WO2022049266A1 - Device for electrolytic production of hydrogen - Google Patents

Device for electrolytic production of hydrogen Download PDF

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Publication number
WO2022049266A1
WO2022049266A1 PCT/EP2021/074419 EP2021074419W WO2022049266A1 WO 2022049266 A1 WO2022049266 A1 WO 2022049266A1 EP 2021074419 W EP2021074419 W EP 2021074419W WO 2022049266 A1 WO2022049266 A1 WO 2022049266A1
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WO
WIPO (PCT)
Prior art keywords
anion exchange
exchange membrane
ceramic material
electrode assembly
elements
Prior art date
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PCT/EP2021/074419
Other languages
French (fr)
Inventor
Rémi Costa
Li Wang
Matthias RIEGRAF
Aldo Saul GAGO RODRIGUEZ
Vincent WILKE
Original Assignee
Deutsches Zentrum für Luft- und Raumfahrt e.V.
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Application filed by Deutsches Zentrum für Luft- und Raumfahrt e.V. filed Critical Deutsches Zentrum für Luft- und Raumfahrt e.V.
Priority to DE112021004643.8T priority Critical patent/DE112021004643T5/en
Publication of WO2022049266A1 publication Critical patent/WO2022049266A1/en

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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
    • 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
    • C25B13/00—Diaphragms; Spacing elements
    • C25B13/04—Diaphragms; Spacing elements characterised by the material
    • C25B13/05—Diaphragms; Spacing elements characterised by the material based on inorganic materials
    • C25B13/07—Diaphragms; Spacing elements characterised by the material based on inorganic materials based on ceramics
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
    • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms
    • C25B9/23—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms comprising ion-exchange membranes in or on which electrode material is embedded
    • 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 invention relates to a device for the electrolytic production of hydrogen from an aqueous solution as well as an anion exchange membraneelectrode assembly for the electrolytic production of hydrogen from an aqueous solution.
  • AEL alkaline water electrolysis
  • PEM proton exchange membrane
  • PEM electrolysers are able to overcome most of these restrictions, being a versatile player with the advantages of compact system design, fast response, dynamic operation and excellent overload capacity and high voltage efficiency.
  • the high capital expenditure hinders its large-scale deployment, which is mainly caused by the titanium bipolar plates and catalyst coated membranes (CCM) that contain platinum group materials.
  • CCM catalyst coated membranes
  • Anion exchange membrane (AEM) electrolysers have attracted significant interest only very recently due to significant breakthroughs of AEMs and related ionomers, and have demonstrated the potential to combine advantages of AEL (low cost materials) and PEM (high performance).
  • the advantages of AEM electrolysers include:
  • WO201 1004343A1 discloses a device for the production on-demand of hydrogen by electrolysis of aqueous solutions from a dry cathode.
  • CeO2-La2O3 powder that is blended with Ni and carbon was used as cathode catalyst in an AEM electrolyser to promote hydrogen evolution reaction.
  • Another object of the invention is to provide an anion exchange membrane-electrode assembly for such a device for the electrolytic production of hydrogen from an aqueous solution.
  • an anion exchange membraneelectrode assembly for the electrolytic production of hydrogen from an aqueous solution, comprising a positive electrode on one side of an anion exchange membrane and a negative electrode on the opposite side of the anion exchange membrane.
  • the anion exchange membraneelectrode assembly further comprises a ceramic material with alkaline surface properties.
  • the ceramic material comprises at least one of a group enclosing compounds of a structure of ABi- y RE y Os-a with 0 ⁇ y ⁇ 1 , wherein A being one or more elements from the Alkaline Earth metal group, and B being at least one of the following elements: Ti, Zr, Ce, Hf, Sn, In, and RE being one or more elements from the Rare Earth Elements.
  • the ceramic material works as a so-called alkaline promoter.
  • a ceramic material with alkaline surface properties the adsorption of water at the surface may advantageously be enhanced.
  • the problem of wettability and stability issues of the membrane and/or the electrodes, which occurs in prior art, may be solved.
  • Ceramic material into the membrane and/or the electrodes may serve to weaken the HO-H bond of an adsorbed water molecule, in order to promote localized alkaline environment, which may advantageously support alkaline promotion.
  • the ceramic material may comprise BaCei-x-yZr x Y y O3-a, BaSnOs, BaZrOs, BaHfOs, CaZrOs, Bai- x CaxCei-x-yZr x YyO3-a, (La-i - y Ca y )2(Cei -xZr x )2O7-a, with 0 ⁇ x ⁇ 1 and 0 ⁇ y ⁇ 1.
  • RE rare-earth
  • M Nb,Ta
  • lanthanum tungstate acceptor-doped rare-earth (RE) ortho- niobates and ortho-tantalates
  • the parameter a represents the deviation to the stoichiometric content of oxygen in the above listed materials at equilibrium.
  • single or mixed oxides of the Rare Earth Elements may be used: for instance materials from the solid solution Cei- x RE x O2-a with 0 ⁇ x ⁇ 1 and RE being one or more Rare Earth Element and the parameter a represents the deviation to the stoichiometric content of oxygen in the solid solution at equilibrium.
  • any composite mixture of the above mentioned materials i.e. for instance CeO2 + LaFs, may be comprised in the ceramic material.
  • any ceramic material characterized with a negative hydration enthalpy may favorably be comprised in the ceramic material used in the anion exchange membrane-electrode assembly.
  • the ceramic material may be of perovskite structure or related, in particular double perovskite AA'B20S+6 and Ruddlesden-Popper An+iBnOsn+i phases.
  • A’ is a cation of the same groups of elements as elements A with A being one or more elements from the Alkaline Earth metal group.
  • A’ is a Lanthanide when A is an Alkaline Earth and vice versa.
  • n is a positive integer (i.e. , 1 , 2, 3, 4... ) and the parameter s represents the deviation to the stoichiometric content of oxygen in the solid solution at equilibrium.
  • the ceramic material works as a so-called alkaline promoter.
  • alkaline promoter By adding such a ceramic material with alkaline surface properties the adsorption of water at the surface may advantageously be enhanced.
  • the problem of wettability and stability issues of the membrane and/or the electrodes, which occurs in prior art, may be solved.
  • Ceramic material into the membrane and/or the electrodes may serve to weaken the HO-H bond of an adsorbed water molecule, in order to promote localized alkaline environment, which may advantageously support alkaline promotion.
  • the ceramic material may be integrated, in particular in a powder form, into at least one of the electrodes.
  • a ceramic material with alkaline surface properties the adsorption of water at the surface may advantageously be enhanced.
  • Integrating ceramic material into the membrane and/or the electrodes may serve to weaken the HO-H bond of an adsorbed water molecule, in order to promote localized alkaline environment, which may advantageously support alkaline promotion.
  • the physical effects of integrating the ceramic material may advantageously be enhanced by dispersing it in a fine granular way into the carrier as the membrane or the electrode material.
  • the ceramic material may be blended with an ionomer and/or a catalyst of the at least one of the electrode.
  • the ceramic material may be integrated in a very direct way into the electrode material.
  • the ceramic material may be integrated in a very fine granular dispersion in the electrode material.
  • the ceramic material may be integrated into the anion exchange membrane.
  • Integrating ceramic material into the membrane may serve to weaken the HO-H bond of an adsorbed water molecule, in order to promote localized alkaline environment, which may advantageously support alkaline promotion.
  • the ceramic material may be blended with an ionomer and/or a polymer of the anion exchange membrane.
  • the ceramic material may be integrated in a very direct way into the membrane material.
  • the ceramic material may be integrated in a very fine granular dispersion in the membrane material.
  • the ceramic material in particular in a powder form, may be coated, in particular directly coated, on at least one side of the anion exchange membrane.
  • the ceramic material may comprise a specific surface area of at least 1 m 2 /g, preferably of at least 10 m 2 /g and more preferably of at least 20 m 2 /g.
  • the anion exchange membrane may comprise 0.1 wt% to 50 wt% of ceramic material, and/or one or both the electrodes may comprise 0.1 wt% to 80 wt% of ceramic material. Even low alkaline promoter content enables providing alkaline surface properties in order to effect the production of hydrogen in a favorable manner.
  • the ceramic material may comprise one or more constitutive elements in an oxidized state in combination with one or more of a halogen, preferably fluorine, and/or one or more of a chalcogen, preferably oxygen.
