WO2022032340A1 - Catalyseur - Google Patents

Catalyseur Download PDF

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Publication number
WO2022032340A1
WO2022032340A1 PCT/AU2021/050882 AU2021050882W WO2022032340A1 WO 2022032340 A1 WO2022032340 A1 WO 2022032340A1 AU 2021050882 W AU2021050882 W AU 2021050882W WO 2022032340 A1 WO2022032340 A1 WO 2022032340A1
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catalyst
cnts
oxygen
con
electrolyser
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PCT/AU2021/050882
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English (en)
Inventor
Xunyu LU
Rose Amal
Qingran Zhang
Jian Pan
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Newsouth Innovations Pty Limited
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Priority claimed from AU2020902843A external-priority patent/AU2020902843A0/en
Application filed by Newsouth Innovations Pty Limited filed Critical Newsouth Innovations Pty Limited
Publication of WO2022032340A1 publication Critical patent/WO2022032340A1/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/08—Heat treatment
    • B01J37/082—Decomposition and pyrolysis
    • B01J37/086—Decomposition of an organometallic compound, a metal complex or a metal salt of a carboxylic acid
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
    • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
    • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/74—Iron group metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
    • B01J27/24—Nitrogen compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/08—Heat treatment
    • B01J37/082—Decomposition and pyrolysis
    • B01J37/088—Decomposition of a metal salt
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B15/00—Peroxides; Peroxyhydrates; Peroxyacids or salts thereof; Superoxides; Ozonides
    • C01B15/01—Hydrogen peroxide
    • C01B15/029—Preparation from hydrogen and oxygen
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B15/00—Peroxides; Peroxyhydrates; Peroxyacids or salts thereof; Superoxides; Ozonides
    • C01B15/01—Hydrogen peroxide
    • C01B15/029—Preparation from hydrogen and oxygen
    • C01B15/0295—Preparation from hydrogen and oxygen by electrical discharge
    • 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
    • C25B1/28—Per-compounds
    • C25B1/30—Peroxides
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/02—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form
    • C25B11/03—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form perforated or foraminous
    • C25B11/031—Porous electrodes
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/02—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
    • C25B11/032—Gas diffusion electrodes
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
    • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
    • C25B11/054—Electrodes comprising electrocatalysts supported on a carrier
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
    • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
    • C25B11/055—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
    • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
    • C25B11/055—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material
    • C25B11/057—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material consisting of a single element or compound
    • C25B11/065—Carbon
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
    • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
    • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
    • C25B11/075—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/18—Carbon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/18—Carbon
    • B01J21/185—Carbon nanotubes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Definitions

  • the invention relates to catalysts for the production of hydrogen peroxide, and to methods and apparatus for the use of such catalysts.
  • the invention is not limited to this particular field of use.
  • Hydrogen peroxide is an important chemical commodity that has been widely used as an environmentally benign oxidant and a potential energy carrier in various applications, including wastewater treatment, disinfection, chemical synthesis, paper/pulp bleaching, semiconductor cleaning and fuel cells.
  • wastewater treatment disinfection, chemical synthesis, paper/pulp bleaching, semiconductor cleaning and fuel cells.
  • disinfection disinfection
  • chemical synthesis paper/pulp bleaching
  • semiconductor cleaning and fuel cells semiconductor cleaning and fuel cells.
  • the global demand of H2O2 is growing rapidly, reaching US$4.0 billion in 2017 and is expected to further increase to around US$5.5 billion by 2023.
  • Currently, over 95% of H2O2 is produced in a concentrated form using the anthraquinone process.
  • Electrochemical oxygen reduction provides a feasible way to synthesize hydrogen peroxide per demand, requiring the clean electrons, O2 and water as the only reactants.
  • the oxygen reduction reaction (ORR) method will enable the decentralized production of H2O2 on demand under ambient reaction conditions without any hazardous by-products.
  • ORR process is integrated with renewable electricity supplies (e.g. generation by photovoltaic cells or wind turbines), the H2O2 generated can be regarded as a renewable chemical.
  • chelating agents e.g. ethylenediamine tetraacetic acid
  • chelating agents e.g. ethylenediamine tetraacetic acid
  • the inventors of the present application have surprisingly developed an effective method to stabilize metal-N active species as well as maintain their high selectivity towards H2O2 production under corrosive reaction environments, such as in the presence of strong acids.
  • the present inventors have focussed on an approach of forming single-atom catalysts (SACs) on a carbon substrate to stabilize N-coordinated transition-metal centers (metal-Nx). Without wishing to be bound by theory, it is thought that the conductive nature of a carbon substrate enables maximal exposure of the active metal-N x sites.
  • the inventors have also surprisingly found that epoxide modification of the substrate provides improved selectivity of catalysts for peroxide formation.
  • a catalyst comprising a conductive carbon substrate doped with nitrogen and a transition-metal, wherein the carbon substrate comprises an epoxy group.
  • the catalyst comprises a conductive carbon substrate doped with nitrogen and a transition-metal, and the carbon substrate is adapted to comprise epoxy functionality.
  • the catalyst is a heterogeneous catalyst.
  • the nitrogen is coordinated to the transition-metal. It may form, for example, a metal-N x group, wherein x is an integer from 2 to 6, preferably 4.
  • the conductive carbon substrate is selected from the group consisting of: carbon nanotubes, vertical graphene, metal-organic framework (MOF)-derived carbon, carbon fibre paper, carbon felt, and combinations thereof.
  • MOF metal-organic framework
  • the conductive carbon substrate comprises carbon nanotubes.
  • the carbon nanotubes may have a diameter of from about 5 nm to about 100 nm, or from about 10 nm to about 30 nm. They may, for example, have an average diameter of about 5, 10, 20, 25, 30, 40, 50, 60, 70, 80, 90, or 100 nm.
  • the conductive carbon substrate comprises vertical graphene.
  • the graphene may have a mean aspect ratio of at least about 20, or at least about 50, 100, 200, 500, 1000, 2000, 5000, 10 4 , or 10 5 . It may be from about 20 to about 10 6 , or from about 10 2 to 10 6 , 10 3 to 10 6 , 10 4 to 10 6 , 10 5 to 10 6 , 20 to 10 5 , 20 to 10 4 , 20 to 10 3 , 20 to 10 2 , 10 2 to 10 3 , 10 3 to 10 4 , or 10 4 to 10 5 .
  • the aspect ratio may be defined as the ratio of the minimum non-thickness dimension to the average thickness.
  • the graphene may be non-uniform in shape, but on average may have non-thickness dimension at least 20 times greater than its average thickness.
  • the graphene may have an average thickness of less than about 50 nm, or less than about 20, 10, 5, 2 or 1 nm.
  • the graphene may comprise particles formed from a number of sheets of laminar material. The average number of individual sheets in each particle may be 1 or may be greater than about 1 , or greater than about 2,
  • the conductive carbon substrate is mesoporous. It may have an average pore diameter of about 2 nm to about 50 nm. The average pore diameter may be, for example, about 2, 5, 10, 20, 30, 40, or 50 nm.
