WO2022064414A1 - Électrodes contenant du cuivre et des oxydes de cuivre et leur procédé de préparation - Google Patents

Électrodes contenant du cuivre et des oxydes de cuivre et leur procédé de préparation Download PDF

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WO2022064414A1
WO2022064414A1 PCT/IB2021/058681 IB2021058681W WO2022064414A1 WO 2022064414 A1 WO2022064414 A1 WO 2022064414A1 IB 2021058681 W IB2021058681 W IB 2021058681W WO 2022064414 A1 WO2022064414 A1 WO 2022064414A1
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electrode
copper
cathode
anode
immersed
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Alessandra Tacca
Roberto Paglino
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Eni S.P.A.
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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
    • 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
    • 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
    • C25B3/00—Electrolytic production of organic compounds
    • C25B3/20—Processes
    • C25B3/25—Reduction
    • C25B3/26—Reduction of carbon dioxide

Definitions

  • the present invention relates to electrodes containing copper and copper oxides and a method for the preparation thereof.
  • Said electrodes can be used to electrochemically reduce carbon dioxide to produce alcohols, such as ethanol and n-propanol.
  • the alcohols thus produced can then be used as fuel carriers or carriers for the production of fuels, thus enhancing the value of carbon dioxide.
  • the present invention relates to a method for screening electrodes containing copper, also commercially available .
  • the carbon dioxide in the air is a potential source of carbon for fuel production.
  • electro-reducing CO2 energy can be stored in chemical bonds. To make this process possible, it is necessary to develop efficient and CO2 selective electro-catalysts.
  • the main criticality of copper-containing electrodes is the poor stability of the electrode itself.
  • the article "M. Le et al. , Journal of the Electrochemical society, 158 (5) , E45-E49, 2011” explains, for example, how methanol production tends to decrease after 30 minutes of reduction, while the amount of methane increases. The authors attribute this change in composition to the reduction of the electrodes to metallic copper, which is catalytic for methane production.
  • Christina Li Christina W. Li et al. J. Am. Chem. Soc. 2012, 134, 7231-7234
  • the electrodes are defined as stable on deactivation, but are tested for up to 7 hours.
  • the special preparation process gives the electrode the morphology needed to reduce carbon dioxide efficiently and with improved yields.
  • copper oxides with Cu (I) and Cu (II) oxidation states are formed on the copper electrode, forming a uniform layer of spherical nanoparticles with a diameter ranging from 20 nm to 60 nm, distributed over the entire electrode.
  • Such layers turn out to be nucleation centers of needle-shaped dendritic structures of around microns in size, which develop mainly in one direction.
  • the dendritic structures unevenly cover the electrode surface.
  • the spherical nanoparticles of the Cu (I) and Cu (II) oxide layers aggregate into clustered structures consisting of spheroidal aggregates of sub-micrometric dimensions.
  • sub-micrometric dimensions means dimensions lower than or equal to 1 pm.
  • spheroidal aggregates means a set of particles whose shape is a spheroid.
  • a spheroid is a three-dimensional surface obtained by rotation of an ellipse around one of its principal axes.
  • An object of the present invention is therefore an electrode containing copper and copper oxides with Cu (I) and Cu (II) oxidation state, wherein said oxides form a layer of spherical nanoparticles having a diameter ranging from 20 nm to 60 nm and are nucleation centers of needlelike dendritic structures that develop mainly following a direction .
  • a further object of the present invention is an electrode containing copper and copper oxides with Cu (I) and Cu(II) oxidation state, wherein said oxides form a layer of spherical nanoparticles having a diameter ranging from 20 nm to 60 nm, which aggregate in cluster structures made up of spheroidal aggregates of sub-micrometric dimensions.
  • a further object of the present invention is a redox process, at a temperature of at least 25°C, to prepare a copper-containing electrode, comprising the following stages : o immersing in an aqueous alkaline solution a copper- containing electrode acting as an anode, a reference electrode, a counter-electrode containing Group VIIIB metals or steel that acts as a cathode, and an ion exchange membrane; said membrane creating two separate compartments, an anode compartment where the electrode and the reference electrode are immersed, a cathode compartment where the counter-electrode is immersed; o applying and controlling a potential difference between anode and cathode in two modes: o -in the main mode, by applying a potential ramp with a scanning speed of 0.01 Volt/second until a potential between 1.2V - 2.5V vs Ref.