  • a halogen preferably fluorine
  • a chalcogen preferably oxygen
  • the one or more constitutive elements of the ceramic material and the bound halogen and/or chalcogen atoms may differ by an average difference in electronegativity on the Pauling scale of at least 1.7, preferably of at least 2.
  • alkaline surface properties may be enabled in an advantageous way.
  • the one or more constitutive elements of the ceramic material may be essentially insoluble in water.
  • the constitutive elements of the ceramic material may not leach, preferably not even partially, into water in order to provide a durable and effective support of the electrolysis process.
  • the ceramic material may be characterized by being irreducible or only partly reducible under application of electrolysis operating conditions, in particular at a cell voltage below 2.5 V.
  • the ceramic material may not be fully reducible, under application of electrolysis operating conditions, which is typically at a cell voltage below 2.5 V, in order to provide a durable and effective support of the electrolysis process.
  • a device for the electrolytic production of hydrogen from an aqueous solution comprising a positive half-cell, a negative half-cell, wherein one part of an anion exchange membrane-electrode assembly is assigned to the positive half-cell and another part of the anion exchange membrane-electrode assembly is assigned to the negative half-cell, the anion exchange membrane-electrode assembly comprising an anion exchange membrane- and comprising a positive electrode facing the positive half-cell on one side of an anion exchange membrane and a negative electrode facing the negative half-cell on the opposite side of the anion exchange membrane.
  • the anion exchange membrane-electrode assembly comprises a ceramic material with alkaline surface properties.
  • the ceramic material preferably works as a so-called alkaline promoter.
  • a ceramic material with alkaline surface properties the adsorption of water at the surface may advantageously be enhanced.
  • the wettability of the membrane and/or the electrodes which is an unsolved problem known in prior art, is improved.
  • integrating ceramic material into the membrane and/or the electrodes serves to weaken the HO-H bond of an adsorbed water molecule, resulting in promotion of a localized alkaline environment, which advantageously supports alkaline promotion.
  • the high local alkalinity ensures the fast kinetics of hydrogen evolution reaction in the cathode and oxygen evolution reaction in the anode, as well as facilitates the high ion exchange capacity (IEC) of AEM and ionomer.
  • IEC ion exchange capacity
  • the inventive device can thus be operated with lower concentrations of corrosive chemicals such as using KOH aqueous solutions at lower concentrations, leading to an improvement of the cell performance and the lifetime of the electrolysis device.
  • AEM water electrolysis technology with improved devices, in particular comprising advantageous anion exchange membrane-electrode assemblies according to inventive embodiments offers a great possibility for cost-effective green hydrogen production.
  • the device for the electrolytic production of hydrogen from an aqueous solution can advantageously be provided for green hydrogen production by water electrolysis.
  • the anion exchange membrane-electrode assembly may also advantageously be used for operation in fuel cells.
  • the anion exchange membrane-electrode assembly may optionally be implemented for use in unitized regenerative fuel cells.
  • inventive anion exchange membrane-electrode assembly may generally be used for electrochemical cells with reactions promoted in alkaline environment, e.g. metal - air batteries, electrochemical membrane reactors with alkaline reaction and the like.
  • the ceramic material may be integrated, in particular in a powder form, into at least one of the electrodes and/or the anion exchange membrane.
  • a ceramic material with alkaline surface properties the adsorption of water at the surface may advantageously be enhanced.
  • Integrating ceramic material into the membrane and/or the electrodes may serve to weaken the HO-H bond of an adsorbed water molecule, in order to promote localized alkaline environment, which may advantageously support alkaline promotion.
  • the physical effects of integrating the ceramic material may advantageously be enhanced by dispersing it in a fine granular way into the carrier as the membrane or the electrode material.
  • the ceramic material may be blended with an ionomer and/or a catalyst of at least one of the electrodes.
  • the ceramic material may be integrated in a very direct way into the electrode material.
  • the ceramic material may be integrated in a very fine granular dispersion in the electrode material.
  • the ceramic material may be integrated into the anion exchange membrane.
  • Integrating ceramic material into the membrane may serve to weaken the HO-H bond of an adsorbed water molecule, in order to promote localized alkaline environment, which may advantageously support alkaline promotion.
  • the ceramic material may be blended with an ionomer and/or a polymer of the anion exchange membrane.
  • the ceramic material may be integrated in a very direct way into the membrane material.
  • the ceramic material may be integrated in a very fine granular dispersion in the membrane material.
  • the ceramic material may not necessarily be electro-conductive and/or connected to a catalyst.
  • the ceramic material in powder form may be coated, in particular directly coated, on at least one side of the anion exchange membrane.
  • the alkaline properties of the ceramic material may be directly exposed to adsorbing water molecules in order to enhance the adsorption of water molecules and weaken the HO-H bond of the adsorbed water molecule.
  • the ceramic material may comprise a specific surface area of at least 1 m 2 /g, preferably of at least 10 m 2 /g and more preferably of at least 20 m 2 /g.
  • the fine granular dispersion of the ceramic material in powder form supports enabling the alkaline surface properties in order to enhance the adsorption of water molecules and weaken the HO-H bond of the adsorbed water molecule.
  • the anion exchange membrane may comprise 0.1 wt% to 50 wt% of ceramic material, and/or one or both the electrodes may comprise 0.1 wt% to 80 wt% of ceramic material. Even low alkaline promoter content enables providing alkaline surface properties in order to effect the production of hydrogen in a favorable manner.
  • the ceramic material may comprise one or more constitutive elements in an oxidized state in combination with one or more of a halogen, preferably fluor, and/or one or more of a chalcogen, preferably oxygen.
  • a halogen preferably fluor
  • a chalcogen preferably oxygen
  • the one or more constitutive elements of the ceramic material and the bound halogen and/or chalcogen atoms may differ by an average difference in electronegativity on the Pauling scale of at least 1.7, preferably of at least 2.
  • alkaline surface properties may be enabled in an advantageous way.
  • the Pauling scale well-known in the art proposes an electronegativity scale which depends on bond energies, as a development of valence bond theory.
  • the Pauling scale gives a dimensionless quantity, on a relative scale running from 0.79 to 3.98, for instance 2.20 for hydrogen.
  • the one or more constitutive elements of the ceramic material may be essentially insoluble in water.
  • the constitutive elements of the ceramic material may not leach, preferably not even partially, into water in order to provide a durable and effective support of the electrolysis process.
  • the ceramic material may be characterized by being irreducible or only partly reducible under application of electrolysis operating conditions, in particular at a cell voltage below 2.5 V.
  • the ceramic material may not be fully reducible, under application of electrolysis operating conditions, which is typically at a cell voltage below 2.5 V, in order to provide a durable and effective support of the electrolysis process.
  • the ceramic material may be either electrochemically active or electrochemically inactive towards a hydrogen evolution reaction or an oxygen evolution reaction. It is not necessary that the ceramic material is electro-conductively connected to catalytic materials.
  • the ceramic material is not consumed during production of hydrogen or oxygen and the alkaline surface properties are maintained during operation of the device.
  • the ceramic material may comprise at least one of a group enclosing compounds of a structure of ABi- y RE y O3-a with 0 ⁇ y ⁇ 1 , where A is one or more elements from the Alkaline Earth metal group, and B is at least one of the following elements: Ti, Zr, Ce, Hf, Sn, In, and RE is one or more element from the Rare Earth Elements.
  • single or mixed oxides of the Rare Earth Elements may be used: for instance materials from the solid solution Cei- x RE x O2-a with 0 ⁇ x ⁇ 1 and RE being one or more Rare Earth Element and the parameter a represents the deviation to the stoichiometric content of oxygen in the solid solution at equilibrium.
  • Further single or mixed fluorides of the Rare Earth Elements, and Alkaline Earth Metals may be used, such as LaFs, CaF2.
  • any composite mixture of the above mentioned materials i.e. for instance CeO2 + LaFs, may be comprised in the ceramic material.
  • the ceramic material may be of perovskite structure or related, in particular double perovskite AA'B20s+6 and Ruddlesden-Popper An+iBnOsn+i phases.
  • A’ is a cation of the same groups of elements as elements A with A being one or more elements from the Alkaline Earth metal group.
  • A’ is a Lanthanide when A is an Alkaline Earth and vice versa.