  • the transition metal is selected from the group consisting of: cobalt, nickel, iron, and combinations thereof. In certain embodiments it is a metal selected from IUPAC Group 8, IUPAC Group 9, and IUPAC Group 10. It may be, for example, selected from IUPAC Group 9.
  • the transition metal is cobalt.
  • the transition metal concentration in the catalyst is from about 0.01 wt.% to about 30 wt.%, or it may be from about 0.01 wt.% to about 15 wt.%, about 0.1 wt.% to about 15 wt.%, about 0.1 wt.% to about 10 wt.%, about 0.1 wt.% to about 5 wt.%, or about 0.1 wt.% to about 1 wt.%. It may be present, for example, at about 0.01 , 0.02, 0.05, 0.1 , 0.2, 0.5, 1 , 2, 5, 10, 15, 20, or 30 wt.%
  • the nitrogen concentration in the catalyst is from about 0. 1 at.% to about 30 at.%, or it may be from about 0.1 at.% to about 15 at.%, about 0.1 at.% to about 10 at.%, about 0.1 at.% to about 5 at.%, or about 0.1 at.% to about 1 at.%. It may be present, for example, at about 0.1 , 0.2, 0.5, 1 , 2, 5, 10, 15, 20, or 30 at.%. In some embodiments, the concentration values above may refer to wt.%.
  • the C-O-C (i.e. epoxy) oxygen concentration in the catalyst is from about 0.01 at.% to about 30 at.%, or it may be from about 0.01 at.% to about 15 at.%, about 0.1 at.% to about 15 at.%, about 0.1 at.% to about 10 at.%, about 0.1 at.% to about 5 at.%, or about 0.1 at.% to about 1 at.%. It may be present, for example, at about 0.01 , 0.02, 0.05, 0.1 , 0.2, 0.5, 1 , 2, 5, 10, 15, 20, or 30 at.%. In some embodiments, the concentration values above may refer to wt.%.
  • the epoxy group is the predominant oxygen functionality.
  • the ratio of epoxy groups to non-epoxy oxygen containing groups is from about 1 :3 to about 100:1 , or from about 1 :2 to about 50:1 , about 1 :1 to about 50:1 , about 1 :1 to about 10:1 , about 1 :1 to about 5:1 , about 1 :1 to about 2.5:1 , about 1 :1 to about 2:1 , or about 1 :1 to about 1 .5:1 .
  • the percentage of epoxy groups with respect to the total number of oxygen containing groups may be greater than or equal to about 25 at.%, or it may be greater than or equal to about 20 at.%, 30 at.%, 40 at.%, 50 at.%, 60 at.%, 70 at.%, 80 at.%, 90 at.%, or 95 at.%. In some embodiments, the percentage values above may refer to wt.%.
  • the carbon support is a carbon nanotube or vertical graphene or a combination of said structures.
  • the metal may be any suitable metal that provides a suitable catalytic effect, with cobalt particularly preferred.
  • the metal can be loaded onto the carbon support in any amount, with relatively high loadings (15% or greater) preferred to obtain optimum catalytic activity per mass of catalyst.
  • a catalyst for preparing hydrogen peroxide comprising an Co/N co-doped carbon nanotube and an epoxy group as the predominant oxygen functional species.
  • the ratio of epoxy groups to non-epoxy oxygen containing groups is from about 1 :3 to about 100:1 , or from about 1 :2 to about 50:1 , about 1 :1 to about 50:1 , about 1 :1 to about 10:1 , about 1 :1 to about 5:1 , about 1 :1 to about 2.5:1 , about 1 :1 to about 2:1 , or about 1 :1 to about 1 .5:1 .
  • the percentage of epoxy groups with respect to the total number of oxygen containing groups may be greater than or equal to about 25 at.%, or it may be greater than or equal to about 20 at.%, 30 at.%, 40 at.%, 50 at.%, 60 at.%, 70 at.%, 80 at.%, 90 at.%, or 95 at.%. In some embodiments, the percentage values above may refer to wt.%.
  • a catalyst for preparing hydrogen peroxide comprising an Co/N co-doped vertical graphene and an epoxy group as the predominant oxygen functional species.
  • the ratio of epoxy groups to non-epoxy oxygen containing groups is from about 1 :3 to about 100:1 , or from about 1 :2 to about 50:1 , about 1 :1 to about 50:1 , about 1 :1 to about 10:1 , about 1 :1 to about 5:1 , about 1 :1 to about 2.5:1 , about 1 :1 to about 2:1 , or about 1 :1 to about 1 .5:1 .
  • the percentage of epoxy groups with respect to the total number of oxygen containing groups may be greater than or equal to about 25 at.%, or it may be greater than or equal to about 20 at.%, 30 at.%, 40 at.%, 50 at.%, 60 at.%, 70 at.%, 80 at.%, 90 at.%, or 95 at.%. In some embodiments, the percentage values above may refer to wt.%.
  • a method of producing a catalyst comprising a conductive carbon substrate doped with nitrogen and a transition metal, said method comprising the following steps: heating a mixture comprising a carbon containing species, a nitrogen containing species and a transition metal containing species under such conditions to thereby produce the catalyst, and oxidising the conductive carbon substrate to introduce additional oxygen functionality to the conductive carbon substrate, wherein the additional oxygen functionality comprises one or more epoxy groups.
  • the additional oxygen functionality is predominantly epoxy groups.
  • the ratio of epoxy groups to non-epoxy oxygen containing groups after the oxidising step is from about 1 :3 to about 100:1 , or from about 1 :2 to about 50:1 , about 1 :1 to about 50:1 , about 1 :1 to about 10:1 , about 1 :1 to about 5:1 , about 1 :1 to about 2.5:1 , about 1 :1 to about 2:1 , or about 1 :1 to about 1 .5:1 .
  • the percentage of epoxy groups with respect to the total number of oxygen containing groups after the oxidising step may be greater than or equal to about 25 at.%, or it may be greater than or equal to about 20 at.%, 30 at.%, 40 at.%, 50 at.%, 60 at.%, 70 at.%, 80 at.%, 90 at.%, or 95 at.%. In some embodiments, the percentage values above may refer to wt.%.
  • the catalyst, conductive carbon substrate, and transition metal may be as hereinbefore described with respect to the first aspect.
  • the transition metal containing species is selected from the group consisting of nitrate, chloride or acetate salts of cobalt, iron or nickel, or a zeolitic imidazolate framework (e.g. ZIF-8).
  • the carbon containing species and/or nitrogen containing species comprises dicyanamide, aniline or a zeolitic imidazolate framework (e.g. ZIF-8).
  • the method further comprises a step of reducing the conductive carbon substrate to reduce non-epoxy oxygen functionality.
  • the oxidising and/or reducing are conducted electrochemically.
  • the oxidation and/or reduction steps may alternatively be a chemical oxidation and/or reduction, i.e. using a chemical oxidant and/or reductant rather than an electrochemical process.
