not overlap each other.
  • FIG. 9( a ) depicts how the assembly in FIG. 8( c ) may be turned into an example water electrolyser.
  • a hollow tube (typically comprising of an electrically insulating polymer) is attached to the assembly in FIG. 8( c ) as shown in FIG. 9( a ).
  • the tube is segregated into a forward chamber 910 and a rear chamber 920 which are not connected to each other.
  • the anodes and cathode are attached to the tube in such a way that their unsealed edges open into the internal chambers of the tube.
  • the unsealed edges of the cathode open exclusively into the rear chamber of the tube 920 , while the unsealed edges of the anode open exclusively into the forward chamber of the tube 910 .
  • the anodes and cathodes may be electrically connected in series (bipolar design) or parallel (unipolar design), with a single external electrical connection for the positive pole and another single external electrical connection for the negative pole (as shown in FIG. 9( a )).
  • FIG. 9( d )-( e ) depicts possible, non-limiting connection pathways for a unipolar design ( FIG. 9( d )) and a bipolar design ( FIG. 9( e )). Other connection pathways are possible.
  • water is allowed to permeate through the flow-channel spacers in the direction (out of the page) shown in FIG. 9( a )).
  • water is present at and fills the intervening space between the anodes and cathodes.
  • the multi-layered arrangement of flat-sheet materials may be rolled up into a spiral-wound arrangement as shown in 940 ( FIG. 9( b ).
  • the spiral wound arrangement may then be encased in a polymer casing 950 , which holds the spiral-wound element in place within a module ( 950 ) whilst nevertheless allowing for water to transit through the module as shown in FIG. 9( b ).
  • hydrogen gas is generated and exits the module at the rear tube as shown.
  • Oxygen gas is generated at the forward tube as shown.
  • FIG. 9( c ) An alternative arrangement is depicted in FIG. 9( c ).
  • the collection tube is not segmented into a forward and a rear collection chamber. Rather the tube is segmented down its length into two separate chambers.
  • the flat-sheet anodes and cathodes are attached to the tube in such a way that the unsealed edges of the anodes empty into one of these chamber and the unsealed edges of the cathodes empty into the other of these chambers.
  • the module allows for water to transit through as shown in FIG. 9( c ).
  • Water electrolysis modules of the type depicted in 950 typically display high internal surface area but a relatively small overall footprint. A range of other options exist to fabricate a spiral wound water electrolysis module. In order to demonstrate some of the other, non-limiting options for fabricating spiral wound electrolysers, reference is made to FIGS. 10 and 11 .
  • FIG. 10 illustrates another approach to the manufacture of a spiral wound electrolyser module.
  • the cathode 730 is sealed 731 at three of the four edges, with the fourth edge left unsealed 732 as shown ( FIG. 10( a )).
  • the anode 720 is sealed 721 at three of the four edges, with the fourth edge left unsealed 722 as shown ( FIG. 10( b )).
  • the anodes and cathodes are then stacked as shown in FIG. 10( c ) with intervening flow-channel spacers of the type depicted in FIG. 7 . Note that the unsealed edges of the anodes all line up with each other along the left edge, whereas the unsealed edges of the cathodes line up with each other along the right edge.
  • FIG. 11( a ) depicts how the assembly in FIG. 10( c ) may be turned into a water electrolyser of the present invention.
  • a hollow tube 1110 is attached to the left side of the assembly in FIG. 10( c ) as shown in FIG. 11( a ).
  • the anodes are attached to the tube 1110 in such a way that their unsealed edges open into the internal vacancy of the tube 1110 .
  • Another tube 1120 is attached to the right side of the assembly.
  • the cathode is attached to the tube 1120 in such a way that their unsealed edges open into the internal vacancies of the tube 1120 .
  • the modular arrangement shown in 1140 in FIG. 11( b ) comprises of two, roughly equally thick, spiral wound elements encased by a polymer casing 1140 .
  • the casing allows water to pass through the module as shown.