  • n is a positive integer (i.e. , 1 , 2, 3, 4... ) and the parameter s represents the deviation to the stoichiometric content of oxygen in the solid solution at equilibrium.
  • These materials may offer favorable alkaline surface properties for enhancing the adsorption of water molecules and weakening the HO-H bond of the adsorbed water molecule.
  • the ceramic material may comprise BaCei-x-yZr x Y y O3-a, BaSnOs, BaZrOs, BaHfOs, CaZrOs, Bai- x Ca x Cei- x-y Zr x Y y O3-a, (La-i - y Ca y )2(Ce-i -xZr x )2O7-a, with 0 ⁇ x ⁇ 1 and 0 ⁇ y ⁇ 1.
  • the ceramic material may comprise acceptor-doped rare-earth (RE) ortho- niobates and ortho-tantalates, e.g.
  • RE rare-earth
  • the parameter a represents the deviation to the stoichiometric content of oxygen in the above listed materials at equilibrium.
  • any ceramic material characterized with a negative hydration enthalpy may favorably be comprised in the ceramic material used in the anion exchange membrane-electrode assembly of the inventive device.
  • Figure 1 a functional design of a device for the electrolytic production of hydrogen from an aqueous solution using an anion exchange membrane according to an embodiment of the invention
  • Figure 2 a schematic view of an anion exchange membrane-electrode assembly of the device for the electrolytic production of hydrogen from an aqueous solution according to Figure 1 ;
  • FIG. 3 an anion exchange membrane of an anion exchange membrane-electrode assembly according to an embodiment of the invention with ceramic material integrated into the membrane;
  • Figure 4 a part of an anion exchange membrane-electrode assembly according to an embodiment of the invention with ceramic material integrated into one of the electrodes;
  • Figure 5 results of device performance measurements of a device according to an embodiment of the invention operated with 1 M KOH aqueous solution, compared to results of a conventional device;
  • Figure 6 results of device performance measurements of a device according to an embodiment of the invention operated with deionized water, compared to results of a conventional device
  • Figure 7 results of stability measurements of a device according to an embodiment of the invention operated with deionized water, compared to results of a conventional device.
  • Figure 1 depicts a functional design of a device 100 for the electrolytic production of hydrogen from an aqueous solution 18 using an anion exchange membrane 12 according to an embodiment of the invention.
  • the device 100 comprises a positive half-cell 20 and a negative half-cell 22.
  • One part of an anion exchange membrane-electrode assembly 10 is assigned to the positive half-cell 20 and one part of the anion exchange membrane-electrode assembly 10 is assigned to the negative half-cell 22.
  • the half-cells 20, 22 are connected by an anion exchange membrane 12 of the anion exchange membrane-electrode assembly 10, which is depicted in a schematic way in Figure 2.
  • the anion exchange membrane-electrode assembly 10 comprises a positive electrode 14 facing the positive half-cell 20 on one side 28 of an anion exchange membrane 12 and a negative electrode 16 facing the negative half-cell 22 on the opposite side 30 of the anion exchange membrane 12.
  • the positive electrode 14 is called anode and the negative electrode is called cathode.
  • the feedstock can be a diluted alkaline solution 18 (e.g. KOH, NaOH), deionized water and other kinds of aqueous salt solutions (e.g. K2CO3, KHCO3 ... ).
  • a diluted alkaline solution 18 e.g. KOH, NaOH
  • deionized water e.g. K2CO3, KHCO3 ...
  • other kinds of aqueous salt solutions e.g. K2CO3, KHCO3 ...
  • the device 100 To operate the device 100, normally only one kind of the above mentioned feedstock is fed to the device 100, either into the negative half-cell 22, the positive half-cell 20 or into both half-cells 20, 22. In the case of feeding only one side (e.g. the negative half-cell 22) of the device 100, the other side (the positive half-cell 20) will be also filled with the same solution due to osmotic drag.
  • the anion exchange membrane-electrode assembly 10 comprises a ceramic material 50 with alkaline surface properties.
  • the ceramic material works as a so-called alkaline promoter.
  • alkaline promoter By adding a ceramic material with alkaline surface properties the adsorption of water at the surface may advantageously be enhanced.
  • the problem of wettability of the membrane 12 and/or the electrodes 14, 16, which occurs in prior art, may be solved.
  • Ceramic material into the membrane 12 and/or the electrodes 14, 16 may serve to weaken the HO-H bond of an adsorbed water molecule, in order to promote localized alkaline environment, which may advantageously support alkaline promotion.
  • the inventive device may thus be operated with lower concentrations of corrosive chemicals such as low concentrated KOH aqueous solutions 18, leading to greater lifetimes of the electrolysis device 100.
  • Both electrodes 14, 16 comprise a catalytically active part 24, 26, which is positioned adjacent to the anion exchange membrane 12, and a current collector 34, 36.
  • the anion exchange membrane-electrode assembly 10 is enclosed by bipolar plates 44, 46 at both ends.
  • the bipolar plates 44, 46 serve for setting the anion exchange membrane-electrode assembly 10 under a given pressure for proper operation in the device 100.
  • the bipolar plates 44, 46 are electrically conducting parts, which are in direct electrical connection to the current collectors 34, 36 of the electrodes 14, 16.
  • the device 100 is connected via the bipolar plates 44, 46 to a voltage source 40.
  • the OH’ is not necessarily from the aqueous alkaline solution 18, ideally it should directly come from the solid ionomer in the anion exchange membrane 12 and then react on the catalyst surface and evolve an O2 molecule.
  • the cathode reaction in the negative half-cell 22 is given by the equation 2 H2O + 2 e’ 4 2 OH’ + H2.
  • hydrogen is evolved by oxidizing water molecules and consuming two electrons.
  • OH’ is produced which is transmitted through the anion exchange membrane 12 to the positive half-cell 20.
  • the ceramic material 50 may be integrated, in particular in a powder form, into at least one of the electrodes 14, 16 and/or the anion exchange membrane 12. Integrating ceramic material 50 into the membrane 12 and/or the electrodes 14, 16 may serve to weaken the HO-H bond of an adsorbed water molecule, in order to promote localized alkaline environment, which may advantageously support alkaline promotion.
  • the ceramic material 50 may be integrated in a very fine granular dispersion in the electrode material.
  • the ceramic material 50 for instance in powder form, may be directly coated on at least one side 28, 30 of the anion exchange membrane 12.
  • the ceramic material 50 may comprise one or more constitutive elements in an oxidized state in combination with one or more of a halogen, preferably fluor, and/or one or more of a chalcogen, preferably oxygen. Further, the one or more constitutive elements of the ceramic material 50 and the bound halogen and/or chalcogen atoms may differ by an average difference in electronegativity on the Pauling scale of at least 1.7, preferably of at least 2.
  • the one or more constitutive elements of the ceramic material 50 may be essentially insoluble in water.
  • the ceramic material 50 may be characterized by being irreducible or only partly reducible under application of electrolysis operating conditions, in particular at a cell voltage below 2.5 V.
  • a ceramic material 50 at least one of a group enclosing compounds of a structure of ABi- y RE y O3-a with 0 ⁇ y ⁇ 1 , where A is one or more elements from the Alkaline Earth metal group, and B is at least one of the following elements: Ti, Zr, Ce, Hf, Sn, In, and RE is one or more element from the Rare Earth Elements.
  • the parameter a means the deviation to the stoichiometric content of oxygen in the solid solution at equilibrium.
  • the ceramic material may comprise BaCei- x-y Zr x Y y O3-a, BaSnOs, BaZrOs, BaHfOs, CaZrOs, Bai- x Ca x Cei- x-y Zr x Y y O3-a, (Lai - y Ca y )2(Cei -xZr ⁇ Oy-a, with 0 ⁇ x ⁇ 1 and 0 ⁇ y ⁇ 1.
  • the parameter a represents the deviation to the stoichiometric content of oxygen in the above listed compounds at equilibrium.
  • the ceramic material may be of perovskite structure or related, in particular double perovskite AA'B20s+6 and Ruddlesden-Popper An+iBnOsn+i phases, where A’ is a cation of the same groups of elements as elements A with A being one or more elements from the Alkaline Earth metal group.
  • A’ is a Lanthanide when A is an Alkaline Earth and vice versa
  • n is a positive integer (i.e. , 1 , 2, 3, 4... ) and the parameter 5 represents the deviation to the stoichiometric content of oxygen in the solid solution at equilibrium.