  • the described and claimed electrode can be used to reduce carbon dioxide according to a process described below, forming alcohols, formate, acetate and carbon monoxide.
  • the process for reducing carbon dioxide to form alcohols, formate, acetate and carbon monoxide comprises the following stages:
  • an electrochemical cell including o an electrode containing copper and copper oxides as described and claimed in the present patent application, and acting as a cathode; o a counter-electrode acting as an anode, containing oxidation-resistant metals, preferably selected from the metals belonging to Group VIIIB of the Periodic Table of Elements, or steels, most preferably platinum; and o a reference electrode, o an ion exchange membrane, which creates two separate compartments, a cathode compartment where the electrode and the reference electrode are immersed, an anode compartment where the counter-electrode is immersed, said electrodes, counter-electrode and membrane being immersed in a basic aqueous solution containing alkali metals (known in the text as the electrolytic solution or electrolyte) ;
  • the process described and claimed in the present patent application allows to prepare the electrode directly in the electrochemical cell which will then be used for the carbon dioxide reduction process (in situ preparation) . Thanks to this process, the electrode has a particular morphology, as described above and illustrated for example in Figures 3, 11-14, which confers greater faradic efficiency to the cell and leads to higher yields in the carbon dioxide reduction process.
  • Anodizing of copper-containing electrodes in situ means that no further stages of synthesis and deposition, or even further annealing or cooling stages, are required before the test stage.
  • the electrodes obtained by the described and claimed process show good stability over time without altering the catalytic properties, but even improving them over time.
  • the electrodes produced in this way are found to recover from any drop in performance during their operation in the carbon dioxide reduction process, for example by working at 50 mA (l.l“10 6 mA/m 2 ) for up to 4 days of use of the same electrode on consecutive days, showing larger catalytic surfaces and an increase in CO2 reduction products. Reducing at increasing currents from 25 to 150 mA ( 5.3 ⁇ 10 5 -3.2 ⁇ 10 6 mA/m 2 ) for 5 consecutive days, the electro-catalytic system is optimized in terms of activation speed and selectivity towards alcohols.
  • Figure 1 shows the diagram of an electrochemical cell used for CO2 reduction, where 1 is the potentiostat /galvanostat , 2 is the CO2 bubbling tube, 3 the N2 bubbling tube, 4 the cathode compartment, 5 the anode compartment, 6 the separation membrane, 7 the working electrode, 8 the reference electrode and 9 the counter-electrode.
  • the anode and cathode compartments contain two different alkaline aqueous solutions.
  • Figure 2 shows anodizing curves obtained by applying an increasing potential of 1.2V, 1.4V, 1.6V, 1.8V and 2V vs Ag/AgCl, relative to example 2, i.e. , the main operating mode .
  • Figure 3 shows scanning electron microscope SEM images of the morphology of anodized copper wire at 5000X magnification, generated by anodizing at 2V vs Ag/AgCl potential, using the main operating mode and referring to Example 3.
  • Figure 4 shows the galvanostat ic curve E vs t of CO2 reduction and refers to Example 5.
  • Image A shows the full NMR spectrum of the electrolyte after galvanostat ic reduction to 50 mA for 6 hours, carried out in Example 6.
  • Figure 5 shows the magnification of the area highlighted in the full spectrum of Figure 5, Image A.
  • Figure 5 Images A and B refer to examples 5 and 6.
  • Figure 6 illustrates the faradic efficiencies obtained by processing data from NMR analyses for the formation of ethanol, acetic acid, formic acid and 1-propanol after galavanostat ic reduction of CO2 for 6 hours, referring to Example 6.
  • Figure 7 shows the characteristic trend of the cyclic voltammetry curves applied to an electrode containing copper and copper oxides CU/CU2O obtained by means of anodizing process, which proved to be an efficient catalyst for the reduction of carbon dioxide, referring to example 7.
  • Figure 8 shows the effect of the post-passivation treatment; it refers to comparative example 1 and shows the development of an anodizing curve in which the application of the potential was stopped immediately after the oxidation peak.
