EP4281600A1 - Ensemble catalyseur d'électrode à réaction de dégagement d'oxygène, son utilisation et procédé de production dudit ensemble - Google Patents

Ensemble catalyseur d'électrode à réaction de dégagement d'oxygène, son utilisation et procédé de production dudit ensemble

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Publication number
EP4281600A1
EP4281600A1 EP22700920.6A EP22700920A EP4281600A1 EP 4281600 A1 EP4281600 A1 EP 4281600A1 EP 22700920 A EP22700920 A EP 22700920A EP 4281600 A1 EP4281600 A1 EP 4281600A1
Authority
EP
European Patent Office
Prior art keywords
oxygen evolution
evolution reaction
electrode catalyst
catalyst
reaction electrode
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP22700920.6A
Other languages
German (de)
English (en)
Inventor
Adèle PEUGEOT
Marc Fontecave
Charles CREISSEN
Moritz Wilhelm SCHREIBER
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
College de France
TotalEnergies Onetech SAS
Original Assignee
College de France
TotalEnergies Onetech SAS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by College de France, TotalEnergies Onetech SAS filed Critical College de France
Publication of EP4281600A1 publication Critical patent/EP4281600A1/fr
Pending legal-status Critical Current

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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
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/02—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form
    • C25B11/03—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form perforated or foraminous
    • C25B11/031—Porous electrodes
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
    • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
    • C25B11/052—Electrodes comprising one or more electrocatalytic coatings on a substrate
    • 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
    • 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
    • C25B11/061—Metal or alloy
    • 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
    • C25B11/077—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound the compound being a non-noble metal oxide
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
    • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
    • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
    • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D3/00—Electroplating: Baths therefor
    • C25D3/02—Electroplating: Baths therefor from solutions
    • C25D3/12—Electroplating: Baths therefor from solutions of nickel or cobalt
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/60—Electroplating characterised by the structure or texture of the layers
    • C25D5/605—Surface topography of the layers, e.g. rough, dendritic or nodular layers

Definitions

  • the present disclosure relates to an electrode catalyst assembly suitable for catalyzing the oxygen evolution reaction, a method for producing such electrode catalyst assembly and use of such an electrode catalyst assembly in the oxygen evolution reaction.
  • the oxygen evolution reaction is one of the most relevant anodic reactions within electrochemical cells, where it is coupled to the hydrogen evolution reaction (HER) or the CO 2 reduction reaction (CO 2 RR) to energy-dense carbon compounds at the cathode. It is thus of high relevance for electrochemical energy conversion and storage technologies. Oxygen generation from water oxidation at the anode is typically carried out in acidic or alkaline conditions. Operation in alkaline conditions allows the use of cheap, efficient and stable non-precious-metal catalysts, in contrast to acidic conditions, in which only expensive and scarce noble metal-based catalysts such as lrO 2 and RuO 2 exhibit significant stability.
  • OER catalysts comprising earth-abundant elements
  • identifying efficient, cheap and stable OER catalysts comprising earth-abundant elements is of fundamental importance and has been a prominent field of research during the last 20 years.
  • OER catalysts reported so far, mixed nickel/iron/cobalt oxides, in particular, have shown stable low overpotentials at relevant geometric current densities.
  • nickel foam (NF) support is an efficient current collector and good support for active material deposition, due to its conductivity, mechanical strengths, relative inertness at alkaline pH and low cost.
  • Nickel foam shows extended geometric surface areas and fine three-dimensional structures which make it attractive as a support for heterogeneous catalyst (see the study of Chaudhari N. K., et al., entitled “Nanostructured material on 3D nickel foam as electrocatalysts for water splitting”, Nanoscale, 2017, 9, 12231-12247).
  • the porous nature of the nickel foam with nickel dendrites offers a large number of interconnected pores which permit the penetration and the percolation of electrolyte species into the inner region of hollow dendrites, facilitating the redox reaction of urea. Moreover, more active sites are offered for urea adsorption.
  • the oxygen evolution reaction electrode catalyst assembly wherein a catalyst comprising one or more iron oxides is deposited on a support comprising nickel foam that shows a high electrochemically surface area (ECSA); for example, on a support comprising nickel foam that shows a dendrite morphology.
  • ECSA electrochemically surface area
  • the present disclosure provides an oxygen evolution reaction electrode catalyst assembly (i.e. OER electrode catalyst assembly) comprising a multi-metallic catalyst and a support, with the catalyst being deposited on the support, the catalyst comprising one or more iron oxides, the oxygen evolution reaction electrode catalyst assembly is remarkable in that it has a double layer capacitance of at least 6.0 mF as determined by cyclic voltammetry in the range between +0.95 V and +1.05 V versus RHE (reversible hydrogen electrode), and in that the support comprises dendritic nickel foam comprising nickel dendrites. It has been found that the combination of a support being a nickel foam that shows a high ECSA, (i.e...
  • a support being or comprising a dendritic nickel foam) with one or more iron oxides shows an improved double-layer capacitance by comparison to the regular supports. It has also been found that such improved double-layer capacitance allows a reduction of the overpotential values during an oxygen evolution reaction.
  • the nickel foam that shows a high ECSA is or comprises dendritic nickel foam with nickel dendrites that are devoid of dopants.
  • the dendritic nickel foam is a nickel foam that shows a dendrite morphology evidenced by scanning electron microscopy with dendrites.
  • the presence of the dendritic morphology on the nickel foam is reflected by an improved doublelayer capacitance of at least 2.0 mF of the support; preferably at least 4.0 mF.
  • a synergy is obtained between the support and the catalyst that leads to a substantial improvement in the performance of these OER electrode catalyst assembly.
  • the OER electrode catalyst assembly can show overpotential values below 260 mV when the oxygen evolution reaction is carried out at a current density of 100 mA cm -2 , at pH 14 and in 1 .0 M electrolyte solution; for example, below 255 mV; for example, at most 250 mV; for example, below 250 mV.
  • the OER electrode catalyst assembly can show overpotential values of at least 200 mV when the oxygen evolution reaction is carried out at a current density of 100 mA cm -2 , at pH 14 and in 1 .0 M electrolyte solution; for example, at least 210 mV or at least 220 mV.
  • the OER electrode catalyst assembly can show overpotential values below 210 mV when the oxygen evolution reaction is carried out at a current density of 10 mA cm -2 at pH 14 and in 1.0 M electrolyte solution; for example, below 205 mV; for example, at most 200 mV; for example, below 200 mV.
  • the OER electrode catalyst assembly can show overpotential values of at least 180 mV when the oxygen evolution reaction is carried out at a current density of 10 mA cm -2 at pH 14 and in 1.0 M electrolyte solution; for example, at least 190 mV or at least 195 mV.
  • the oxygen evolution reaction electrode catalyst assembly has a double layer capacitance of at least 6.0 mF or at least 7.0 mF as determined by cyclic voltammetry in the range between +0.95 V and +1 .05 V versus RHE; for example, of at least 7.5 mF, or at least 8.0 mF, or at least 8.5 mF, or at least 9.0 mF or at least 9.3 mF, or at least 9.5 mF, or at least 9.8 mF, or at least 10.0 mF.