  • FIG. 3 depicts an anion exchange membrane 12 of an anion exchange membrane-electrode assembly 10 according to an embodiment of the invention with ceramic material 50 integrated into the membrane 12.
  • the ceramic material 50 may be blended with an ionomer 54 and/or a polymer 56 of the anion exchange membrane 12.
  • Figure 4 depicts a part of an anion exchange membrane-electrode assembly 10 according to an embodiment of the invention with ceramic material 50 integrated into a catalytically active part 24, 26 of one of the electrodes 14, 16.
  • a small spot of a catalytically active part 24, 26 of the electrodes 14, 16 is enlarged in order to show the dispersion of the ceramic material 50 in the catalytic layer of the electrodes 14, 16.
  • the ceramic material 50 may be blended with an ionomer 54 and/or a catalyst 52 of the electrode 16.
  • the ceramic material 50 may be dispersed in a fine granular way, in particular in powder form, in the material of the anion exchange membrane 12 and in the material of the electrodes 14, 16.
  • the ceramic material 50 may comprise a specific surface area of at least 1 m 2 /g, preferably of at least 10 m 2 /g and more preferably of at least 20 m 2 /g.
  • lower concentrations of the ceramic material 50 in the material of the anion exchange membrane 12 and in the material of the electrode 16 may be sufficient for providing the desired alkaline surface properties. Therefore, the anion exchange membrane 12 may comprise 0.1 wt% to 50 wt% of ceramic material 50, and/or one or both the electrodes 14, 16 comprise 0.1 wt% to 80 wt% of ceramic material 50.
  • BaZro.8Ceo.iYo.iOi-a where a represents the deviation to the stoichiometric content of oxygen in the compound at equilibrium, was introduced into the catalytically active parts on both anode and cathode of an anion exchange membrane of a device 64 for electrolytic production of hydrogen.
  • the other parameters of the device 64 were kept the same as in the device 66.
  • the catalyst in the anode comprised NiO powder; whereas the catalyst in the cathode comprised Pt/C powder.
  • Performance and stability of the resulting device 64 were measured and compared to a conventional device 66.
  • the performance was tested with three voltage cycles from 0 V up to 2.5 V.
  • the voltage characteristics II increases with an approximately parabolic rate, having the current density axis as symmetry axis of the parabola.
  • 1M KOH is fed as a feedstock to the device 64, 66, the three voltage curves overlap for each device 64, 66, indicating no short-time degradation.
  • Figure 6 depicts results of performance measurements with the two devices 64, 66 tested with deionized water.
  • the cell voltage II in V is recorded as a function of the current density J in A/cm 2
  • the curves for the different cycles C of both devices 64, 66, exhibiting degradation of both devices 64, 66, are shifted to the left from cycle 1 to cycle 3.
  • the voltage dependencies vs. current densities are similar to Figure 5.
  • both devices 64, 66 show the degradation in the initial stage.
  • the device 64 which contains ceramic material as an alkaline promoter, shows a better stability than the conventional device 66, the voltage showing a slight increase over time only, showing no step at 68 indicating the break of 14 hours of operation.

Abstract

The invention relates to an anion exchange membrane-electrode assembly (10) for the electrolytic production of hydrogen from an aqueous solution (18), comprising a positive electrode (14) on one side (28) of an anion exchange membrane (12) and a negative electrode (16) on the opposite side (30) of the anion exchange membrane (12), and comprising a ceramic material (50) with alkaline surface properties, wherein the ceramic material (50) comprises at least one of a group enclosing compounds with a formula AB1-yREyO3-α with 0 ≤ y ≤ 1, wherein A being one or more elements from the Alkaline Earth or Lanthanide metal group, and B being at least one of the following elements: Ti, Zr, Ce, Hf, Sn, In, transition metal, and RE being one or more elements from the Rare Earth Elements.

Description

Description
Title
Device for electrolytic production of hydrogen
Technical Field
The invention relates to a device for the electrolytic production of hydrogen from an aqueous solution as well as an anion exchange membraneelectrode assembly for the electrolytic production of hydrogen from an aqueous solution.
Prior Art
Market available low temperature water electrolysis technologies for green hydrogen production are dominated by conventional alkaline water electrolysis (AEL) and proton exchange membrane (PEM) electrolysis that has been quickly advanced in the last twenty years. AEL is technologically mature and has been used in industry for many decades, based on a design with two Ni-based electrodes that are separated by a diaphragm. However its performance is limited by restrictions and disadvantages including low current density, small range of operation (e.g. low partial load range and low operating pressure) and the necessity to use highly concentrated potassium hydroxide solution KOH (normally 6M concentration) which needs to be circulated. PEM electrolysers are able to overcome most of these restrictions, being a versatile player with the advantages of compact system design, fast response, dynamic operation and excellent overload capacity and high voltage efficiency. The high capital expenditure, however, hinders its large-scale deployment, which is mainly caused by the titanium bipolar plates and catalyst coated membranes (CCM) that contain platinum group materials. Moreover, the scarcity of iridium, the only technically feasible anode catalyst for PEM electrolysers, further impedes it from Tera Watt-scale production in the long run.
Anion exchange membrane (AEM) electrolysers have attracted significant interest only very recently due to significant breakthroughs of AEMs and related ionomers, and have demonstrated the potential to combine advantages of AEL (low cost materials) and PEM (high performance). The advantages of AEM electrolysers include:
• They have all the merits of PEM electrolysers, but can eliminate expensive precious metal group catalysts and titanium components that in future may account for more than 50 % cost of PEM electrolysis systems;
• They do not require the high concentration KOH electrolyte as feedstock unlike traditional AEL and enable the use of both deionized water and low concentration KOH/other types salts as electrolyte which are less corrosive and operator-friendly;
• #AEM may enable the pressurization of only the hydrogen side, if the membrane is sufficiently mechanically stable, thus increasing the system efficiency.
Despite the numerous benefits of AEM water electrolysis, the technology itself still requires significant development to reach maturity for large scale deployment. One of the main hurdles is their durability with pure water feed, diluted KOH or other types of salts electrolyte. In KR101584725B1 , an alkaline anion exchange membrane water electrolyser is disclosed, using Ni electrodeposited hydrophilic porous carbon material.
WO201 1004343A1 discloses a device for the production on-demand of hydrogen by electrolysis of aqueous solutions from a dry cathode.
In W02007082898A2, the use of metal catalysts for the production of hydrogen by the electrolysis of water in electrolysers containing anionic exchange solid polymer membranes with nanostructured catalytic material, as well as respective electrolysers, and processes for the production of hydrogen by the electrolysis of water are proposed.
In recent publications (Pavel et al, Angew. Chem. Int. Ed., 2014, 53, 1378 - 1381 ; Vincent et al., Int. J. Electrochem. Sci., 13 (2018) 11347 - 11358), CeO2-La2O3 powder that is blended with Ni and carbon was used as cathode catalyst in an AEM electrolyser to promote hydrogen evolution reaction.
Disclosure of the Invention
It is an object of the invention to provide a highly efficient and durable device for the electrolytic production of hydrogen from an aqueous solution.
Another object of the invention is to provide an anion exchange membrane-electrode assembly for such a device for the electrolytic production of hydrogen from an aqueous solution. The objects of the invention are achieved by the features of the independent claims. The other claims, the description and the drawings describe advantageous embodiments of the invention.
According to an aspect of the invention an anion exchange membraneelectrode assembly for the electrolytic production of hydrogen from an aqueous solution is proposed, comprising a positive electrode on one side of an anion exchange membrane and a negative electrode on the opposite side of the anion exchange membrane. The anion exchange membraneelectrode assembly further comprises a ceramic material with alkaline surface properties. The ceramic material comprises at least one of a group enclosing compounds of a structure of ABi-yREyOs-a with 0 < y < 1 , wherein A being one or more elements from the Alkaline Earth metal group, and B being at least one of the following elements: Ti, Zr, Ce, Hf, Sn, In, and RE being one or more elements from the Rare Earth Elements.
The ceramic material works as a so-called alkaline promoter. By adding a ceramic material with alkaline surface properties the adsorption of water at the surface may advantageously be enhanced. Thus the problem of wettability and stability issues of the membrane and/or the electrodes, which occurs in prior art, may be solved.