  • the two inner tubes separately collect and yield the hydrogen and oxygen that is generated.
  • the modular arrangement shown in 1150 in FIG. 11( c ) comprises of one spiral wound element incorporating the left hand collection tube (oxygen generation) and encased by a polymer casing 1140 , with the other collection tube (hydrogen generation) located on the outer surface of the module.
  • the casing allows water to pass through the module as shown.
  • the inner tube collects and supplies the oxygen that is generated.
  • the outer tube collects and supplies the hydrogen that is generated.
  • Such water electrolysis modules have a high internal surface area but a relatively small overall footprint or external area, they can be operated at relatively low overall current densities.
  • a typical current density would be 10 mA/cm 2 , which is two orders of magnitude smaller than the current densities currently employed in most commercial water electrolysers. At so low a current density, it is possible to generate hydrogen with near to or greater than 90% energy efficiency HHV.
  • the electrical power requirements and options for series and parallel electrical arrangement of the individual cells in such modules are discussed in detail in Example 6.
  • Hollow-Fibre Module An Electrochemical Reactor Comprising a Multi-Layer, Hollow-Fibre Configuration
  • FIG. 12 depicts schematically and in principle how a set of hollow-fibre anode and cathode electrodes may be configured for an example water electrolyser.
  • a set of conductive catalytic hollow-fibre materials 1200 may be aligned and housed within a casing 1200 that allows for water to be transported around the array of hollow-fibre materials.
  • To construct a hollow-fibre water electrolyser reactor one can start with the hydrophobic hollow-fibre material with built-in gas spacer 200 depicted in FIG. 4( b ). Upon the surface of this material a conductive layer is deposited, typically using vacuum metallization. In the case of an alkaline electrolyser, the conductive layer is typically nickel (Ni).
  • Ni layers of 20-50 nm may be deposited.
  • the Ni-coated materials may then be subjected to dip-coating using electroless nickel plating, to thicken the conducting Ni layer on their surface.
  • a catalyst may be deposited upon the conducting Ni surface.
  • the hollow fibre anode or cathode thus prepared is electrically isolated from other electrodes when in operation, it would typically be further coated with a layer of porous Teflon or sulfonated fluorinated polymer using a standard dip-coating procedure well-known in the art.
  • a layer of porous Teflon or sulfonated fluorinated polymer such as these, the hollow-fibre anode 1320 and hollow-fibre cathode 1310 in FIG. 13 may be prepared.
  • the cathodes and anodes thus prepared are then sealed at their both ends using simple heat sealing or a laser sealing process. If necessary, the hollow-fibre gas permeable materials may be sealed prior to the deposition of the conductive and catalytic layers upon their surface.
  • the cathode and anode hollow fibres are then interdigitated as shown schematically in FIG. 13 , with their ends lying in a non-interdigitated fashion on opposite sides.
  • the anode hollow fibres 1320 have their non-interdigitated ends on the right and the cathode hollow fibres 1310 have their non-interdigitated ends on the left.
  • a conductive adhesive is then cast about the non-interdigitated ends of the anode hollow-fibres 1320 .
  • the adhesive is allowed to set, whereafter a conductive adhesive is cast about the non-interdigitated ends of the cathode hollow-fibres 1310 .
  • the two adhesives are sawn through with a fine bandsaw, opening up the one end of the sealed hollow fibres.
  • the anode hollow fibres 1320 are now open on the right-hand side of the interdigitated assembly (as shown in FIG. 13 ), while the cathode hollow fibres 1310 are open at the left hand side of the interdigitated assembly (as shown in FIG. 13 ).
  • the interdigitated assembly is then encased in a polymer case 1330 which allows water to pass between the interdigitated hollow-fibres but not into their internal gas collection channels.
  • the anodes and cathodes are then preferably, though not necessarily, connected in parallel with each other (unipolar design), with the negative external pole connected to the left-hand (cathode) conducting adhesive plug and the positive external pole connected to the right-hand (anode) conducting adhesive plug.