  • the oxygen evolution reaction electrode catalyst assembly has a double layer capacitance of at most 15.0 mF as determined by cyclic voltammetry in the range between +0.95 V and +1.05 V versus RHE; for example, at most 14.0 mF; or at most 13.0 mF; or at most 12.5 mF; or at most 12.0 mF.
  • the one or more iron oxides are or comprise MeFeOx with Me being one or more transition metals.
  • the one or more iron oxides are or comprise MeFeOx MeFeOx wherein Me is a transition metal selected from Co, Ni, V, Mo, and any mixture thereof; more preferably, the catalyst is MeFeOx MeFeOx wherein Me is a transition metal selected from Co, Ni, V, Mo, and any mixture thereof.
  • the atomic content of Me is equal to or greater than the atomic content of Fe; for example the Me: Fe ratio is at least 3.1 ; for example, the Me: Fe ratio is at least 4:1 .
  • the catalyst further comprises at least one transition metal selected from Co, Ni, Cu, V, Mo, and any mixture thereof.
  • the catalyst further comprises at least one transition metal selected from Co, Ni, V, Mo, and any mixture thereof ; for example, selected from Ni and/or Co.
  • the catalyst may be or comprise MeFeOx wherein Me is Ni and/or Co.
  • the catalyst is devoid of Cu.
  • the catalyst further comprises at least one transition metal selected from Ni and/or Co with the atomic content of Ni and/or Co being equal to or greater than the atomic content of Fe.
  • the catalyst or the one or more iron oxides are or comprise NiFe-OOH.
  • the catalyst or the one or more iron oxides are or comprise one or more iron selenidederived oxides; with preference, the one or more iron selenide-derived oxides are selected from NiFeSe-dO and/or CoFeSe-dO.
  • the one or more iron selenide-derived oxides are selected from NiFeSe-dO with a Ni: Fe ratio being about 4:1.
  • the one or more iron selenide-derived oxides are selected from CoFeSe-dO with a Co: Fe ratio being about 4:1.
  • the catalyst or the one or more iron oxides comprise one or more nickel-iron selenide-derived oxides and/or cobalt iron selenide-derived oxides wherein the atomic content of iron is lower than the atomic content of nickel and/or of cobalt respectively.
  • said catalyst is or comprises Nio8Feo 2 Se 2 -dO.
  • said catalyst is or comprise Coo 8Feo 2 Se 2 -dO.
  • said oxygen evolution reaction electrode catalyst assembly has a Tafel slope of at most 70 mV decade -1 as determined by chronopotentiometry measurements conducted in an aqueous 1 M solution of KOH, more preferably of at most 65 mV decade -1 , even more preferably of at most 64 mV decade -1 .
  • the metal content of the catalyst is at most 160 pmol as measured by inductively coupled plasma - mass spectroscopy (ICP-MS) on the catalyst with a 1 cm 2 geometric area; for example, at most 150 pmol; for example, at most 145 pmol; for example, at most 140 pmol.
  • the metal content of the catalyst is at least 20 pmol as measured by inductively coupled plasma - mass spectroscopy (ICP-MS) on the catalyst with a 1 cm 2 geometric area; for example, at least 30 pmol; for example, at least 40 pmol; for example, at least 50 pmol.
  • said catalyst has a metal molar activity of at least 60 mA cm -2 mmol -1 ; preferably at least 80 mA cm -2 mmol -1 , more preferably at least 100 mA cm -2 mmol -1 , even more preferably at least 500 mA cm -2 mmol -1 .
  • the mass loading of the catalyst over the support is ranging between 0.5 mg cm -2 and 40 mg cm -2 .
  • the mass loading is determined by weighing the material before and after catalyst deposition.
  • the nickel foam is porous with a pore size diameter ranging from 100 pm to 1000 pm as determined by scanning electron microscopy, for example, ranging from 200 to 900 pm; for example, ranging from 300 to 800 pm; for example, ranging from 350 to 700 pm; for example, ranging 400 pm to 600 pm.
  • the dendrite morphology can be evidenced by scanning electron microscopy or reflected by an improved electrochemically active surface area of the nickel foam, or reflected by an improved double-layer capacitance.
  • the support has a double-layer capacitance of at least 2.0 mF as determined by cyclic voltammetry in the range between +0.95 V and +1 .05 V versus RHE; for example, at least 2.5 mF; for example, at least 3.0 mF; for example, at least 3.5 mF; for example, at least 4.0 mF; for example, at least 4.5 mF.
  • the support has a double-layer capacitance of at most 8.0 mF as determined by cyclic voltammetry in the range between +0.95 V and +1.05 V versus RHE; for example, at most 7.0 mF; or at most 6.0 mF; or at most 5.5 mF; or at most 5.0 mF.
  • said dendritic nickel foam has an electrochemically active surface area of at least 70 cm 2 cm geo ' 2 , preferably at least 75 cm 2 cm geo ' 2 , more preferably at least 80 cm 2 cm geo ' 2 .
  • the nickel foam shows a dendrite morphology evidenced by scanning electron microscopy with nickel dendrites; wherein, the one or more of the following is true: the one or more dendrites are porous with a pore size diameter ranging between 0.5 pm and 40 pm as determined by scanning electron microscopy; for example, ranging from 1 to 30 pm; for example, ranging from 2 to 20 pm; for example, ranging from 3 to 10 pm; for example, ranging 4 pm to 8 pm; and/or the one or more dendrites are free of dopant; and/or the one or more dendrites are free of Fe.
  • the present disclosure provides an oxygen evolution reaction electrode catalyst assembly obtained by depositing an oxygen evolution reaction electrode catalyst comprising one or more iron oxides on a support being dendritic nickel foam that shows a dendrite morphology evidenced by scanning electron microscopy with nickel dendrites wherein the dendritic nickel foam is selected to have a double-layer capacitance of at least 4.0 mF as determined by cyclic voltammetry in the range between +0.95 V and +1 .05 V versus RHE.
  • said step of depositing comprises hydrothermal formation of layered double hydroxides of said one or more iron oxides, followed by selenisation and subsequent oxidation.
  • the dendritic nickel foam is obtained by electrodeposition of nickel on said nickel foam.
  • the present disclosure provides a method for producing the oxygen evolution reaction electrode catalyst assembly according to the first aspect, remarkable in that said method comprises a step (a) of providing a support being dendritic nickel foam that shows a dendrite morphology evidenced by scanning electron microscopy with nickel dendrites wherein the dendritic nickel foam is selected to have a double-layer capacitance of at least 4.0 mF as determined by cyclic voltammetry in the range between +0.95 V and +1.05 V versus RHE followed by a step (b) of depositing a catalyst comprising one or more iron oxides on said support.
  • step (b) comprises the hydrothermal formation of layered double hydroxides, followed by selenisation and subsequent oxidation.
  • step (a) comprises providing nickel foam followed by a step of electrodeposition of nickel on said nickel foam to obtain a dendritic nickel foam.