Further integrating ceramic material into the membrane and/or the electrodes may serve to weaken the HO-H bond of an adsorbed water molecule, in order to promote localized alkaline environment, which may advantageously support alkaline promotion.
These materials may offer favorable alkaline surface properties for enhancing the adsorption of water molecules and weakening the HO-H bond of the adsorbed water molecule. For instance, the ceramic material may comprise BaCei-x-yZrxYyO3-a, BaSnOs, BaZrOs, BaHfOs, CaZrOs, Bai-xCaxCei-x-yZrxYyO3-a, (La-i - yCay)2(Cei -xZrx)2O7-a, with 0 < x < 1 and 0 < y < 1. Further, the ceramic material may comprise acceptor-doped rare-earth (RE) ortho- niobates and ortho-tantalates, e.g. RE-i-xAxMCM (M=Nb,Ta), or lanthanum tungstate. The parameter a represents the deviation to the stoichiometric content of oxygen in the above listed materials at equilibrium.
Further, single or mixed oxides of the Rare Earth Elements may be used: for instance materials from the solid solution Cei-xRExO2-a with 0 < x < 1 and RE being one or more Rare Earth Element and the parameter a represents the deviation to the stoichiometric content of oxygen in the solid solution at equilibrium.
Further single or mixed fluorides of the Rare Earth Elements, and Alkaline Earth Metals may be used, such as LaFs, CaF2.
Advantageously, any composite mixture of the above mentioned materials, i.e. for instance CeO2 + LaFs, may be comprised in the ceramic material.
Further, any ceramic material characterized with a negative hydration enthalpy may favorably be comprised in the ceramic material used in the anion exchange membrane-electrode assembly.
According to an advantageous embodiment of the assembly, the ceramic material may be of perovskite structure or related, in particular double perovskite AA'B20S+6 and Ruddlesden-Popper An+iBnOsn+i phases.
A’ is a cation of the same groups of elements as elements A with A being one or more elements from the Alkaline Earth metal group. In particular A’ is a Lanthanide when A is an Alkaline Earth and vice versa. n is a positive integer (i.e. , 1 , 2, 3, 4... ) and the parameter s represents the deviation to the stoichiometric content of oxygen in the solid solution at equilibrium.
The ceramic material works as a so-called alkaline promoter. By adding such a ceramic material with alkaline surface properties the adsorption of water at the surface may advantageously be enhanced. Thus the problem of wettability and stability issues of the membrane and/or the electrodes, which occurs in prior art, may be solved.
Further integrating ceramic material into the membrane and/or the electrodes may serve to weaken the HO-H bond of an adsorbed water molecule, in order to promote localized alkaline environment, which may advantageously support alkaline promotion.
According to an advantageous embodiment of the assembly, the ceramic material may be integrated, in particular in a powder form, into at least one of the electrodes. By adding a ceramic material with alkaline surface properties the adsorption of water at the surface may advantageously be enhanced. Thus the problem of wettability of the membrane and/or the electrodes, which occurs in prior art, may be solved. Integrating ceramic material into the membrane and/or the electrodes may serve to weaken the HO-H bond of an adsorbed water molecule, in order to promote localized alkaline environment, which may advantageously support alkaline promotion. The physical effects of integrating the ceramic material may advantageously be enhanced by dispersing it in a fine granular way into the carrier as the membrane or the electrode material. According to an advantageous embodiment of the assembly, the ceramic material may be blended with an ionomer and/or a catalyst of the at least one of the electrode. Thus the ceramic material may be integrated in a very direct way into the electrode material. Despite the ceramic material may be integrated in a very fine granular dispersion in the electrode material.
According to an advantageous embodiment of the assembly, the ceramic material may be integrated into the anion exchange membrane. Thus the problem of wettability and stability issues of the membrane, which occurs in prior art, may be solved. Integrating ceramic material into the membrane may serve to weaken the HO-H bond of an adsorbed water molecule, in order to promote localized alkaline environment, which may advantageously support alkaline promotion.
According to an advantageous embodiment of the assembly, the ceramic material may be blended with an ionomer and/or a polymer of the anion exchange membrane. Thus the ceramic material may be integrated in a very direct way into the membrane material. Despite the ceramic material may be integrated in a very fine granular dispersion in the membrane material.
According to an advantageous embodiment of the assembly, the ceramic material, in particular in a powder form, may be coated, in particular directly coated, on at least one side of the anion exchange membrane. By direct coating of the ceramic material on the side of the membrane the alkaline properties of the ceramic material may be directly exposed to adsorbing water molecules in order to enhance the adsorption of water molecules and weaken the HO-H bond of the adsorbed water molecule. According to an advantageous embodiment of the assembly, the ceramic material may comprise a specific surface area of at least 1 m2/g, preferably of at least 10 m2/g and more preferably of at least 20 m2/g.
According to an advantageous embodiment of the assembly, the anion exchange membrane may comprise 0.1 wt% to 50 wt% of ceramic material, and/or one or both the electrodes may comprise 0.1 wt% to 80 wt% of ceramic material. Even low alkaline promoter content enables providing alkaline surface properties in order to effect the production of hydrogen in a favorable manner.
According to an advantageous embodiment of the assembly, the ceramic material may comprise one or more constitutive elements in an oxidized state in combination with one or more of a halogen, preferably fluorine, and/or one or more of a chalcogen, preferably oxygen. Thus alkaline surface properties may be enabled in an advantageous way.
According to an advantageous embodiment of the assembly, the one or more constitutive elements of the ceramic material and the bound halogen and/or chalcogen atoms may differ by an average difference in electronegativity on the Pauling scale of at least 1.7, preferably of at least 2. Thus alkaline surface properties may be enabled in an advantageous way.
According to an advantageous embodiment of the assembly, the one or more constitutive elements of the ceramic material may be essentially insoluble in water. Favorably the constitutive elements of the ceramic material may not leach, preferably not even partially, into water in order to provide a durable and effective support of the electrolysis process. According to an advantageous embodiment of the assembly, the ceramic material may be characterized by being irreducible or only partly reducible under application of electrolysis operating conditions, in particular at a cell voltage below 2.5 V. Preferably, the ceramic material may not be fully reducible, under application of electrolysis operating conditions, which is typically at a cell voltage below 2.5 V, in order to provide a durable and effective support of the electrolysis process.
According to another aspect of the invention, a device for the electrolytic production of hydrogen from an aqueous solution is proposed, the device comprising a positive half-cell, a negative half-cell, wherein one part of an anion exchange membrane-electrode assembly is assigned to the positive half-cell and another part of the anion exchange membrane-electrode assembly is assigned to the negative half-cell, the anion exchange membrane-electrode assembly comprising an anion exchange membrane- and comprising a positive electrode facing the positive half-cell on one side of an anion exchange membrane and a negative electrode facing the negative half-cell on the opposite side of the anion exchange membrane. The anion exchange membrane-electrode assembly comprises a ceramic material with alkaline surface properties.
The ceramic material preferably works as a so-called alkaline promoter. By adding a ceramic material with alkaline surface properties the adsorption of water at the surface may advantageously be enhanced. Thus the wettability of the membrane and/or the electrodes, which is an unsolved problem known in prior art, is improved. Further, integrating ceramic material into the membrane and/or the electrodes serves to weaken the HO-H bond of an adsorbed water molecule, resulting in promotion of a localized alkaline environment, which advantageously supports alkaline promotion. The high local alkalinity ensures the fast kinetics of hydrogen evolution reaction in the cathode and oxygen evolution reaction in the anode, as well as facilitates the high ion exchange capacity (IEC) of AEM and ionomer.
The inventive device can thus be operated with lower concentrations of corrosive chemicals such as using KOH aqueous solutions at lower concentrations, leading to an improvement of the cell performance and the lifetime of the electrolysis device.
Advantageously, one of the main hurdles of technical feasibility concerning the durability of the membrane/ionomer and electrodes for expected long term operation in AEM water electrolysis with pure water feed or diluted KOH or other types of salts electrolyte can be solved.
Further, the problem of relatively low performance due to high overpotentials, leading to a low efficiency of the electrolysis process, can also advantageously be prevented.
Thus, AEM water electrolysis technology with improved devices, in particular comprising advantageous anion exchange membrane-electrode assemblies according to inventive embodiments offers a great possibility for cost-effective green hydrogen production.