  • Figure 9 refers to example 8 and shows the cyclic voltammetry curves in the range -0.2V-1.5V vs Ag/AgCl to monitor the current carried by the electrodes in tests carried out on successive days.
  • Figure 10 shows the faradic efficiency for ethanol and propanol production in tests carried out on successive days with the same electrode, as described in example 8.
  • Figures 11 and 12 illustrate scanning electron microscope SEM images of the anodized copper wire at 2V and 1.8V respectively using the main operating mode, at 5000X magnification.
  • Figures 11 and 12 show the dendritic structures .
  • Figure 13 shows scanning electron microscope SEM images of the anodized copper wire at 1.4V using the main operating mode.
  • Figure 13 shows the absence of dendritic structures.
  • Figure 14 shows scanning electron microscope SEM images of the anodized copper wire using the secondary operating mode based on voltammetric cycles.
  • Figure 14 refers to example 9.
  • the described and claimed electrode contains copper and copper oxides with Cu (I) and Cu (II) oxidation states. These oxides form a layer of spherical nanoparticles with a diameter ranging from 20 nm to 60 n. Spherical nanoparticles are nucleation centers of needle-shaped dendritic structures that develop mainly following a direction. This type of electrode, for example, is shown in Figures 11 and 12.
  • the spherical nanoparticles aggregate into clustered structures consisting of spheroidal aggregates of sub-micrometric dimensions. This type of electrode is shown in Figure 14.
  • the described and claimed electrodes can preferably be prepared.
  • an electrode containing copper acting as an anode (7) , a reference electrode (8) , a counterelectrode acting as a cathode (9) containing metals which must not be oxidized, preferably selected from Group VIIIB metals or steel, more preferably platinum, and an ion exchange membrane (6) are immersed.
  • Said membrane creates two separate zones: an anodic zone in which the copper electrode and the reference electrode are immersed, and a cathodic zone in which the counter-electrode is immersed.
  • the reference electrode can be selected from a saturated calomel (SCE) , or an electrode containing silver and silver chloride (referred to as Ag/AgCl) .
  • a potential difference is applied and controlled between the anode and cathode in two alternative operating modes.
  • a potential ramp is applied with a scanning speed of 0.01 Volt/second until a potential between 1.2 V - 2.5 V vs Ref. is reached and said potential difference is maintained for a period of at least 3 minutes .
  • the potential difference is applied by means of one or more voltammetric cycles, starting from a minimum value of -IV vs Ref. and increasing the maximum value up to 2.5V vs Ref. where Ref. indicates a reference electrode, increasing the number of cycles until a current of at least 400 mA (8.5“10 6 mA/m 2 ) is reached.
  • the preparation process is based on a redox reaction carried out at a temperature of at least 25°C and preferably not more than 30°C.
  • aqueous alkaline solutions can be the same or different in the anode and cathode compartments.
  • the aqueous alkaline solutions can contain oxides or carbonates of alkali metals.
  • the latter can preferably be selected from lithium (Li) , sodium (Na) , potassium (K) , rubidium (Rb) , caesium (Cs) and Francium (Er) ; more preferably potassium. More preferably, they can be selected from KHCO 3 or KOH.
  • a potential AV between 1.5V and 2.5V vs Ref. is preferably achieved, more preferably between 2V vs Ref and 2.5V vs Ref. , even more preferably 2V vs. Ref.
  • said potentials are maintained for at least 5 minutes, more preferably for at least 10 minutes so as to complete the oxidation.
  • the AV applied to each stage of the ramp is 0.01V, equal to 0. OlV/s .
  • the minimum time applied during the main operating mode is necessary to complete the post-passivation stage of the electrode, which is important for the formation of the morphologies shown in the present description and for improving the selectivity to alcohols.
  • the described and claimed electrodes are subjected to a test stage to assess which ones show adequate selectivity to alcohols in the carbon dioxide electrochemical reduction process. This test is carried out by electrochemically reducing CO2 as a function of the anodizing potential and evaluating the reduction products obtained. It has been observed that electrodes obtained at high maximum potentials (1.8V-2V vs. Ref. ) show greater selectivity towards alcohols.