  • the method further comprises the step (c) of recovering the oxygen evolution reaction electrode catalyst assembly as defined in the first aspect.
  • the present disclosure provides the use of the oxygen evolution reaction electrode catalyst assembly as defined in the first or in the second aspect or as produced by the method according to the third aspect in an oxygen evolution reaction carried out under alkaline conditions.
  • the disclosure provides for a process for generating molecular oxygen by an oxygen evolution reaction, the process comprising a step of providing water and a step of water oxidation in presence of an oxygen evolution reaction electrode catalyst assembly; the process is remarkable in that the oxygen evolution reaction electrode catalyst assembly is according to the first or the second aspect or is an oxygen evolution reaction electrode catalyst assembly produced according to the third aspect.
  • said water oxidation is carried out at a current density ranging between 10 mA cnv 2 and 100 mA cm -2 , or between 50 mA cm -2 and 100 mA cm -2 .
  • said water oxidation is carried out at a pH ranging from 11.5 to 15; for example, from 12 to 14.
  • said water oxidation is carried out in presence of an electrolyte solution comprising one or more basic electrolytes.
  • the one or more basic electrolytes are or comprise at least one selected from KOH and NaOH.
  • the one or more basic electrolytes are or comprise KOH.
  • said water oxidation is carried out in presence of an electrolyte solution of a concentration ranging from 0.1 to 5.0 M; for example, from 0.8 to 4.5 M.
  • the water oxidation can be carried out under static condition or flux conditions.
  • the oxygen evolution reaction electrode catalyst assembly is selected to show overpotential values below 210 mV at a current density of 10 mA cm -2 at pH 14 and in 1.0 M electrolyte solution; and/or overpotential values below 260 mV at a current density of 100 mA cm -2 at pH 14 and in 1.0 M electrolyte solution. Description of the figures
  • FIG. 13 Flow electrochemical setup for the evaluation of catalysts’ stability.
  • the catalyst was loaded in a two-compartment cell, separated by a National® membrane.
  • a platinum mesh stacked with a platinum foil was used as the cathode.
  • 100 mL of 1 M KOH solution was recirculated from an electrolyte container in each compartment at a 9 mL min -1 flow rate.
  • a constant current density of 100 mA cm -2 was applied for 10 hours.
  • the gas produced in the anodic compartment was analysed by gas chromatography. An aliquot of anolyte was collected every hour. The aliquots collected were analysed in Inductively coupled plasma mass spectroscopy (ICP-MS).
  • ICP-MS Inductively coupled plasma mass spectroscopy
  • concentrations were determined by ICP-MS.
  • the bottom plot shows Ni, Co and Fe concentrations (in pg L -1 ) in the aqueous solution of 1 M KOH electrolyte flowing in the anode compartment during the stability test with NF (black) or Co y Fei. y Se2/NiNF (grey) used as the anode. Such concentrations were determined by ICP-MS.
  • HM metal content measured in catalysts with a 1 cm 2 geometric area.
  • the surface of the catalysts was removed from the NF support, dissolved in nitric acid and analysed in inductively coupled plasma - mass spectroscopy (ICP-MS).
  • ICP-MS inductively coupled plasma - mass spectroscopy
  • the surface layer could not be removed in the case of NiFe-OOH and CoV-O.
  • nw is the total number of metal atoms, regardless of their nature.
  • NiFeSe and NiFeSe- dO are used as a synonymous respectively for Ni x Fei. x Se2 and Ni x Fei. x Se2-dO, with x ranging between 0.1 and 1.
  • CoFeSe and CoFeSe-dO are used as a synonymous respectively for Co y Fei. y Se2 and Co y Fei. y Se2-dO, with y ranging between 0.1 and 1.
  • Pj stands for inorganic phosphate.
  • the present disclosure relates to an oxygen evolution reaction electrode catalyst assembly (i.e. OER electrode catalyst assembly), said OER electrode catalyst assembly comprising a multi-metallic catalyst and a support with the catalyst being deposited on the support, the catalyst comprising one or more iron oxides, the OER electrode catalyst assembly is remarkable in that the support comprises dendritic nickel foam.
  • OER electrode catalyst assembly i.e. OER electrode catalyst assembly
  • said OER electrode catalyst assembly comprising a multi-metallic catalyst and a support with the catalyst being deposited on the support, the catalyst comprising one or more iron oxides
  • the OER electrode catalyst assembly is remarkable in that the support comprises dendritic nickel foam.
  • oxygen evolution reaction electrode catalyst assembly of the present disclosure is comprising a multi-metallic catalyst and a support, with the catalyst being deposited on the support, the catalyst comprising one or more iron oxides, the electrode catalyst assembly is remarkable in that it has a double layer capacitance of at least 6.0 mF as determined by cyclic voltammetry in the range between +0.95 V and +1.05 V versus RHE and in that the support comprises dendritic nickel foam comprising nickel dendrites.
  • the one or more iron oxides are or comprise MeFeOx with Me being a transition metal.
  • the catalyst further comprises at least one transition metal selected from Co, Ni, Cu, V, Mo and any mixture thereof; preferably, selected from Co, Ni, Cu, V, Mo and any mixture thereof; more preferably selected from Ni and/or Co.
  • the catalyst may be or comprise MeFeOx wherein Me is a transition metal selected from Co, Ni, V, Mo, and any mixture thereof; preferably is Ni and/or Co.
  • the catalyst is devoid of Cu.
  • the catalyst or the one or more iron oxides are or comprise NiFe-OOH.
  • the OER electrode catalyst assembly shows an overpotential of 250 mV when the oxygen evolution reaction is carried out at a current density of 100 mA cm -2 at pH 14 and in 1.0 M electrolyte solution.
  • the catalyst or the one or more iron oxides are or comprise one or more iron selenide-derived oxides.
  • the one or more iron selenide-derived oxides are selected from NiFeSe-dO and/or CoFeSe-dO.
  • the one or more iron selenidederived oxides are selected from NiFeSe-dO with a Ni: Fe ratio being at least 4:1.
  • the one or more iron selenide-derived oxides are selected from CoFeSe-dO with a Co: Fe ratio being at least 4:1.
  • the catalyst or the one or more iron oxides comprise one or more nickel iron selenide-derived oxides and/or cobalt iron selenide-derived oxides wherein the atomic content of iron is lower than the atomic content of nickel and/or of cobalt respectively.
  • said catalyst is or comprise Nio.8Feo.2Se2--dO.
  • the OER electrode catalyst assembly shows an overpotential of 198 mV when the oxygen evolution reaction is carried out at a current density of 10 mA cm -2 at pH 14 and in 1.0 M electrolyte solution; and an overpotential of 247 mV when the oxygen evolution reaction is carried out at a current density of 100 mA cm -2 at pH 14 and in 1.0 M electrolyte solution.
  • said catalyst is or comprises Coo.8Feo.2Se2-dO.
  • the OER electrode catalyst assembly shows an overpotential of 195 mV when the oxygen evolution reaction is carried out at a current density of 10 mA cm -2 at pH 14 and in 1.0 M electrolyte solution; and an overpotential of 247 mV when the oxygen evolution reaction is carried out at a current density of 100 mA cm -2 at pH 14 and in 1.0 M electrolyte solution.