The device for the electrolytic production of hydrogen from an aqueous solution can advantageously be provided for green hydrogen production by water electrolysis. The anion exchange membrane-electrode assembly may also advantageously be used for operation in fuel cells. Particularly, the anion exchange membrane-electrode assembly may optionally be implemented for use in unitized regenerative fuel cells.
Further, the inventive anion exchange membrane-electrode assembly may generally be used for electrochemical cells with reactions promoted in alkaline environment, e.g. metal - air batteries, electrochemical membrane reactors with alkaline reaction and the like.
According to an advantageous embodiment of the device, the ceramic material may be integrated, in particular in a powder form, into at least one of the electrodes and/or the anion exchange membrane. By adding a ceramic material with alkaline surface properties the adsorption of water at the surface may advantageously be enhanced. Thus the problem of wettability of the membrane and/or the electrodes, which occurs in prior art, may be solved. Integrating ceramic material into the membrane and/or the electrodes may serve to weaken the HO-H bond of an adsorbed water molecule, in order to promote localized alkaline environment, which may advantageously support alkaline promotion. The physical effects of integrating the ceramic material may advantageously be enhanced by dispersing it in a fine granular way into the carrier as the membrane or the electrode material.
According to an advantageous embodiment of the device, the ceramic material may be blended with an ionomer and/or a catalyst of at least one of the electrodes. Thus the ceramic material may be integrated in a very direct way into the electrode material. Besides, the ceramic material may be integrated in a very fine granular dispersion in the electrode material. According to an advantageous embodiment of the device, the ceramic material may be integrated into the anion exchange membrane. Thus the problem of wettability and fast dysfunction (the loss of functional groups during the operation resulting in a lower IEC) of the membrane, which occurs in prior art, may be solved. Integrating ceramic material into the membrane may serve to weaken the HO-H bond of an adsorbed water molecule, in order to promote localized alkaline environment, which may advantageously support alkaline promotion.
According to an advantageous embodiment of the device, the ceramic material may be blended with an ionomer and/or a polymer of the anion exchange membrane. Thus the ceramic material may be integrated in a very direct way into the membrane material. Besides, the ceramic material may be integrated in a very fine granular dispersion in the membrane material. The ceramic material may not necessarily be electro-conductive and/or connected to a catalyst.
According to an advantageous embodiment of the device, the ceramic material in powder form may be coated, in particular directly coated, on at least one side of the anion exchange membrane. By direct coating of the ceramic material on the side of the membrane the alkaline properties of the ceramic material may be directly exposed to adsorbing water molecules in order to enhance the adsorption of water molecules and weaken the HO-H bond of the adsorbed water molecule.
According to an advantageous embodiment of the device, the ceramic material may comprise a specific surface area of at least 1 m2/g, preferably of at least 10 m2/g and more preferably of at least 20 m2/g. The fine granular dispersion of the ceramic material in powder form supports enabling the alkaline surface properties in order to enhance the adsorption of water molecules and weaken the HO-H bond of the adsorbed water molecule. According to an advantageous embodiment of the device, the anion exchange membrane may comprise 0.1 wt% to 50 wt% of ceramic material, and/or one or both the electrodes may comprise 0.1 wt% to 80 wt% of ceramic material. Even low alkaline promoter content enables providing alkaline surface properties in order to effect the production of hydrogen in a favorable manner.
According to an advantageous embodiment of the device, the ceramic material may comprise one or more constitutive elements in an oxidized state in combination with one or more of a halogen, preferably fluor, and/or one or more of a chalcogen, preferably oxygen. Thus alkaline surface properties may be enabled in an advantageous way.
According to an advantageous embodiment of the device, the one or more constitutive elements of the ceramic material and the bound halogen and/or chalcogen atoms may differ by an average difference in electronegativity on the Pauling scale of at least 1.7, preferably of at least 2. Thus alkaline surface properties may be enabled in an advantageous way.
The Pauling scale well-known in the art proposes an electronegativity scale which depends on bond energies, as a development of valence bond theory. The Pauling scale gives a dimensionless quantity, on a relative scale running from 0.79 to 3.98, for instance 2.20 for hydrogen.
According to an advantageous embodiment of the device, the one or more constitutive elements of the ceramic material may be essentially insoluble in water. Favorably the constitutive elements of the ceramic material may not leach, preferably not even partially, into water in order to provide a durable and effective support of the electrolysis process. According to an advantageous embodiment of the device, the ceramic material may be characterized by being irreducible or only partly reducible under application of electrolysis operating conditions, in particular at a cell voltage below 2.5 V. Preferably, the ceramic material may not be fully reducible, under application of electrolysis operating conditions, which is typically at a cell voltage below 2.5 V, in order to provide a durable and effective support of the electrolysis process.
Advantageously, the ceramic material may be either electrochemically active or electrochemically inactive towards a hydrogen evolution reaction or an oxygen evolution reaction. It is not necessary that the ceramic material is electro-conductively connected to catalytic materials.
Advantageously, the ceramic material is not consumed during production of hydrogen or oxygen and the alkaline surface properties are maintained during operation of the device.
According to an advantageous embodiment of the device, the ceramic material may comprise at least one of a group enclosing compounds of a structure of ABi-yREyO3-a with 0 < y < 1 , where A is one or more elements from the Alkaline Earth metal group, and B is at least one of the following elements: Ti, Zr, Ce, Hf, Sn, In, and RE is one or more element from the Rare Earth Elements.
Further, single or mixed oxides of the Rare Earth Elements may be used: for instance materials from the solid solution Cei-xRExO2-a with 0 < x < 1 and RE being one or more Rare Earth Element and the parameter a represents the deviation to the stoichiometric content of oxygen in the solid solution at equilibrium. Further single or mixed fluorides of the Rare Earth Elements, and Alkaline Earth Metals may be used, such as LaFs, CaF2.
Advantageously, any composite mixture of the above mentioned materials, i.e. for instance CeO2 + LaFs, may be comprised in the ceramic material.
Advantageously, the ceramic material may be of perovskite structure or related, in particular double perovskite AA'B20s+6 and Ruddlesden-Popper An+iBnOsn+i phases.
A’ is a cation of the same groups of elements as elements A with A being one or more elements from the Alkaline Earth metal group. In particular A’ is a Lanthanide when A is an Alkaline Earth and vice versa. n is a positive integer (i.e. , 1 , 2, 3, 4... ) and the parameter s represents the deviation to the stoichiometric content of oxygen in the solid solution at equilibrium.
These materials may offer favorable alkaline surface properties for enhancing the adsorption of water molecules and weakening the HO-H bond of the adsorbed water molecule.
For instance, the ceramic material may comprise BaCei-x-yZrxYyO3-a, BaSnOs, BaZrOs, BaHfOs, CaZrOs, Bai-xCaxCei-x-yZrxYyO3-a, (La-i - yCay)2(Ce-i -xZrx)2O7-a, with 0 < x < 1 and 0 < y < 1. Further, the ceramic material may comprise acceptor-doped rare-earth (RE) ortho- niobates and ortho-tantalates, e.g. REI-XAXMO4 (M=Nb,Ta), or lanthanum tungstate. The parameter a represents the deviation to the stoichiometric content of oxygen in the above listed materials at equilibrium. Further, any ceramic material characterized with a negative hydration enthalpy may favorably be comprised in the ceramic material used in the anion exchange membrane-electrode assembly of the inventive device.
Brief Description of the Drawings
The present invention together with the above-mentioned and other objects and advantages may best be understood from the following detailed description of the embodiments, but not restricted to the embodiments, wherein is shown in:
Figure 1 a functional design of a device for the electrolytic production of hydrogen from an aqueous solution using an anion exchange membrane according to an embodiment of the invention;
Figure 2 a schematic view of an anion exchange membrane-electrode assembly of the device for the electrolytic production of hydrogen from an aqueous solution according to Figure 1 ;
Figure 3 an anion exchange membrane of an anion exchange membrane-electrode assembly according to an embodiment of the invention with ceramic material integrated into the membrane;
Figure 4 a part of an anion exchange membrane-electrode assembly according to an embodiment of the invention with ceramic material integrated into one of the electrodes;
Figure 5 results of device performance measurements of a device according to an embodiment of the invention operated with 1 M KOH aqueous solution, compared to results of a conventional device;
Figure 6 results of device performance measurements of a device according to an embodiment of the invention operated with deionized water, compared to results of a conventional device; and
Figure 7 results of stability measurements of a device according to an embodiment of the invention operated with deionized water, compared to results of a conventional device.