  • Bipolar designs are also possible in which individual fibres, or bundles of fibres are connected in series with each other so that hydrogen is generated in the hollow-fibres open at the left-hand side of the electrolyser and oxygen in the hollow-fibres open at the right-hand side of the electrolyser.
  • oxygen is generated at the surface anode hollow-fibres.
  • the hydrogen passes through the hydrophobic pores 240 of the hollow fibre into the internal gas collection channel 270 of the anodes, without forming bubbles at the surface of the anode.
  • the oxygen is channeled as shown in FIG. 13 into the oxygen outlet at the right of the reactor in FIG. 13 .
  • the module depicted in FIG. 13 generates hydrogen and oxygen upon application of a suitable voltage and when water is passed through the module.
  • the anode and cathode hollow fibres have not been interdigitated, but have instead been incorporated in two separate multi-layer arrangements that face each other.
  • a set of parallel hollow-fibre cathodes 1410 have been located together within the module housing 1430
  • a set of parallel hollow-fibre anodes 1420 have been located together in the module housing 1430 .
  • a proton exchange membrane or material may optionally be present between the cathode and the anode hollow-fibres.
  • hollow-fibre based water electrolysis modules have a high internal surface area but a relatively small overall footprint, they can be operated at relatively low overall current densities.
  • a typical current density would be 10 mA/cm 2 . which is two orders of magnitude smaller than the current densities currently employed in most commercial water electrolysers. At so low a current density, it is possible to generate hydrogen with near to or greater than 90% energy efficiency HHV.
  • the electrical power requirements and options for series and parallel electrical arrangement of the individual cells in such modules are discussed in detail in Example 6.
  • FIG. 15 depicts schematically how water electrolyser modules may be assembled into larger units that constitute an electrolyser plant.
  • Three modules 1510 (of the same type described as 950 in FIG. 9( c )) are attached to each other via robust “quick-fit” fittings 1520 , that correctly connect the separate hydrogen and oxygen gas collections channels together in a secure way.
  • the combined modules are then pushed into a thick metal tube 1530 which is sealed with a thick metal cover plate 1540 at each end.
  • the cover plates 1540 allow for the transportation of water through the tube and permit the gas collection tubes to protrude outside of the tube. Water is then passed through the sealed tube 1550 as shown, while a voltage is applied to the combined anodes and cathodes in the modules within the tube.
  • the resulting hydrogen and oxygen that is generated is collected as shown at the bottom right of FIG. 15 .
  • the tube 1530 acts as a second containment vessel for the hydrogen that is generated and thereby carries out a safety function for the electrolyser.
  • the configuration depicted in FIG. 15 is for a water electrolyser plant. In such plants, multiple tubes containing modules may be combined as shown in the photograph in FIG. 16 . Tubular arrangements of water electrolyser modules may be combined in a similar way.
  • the contact angles are typically 100-115°.
  • the surface tension of water is typically 0.07197 N/m at 25° C. If the water contains an electrolyte such as 1 M KOH, then the surface tension of the water typically increases to 0.07480 N/m.
  • the pores should preferably have a radius of less than 0.5 microns, more preferably less than 0.25 microns, and still more preferably around 0.1 microns or lower. In this way there would be a diminishing possibility of an applied pressure causing water to be driven into the gas channels.
  • the PTFE material pores should preferably have a radius or other characteristic dimension of less than 0.1 microns, more preferably less than 0.05 microns, and still more preferably about 0.025 microns or lower.
  • modules of the types depicted in 950 , 1140 , 1150 , 1210 , 1330 , and 1430 may be connected in series or parallel, or combinations thereof.
  • Modules containing cells in parallel electrical arrangements are termed unipolar modules.
  • Modules containing cells in series electrical arrangements are termed bipolar modules (see, for example, FIG. 9( d )-( e )).
  • the modules e.g. 1510 in FIG. 15
  • the overall electrolyser should be constructed in such a way that the electrical losses involved in converting residential or industrial AC power to DC are minimized to, ideally, well less than 10%.