  • the ratio of epoxy groups to non-epoxy oxygen containing groups of the conductive carbon substrate is higher after the oxidising and reducing steps than prior to the oxidising and reducing steps.
  • the ratio of epoxy groups to non-epoxy oxygen containing groups may increase by from about 10 % to about 500 % as a result of the oxidisation and reduction steps, or it may increase by from about 10% to about 400%, about 10% to about 200%, about 10% to about 100%, or about 50% to about 200%. It may, for example, increase by about 10, 20, 50, 100, 200, or 500%.
  • the heating is a pyrolysis.
  • the pyrolysis may be performed at a temperature of from about 500 °C to about 1000 °C, or about 600 °C to about 1000°C, or about 700 °C to about 900°C. It may be at a temperature of about 500, 600, 700, 800, 900, or 1000°C.
  • the heating may be performed for a period of from about 1 hour to about 8 hours, or from about 1 hour to about 6 hours, about 1 hour to about 5 hours, about 3 hours to about 6 hours, or about 3 hours to about 4 hours. It may be performed for a period of about 1 , 2, 3, 3.1 , 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 4, 5, or 6 hours.
  • oxidising the carbon support comprising a doped metal may produce an oxidised carbon support comprising epoxy oxygen groups and other oxygen groups including ketonic oxygen. Reducing takes place to convert and/or modify non-epoxy oxygen groups, preferably such that the ketonic oxygen species are minimised (i.e., substantially reduced or substantially eliminated in total number) and epoxy oxygen groups are maximised (i.e., substantially increased in total number, or are the predominant oxygencontaining groups present).
  • the oxidising and reducing may be conducted electrochemically.
  • the carbon support may be a carbon nanotube or vertical graphene.
  • the metal may be a transition metal, such as cobalt.
  • a method of preparing a catalyst for preparing hydrogen peroxide comprising an Co/N co-doped carbon nanotube and an epoxy group as the sole or predominant oxygen functional species comprising the steps of:
  • a method of preparing a catalyst for preparing hydrogen peroxide comprising an Co/N co-doped vertical graphene and an epoxy group as the sole or predominant oxygen functional species comprising the steps of:
  • the method according to the second aspect may produce the catalyst according to the first aspect.
  • the catalyst according to the first aspect may be produced using the method according to the second aspect.
  • a catalyst produced according to the method of the second aspect In a third aspect of the invention there is provided a catalyst produced according to the method of the second aspect. [00050] In a fourth aspect of the invention there is provided use of the catalyst according to the first or third aspect as a cathode catalyst.
  • an electrolyser for producing hydrogen peroxide from oxygen and water, the electrolyser comprising a cathode which comprises a catalyst layer comprising the catalyst according to the first or third aspect.
  • the cathode is on an electrolyte facing side and the electrolyser further comprises a hydrophobic gas permeable layer on an oxygen input side.
  • the hydrophobic gas permeable layer is formed from polytetrafluoroethylene, such as a polytetrafluoroethylene coating layer or membrane, or is formed from an aggregate of polytetrafluoroethylene nanoparticles.
  • the catalyst layer and hydrophobic gas permeable layer are (immediately) adjacent each other.
  • the catalyst layer and hydrophobic gas permeable layer are present in conjunction with a mechanical support layer, such as carbon paper or a perforated metal substrate.
  • a mechanical support layer such as carbon paper or a perforated metal substrate.
  • the catalyst layer may comprise vertical graphene and the mechanical support layer may comprise a graphene growth support.
  • an electrolyser for producing hydrogen peroxide from oxygen and water, the electrolyser comprising a cathode which comprises a catalyst layer comprising a catalyst according to the first or third aspect on an electrolyte facing side and a hydrophobic gas permeable layer on an oxygen input side.
  • the catalyst layer and hydrophobic gas permeable layer are (immediately) adjacent each other.
  • the catalyst layer and hydrophobic gas permeable layer are present in conjunction with a mechanical support layer, such as carbon paper or a perforated metal substrate.
  • the catalyst layer comprises vertical graphene and the support layer is a graphene growth support.
  • a seventh aspect of the invention there is provided a method of synthesising hydrogen peroxide comprising providing oxygen in an acidic or neutral aqueous media to an electrolyser according to the sixth aspect under reducing conditions.
  • the electrolyser produces at least about 100 mg L -1 h’ 1 , or at about least 5000 mg L -1 h -1 hydrogen peroxide. It may produce hydrogen peroxide at a rate of from about 100 to about 50000 mg L -1 h’ 1 , or from about 200 to about 50000, about 500 to about 50000, about 1000 to about 50000, or about 10000 to about 50000 mg L -1 h -1 . It may produce hydrogen peroxide at a rate of, for example, about 100, 200, 500, 1000, 2000, 5000, 10000, 20000, or 50000 mg L’ 1 h 1 .
  • the acidic or neutral media may have a pH of from about 0 to about 8, or about 1 to about 7, about 2 to about 7, about 3 to about 7. It may, for example, be about 0, 1 , 2, 3, 4, 5, 6, or 7, or 8.
  • the electrolyser produces hydrogen peroxide at a concentration of least about 100 mg L -1 (0.01 wt.%), or at least about 2000 mg L -1 (0.2 wt.%), or at least about 5000 mg L -1 (0.5 wt.%), or at least about 30000 mg L -1 (3 wt.%). It may produce hydrogen peroxide at a concentration of from about 100 to about 50000 mg L’ 1 , or from about 200 to about 50000, about 500 to about 50000, about 1000 to about 50000, or about 10000 to about 50000 mg L -1 . It may produce hydrogen peroxide at a concentration of, for example, about 100, 200, 500, 1000, 2000, 5000, 10000, 20000, or 50000 mg L 1 .
  • an eighth aspect of the invention there is provided a method of synthesising Fenton’s reagent comprising providing a source of Fe 2+ and oxygen in an acidic or neutral aqueous media to an electrolyser according to the sixth aspect under reducing conditions.
  • a ninth aspect of the invention there is provided a method for improving the selectivity of a catalyst for hydrogen peroxide production, said catalyst comprising a conductive carbon substrate doped with nitrogen and a transition-metal, the method comprising the following steps: oxidising the conductive carbon substrate to introduce additional oxygen functionality to the conductive carbon substrate, wherein the additional oxygen functionality includes one or more epoxy groups; and reducing the conductive carbon substrate to reduce non-epoxy oxygen functionality.
  • the following options may be used in conjunction with the ninth aspect, either individually or in any combination.
  • the oxidising step promotes the production of surface 02 and/or 04 groups and/or suppresses the production of surface 01 groups, wherein 01 groups are oxygen species having an average binding energy of 531.2 ⁇ 0.2 eV, 02 groups are oxygen species having an average binding energy of 532.3 ⁇ 0.2 eV, 03 groups are oxygen species having an average binding energy of 533.3 ⁇ 0.2 eV, and 04 groups are oxygen species having an average binding energy of 534.2 ⁇ 0.2 eV.