Detailed Description of the Drawings
In the drawings, like elements are referred to with equal reference numerals. The drawings are merely schematic representations, not intended to portray specific parameters of the invention. Moreover, the drawings are intended to depict only typical embodiments of the invention and therefore should not be considered as limiting the scope of the invention.
Figure 1 depicts a functional design of a device 100 for the electrolytic production of hydrogen from an aqueous solution 18 using an anion exchange membrane 12 according to an embodiment of the invention.
The device 100 comprises a positive half-cell 20 and a negative half-cell 22. One part of an anion exchange membrane-electrode assembly 10 is assigned to the positive half-cell 20 and one part of the anion exchange membrane-electrode assembly 10 is assigned to the negative half-cell 22. The half-cells 20, 22 are connected by an anion exchange membrane 12 of the anion exchange membrane-electrode assembly 10, which is depicted in a schematic way in Figure 2.
The anion exchange membrane-electrode assembly 10 comprises a positive electrode 14 facing the positive half-cell 20 on one side 28 of an anion exchange membrane 12 and a negative electrode 16 facing the negative half-cell 22 on the opposite side 30 of the anion exchange membrane 12. The positive electrode 14 is called anode and the negative electrode is called cathode.
Basically, three strategies exist to feed the device 100 with aqueous solution 18:
- Feed into the negative half-cell 22;
- Feed into the positive half-cell 20; or
- Feed into both negative half-cell 22 and positive half-cell 20.
The feedstock can be a diluted alkaline solution 18 (e.g. KOH, NaOH), deionized water and other kinds of aqueous salt solutions (e.g. K2CO3, KHCO3 ... ).
To operate the device 100, normally only one kind of the above mentioned feedstock is fed to the device 100, either into the negative half-cell 22, the positive half-cell 20 or into both half-cells 20, 22. In the case of feeding only one side (e.g. the negative half-cell 22) of the device 100, the other side (the positive half-cell 20) will be also filled with the same solution due to osmotic drag.
According to an embodiment of the invention, the anion exchange membrane-electrode assembly 10 comprises a ceramic material 50 with alkaline surface properties. The ceramic material works as a so-called alkaline promoter. By adding a ceramic material with alkaline surface properties the adsorption of water at the surface may advantageously be enhanced. Thus the problem of wettability of the membrane 12 and/or the electrodes 14, 16, which occurs in prior art, may be solved.
Further integrating ceramic material into the membrane 12 and/or the electrodes 14, 16 may serve to weaken the HO-H bond of an adsorbed water molecule, in order to promote localized alkaline environment, which may advantageously support alkaline promotion.
The inventive device may thus be operated with lower concentrations of corrosive chemicals such as low concentrated KOH aqueous solutions 18, leading to greater lifetimes of the electrolysis device 100.
Both electrodes 14, 16 comprise a catalytically active part 24, 26, which is positioned adjacent to the anion exchange membrane 12, and a current collector 34, 36.
The anion exchange membrane-electrode assembly 10 is enclosed by bipolar plates 44, 46 at both ends. The bipolar plates 44, 46 serve for setting the anion exchange membrane-electrode assembly 10 under a given pressure for proper operation in the device 100. The bipolar plates 44, 46 are electrically conducting parts, which are in direct electrical connection to the current collectors 34, 36 of the electrodes 14, 16.
The device 100 is connected via the bipolar plates 44, 46 to a voltage source 40.
An overall reaction equation for the electrolytic reaction is given by
H2O -> >2 O2 + H2. Due to this equation oxygen and hydrogen are evolved by the device 100. The anode reaction in the positive half-cell 20 is given by the equation
2 OH- -> H2O + % O2 + 2 e the OH’ produced at the negative electrode 16 and migrated into the positive electrode 14, then react on the catalyst surface in the catalytically active part 24 of the positive electrode 14, forming oxygen and meantime release two electrons. Here the OH’ is not necessarily from the aqueous alkaline solution 18, ideally it should directly come from the solid ionomer in the anion exchange membrane 12 and then react on the catalyst surface and evolve an O2 molecule.
The cathode reaction in the negative half-cell 22 is given by the equation 2 H2O + 2 e’ 4 2 OH’ + H2. At the cathode 16 hydrogen is evolved by oxidizing water molecules and consuming two electrons. OH’ is produced which is transmitted through the anion exchange membrane 12 to the positive half-cell 20.
The ceramic material 50 may be integrated, in particular in a powder form, into at least one of the electrodes 14, 16 and/or the anion exchange membrane 12. Integrating ceramic material 50 into the membrane 12 and/or the electrodes 14, 16 may serve to weaken the HO-H bond of an adsorbed water molecule, in order to promote localized alkaline environment, which may advantageously support alkaline promotion. The ceramic material 50 may be integrated in a very fine granular dispersion in the electrode material.
In an alternative embodiment, the ceramic material 50, for instance in powder form, may be directly coated on at least one side 28, 30 of the anion exchange membrane 12.
The ceramic material 50 may comprise one or more constitutive elements in an oxidized state in combination with one or more of a halogen, preferably fluor, and/or one or more of a chalcogen, preferably oxygen. Further, the one or more constitutive elements of the ceramic material 50 and the bound halogen and/or chalcogen atoms may differ by an average difference in electronegativity on the Pauling scale of at least 1.7, preferably of at least 2.
The one or more constitutive elements of the ceramic material 50 may be essentially insoluble in water.
Further, the ceramic material 50 may be characterized by being irreducible or only partly reducible under application of electrolysis operating conditions, in particular at a cell voltage below 2.5 V.
As a ceramic material 50 at least one of a group enclosing compounds of a structure of ABi-yREyO3-a with 0 < y < 1 , where A is one or more elements from the Alkaline Earth metal group, and B is at least one of the following elements: Ti, Zr, Ce, Hf, Sn, In, and RE is one or more element from the Rare Earth Elements. The parameter a means the deviation to the stoichiometric content of oxygen in the solid solution at equilibrium.
For instance, the ceramic material may comprise BaCei-x-yZrxYyO3-a, BaSnOs, BaZrOs, BaHfOs, CaZrOs, Bai-xCaxCei-x-yZrxYyO3-a, (Lai -yCay)2(Cei -xZr^Oy-a, with 0 < x < 1 and 0 < y < 1. Further, the ceramic material may comprise acceptor-doped rare-earth (RE) ortho- niobates and ortho-tantalates, e.g. RE-i-xAxMCM (M=Nb,Ta), or lanthanum tungstate. The parameter a represents the deviation to the stoichiometric content of oxygen in the above listed compounds at equilibrium.
In particular, the ceramic material may be of perovskite structure or related, in particular double perovskite AA'B20s+6 and Ruddlesden-Popper An+iBnOsn+i phases, where A’ is a cation of the same groups of elements as elements A with A being one or more elements from the Alkaline Earth metal group. In particular A’ is a Lanthanide when A is an Alkaline Earth and vice versa, n is a positive integer (i.e. , 1 , 2, 3, 4... ) and the parameter 5 represents the deviation to the stoichiometric content of oxygen in the solid solution at equilibrium.
Figure 3 depicts an anion exchange membrane 12 of an anion exchange membrane-electrode assembly 10 according to an embodiment of the invention with ceramic material 50 integrated into the membrane 12.
On the right hand side of the Figure 3 a small spot of the membrane 12 is enlarged in order to show the dispersion of the ceramic material 50 in the material of the membrane 12. As is depicted, the ceramic material 50 may be blended with an ionomer 54 and/or a polymer 56 of the anion exchange membrane 12.
Figure 4 depicts a part of an anion exchange membrane-electrode assembly 10 according to an embodiment of the invention with ceramic material 50 integrated into a catalytically active part 24, 26 of one of the electrodes 14, 16.
On the right hand side of the Figure 4 a small spot of a catalytically active part 24, 26 of the electrodes 14, 16 is enlarged in order to show the dispersion of the ceramic material 50 in the catalytic layer of the electrodes 14, 16. As is depicted, the ceramic material 50 may be blended with an ionomer 54 and/or a catalyst 52 of the electrode 16.