  • the substitution of selenium by oxygen allows more active sites to be exposed, in line with significantly higher densities of available active sites for the OER electrode catalyst assembly comprising selenium in comparison with OER electrode catalyst assembly devoid of selenium.
  • the presence of selenium atoms can be used as a piece of evidence related to the method of preparation of the OER electrode catalyst assembly wherein a selenisation step is performed.
  • the selenium is present in the catalyst at an atomic content of at most 4.0 % as determined by EDX (excitation voltage 15 kV); for example, at most 3.0 %; for example, at most 2.5 %; for example, at most 2.0 %.
  • the selenium is present in the catalyst at an atomic content ranging from 0.5 to 2.5% % as determined by EDX (excitation voltage 15 kV).
  • the OER electrode catalyst assembly of the present disclosure shows an increased structuration that leads to significant improvement of the tested catalysts.
  • the dendritic morphology of the nickel foam support allows having a greater electrochemically active surface area.
  • said support has a surface area of at least 70 cm 2 cm geo ' 2 , preferably at least 75 cm 2 cm geo ' 2 , more preferably at least 80 cm 2 cm geo ' 2 .
  • the dendritic morphology of the nickel foam is or comprises nickel dendrites and/or the dendritic morphology of the nickel foam is free of dopant.
  • the nickel dendrites are free of dopant, preferably, the nickel dendrites are free of Fe.
  • the nickel foam of said support is porous with a pore size ranging from 100 pm to 1000 pm as determined by scanning electron microscopy, for example, ranging from 200 to 900 pm; for example, ranging from 300 to 800 pm; for example, ranging from 350 to 700 pm; for example, ranging 400 pm to 600 pm.
  • the one or more dendrites of the nickel foam are also porous with a pore size ranging from 0.5 pm to 40 pm as determined by scanning electron microscopy, for example, ranging from 1 to 30 pm; for example, ranging from 2 to 20 pm; for example, ranging from 3 to 10 pm; for example, ranging 4 pm to 8 pm.
  • the porosity of the OER electrode catalyst assembly of the present disclosure advantageously further shows the presence of smaller pores resulting from the layered structure of the OER electrode catalyst assembly.
  • Such smaller pores have a size ranging between 30 nm and 100 nm as determined by scanning electron microscopy, preferably ranging between 35 nm and 95 nm, more preferably ranging between 40 nm and 90 nm.
  • said OER electrode catalyst assembly has a Tafel slope of at most 70 mV decade -1 as determined by chronopotentiometry measurements conducted in an aqueous 1 M solution of KOH, more preferably of at most 65 mV decade -1 , even more preferably of at most 64 mV decade -1 .
  • the lower the Tafel slope of an OER electrode catalyst assembly the slower the increase in the overpotential with an increasing current density. Also, a small value for the Tafel slope is expected when one deals with a highly active electrocatalyst.
  • said OER electrode catalyst assembly has a double layer capacitance of at least 6.0 mF or at least 7.0 mF as determined by cyclic voltammetry in the range between +0.95 V and +1 .05 V versus RHE, more preferably of at least 7.5 mF, even more preferably of at least 8.0 mF, most preferably of at least 8.5 mF, even most preferably of at least 9.0 mF or at least 9.3 mF, or at least 9.5 mF, or at least 9.8 mF, or at least 10.0 mF.
  • the OER electrode catalyst assembly has a double layer capacitance of at most 15.0 mF as determined by cyclic voltammetry in the range between +0.95 V and +1.05 V versus RHE; for example, at most 14.0 mF; or at most 13.0 mF; or at most 12.5 mF; or at most 12.0 mF.
  • said OER electrode catalyst assembly has a metal molar activity of at least 60 mA cm -2 mmol -1 , or at least 70 mA cm -2 mmol -1 , or at least 80 mA cm -2 mmol -1 , or at least 90 mA cm -2 mmol -1 , or at least 100 mA cm -2 mmol -1 or at least 250 mA cm -2 mmol -1 , or at least 500 mA cm -2 mmol -1 , or at least 510 mA cm -2 mmol -1 , or at least 515 mA cm -2 mmol -1 .
  • the metal content of the catalyst is at most 160 pmol as measured by inductively coupled plasma - mass spectroscopy (ICP-MS) on the catalyst with a 1 cm 2 geometric area; for example, at most 150 pmol; for example, at most 145 pmol; for example, at most 140 pmol.
  • the metal content of the catalyst is at least 20 pmol as measured by inductively coupled plasma - mass spectroscopy (ICP-MS) on the catalyst with a 1 cm 2 geometric area; for example, at least 30 pmol; for example, at least 40 pmol; for example, at least 50 pmol.
  • the method to produce the OER electrode catalyst assembly according to the disclosure comprises providing a support comprising dendritic nickel foam followed by the deposition of a catalyst comprising one or more iron oxides on said support.
  • providing a support comprising dendritic nickel foam comprises providing nickel foam followed by a step of electrodeposition of nickel on a nickel foam to form a support comprising dendritic nickel foam; with preference, the nickel foam is pretreated before performing the electrodeposition step and/or the electrodeposition step is performed using an aqueous solution of NiCh.
  • performing a pretreatment may help the formation of Ni seeds at the surface of NF, which then improves the electrodeposition step.
  • the pretreatment can comprise soaking the nickel foam in a solution of Nickel (II) chloride at a concentration ranging from 0.5 to 5.0 M.
  • the deposition of a catalyst on said support comprises the hydrothermal formation of layered double hydroxides; with preference, followed by selenisation and subsequent oxidation.
  • an oxygen evolution reaction electrode catalyst assembly obtained by depositing an oxygen evolution reaction electrode catalyst comprising one or more iron oxides on a support being nickel foam selected to have a double-layer capacitance of at least 4.0 mF as determined by cyclic voltammetry in the range between +0.95 V and +1.05 V versus RHE. More particularly, this allows for obtaining NiFeSe and CoFeSe -derived oxides.
  • the deposition of the catalyst on the support is performed during the hydrothermal step.
  • the support is introduced in the autoclave, and the catalyst (i.e. the active phase) grows directly on its surface. It is understood that the catalyst is an oxide, with a low content of selenium.
  • the catalyst is called “Se-derived oxides” as the selenide precursor has an important impact on the activity of the catalysts.
  • said hydrothermal formation is carried out at a temperature ranging between 100°C and 150°C, preferably between 110°C and 140°C.
  • said selenisation comprises providing selenium powder and at least one reducing agent, such as hydrazine.
  • said selenisation is carried out at a temperature of at least 150°C, preferably of at least 160°C, more preferably of at least
  • said subsequent oxidation is carried out electrochemically, advantageously at a current density of at least 3 mA cm -2 , preferably at least 4 mA cm -2 , more preferably at least 5 mA cm -2 .
  • said subsequent oxidation is carried out under alkaline conditions, for example at a pH ranging from 11.5 to 15, or from 12 to 14.