  • the reducing step suppresses the production of surface 03 and/or 04 groups.
  • overall the concentration of 02 groups is higher than without the oxidising and reducing treatment steps.
  • the method of the ninth aspect may be a component of the method according to the second aspect.
  • the method of the second aspect may incorporate the method according to the ninth aspect.
  • a membrane comprising the catalyst according to the first or third aspect.
  • the membrane comprises a perfluorosulfonate resin.
  • a perfluorosulfonate resin A person of skill in the art will appreciate that other suitable membrane materials may be used.
  • the membrane may be used in the electrolyser according to the sixth aspect.
  • the electrolyser of the sixth aspect may comprise the membrane according to the tenth aspect.
  • an electrolyser for producing hydrogen peroxide from oxygen and water, the electrolyser comprising the membrane according to the tenth aspect.
  • transitional phrase “consisting essentially of” is used to define a composition, process or method that includes materials, steps, features, components, or elements, in addition to those literally disclosed, provided that these additional materials, steps, features, components, or elements do not materially affect the basic and novel characteristic(s) of the claimed invention.
  • the term “consisting essentially of” occupies a middle ground between “comprising” and “consisting of”.
  • the terms “predominantly”, “predominant”, and “substantially” as used herein shall mean comprising more than 50% by weight, unless otherwise indicated.
  • the terms “about,” “approximately” and “substantially” are understood to refer to the range of - 10% to +10% of the referenced number, preferably -5% to +5% of the referenced number, more preferably -1 % to + 1 % of the referenced number, most preferably -0.1 % to +0.1 % of the referenced number.
  • conductive carbon substrate means an electrically conductive substrate that predominantly comprises carbon. In certain embodiments it may consist essentially of carbon optionally with some minor non-carbon impurities, wherein the minor impurities are less than about 2%, 1%, or 0.5% by weight of the total weight of the substrate. In certain embodiments the substrate may have a conductivity of greater than or equal to about 10 2 S/m, or greater than or equal to about 10 3 S/m, 10 4 S/m, or 10 5 S/m.
  • epoxy group refers broadly to any C-O-C group, including where the two carbons adjacent the oxygen are directly bonded to each other, and where the two carbons adjacent the oxygen are not directly bonded to each other (like ether groups).
  • epoxy group means a C-O-C group where the two carbons adjacent the oxygen are directly bonded to each other.
  • epoxy functionality with respect to the carbon substrate refers to the number of epoxy groups of the substrate.
  • the substrate having increased epoxy functionality means an increase in the number of epoxy groups of the substrate.
  • oxygen functionality with respect to the carbon substrate refers to the number of oxygen-containing groups of the substrate (whether epoxy groups or not).
  • the substrate having increased oxygen functionality means an increase in the number of oxygen-containing groups of the substrate.
  • Oxygen containing groups include C-O-C groups, carbonyl groups, and other groups having at least one oxygen atom.
  • non-epoxy oxygen functionality with respect to the carbon substrate refers to the number of non-epoxy oxygen-containing groups of the substrate. That is, the number of oxygen-containing groups that are not epoxy groups.
  • the substrate having increased non-epoxy oxygen functionality means an increase in the number of non-epoxy oxygen-containing groups of the substrate.
  • Non- epoxy oxygen-containing groups include, for example, ketonic oxygen groups and other non C-O-C groups having at least one oxygen atom.
  • the terms “carbon containing species”, “nitrogen containing species” and “transition metal containing species” respectively mean a material comprising at least one carbon atom, a material comprising at least one nitrogen atom, and a material comprising at least one transition metal atom, respectively.
  • the “carbon containing species” and “nitrogen containing species” may be the same material.
  • the “nitrogen containing species” and “transition metal containing species” may be the same material.
  • the “carbon containing species” and “transition metal containing species” may be the same material.
  • the “carbon containing species”, “nitrogen containing species” and “transition metal containing species” are the same material.
  • Carbon fiber paper CPP
  • carbon nanotubes CNTs
  • chemical vapor deposition CVD
  • cobalt/nitrogen doped carbon nanotubes CoN@CNTs
  • cobalt/nitrogen doped vertical graphenes CoN@VGs
  • cobalt(ll) phthalocyanine CoPc
  • energy dispersive X-ray spectroscopy EDS
  • dimethyl sulfoxide DMSO
  • electrochemical activation EA
  • electrochemically activated cobalt/nitrogen doped carbon nanotubes EA- CoN@CNTs
  • electrochemical oxidation EO
  • electrochemically oxidised cobalt/nitrogen doped carbon nanotubes EO-CoN@CNTs
  • electrochemical reduction ER
  • electrochemical treatment E
  • ELS electron energy loss spectroscopy
  • EXAFS extended X- ray absorption fine structure
  • EXAFS faradaic efficiency
  • FE Fourier transformed
  • FTIR Fourier-transform infrared
  • Figure 1 shows a microstructural analysis of an example CoN@CNTs catalyst: a) SEM images of CoN@CNTs. Inset is the high-resolution SEM image of a selected area of CoN@CNTs. b) TEM image of CoN@CNTs showing a bamboo-like structure of the carbon nanotubes. c) HAADF-STEM image (top-left) and corresponding EDS maps of CoN@CNTs for O (top-right), N (bottom-left), and Co (bottom-right). d) HAADF-STEM image of the CoN@CNTs showing many Co atoms (circled) well- dispersed in the carbon layers. e) EELS analysis of selected area in (d) showing the signals of Co. f) XPS elemental survey of CoN@CNTs.
  • Figure 2 shows oxygen reduction performance of an example CoN@CNTs catalyst: a) RRDE voltammograms of CoN@CNTs and NG at 1600 rpm in an Os-saturated 0.1 M HCIO4 electrolyte with disc current and ring current. b) RRDE voltammograms of fresh and aged CoN@CNTs at 1600 rpm in an O2- saturated 0.1 M HCIO4 electrolyte with disc current and ring current. All potentials are recorded without iR correction. c) XPS elemental survey of CoN@CNTs and aged CoN@CNTs. d) XPS O1 s spectra of CoN@CNTs and aged CoN@CNTs.
  • FIG 3 shows electrochemical activation (EA) of an example CoN@CNTs catalyst:
  • H2O2 production amount (determined via the potassium permanganate titration) as a function of time on the EA-CoN@CNT s. Current (thick curve) and concentration (dashed o) behaviour with time for the electrochemical H2O2 production is shown.
  • Figure 4 shows ORR activities of an example HE-CoN@CNTs catalyst: a) RRDE measurements of HE-CoN@CNTs for ORR in 0.1 M HCIO4 solution purged with O2 and air. b) Calculated H2O2 selectivity on HE-CoN@CNTs in O2- and air- saturated 0.1 M HCIO4 based on the RRDE measurements.
  • Figure 5 shows the Co K-edge (a) XANES spectra and (b) FT-EXAFS spectra of a CoN@CNTs composite, CoPc and Co foil; and (c) FT-EXAFS curve-fitting analysis of the CoN@CNTs composite.