  • the power requirements of the overall electrolyser configuration will be matched to the three-phase residential or industrial power supply that is available. This ensures virtually 100% efficiency in AC to DC conversion.
  • the optimum overall electrical configuration for an example electrolyser can be determined by aiming to match its power requirement to the industrial or residential three-phase power that is available. If this can be achieved, then the power loss in going from AC to DC can be limited to essentially zero, since only diodes and capacitors are required for the rectifier, and not a transformer.
  • three-phase mains power provides 600 Volts DC, with a maximum current load of 120 Amps.
  • the electrolyser would need 375 cells in series in order to draw 600 Volts DC.
  • Each individual cell will then experience a voltage of 1.6 Volt DC.
  • the overall current drawn by such an electrolyser would be 100 Amps, giving an overall power of 60 kW.
  • the AC to DC conversion unit in the power supply required for such an electrolyser would be a very simple arrangement of six diodes and beverage-can sized capacitors wired in a delta arrangement of the type shown in FIG. 17 .
  • Units of this type are currently commercially available (for example, the “SEMIKRON—SKD 160/16—BRIDGE RECTIFIER, 3 PH, 160A, 1600V”.
  • the cost of the power supply would also be minimized and, effectively, trivial or non limitation overall.
  • Another approach is to subject the three-phase power to half-wave rectification using a very simple circuit that again utilizes only diodes and capacitors and thereby avoids electrical energy losses.
  • An electrolyser tailored to half-wave rectified 300 Volt DC would ideally contain 187 individual cells of the above type in series.
  • Such an electrolyser could be constructed of 9 bipolar modules connected in series, which comprise of 180 individual cells. Each cell would experience 1.67 Volts DC. The overall current drawn would be 96 Amps.
  • Such an electrolyser would generate 16.2 kg of hydrogen per 24 hour day. It could be plugged into a standard three-phase wall socket.
  • Electrochemical Reactor Comprising a Multi-Layer, Flat-Sheet Configuration (‘Plate-and-Frame Type Module’)
  • FIG. 18( a ) provides an exploded view that illustrates how multiple, single-ply or sheet material electrodes may be combined within a ‘plate-and-frame’ type electrolyser. The following items are sandwiched or adjoined into an example electrolyser structure:
  • assembly 1720 may act as a highly efficient electrolyser.
  • Aqueous solution (1 M KOH) is introduced into the space between the electrodes via ports 1730 and 1740 .
  • the water fills the volume within spacer 1670 .
  • an electrical voltage is then applied over the copper connectors 1660 and 1710 , then the water is split into hydrogen and oxygen.
  • the gases move through their respective material electrodes. Oxygen gas exits the device at ports 1750 and 1760 . Hydrogen exits the device at the corresponding ports on the back side of assembly 1720 .
  • FIG. 18( c )-( d ) illustrates how this may be done.
  • two assemblies 1720 are combined by incorporating a gas collecting spacer unit 1770 between them.
  • the spacer unit contains a hydrogen outlet 1780 , that collects hydrogen from each of the adjacent assemblies 1720 .
  • both of the cathodes 1690 of assemblies 1720 are attached to the spacer 1770 , which has a porous internal structure 1790 , through which the generated hydrogen may pass prior to exiting at outlet 1780 .
  • the anodes 1640 of assemblies 1720 are located on the outside of the stack, causing oxygen to be transmitted via outlet 1750 and 1760 , on the outer sides of the resulting ‘plate-and-frame’ electrolyser.
  • FIG. 19 depicts data for the operation of the device shown in FIG. 18 ( a )-( b ) at an applied cell voltage of 1.6 V (94% electrical efficiency, HHV), over three days of operation, with repeated, intermittent ‘on’ and ‘off’ switching.
  • the device generates gases at a relatively constant rate, consuming around 10-12 mA/cm 2 of current in doing so.
  • the device was tested at both 1.5 V (99% electrical efficiency, HHV) and 1.6 V (94% electrical efficiency, HHV), as shown.
  • 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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