  • said subsequent oxidation is advantageously carried out in presence of an electrolyte solution comprising one or more basic electrolytes.
  • the one or more basic electrolytes are or comprise at least one selected from KOH and NaOH. More preferably, the one or more basic electrolytes are or comprise KOH.
  • said subsequent oxidation is carried out in presence of an electrolyte solution of a concentration ranging from 0.1 to 5.0 M; for example, from 0.8 to 4.5 M.
  • the selenium is present in the catalyst at an atomic content of at least 40 % as determined by EDX (excitation voltage 15 kV); for example, at least 45 %; for example, at least 50%; for example, at least 55%.
  • EDX excitation voltage 15 kV
  • the selenium is present in the catalyst at an atomic content of at most 4.0 % as determined by EDX (excitation voltage 15 kV); for example, at most 3.0 %; for example, at most 2.5 %; for example, at most 2.0 %.
  • EDX excitation voltage 15 kV
  • the OER electrode catalyst assembly was then used in an oxygen evolution reaction preferably carried out under alkaline conditions.
  • the disclosure provides for a process for generating molecular oxygen by an oxygen evolution reaction, the process comprising a step of providing water and a step of water oxidation in presence of an OER electrode catalyst assembly; the process is remarkable in that the OER electrode catalyst assembly is comprising a multi-metallic catalyst and a support with the catalyst being deposited on the support, the catalyst comprising one or more iron oxides, and the support comprises dendritic nickel foam.
  • the alkaline conditions of the oxygen evolution reaction comprise the use of a basic electrolyte, such as a solution of KOH.
  • concentration of KOH is ranging between 0.8 M and 1.2 M.
  • said oxygen evolution reaction is carried out at a current density ranging between 10 mA cm -2 and 100 mA cm -2 , or between 50 mA cm -2 and 100 mA cm -2 .
  • the current density of the said oxygen evolution reaction is at least 50 mA cm -2 .
  • said water oxidation is carried out at a pH ranging from 11.5 to 15; for example, from 12 to 14.
  • said water oxidation is carried out in presence of an electrolyte solution comprising one or more basic electrolytes.
  • the one or more basic electrolytes are or comprise at least one selected from KOH and NaOH.
  • the one or more basic electrolytes are or comprise KOH.
  • said water oxidation is carried out in presence of an electrolyte solution of a concentration ranging from 0.1 to 5.0 M; for example, from 0.8 to 4.5 M.
  • the water oxidation can be carried out under static condition or flux conditions.
  • the flux conditions comprise an electrolyte flow ranging between 5 ml min -1 and 15 ml min -1 , more preferably ranging between 7 ml min -1 and 13 ml min -1 .
  • SEM images were collected on a Sll-70 Hitachi FEGSEM. SEM measurements have been used for examining the catalyst surface morphologies. The powder sample is first dissolved in an aqueous nitric acid solution before the measurements.
  • Cyclic voltammetry measurements are used to determine the double-layer capacitance of the catalyst.
  • ICP-MS Inductively coupled plasma - mass spectroscopy
  • ICP-MS measurements were performed on an ICP-QMS 7900 Agilent apparatus. ICP-MS measurements allow evaluating the metal content. They were used to determine the metal content of the catalyst or the metal content in the electrolyte solution.
  • SEM images were collected on a Sll-70 Hitachi FEGSEM eguipped with an X-Max 50 mm 2 Oxford spectrometer for EDX measurements.
  • the combination of SEM-EDX allows for the determination of the elemental composition of the catalysts.
  • the powder sample is first dissolved in an agueous nitric acid solution before the measurements.
  • ICP-OES Inductively coupled plasma - optical emission spectrometry
  • ICP-OES measurements were performed on a Thermo Scientific iCAP 6300 duo device. ICP- OES measurements allow determining the elemental composition of the catalysts. The powder sample is first dissolved in an agueous nitric acid solution before the measurements.
  • Electrochemical characterization A two-compartment cell separated by a glass frit was used for electrochemical measurements.
  • the electrolyte was an aqueous solution of 1 M KOH.
  • the working electrode was positioned in the cell to minimize the distance to the reference electrode (» 1 mm), thus avoiding a large contribution from the cell in the ohmic drop (the resistance was always between 0.1 and 0.25 Q).
  • ENemst EH 2 O/O2 - 0.059 log pH + 0.015 log po 2 -
  • the thermodynamic potential is given by the following equation:
  • E N emst EH 2 O/O 2 - 0.059log pH.
  • Step 1 Consecutive linear sweep voltammetry (LSV) scans were performed at a scan rate of 10 mV s -1 until the response was stable.
  • Step 2 To study the oxygen evolution reaction kinetics, it is important to avoid any transient oxidation process such as the oxidation of Ni(OH)2 to NiOOH.
  • the (/, E ; ) data points were collected.
  • Step 3 The short-term stability of the different samples in each electrolyte was tested by running electrolysis at a fixed current density j of 50 mA cm -2 for 30 minutes under stirring. The pH of the electrolyte in the anode compartment did not change during electrolysis.
  • Electrochemically active surface area evaluation The double-layer capacitance CDL values were determined electrochemically in an aqueous solution of 1 M KOH. All measurements were conducted in the voltage range +0.95 - +1.05 V vs RHE as it is a non-Faradaic region for most of the studied samples as well as for the NF support. An exception was made for Cu-O, which shows a Faradaic process in this region and therefore the double layer capacitance was measured in the range +0.66 - +0.76 V vs RHE for this sample. The difference between the anodic and cathodic charging currents A was obtained from CV scans at different scan rates (from 20 to 600 mV s“ 1 ).
  • Stability test in flow conditions Stability measurements was performed in a two-electrode electrochemical flow cell FLC-Standard purchased from Sphere Energy ( Figure 13). The potential was measured using a leak-free Ag/AgCI/KCl3.4M micro reference (Innovative Instruments Ltd.). The gas produced in the anodic compartment was analysed by gas chromatography every 30 minutes using an SRI 8610C gas chromatograph equipped with a packed Molecular Sieve 5 A column for permanent separation. Argon (Linde 5.0) was used as the carrier gas; the flow rate was regulated using a mass flow controller (Bronkhorst). A thermal conductivity detector (TCD) was used to quantify O2.
  • the Faradaic efficiency was calculated by dividing the measured amount of oxygen by the theoretical amount of O2 expected.
  • 0o2, measured and 0o2, expected are the measured and expected amounts of O2, Q the charge passed and Fthe Faraday constant.
  • An aliquot of anolyte was collected every hour. The aliquots collected were analysed via inductively coupled plasma - mass spectrometry (ICP-MS).
  • NF was used as support for the comparative catalyst assemblies. 1 cm 2 square foams were cut, and an additional section was left for electrical contact. This area was partially covered with epoxy glue to delimit the 1 cm 2 area as precisely as possible. These foams were pretreated by soaking in a 3 M HCI solution for 10 minutes, to remove the nickel oxide layer formed at the surface when in contact with air. Then the substrates were sonicated for 5 minutes in ethanol, 5 minutes in water and dried with compressed air before use.