  • Figure 6 shows calculated H2O2 selectivity on CoN@CNTs based on the RRDE measurements.
  • Figure 7 shows TEM images of: (a) FeN@CNTs and (d) NiN@CNTs composites.
  • Figure 8 shows ORR polarization curves of CoN@CNTs before and after adding 5 mM SCN ions into the 0.1 M HCIO4 electrolyte.
  • Figure 9 shows chronoamperometry performed using the RRDE system with the glassy carbon disk and Pt ring held at 0.55 and 1.2 V vs. RHE, respectively, in 0.1 M HCIO4.
  • Figure 10 shows polarization curves of the electrochemical oxidation applied on CoN@CNTs.
  • the Pt ring was held at 0.2 V during the oxidation process to detect the possible O2 evolved from the oxidation process.
  • Figure 11 shows polarization curves of the reduction process applied on the CoN@CNTs. The ring was held at 1 .2 V during the reduction process to detect the possible H2O2 formed from the ORR reduction process.
  • Figure 12 shows: (a) the ratios of different oxygen species within the total amount of oxygen in aged CoN@CNTs, EO-CoN@CNTs and EA-CoN@CNTs powders; and (b) the atomic percentages of different oxygen functional groups within the aged CoN@CNTs, EOCoN@CNTs and EA-CoN@CNTs powders. All these results were obtained by XPS O 1 s measurements and analysis.
  • Figure 13 shows: (a) H2O2 selectivity obtained from both RRDE measurements and chemical titration for the electro-activated CoN@CNTs in an O2- saturated 0.1 M HCIO4 electrolyte; and (b) /-t curves obtained from the H2O2 bulk production on the electro-activated carbon fibre paper electrode loaded with EA-CoN@CNTs under different operation potentials for the chemical titration.
  • Figure 14 shows: (a) XPS O1 s spectra of the aged CoN@CNTs and HTCoN@CNTs, showing an apparent emergence of epoxy groups on CoN@CNTs after H2O2 treatment; and (b) background-corrected FTIR spectrum of HT-CoN@CNTs.
  • Figure 15 shows: (a) calculated H2O2 selectivity of HT-CoN@CNTs and aged CoN@CNTs from the RRDE measurements; and (b) RRDE voltammograms of the aged CoN@CNTs before and after H2O2 treatment (HT) at 1600 rpm in an 02-saturated 0.1 M HCIO4 electrolyte with disc current and ring current.
  • Figure 16 shows: (a) XPS O 1 s spectrum of HE-CoN@CNTs, showing an apparent emergence of epoxy groups on CoN@CNTs after both H2O2 and electrochemical treatment; (b) XPS N 1 s spectra of the aged CoN@CNTs and HE-CoN@CNTs; (c) XPS Co 2p spectra of the aged CoN@CNTs and HE-CoN@CNTs; and (d) background-corrected FTIR spectrum of HE-CoN@CNTs.
  • Figure 17 shows: (a) XPS elemental survey of the HE-CoN@CNTs sample before and after 12-hour testing session for C>2 reduction in 0.1 M HCIO4; and high resolution XPS (b) Co 2p spectra, (c) O 1 s and (d) N 1 s of the HE-CoN@CNTs sample before and after 12-hour testing session for O2 reduction in 0.1 M HCIO4.
  • Figure 18 shows background-corrected FTIR spectrum of the HE- CoN@CNTs sample after 12-hour testing session for O2 reduction in 0.1 M HCIO4, showing clear emergence of epoxy groups.
  • Figure 19 shows an SEM image of an example 3D structured membrane incorporating the catalyst.
  • Figure 20 shows a schematic diagram of an example electrochemical cell design incorporating the membrane.
  • Figure 21 shows a schematic diagram of an example electrolyser items 4 & 6 (from Figure 20), with flow channel and gas mass transport channel for the electrochemical cell.
  • Figure 22 shows the electrical performance of an example catalyst in an example electrochemical cell.
  • a 100 cm 2 cell can produce 0.45 wt.% neutral H2O2 solution.
  • the first general step in the process of catalyst preparation may involve the synthesis of a metal and N doped carbon catalyst.
  • the metal may be any transition metal, but in certain embodiments is cobalt.
  • the carbon may be in the form of any high surface area conductive carbon. In certain embodiments the carbon may be in the form of carbon nanotubes and/or vertically formed graphene sheets.
  • the catalyst may comprise cobalt/nitrogen doped graphene, for example cobalt/nitrogen doped vertical graphenes (CoN@VGs).
  • CoN@VGs cobalt/nitrogen doped vertical graphenes
  • the high surface area cobalt/nitrogen doped carbon nanotubes may be formed from the pyrolysis of the carbon and metal precursors in Argon, followed by an acid leach to remove metallic debris.
  • VGs vertical graphenes
  • CVD plasma-assisted chemical vapor deposition
  • the Co and N dopants may subsequently be introduced onto the vertical graphene electrode via an electro-polymerization process in an aqueous solution containing both aniline and nitric acid, followed by immersing the polyaniline-coated vertical graphene electrode into the K 3 [Co(CN)6] solution. Then the as-obtained electrode may, for example, be annealed in a nitrogen atmosphere to afford the Co and N co-doped vertical graphene electrode.
  • the catalysts disclosed herein can be prepared by at least two distinct approaches, namely, i) the incorporation of the metal and nitrogen dopants during the stage of formation of the carbon substrate (as per CoN@CNTs), or ii) by first forming the carbon substrate and then subsequently loading that with metal atoms and nitrogen sites postproduction (as per CoN@VGs).
  • ii the incorporation of the metal and nitrogen dopants during the stage of formation of the carbon substrate
  • metal atoms and nitrogen sites postproduction as per CoN@VGs
  • the high surface area metal/N doped catalyst such as a CoN@CNT or CoN@VGs may be subjected to a hitherto unknown sequential electrochemical oxidation/reduction process which further modifies the high surface CoN catalyst to produce a highly specifically epoxy functionalised catalyst, that is a catalyst in which C-O-C groups are present.
  • This catalyst has unique structural properties that make it useful in hydrogen peroxide production.
  • C-O-C epoxy oxygen has been found to be particularly advantageous in the ability of the catalyst to promote peroxide formation.
  • the electrochemical oxidation/reduction process disclosed herein may reduce or at least strongly suppress the formation of ketonic oxygen, which the present inventors have surprisingly found can be particularly deleterious to the production of hydrogen peroxide.
  • the two-step electrochemical oxidation/reduction process involves in turn a sequential electrochemical oxidation and then a reduction.
  • the first step may be oxidation in a suitable medium, such as perchlorate, using, for example, an anodic linear sweep voltammetric scan to produce highly oxygenated CoN@CNTs or CoN@VGs.
  • the oxygen is present in a variety of forms including the desirable epoxy form, undesirable ketonic form, and other forms.
  • the subsequent reduction process may lead to an enhancement of the ratio of epoxy carbons by elimination of non-epoxy oxygen forms, or by conversion of non-epoxy oxygen forms to epoxy forms.