In both embodiments shown in Figure 3 and Figure 4 the ceramic material 50 may be dispersed in a fine granular way, in particular in powder form, in the material of the anion exchange membrane 12 and in the material of the electrodes 14, 16. For providing a large surface, the ceramic material 50 may comprise a specific surface area of at least 1 m2/g, preferably of at least 10 m2/g and more preferably of at least 20 m2/g. In addition, lower concentrations of the ceramic material 50 in the material of the anion exchange membrane 12 and in the material of the electrode 16 may be sufficient for providing the desired alkaline surface properties. Therefore, the anion exchange membrane 12 may comprise 0.1 wt% to 50 wt% of ceramic material 50, and/or one or both the electrodes 14, 16 comprise 0.1 wt% to 80 wt% of ceramic material 50.
In Figure 5 results of device performance measurements of a device 64 according to an embodiment of the invention operated at 60°C with 1 M KOH aqueous solution is depicted, compared to results of a conventional device 66. The cell voltage II in units of V is recorded as a function of the current density J in units of A/cm2
BaZro.8Ceo.iYo.iOi-a, where a represents the deviation to the stoichiometric content of oxygen in the compound at equilibrium, was introduced into the catalytically active parts on both anode and cathode of an anion exchange membrane of a device 64 for electrolytic production of hydrogen. The other parameters of the device 64 were kept the same as in the device 66. As an anion exchange membrane Aemion™ from the company lonomr, situated in Vancouver, Canada, was used. The catalyst in the anode comprised NiO powder; whereas the catalyst in the cathode comprised Pt/C powder.
Performance and stability of the resulting device 64 were measured and compared to a conventional device 66.
For each device 64, 66, the performance was tested with three voltage cycles from 0 V up to 2.5 V. The voltage characteristics II increases with an approximately parabolic rate, having the current density axis as symmetry axis of the parabola. When 1M KOH is fed as a feedstock to the device 64, 66, the three voltage curves overlap for each device 64, 66, indicating no short-time degradation.
Figure 6 depicts results of performance measurements with the two devices 64, 66 tested with deionized water. The cell voltage II in V is recorded as a function of the current density J in A/cm2 The curves for the different cycles C of both devices 64, 66, exhibiting degradation of both devices 64, 66, are shifted to the left from cycle 1 to cycle 3. The voltage dependencies vs. current densities are similar to Figure 5.
It may clearly be seen from the Figure 6, that, when deionized water is used as feedstock, both devices 64, 66 show the degradation in the initial stage.
In Figure 7 results of stability measurements of the two devices 64, 66 are depicted. The cell voltage II in Volts is recorded as a function of the time t in hours. The tests were carried out at 60°C under a current density of 100 mA/cm2 with deionized water. A 14 hour break after 4 hours operation, indicated by reference numeral 68 with turning the device 66 off during the night is marked in the Figure, resulting in a step in the voltage from about 1.9 V to about 2 V after resuming the operation of the device 66.
During the 13.5 hours stability test, the device 64, which contains ceramic material as an alkaline promoter, shows a better stability than the conventional device 66, the voltage showing a slight increase over time only, showing no step at 68 indicating the break of 14 hours of operation.
Based on the results depicted in the Figures 5 to 7, introducing ceramic material as an alkaline promoter into the catalytic layer works, proved by both improved cell performance and stability when operating the device with deionized water. Reference Numerals
10 anion exchange membrane-electrode assembly
12 anion exchange membrane
14 positive electrode
16 negative electrode
18 aqueous solution
20 positive half-cell
22 negative half-cell
24 catalytically active part of positive electrode
26 catalytically active part of negative electrode
28 side
30 side
34 positive current collector
36 negative current collector
40 voltage source
44 bipolar plate
46 bipolar plate
50 ceramic material
52 catalyst
54 ionomer
56 polymer
64 device 1
66 device 2
68 14 h break
100 device

Claims

26 Claims
1. An anion exchange membrane-electrode assembly (10) for the electrolytic production of hydrogen from an aqueous solution (18), comprising a positive electrode (14) on one side (28) of an anion exchange membrane (12) and a negative electrode (16) on the opposite side (30) of the anion exchange membrane (12), and comprising a ceramic material (50) with alkaline surface properties, wherein the ceramic material (50) comprises at least one of a group enclosing compounds with a formula ABi-yREyOs-a with 0 < y < 1 , wherein A being one or more elements from the Alkaline Earth or Lanthanide metal group, and B being at least one of the following elements: Ti, Zr, Ce, Hf, Sn, In, transition metal, and RE being one or more elements from the Rare Earth Elements.
2. The anion exchange membrane-electrode assembly according to claim 1 , wherein the ceramic material (50) is of perovskite structure or related, in particular double perovskite AA'B20s+6 and Ruddlesden- Popper An+iBnOsn+i phases.
3. The anion exchange membrane-electrode assembly according to claim 1 or 2, wherein the ceramic material (50) is integrated, in particular in a powder form, into at least one of the electrodes (14, 16).
4. The anion exchange membrane-electrode assembly according to any one of the preceding claims, wherein the ceramic material (50) is blended with an ionomer (54) and/or a catalyst (52) of at least one of the electrodes (14, 16).
5. The anion exchange membrane-electrode assembly according to any one of the preceding claims, wherein the ceramic material (50) is integrated into the anion exchange membrane (12). The anion exchange membrane-electrode assembly according to claim 5, wherein the ceramic material (50) is blended with an ionomer (54) and/or a polymer (56) of the anion exchange membrane (12). The anion exchange membrane-electrode assembly according to any one of the preceding claims, wherein the ceramic material (50), in particular in powder form, is coated, in particular directly coated, at least one side (24, 26) of the anion exchange membrane (12). The anion exchange membrane-electrode assembly according to any one of the preceding claims, wherein the ceramic material (50) comprises a specific surface area of at least 1 m2/g, preferably of at least 10 m2/g and more preferably of at least 20 m2/g. The anion exchange membrane-electrode assembly according to any one of the preceding claims, wherein the anion exchange membrane (12) comprises 0.1 wt% to 50 wt% of ceramic material (50), and/or one or both the electrodes (14, 16) comprise 0.1 wt% to 80 wt% of ceramic material (50). The anion exchange membrane-electrode assembly according to any one of the preceding claims, wherein the ceramic material (50) comprises one or more constitutive elements in an oxidized state in combination with one or more of a halogen, preferably fluorine, and/or one or more of a chalcogen, preferably oxygen. The anion exchange membrane-electrode assembly according to claim 10, wherein the one or more constitutive elements of the ceramic material (50) and the bound halogen and/or chalcogen atoms differ by an average difference in electronegativity on the Pauling scale of at least 1 .7, preferably of at least 2. The anion exchange membrane-electrode assembly according to claim 10 or 11 , wherein the one or more constitutive elements of the ceramic material (50) are essentially insoluble in water. The anion exchange membrane-electrode assembly according to any one of the preceding claims, wherein the ceramic material (50) is characterized by being irreducible or only partly reducible under application of electrolysis operating conditions, in particular at a cell voltage below 2.5 V. A device (100) for the electrolytic production of hydrogen from an aqueous solution (18), the device (100) comprising
(i) a positive half-cell (20),
(ii) a negative half-cell (22),
(iii) an anion exchange membrane-electrode assembly (10) according to any one of the preceding claims, comprising a ceramic material (50) with alkaline surface properties, wherein one part of the anion exchange membrane-electrode assembly (10) is assigned to the positive half-cell (20) and another part of the anion exchange membrane-electrode assembly (10) is assigned to the negative half-cell (22), the anion exchange membrane-electrode assembly (10) comprising an anion exchange membrane (12), and comprising a positive electrode (14) facing the positive half-cell (20) on one side (28) of the anion exchange membrane (12) and a negative electrode (16) facing the negative halfcell (22) on the opposite side (30) of the anion exchange membrane (12), and wherein the ceramic material (50) comprises at least one of a group enclosing compounds with a formula ABi-yREyOs-a with 0 < y < 1 , wherein A being one or more elements from the Alkaline Earth or Lanthanide metal group, and B being at least one of the following elements: Ti, Zr, Ce, Hf, Sn, In, transition metal, and RE being one or more elements from the Rare Earth Elements.
PCT/EP2021/074419 2020-09-04 2021-09-03 Device for electrolytic production of hydrogen WO2022049266A1 (en)

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