  • the NF support benefits from a relatively high ECSA of approximately 15 cm 2 cm ge o -2 (per geometric square centimetre) estimated using CDL measurement for NF and Cs measurement using a Ni plate electrode ( Figure 1).
  • the dendritic Ni foam support was synthesized as follows. First, a pre-treated Ni foam was soaked in a 0.1 M NiCI 2 6H2O aqueous solution for4 hours. An aqueous solution of NiCI 2 6H2O (0.1 M) and NH4CI (2 M) was prepared and used for electrodeposition. The electrodeposition was performed in a three-necked round-bottomed flask (50 mL solution) using a three- electrode arrangement with a Pt mesh counter electrode and an Ag/AgCI/KCI sa t reference electrode. A constant current of -2.0 A cm -2 was applied for 100 s at the working electrode. The gas produced during deposition was delivered into a gas trap. After deposition, the sample was rinsed thoroughly with water and dried in air.
  • Example 2- Synthesis of PER electrode catalyst assemblies comprising iron-oxide catalyst deposited of a support comprising nickel foam or dendritic nickel foam
  • Catalyst #1 - Cu-O Cu dendrites were deposited from a 0.1 M CUSP4 5H2P and 1.5 M H2SP4 agueous solution (50 mL), according to a procedure of Angew. Chem. Int. Ed., 2017, 56, 4792- 4796. Electrodeposition was performed in a three-necked round-bottomed flask in a three- electrode arrangement using a Pt mesh counter electrode and an Ag/AgCI/KCI sa t reference electrode (BioLogic). A constant current of -3.0 A was applied to the working electrode for 80 seconds under stirring (» 200 rpm). A dark red layer formed during deposition.
  • the sample was rinsed with water and ethanol and dried in the air before annealing in the air (300 °C, 30 minutes, 10 °C min -1 ramp rate).
  • Copper oxide nanoparticles were electrodeposited on the surface from a 0.2 mM Cu(imidazole)2Cl2 solution prepared by dissolving the complex in MeCN: H2O with a 1 :0.03 volume ratio, containing a 0.103 M TBABF4 supporting electrolyte.
  • Electrodeposition was performed in a three-necked round-bottomed flask with 40 mL solution in a three-electrode arrangement using a Ag/AgCI/KCI sa t reference electrode and a platinum wire as the counter electrode.
  • Catalyst #2 - CoPi The procedure was adapted from the Energy Environ. Sci., 2011 , 4, 499- 504. A 0.1 M agueous methylphosphonic acid (MePi) solution was prepared and adjusted to pH 8.5 with KOH. This solution was used due to the higher solubility of the cobalt salt in MePi. CO(NO3)2'6H2O (10 mM total concentration) was added to form the deposition solution.
  • MePi agueous methylphosphonic acid
  • Electrochemical deposition was performed from 100 mL of this solution in a three-necked round-bottomed flask using a three-electrode arrangement with a Pt mesh counter electrode and an Ag/AgCI/KCI sa t reference electrode (BioLogic) under rapid stirring (» 300 rpm). A potential of 1.1 V vs Ag/AgCI was applied to the working electrode for 6 hours. A thick black deposit was obtained. We observed that the film cracked and became very fragile and brittle upon drying. Conseguently, all the electrochemical characterizations were performed directly after synthesis. The sample was rinsed with distilled water, but never dried. The mass loading measured after characterization and subsequent air drying was 35 mg cm -2 .
  • Catalyst #3 - NiMoFe-O Synthesis was adapted from Int. J. Electrochem. Sci., 2008, 3, 908-917 and J. Am. Chem. Soc., 2015, 137, 4347-4357. Ni foams were pre-treated following the method described above.
  • NiSC>4-6H2O (1.157 mmol, 0.304 g)
  • NiCl2'6H2O (1.350 mmol, 0.321 g)
  • Na 2 MoO4-2H 2 O (0.207 mmol, 0.050 g)
  • FeSO 4 '7H 2 O (0.180 mmol, 0.05 g)
  • K3C6H5O7 H2O (0.925 mmol, 0.300 g) and (N ⁇ COs (4.163 mmol, 0.400 g) was prepared in 50 mL H2O, pH 7.
  • Electrochemical deposition was performed from 50 mL of this solution in a three-necked round-bottomed flask using a three-electrode arrangement with a Pt mesh counter electrode and an Ag/AgCI/KCI sa t reference electrode (BioLogic) under rapid stirring (» 200 rpm). A constant current of -861 mA was maintained for 10 minutes to form a dark grey deposit. The sample was rinsed with water and dried in air. The mass loading was 18 mg cm -2 .
  • Catalyst #4 - NiFe-OOH The procedure was reproduced from Energy Environ. Sci., 2018, 77, 2858-2864. FeCl3'6H2O (0.814 mmol) was dissolved in 60 mL of absolute ethanol and sonicated for 5 minutes to form a yellow solution. A second solution was prepared by adding FeCls.6H2O (0.814 mmol) and NH4HCO3 (4.46 mmol) in 60 mL of absolute ethanol. The pretreated NF substrate was immersed in the FeCh-EtOH solution overnight. After this step, the substratewas immersed inthe second solutionfor6 hours understirring. The film was rinsed with H2O and dried in air. The etched mass was -14 mg cm -2 . This negative loading is due to a galvanic replacement reaction occurring between Ni° at the surface of the substrate and Fe 3+ ions in solution.
  • Table 1 Atomic composition of NiFeOOH obtained using EDX (excitation voltage 15 kV) with comparison to the reported values on Ni foam of the reference work.
  • Step 1 Synthesis of NiFe-LDH An aqueous solution containing Ni(NOs)2-6H2O (0.91 mmol), FeSC>4-7H2O (0.23 mmol), NH4F (4.55 mmol) and CH4N2O (11.36 mmol) was prepared. 18.2 mL of this solution was added to a 23 mL Teflon-lined autoclave reactor and a piece of pretreated Ni foam was added. The autoclave was heated to 120°C for 16 hours to form a light green deposit on the nickel foam. The sample was rinsed with EtOH and H2O and dried in air.
  • Step 2 Synthesis of NiFeSe: Se powder (1.70 mmol), NaOH (3.4 mmol) and N2H4 (0.7 mmol, 36.6 L) were dissolved in DMF (11.3 mL). The previously obtained NiFe-LDH sample was added to a 23 mL Teflon-lined autoclave and the solution was added. The autoclave was heated to 180°C for 1 hour to obtain a black deposit of NiFeSe, which was rinsed with water and dried in air.
  • Step 3 Synthesis of NiFeSe-dO: NiFeSe was activated electrochemically in 1 M KOH, by applying a constant current of 5 mA cm -2 for 2 hours, until a stable potential was observed. This led to the formation of the selenide-derived oxide NiFeSe-dO. The mass loading was 6 mg cm -2 .