  • the reduction step may supress ketonic oxygen on the surface of the catalyst.
  • the inventors of the present invention postulate that this two-step oxidation reduction process may exploit the fact that epoxy groups are more thermodynamically stable than either ester or carboxyl groups.
  • the basic principal of catalytic hydrogen peroxide production requires air or oxygen and water to come in contact with the supported catalyst at the reaction cathode.
  • One challenge to be overcome is that the inherent nature of the catalyst, being, for example, an epoxy modified CoN@CNTs or CoN@VG, which is hydrophilic, whereas the air or gaseous oxygen is hydrophobic.
  • the present inventors have found that the hydrophobic layer can be advantageously prepared by, for example, applying a spray of teflon nanoparticles to a support such as carbon fibre paper, and then applying to that the catalyst layer. That arrangement provides good access to the epoxy modified CoN@CNTs or CoN@VG by both the hydrophilic (aqueous) and hydrophobic (gaseous) sides.
  • H2O2 the electrochemical production of H2O2 is thought to proceed via the cathodic reduction of O2 (ORR), which can either produce the desired H2O2 via a 2-electron pathway or H 2 O via an undesired 4-electron pathway.
  • ORR O2
  • the 2-electron-pathway ORR under acid conditions may proceed according to the following reaction:
  • HO2' may be formed via the following two electron pathway ORR:
  • reaction can also be followed by either a further reduction to OH-:
  • the inventors of the present invention have surprising found that the catalysts according to the present invention are capable of selectively producing hydrogen peroxide under acidic or neutral conditions, optionally wherein the pH is less than about 7.
  • the catalyst according to the present invention may be incorporated into an electrolyser device.
  • the device may have an Os/air inlet on its cathode side, a current collector perforated to allow gas movement to the cathode itself (formed from, for example, a teflon nanoparticle gas facing side and a CoN@CNT s or CoN@VGs aqueous facing side), a channel for flow of electrolyte and egress of hydrogen peroxide, an ion exchange membrane, a channel for electrolyte flow, an anode and current collector, and an endpiece to seal the unit.
  • H2O2 concentration of -1200 ppm can readily be accumulated in acidic media within 30 min at 0 V, satisfying most applications including an electro-Fenton process for water treatment at low cost.
  • An electro-Fenton process in water treatment typically would require about 10 ppm of H2O2 or more.
  • the electrocatalysts generally may be inexpensive to manufacture (as they typically do not contain precious metals) and may require only low energy input and may be highly active, with low overpotentials and/or a high selectivity (up to around 100% in certain embodiments).
  • the H2O2 produced may thus be produced in a manner which can be economical and may be eco-friendly, especially when renewable electricity is employed as an energy supply for electrolysers using the catalysts.
  • the method and electrocatalysts disclosed herein are free from toxic elements (such as mercury in a Pt-Hg catalyst).
  • the H2O2 production approach used herein may require clean electrons, oxygen and water as the only reactants, thereby making the H2O2 production method potentially eco-friendly, particularly compared with the traditional anthraquinone method.
  • the methods and devices of the present invention may be suitable for both small and large-scale operation.
  • the simple H2O2 production method disclosed herein may require only a potentiostat as the main equipment, enabling the production of H2O2 in both a small and large scale.
  • on-site production of hydrogen peroxide may be achieved at a desirable rate using the inventive method in remote areas and developing countries, where centralized production is not feasible.
  • clean electricity can be employed to generate H2O2, making it a renewable chemical which traditional methods cannot achieve.
  • the CoN@CNTs composite was prepared by pyrolyzing the carbon and metal precursors in Ar, followed by an acid leaching to remove the accessible metallic debris (see details in the Methods).
  • HAADF-STEM high-angle annular dark field scanning transmission electron microscopy
  • the weak signals at ⁇ 2.3 to 2.7 A in the Co K-edge EXAFS of CoN@CNTs may be ascribed to the Co-Co scattering path originating from a metallic feature in the Co nanoparticles wrapped at the closed end of carbon nanotubes.
  • the weak signals of Co-Co bond suggest a very rare appearance of metallic cobalt nanoparticles in the CoN@CNTs samples, as evidenced from TEM imaging.
  • the higher white line intensity and position compared with CoO indicates the possible existence of positively charged Co with an oxidation state in CoN@CNTs.
  • the slightly lower absorption edge position than that of cobalt(ll) phthalocyanine (CoPc) suggests the valence state of atomic Co may be between 0 and 2 + .
  • the nearly absent appearance of a pre-edge feature (arisen from the forbidden 1 s-to-3d transition) at -7709 eV in the CoN@CNTs indicates a symmetric coordination environment of Co, e.g. C0-N4.
  • the Fourier transformed (FT) Co K- edge EXAFS spectra exhibit the signal of light scattering nearest neighbours at -1.5 A, corresponding to the Co-N/C scattering pair and further corroborating the existence of tetrahedrally coordinated Co (e.g. C0-N4) as revealed by fitting analysis.
  • the weak signals originating from the Co-Co scattering path in a metallic feature might be ascribed to the rare appearance of Co nanoparticles as discussed above.
  • FeN@CNTs and NiN@CNTs composites were prepared via a similar method to the CoN@CNTs and exhibited an analogous nanotube structure (Fig. 7)
  • CoN@VGs electrodes were fabricated through a three-step synthesis process: Firstly, polyaniline was coated onto vertical graphene via an electro-polymerization process. Then Co was adsorbed and reduced onto the polyaniline-coated vertical graphene by surface imine-group reduction. Finally, the as-obtained electrode was pyrolyzed under a nitrogen atmosphere to form the Co and N doped vertical graphene electrode.
  • Fig. 2a shows the polarization curve obtained on CoN@CNTs, with the oxygen reduction current measured on the disk electrode (solid lines) and the H2O2 oxidation current measured on the Pt ring electrode (dashed lines).
  • Fig. 2b compares the RRDE curves obtained with freshly prepared CoN@CNTs and CoN@CNTs that had been exposed to air for one month (named as aged CoN@CNTs). It can be seen from Fig. 2b that /ring on the aged CoN@CNTs drops significantly meanwhile the /disk remains almost unchanged (compared with CoN@CNTs), leading to the H2O2 selectivity ⁇ 30% over the whole potential range.
  • this phenomenon may indicate the occurrence of an undesired oxidation process on the CoN@CNTs composite during the air exposure that has adversely affected its H2O2 productivity.
  • XPS was utilized to reveal the chemical changes between the CoN@CNTs and aged CoN@CNTs composites. As displayed in Fig. 2c, the only noticeable change between these two samples was the increment of O concentration, which rises from 3.50 at.% in CoN@CNTs to 5.17 at.% in aged CoN@CNTs.
  • ketonic groups (01 ) exhibited a noticeable increase, of which the concentration had increased from merely 0.84 at.% in the fresh sample to 2.64 at.% in the aged sample (Table 1). This observation suggests that ketonic groups may be responsible for the receded H2O2 productivity on the aged CoN@CNTs.