  • Table 2 Atomic composition of NiFeSe-dO obtained using EDX (excitation voltage 15 kV), before and after activation with comparison to the reported values on Ni foam of the reference work
  • NiFeSe-dO is Nio.8Feo.2Se2-dO
  • NiFeSe-dO has a metal content of 133 pmol as measured by inductively coupled plasma - mass spectroscopy (ICP-MS) on the OER electrode catalyst assembly with a 1 cm 2 geometric area
  • Step 1 Synthesis of CoFe-LDH An aqueous solution containing Co(NC>3)2-6H 2 O (0.900 mmol), FeSO 4 -7H 2 O (0.227 mmol), NH4F (4.45 mmol) and CH 4 N 2 O (11.16 mmol) was prepared. 18.2 mL of this solution was added to a 23 mL Teflon-lined autoclave reactor and a piece of pre-treated Ni foam was added. The autoclave was closed and heated to 120°C for 16 hours to form a red deposit on the nickel foam. The sample was rinsed with EtOH and H 2 O and dried in air.
  • Step 3 Synthesis of CoFeSe-dO: CoFeSe was activated electrochemically in 1 M KOH, by applying a constant current of 5 mA cm -2 for 2 hours, until a stable potential was observed. This led to the formation of the selenide-derived oxide CoFeSe-dO. The mass loading was 7 mg cm -2 .
  • Table 3 Atomic composition of CoFeSe-dO obtained using EDX (excitation voltage 15 kV), before and after activation with comparison to the reported values on Ni foam of the reference work.
  • Catalyst #7 - FeCoW This material was synthesized according to Science, 2016, 352, 333- 337.
  • FeCh 146.0 mg, 0.9 mmol
  • CoCI 2 116.9 mg, 0.9 mmol
  • WCh 356.9 mg, 0.9 mmol
  • solution B consisted of 2 mL of ethanol and 0.18 mL of water, which was cooled in an ice bath for 2 hours.
  • Solution B was added to solution A, and 1 mL of propylene oxide was slowly added to this mixture. After a few minutes, a dark green gel was formed.
  • This gel was aged for 3 days in ambient conditions and became dark red/brown.
  • the gel was immersed in ethanol and agitated to form a colloidal suspension.
  • This suspension was washed three times with ethanol. 5 mL of the suspension in ethanol were kept and mixed with 250 L of 5 wt.% aqueous National® solution. The solution was sonicated for at least 30 minutes and a homogeneous dispersion was obtained.
  • the ink was drop-cast onto the pre-treated nickel foam (40 mg cm -2 ) and dried in air. Note that we also performed CO2 supercritical drying on another batch but the activity of the catalyst was lower than with the undried colloidal material.
  • Catalyst #8 - CoV-OOH The synthesis was adapted from Energy Environ. Sc/., 2018, 11, 1736-1741.
  • COCI2.6H2O (0.5 mmol) was added to 50 mL H2O under stirring.
  • the flask was heated to 30°C in a water bath.
  • a solution of NaOH (1 mmol) and NH4VO3 (0.17 mmol) in 20 mL of deionized water was prepared and added dropwise to the C0CI2 solution.
  • the solution was maintained at 30°C under stirring for a further 15 min to obtain a green-brown precipitate.
  • the precipitate was washed three times with water and two times with ethanol with centrifugation and disposal of the supernatant between washing steps.
  • the sample was dispersed in 5 mL of ethanol and an ink was prepared by mixing this nanoparticles suspension with 250 L of 5 wt.% aqueous National® solution. The solution was sonicated for at least 30 minutes to obtain a homogeneous dispersion. The ink was drop-cast onto the pre-treated nickel foam (25 mg cm -2 ) and dried in air.
  • Catalyst #9 - CoV-O The synthesis was adapted from a reported procedure described in ACS Catal., 2018, 8, 644-650. C0CI2 (70.11 mg, 0.54 mmol), VCI 3 (28.31 mg, 0.18 mmol), urea (68.11 mg, 1.13 mmol) and trisodium citrate TSC (37,2 mg, 0.14 mmol) were added to 18 mL H2O. As the precursors are air and light-sensitive, the solution was kept in the dark and degassed with Ar for 30 minutes. The solution (18 mL) was transferred into a Teflon-lined autoclave (23 mL capacity) and a piece of the pre-treated Ni foam was added. The autoclave was heated to 150 °C for 14 hours to obtain a very thin deposit. The mass loading was 0.5 mg cm -2 .
  • NiMoFe-0 shows a particularly strong adhesion to the substrate because the presence of nickel in the as-deposited catalyst ensures a continuous interface with NF and thus a small lattice mismatch.
  • EDX was used to confirm the elemental composition. With regards to NiMoFe-O, the use of NF as the support led to small modifications in the chemical composition of the film.
  • CoPi (catalyst #2) was anodically electrodeposited, which resulted in the slow formation of large dendrites with poor adhesion to the NF support (see figure 3D).
  • FeCoW (catalyst #7) (see figure 3E) and CoV-OOH (catalyst #8) (see figure 3F) were synthesized from nanomaterial dispersions mixed with a National ink and drop-cast and dried onto the surface of the support to form thick layers, which remained well attached to the support despite large cracks.
  • the major limitation of this method is the hydrophobicity of dry National which promotes the formation of an air film trapped at the catalyst/electrolyte interface and limits their contact area.
  • NiFe-OOH (catalyst #4) (see figure 3G) was made through the galvanic exchange of the Ni-based substrate with Fe 3+ precursor, followed by the deposition of a bimetallic oxyhydroxide.
  • the support is the only source of nickel, it is etched during the reaction. This ensures a very high adhesion of the catalyst on the support, but also slightly modifies the material by etching its Ni backbone. Nevertheless, this method is particularly interesting as it is very simple.
  • NiFeSe and CoFeSe -derived oxides were synthesized by a more complex three-step procedure involving hydrothermal formation of layered double hydroxides (LDHs), followed by selenisation and subsequent reoxidation.
  • LDHs layered double hydroxides
  • CoV-0 (catalyst #9) was synthesized by a simple one-step hydrothermal procedure involving the coprecipitation of Co and V in a mixed-phase composed of a fine LDH nanostructure (see figure 3J). This method is simple but results in a very low loading on nickel foam.
  • NiNF-catalyst assemblies For NiNF-catalyst assemblies, the above procedure was repeated but the support was changed to be NiNF for all catalyst assemblies.
  • a possible drawback resides in some additional ohmic drop associated with the accumulation of oxygen bubbles at the surface of the electrode, as described in the study of Angulo A., et al., entitled “Influence of bubbles on the energy conversion efficiency of electrochemical reactors” (Joule, 2020, 4, 555-579).
  • NiNF as a support obtains overpotentials in 1 M KOH at 100 mA cm -2 that are below 260 mV for 3 catalyst assemblies, namely CoFeSe-dO/NiNF, NiFeSe-dO/NiNF and NiFe-OOH/NiNF, while this was not achieved with the comparative support NF.
  • the 3 catalyst assemblies have an overpotential in 1 M KOH at 100 mA cm -2 of at most 250 mV, and for CoFeSe-dO/NiNF and NiFeSe- dO/NiNF is below 250 mV.