  • Table 1 Summarization of the content of different O groups in the different CoN@CNTs samples based on the XPS measurement.
  • the content of 02 could be ascribed to the epoxy O.
  • the ratio means the percentage of a certain O group in the total O content, and the atom% reflects the amount of a certain O group in the whole materials.
  • Electrochemical treatment was selected here as an approach to in situ re-construct the surface oxygen functionalities on the carbon-based materials. Nevertheless, by simply performing electrochemical reduction (ER) it is difficult to remove oxygen functional groups (such as ketonic O) that are thermodynamically more stable than the carboxyl groups. Compared with the ER process, the inventors of the present application postulated that an electrochemical oxidation (EO) treatment may be more effective in rebuilding the surface oxygen functional groups on carbon-based materials. Thus, herein, a two-step electrochemical process combing both EO and ER was adopted to treat the aged CoN@CNTs to modify the O functionalities.
  • ER electrochemical reduction
  • EO electrochemical oxidation
  • the aged CoN@CNTs was electrochemically oxidized in a 0.1 M HCIO4 solution (EO-CoN@CNTs) by an anodic linear sweep voltammetric scan (details can be seen in Fig. 10).
  • the aged CoN@CNTs was electrochemically oxidized by conducting an anodic linear scan voltammetry (from 1.2 to 2.4 V vs. RHE) in the 0.1 M HCIO4 solution, during which an anodic peak appeared at ⁇ 2 V and no oxygen evolution was detected at the Pt ring, indicating that the anodic peak was related to a surface oxidation process on CoN@CNTs rather than oxygen evolution.
  • the EO treatment provided the aged CoN@CNTs composite a higher O content (12.66 at.%) owing to the highly positive potential applied that may have caused carbon oxidation.
  • the EO-CoN@CNTs was subjected to an ER treatment to afford the electrochemically activated CoN@CNTs (EA-CoN@CNTs, Fig. 11 ).
  • the aged CoN@CNTs was electrochemically reduced through performing a cathodic linear scan voltammetry (from 0.6 to -0.6 V vs. RHE) in a 0.1 M HCIO4 solution, during which a cathodic peak appeared at ⁇ -0.1 V and no H2O2 was detected at the Pt ring, suggesting the cathodic peak may be related to a surface reduction process on CoN@CNTs.
  • EA-CoN@CNTs were also evaluated in 02-sat. 0.1 M HCIO4 solution.
  • EA-CoN@CNTs exhibited a superior H2O2 productivity that was even higher than the freshly prepared CoN@CNTs.
  • the onset potential of EA-CoN@CNTs at the ring and disk coincided at ⁇ 0.7 V (Fig. 3e), which is the thermodynamic onset potential of the genuine 2-electron pathway of ORR in acid for H2O2 production.
  • C-O-C groups on carbon can also be introduced through chemical approaches and H2O2 treatment (HT) was found to be an effective method.
  • H2O2 treatment H2O2 treatment
  • an aged CoN@CNTs sample was chemically treated in 0.1 M HCIO4 solution containing 5 wt% H2O2 at 70°C for 2 hours.
  • the HECoN@CNTs Compared to both CoN@CNTs and aged CoN@CNTs, the HECoN@CNTs appears to exhibit a significantly higher ratio of N component located at -399. 3 eV (namely N*), corroborating well the potential formation of more pyridonic N that might be converted from the pyridinic N near the HE-generated epoxy groups.
  • Co 2p spectrum of HECoN@CNTs also revealed a slightly positive shift (-0.4 eV) of binding energy of Co-N peak, suggesting an interaction between the HE-generated epoxy groups and Co-N x species via a possible electron-withdrawing effect.
  • the HE- CoN@CNTs composite was capable of maintaining a nearly 100% selectivity of H2O2 production within a wide potential range from 0.3 to 0.6 V (> 95%), exceeding the catalytic performances of those benchmarks and state-of-the-art catalysts, including precious metals, their alloys and recently reported carbon-based materials, in terms of both overpotential and selectivity.
  • FeN@CNTs and NiN@CNTs were prepared using a similar pyrolysis process by changing the type of metal nitrate in the precursors.
  • the EA-CoN@CNTs were obtained by oxidizing the CoN@CNTs electrochemically through conducting an anodic linear sweep voltametric scan from 1 .2 to 2.4 V vs. RHE, followed by an electrochemical reduction process via a cathodic linear sweep voltametric scan from 0.6 to -0.6 V vs. RHE.
  • To prepare the HE-CoN@CNTs the CoN@CNTs sample was treated through a combined H 2 O 2 treatment and electrochemical activation process. Hot alkaline treatment was conducted by heating the aged CoN@CNTs sample in 6 M KOH solution with an autoclave reactor under 180°C for 12 h.
  • TEM Transmission electron microscopy
  • SEM Scanning electron microscopy
  • JEOL 7001 F operated at 5 kV.
  • FTIR measurements were conducted on a PerkinElmer FTIR Spectrometer.
  • X-ray photoelectron spectroscopy (XPS) measurements were carried out on a Thermo ESCALAB250Xi X-ray photoelectron spectrometer using Cu Ka X-rays as the excitation source with a voltage of 12.5 kV and power of 250 W.
  • HAADF-STEM High angle annular dark field-scanning transmission electron microscopy
  • EDX energy dispersive X-ray mapping
  • ICP-MS Inductively coupled plasma mass spectroscopy
  • XAS Co K-edge X-ray absorption spectroscopy
  • O K-edge measurements were performed from 520 eV to 580 eV while Co L-edge measurements were performed from 770 to 810 eV and internally calibrated using MnO and Co foil reference samples respectively. All data processing, energy calibrations, and normalization was performed using the program QANT.
  • CH2O2 5CKMHO4 X VKMHO4 + 2VH2O2
  • CH202 is the H 2 O 2 concentration (mol L -1 )
  • CKMH M is the precise concentration of KMnC solution (mol L -1 )
  • VKMH M is the volume of KMnC solution consumed during titration (mL)
  • V 2O2 is the volume of H 2 O 2 solution.
  • thermoplastic perfluorosulfonate ion-exchange resin was hot-pressed or extruded under 200 to 300 °C with solid templates (including, for example, dissolvable and/or indissoluble metal salts (such as sodium salts, potassium salts, etc.) and/or silica- based material with size from 100nm to 100 pm) into a sheet or filament form.
  • solid templates including, for example, dissolvable and/or indissoluble metal salts (such as sodium salts, potassium salts, etc.) and/or silica- based material with size from 100nm to 100 pm
  • 200g thermoplastic resin was mixed with 10 pm size SiO 2 beads in a volume ratio of 1 :1 as a solid template for the membrane formation.
  • composition was further hot-pressed, or 3D printed into a membrane with a thickness of from 50 pm to 5mm.
  • the hot-press temperature used was from about 200 to 260 °C.
  • the 3D printing method incorporated printing under 300 °C on a 200 °C hotbed.
  • the membrane was treated by base hydrolysis in a solution of 15 wt% KOH, 35 wt% dimethyl sulfoxide (DMSO), and 50 wt% deionised water at 80 °C for 24 - 72 hours, and subsequently dipped into a 5 w% aqueous H 2 O 2 solution at 80 °C for 24 - 72 hours, and then dipped into a 1 M sulfuric acid solution at 80 °C for 24 - 72 hours.
  • DMSO dimethyl sulfoxide
  • the catalysts or catalysts on the conductive substrate were coated on each side or pressed into the membrane to form a 3D structured porous membrane electrode with a thickness of from 60 pm to 15mm.
  • An example membrane is shown in Fig. 19.
  • the membrane-based catalysts were used in a novel designed electrochemical cell to produce a neutral H2O2 solution with a concentration of from about 0.01 wt.% to about 1 wt.%.
  • the electrochemical cell assembly consisted of cell frames, an anode, a cathode, and a membrane. In certain embodiments the anode, cathode and membrane are hot-pressed together. Alternatively, in other certain embodiments the anode, cathode and membrane are not hot-pressed together.
  • FIG. 20 A schematic depiction of an example electrochemical cell (electrolyser) is shown in Fig. 20.
  • the cell comprises an anode current collector 1 with a liquid/gas flow channel, and an anode catalyst layer 2 (which can be, for example, a commercial catalyst with or without a conductive substrate) that together form the anode part of the cell.
  • anode catalyst layer 2 which can be, for example, a commercial catalyst with or without a conductive substrate
  • the cell further comprises a 3D structured membrane 3 housed within a frame 4 which has a flow channel for the membrane 3.
  • the cell additionally comprises a cathode gas layer 5 (which may comprise the catalyst according to the invention, or a commercial catalyst (such as carbon black, active carbon, etc.) with or without a conductive substrate) and a cathode current collector 6 with a gas chamber and dispersers inside.
  • the frame 4, cathode gas layer 5, and cathode current collector 6 together form the cathode side gas/liquid mix system of the cell.
  • the anode current collector 1 , frame 4, and cathode current collector 6 may, for example, be made, for example, of stainless steel, titanium or other suitable metals.
  • This novel design combining the cell and membrane-based electrode provides a new concept and a solution to mix gases and liquids and deliver them to the surface of the catalyst.
  • This design compared with conventional membrane electrodes, may provide more 3-phase interface (solid-liquid-gas (catalysts-water-air)) in the reaction system to facilitate H2O2 generation efficiently and effectively, optionally even in pure water without adding any other chemical or electrolyte.
  • the gas pathway may deliver gas more efficiently without disturbing the liquid.
  • the liquid pathway does not block the gas pathway and effectively flushes the produced H2O2 out of the system.
  • the working temperature of the example cell was between 0 and 80 °C.
  • the membrane with catalyst is incorporated into the designed electrochemical cell with a specially designed cell frame 4 and cathode current collector 6.
  • Fig. 21 shows a diagram of a suitable example design for these components.
  • the cell frame 4 comprises an empty space 7 (shadow) for placing the 3D membrane and/or porous material and also allowing the liquid to flow.
  • the cathode current collector 6, comprises a gas disperser window 8 containing a porous material.
  • the size of the gas disperser window 8 may be, for example, from about 0.5 to about 2 cm, and preferably about 1 cm.
  • the distance between adjacent gas disperser windows 8 in the array shown in Fig. 21 may be from about 0.1 to about 1 cm, and preferably about 0.5 cm.
  • Fig. 22 shows the electrical performance of an example catalyst according to the invention in the example electrochemical cell electrolyser.
  • a 100 cm 2 cell was able to produce a 0.45 wt.% neutral H2O2 solution.
  • a catalyst comprising a carbon support, a doped metal and an epoxy group.
  • the catalyst for preparing hydrogen peroxide comprising an Co/N co-doped carbon nanotube and an epoxy group as the predominant oxygen functional species.
  • the catalyst for preparing hydrogen peroxide comprising an Co/N co-doped vertical graphene and an epoxy group as the predominant oxygen functional species.
  • a method of preparing a catalyst for preparing hydrogen peroxide comprising an Co/N co-doped carbon nanotube and an epoxy group as the sole oxygen functional species comprising the steps of:
  • a method of preparing a catalyst for preparing hydrogen peroxide comprising an Co/N co-doped vertical graphene and an epoxy group as the sole oxygen functional species comprising the steps of : (i) oxidising a Co/N co-doped vertical graphene to produce an oxidised Co/N co-doped vertical graphene comprising at least epoxy and ketonic species
  • An electrolyser for producing hydrogen peroxide from oxygen and water comprising a cathode which comprises a catalyst layer comprising a catalyst according to any one of embodiments 1 to 9 on an electrolyte facing side and a hydrophobic gas permeable layer on an oxygen input side.
  • An electrolyser according to embodiment 18 wherein the hydrophobic gas permeable layer on an oxygen input side is formed from a polytetrafluoroethylene permeable material, such as a polytetrafluoroethylene coating layer or membrane or an aggregate of polytetrafluoroethylene nanoparticles.
  • a method of synthesising hydrogen peroxide comprising providing oxygen in an acidic or neutral aqueous media to an electrolyser according to any one of embodiments 18 to 22 under reducing conditions.
  • a method of synthesising Fenton’s reagent comprising providing a source of Fe 2+ and oxygen in an acidic or neutral aqueous media to an electrolyser according to any one of embodiments 18 to 22 under reducing conditions.

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Abstract

L'invention concerne des catalyseurs comprenant un substrat carboné conducteur dopé avec de l'azote et un métal de transition, le substrat carboné comprenant un groupe époxy. L'invention concerne également des procédés et des électrolyseurs pour la production de peroxyde d'hydrogène à l'aide du catalyseur, et des membranes comprenant le catalyseur.
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Publication number Priority date Publication date Assignee Title
CN114717597A (zh) * 2022-03-27 2022-07-08 苏州大学 一种分子笼包覆金属核壳材料及其制备方法与应用
CN114717597B (zh) * 2022-03-27 2024-05-03 苏州大学 一种分子笼包覆金属核壳材料及其制备方法与应用
CN114849760A (zh) * 2022-06-08 2022-08-05 四川轻化工大学 一种催化剂及其制备方法和应用
CN114849760B (zh) * 2022-06-08 2023-10-17 四川轻化工大学 一种催化剂及其制备方法和应用
CN116190594A (zh) * 2022-12-19 2023-05-30 湖州启源金灿新能源科技有限公司 一种锂离子电池负极用Co催化原位生长CNT的Si/C复合材料的制备方法
CN116190594B (zh) * 2022-12-19 2024-03-22 湖州启源金灿新能源科技有限公司 一种锂离子电池负极用Co催化原位生长CNT的Si/C复合材料的制备方法
CN116371446A (zh) * 2023-04-19 2023-07-04 中国科学院生态环境研究中心 铁氮化合物-碳纳米管复合材料、制备方法及应用

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