  • NiNF as support allows obtaining overpotentials in 1 M KOH at 10 mA cm -2 that is at most 230 mV for 4 catalyst assemblies, namely CoFeSe-dO/NiNF, NiFeSe- dO/NiNF, FeCoW/NiNF and NiFe-OOH/NiNF while this was achieved only for the selenide-derived oxides containing catalyst assemblies with the comparative support NF.
  • the use of NiNF as support in the selenide-derived oxides catalyst assemblies allows achieving an overpotential in 1 M KOH at 10 mA cm -2 of below 200 mV.
  • the /710 obtained for CoFeSe-dO and NiFeSe-dO are among the lowest value reported in the literature so far.
  • the decrease was from 55 to 54 mV decade -1 in the case of NiFeSe-dO, and from 72 to 63 mV decade -1 in the case of CoFeSe-dO.
  • the gain of 20 to 30 mV decade -1 in most cases is significant as it induces a large decrease in the overpotential at high current densities.
  • NiFe-OOH displays a remarkably low Tafel slope of 20 mV decade -1 when deposited on NiNF.
  • catalysts with different morphologies in terms of their intrinsic activities requires determination of the density of electrochemically active sites, a very important yet challenging analysis. Depending on parameters such as their nanostructure, porosity and lattice structure, catalysts can show very different interactions with the surrounding electrolyte.
  • the density of electrochemically active and accessible sites can vary a lot from one catalyst to another. A range of techniques can be used to relate the total OER activity of a catalyst to the intrinsic activity of each active site.
  • the density of accessible active sites can be obtained through the determination of the electrochemically active surface area (ECSA) by means of the double-layer capacitance determination.
  • ECSA electrochemically active surface area
  • OER catalysts behave as capacitors: upon application of a potential, a charge build-up is observed at the catalyst-electrolyte interface.
  • the capacitance of a catalyst in the absence of any Faradaic process is the double layer capacitance CDL.
  • CDL was measured by cyclic voltammetry in the range from +0.95 to +1.05 V vs RHE, which is a non-faradaic and conductive region for all the catalysts (except Cu-0 which was characterized between +0.66 and +0.76 V vs RHE).
  • CDL values for the nine OER catalysts and the NF support are reported, measured in 1 M KOH using electrodes with 1 cm 2 geometric areas (see figure 10). Large differences were indeed observed: some of the studied catalysts have CDL values in the range of 1 mF, slightly larger than that of the Ni foam (0.9 mF), while CoFeSe-dO, NiMoFe- O and NiFeSe-dO have much larger CDL values of 3.65, 2.40 and 2.35 mF, respectively. These results are in line with the observation of extremely fine nanostructures for these three catalysts (see respectively figure 31, 3H and 3C).
  • NiFeSe-dO on NiNF was a factor of four greater than on the NF, reaching a high CDL value of 9.6 mF ( Figure 2A).
  • the CDL value for CoFeSe-dO was roughly three times higher, giving an extremely large CDL value of 10.3 mF ( Figure 2B). Therefore, the use of NiNF support enables a significant increase in the density of accessible active sites.
  • NiNF-deposited catalysts were evaluated using our standard electrochemical characterisation procedure detailed above.
  • the impact of the NiNF support on the catalytic activity of NiFeSe-dO and CoFeSe-dO is shown in figure 11 and 12 respectively.
  • the j-q profiles of figures 11 and 12 are obtained by recording chrono-potentiometric steps in 1 M KOH, under stirring at room temperature, using an 85% iR-correction. For both catalysts, the /710 and /7100 values decreased upon substitution of NF with NiNF.
  • NiFeSe-dO/NiNF and CoFeSe-dO/NiNF perform oxygen evolution at potentials as low as 1.58 ⁇ 0.02 V vs RHE, with outstanding stability, which represents a major improvement as compared to NF.
  • the faradaic efficiency for O2 production (FEo 2 ) was evaluated by measuring the amount of oxygen produced at the anode. During the first hour of the experiment, the headspace of the anolyte container was saturated in gas.
  • FEo 2 was very stable, with mean values of 98.0 ⁇ 1.5 %, 97.8 ⁇ 3.0 % and 98.5 ⁇ 1.9 % for NF, NiFeSe-dO/NiNF and CoFeSe-dO/NiNF respectively. This confirms that oxygen evolution was the only process occurring at the surface of these catalysts.
  • Ni, Co and Fe in the anolyte were measured every hour by ICP-MS (figures 14 and 15, bottom plot).
  • the Ni concentration is in the range 40-120 ppb. This concentration does not increase over time, which proves the very high stability of this support in 1 M KOH under a high current density.
  • the concentration of Fe is comprised between 250 and 450 ppb and is stable over time. This Fe content in a KOH electrolyte is common (see for example the study of Spanos I. et al., entitled “Facile protocol for alkaline electrolyte purification and its influence on a Ni-Co oxide catalyst for the oxygen evolution reaction”, ACS Catal., 2019, 9, 8165-8170).
  • NiFeSe-dO/NiNF a small increase in the Ni concentration was observed at the beginning of the experiment, as it reaches 300 ppb. After this small increase, the concentration slowly stabilises at around 100 ppb, which corresponds to the background concentration measured in the case of NF. No additional Ni was dissolved over the course of the reaction. As a result, NiFeSe-dO/NiNF is an extremely stable catalyst in these conditions. As expected, no Co was detected for NF or NiFeSe-dO /NiNF. In the case of CoFeSe-dO/NiNF, Ni and Co concentrations in the range 200-700 ppb were measured.
  • the evaluation of the total number of moles of metal atoms (DM) in a catalyst on a 1 cm 2 geometric area electrode can provide access to another useful information, namely the mass activity or molar activity.
  • a high molar activity effectively translates into a lower cost, as a lower number of metal atoms are required to perform OER catalysis at a given overpotential.
  • Ni x Fei- x Se2 and Co y Fei. y Se2 have the lowest metal content whereas FeCoW has the highest.
  • Ni x Fei. x Se2 and Co y Fei. y Se2 display the largest current densities but they do it with the lowest amount of metals, therefore they show extremely high metal molar activities (520 and 634 mA cm -2 mmol -1 , respectively). In contrast, all other catalysts have much lower molar activities, in the 20-50 mA cm -2 mmol -1 range.
  • FeCoW while the number of metals is high, only a small fraction is involved in the OER. Consequently, an improved exposition of the metal sites to the electrolyte might be key in the enhancement of OER activity of this catalyst.

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Abstract

La divulgation concerne un ensemble catalyseur d'électrode OER comprenant un catalyseur multi-métallique et un support, le catalyseur étant déposé sur le support, le catalyseur comprenant un ou plusieurs oxydes de fer, l'ensemble catalyseur étant exceptionnel en ce que le support comprend une mousse de nickel dendritique. La divulgation concerne également un procédé de production d'un tel ensemble catalyseur et un processus de génération d'oxygène moléculaire par une réaction de dégagement d'oxygène à l'aide d'un tel ensemble catalyseur.
EP22700920.6A 2021-01-19 2022-01-11 Ensemble catalyseur d'électrode à réaction de dégagement d'oxygène, son utilisation et procédé de production dudit ensemble Pending EP4281600A1 (fr)

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