  • Part of the copper is oxidized to Cu + and part to Cu 2+ , and part of the Cu 2+ passes in solution in the electrolyte.
  • a first stage occurs in which the Cu 2+ ions in solution are deposited on the cathode, reducing to CU2O, and simultaneously the CuO phase previously formed in the anodizing stage is reduced to CU2O, thus regenerating the morphology shown in the SEM photographs shown for example in Figures 3 and 11-12.
  • the reduction of carbon dioxide leads to the formation of carbon monoxide, formic acid, acetic acid, ethanol and n- propanol .
  • voltammetry tests are carried out consisting of a linear scan in cyclic voltammetry (CV) current.
  • CV cyclic voltammetry
  • the purpose of said tests is to assess the formation of copper oxide on the electrode.
  • a linear current scan allows to reduce any CuO formed on the electrode or dissolved in the electrolyte and to estimate in advance the potential that will be reached during the galvanostat ic reduction of carbon dioxide. This allows to measure the efficiency of the electrode.
  • the process for preparing copper-containing electrodes described and claimed in the present patent application can also be applied to commercial electrodes or electrodes produced according to state-of-the-art methods, in order to increase their selectivity to alcohols in the carbon dioxide reduction process, and thereby increase their faradic efficiency.
  • said process is used as a method for testing appropriately pre-selected electrodes (screening stage) .
  • screening stage For example, starting from electrodes prepared by means of the thermal oxidation technique of copper, known in the state of the art, and applying the process described and claimed in the present patent application, it is possible to promote the formation of ethanol and 1-propanol as CO2 reduction products and thus evaluate the efficiency of the electrode .
  • a further object of the present patent application is an electrode containing copper and copper oxides with Cu (I) and Cu (II) oxidation state, said electrode being obtainable with a redox process, at a temperature of at least 25°C, said process comprising the following stages: o immersing in an aqueous alkaline solution a copper- containing electrode acting as an anode, a reference electrode, a counter-electrode containing Group VIIIB metals or steel that acts as a cathode, and an ion exchange membrane; said membrane creating two separate compartments, an anode compartment where the working electrode and the reference electrode are immersed, a cathode compartment where the counterelectrode is immersed; o applying and controlling a potential difference between anode and cathode by one of these two mode: o in the main mode, applying a potential ramp with a scanning speed of 0.01 Volt/second until a potential between 1.2 V - 2.5 V vs Ref.
  • a further object of the present patent application is an electrode containing copper and copper oxides in the Cu (I) and Cu (II) oxidation state, in which said oxides form a layer of spherical nanoparticles having a diameter ranging from 20 nm to 60 nm, said particles being nucleation centers of needle-like dendritic structures which develop mainly following a direction; said electrode obtainable by a redox process, at a temperature of at least 25°C, said process comprising the following stages: o immersing in an aqueous alkaline solution a copper- containing electrode acting as an anode, a reference electrode, a counter-electrode containing Group VIIIB metals or steel that acts as a cathode, and an ion exchange membrane; said membrane creating two separate compartments, an anode compartment where the electrode and the reference electrode are immersed, a cathode compartment where the counter-electrode is immersed; o applying and controlling a potential difference between anode and ca
  • a further object of the present patent application is an electrode containing copper and copper oxides having Cu (I) and Cu (II) oxidation states, in which said oxides form a layer of spherical nanoparticles having a diameter ranging from 20 nm to 60 nm, which aggregate into cluster structures consisting of spheroidal aggregates of submicrometric dimensions, said electrode being obtainable by a redox process, at a temperature of at least 25°C, said process comprising the following stages: o immersing in an aqueous alkaline solution a copper- containing electrode acting as an anode, a reference electrode, a counter-electrode containing Group VIIIB metals or steel that acts as a cathode, and an ion exchange membrane; said membrane creating two separate compartments, an anode compartment where the electrode and the reference electrode are immersed, a cathode compartment where the counter-electrode is immersed; o applying and controlling a potential difference between anode and cathode by
  • the Applicant has also developed a method for selecting electrodes described and claimed in the present patent application. According to this selection method, the following stages are comprised: -providing an electrochemical cell containing an aqueous solution (electrolytic solution) in which the electrode described and claimed in the present patent application is positioned;
  • the screening phase of the electrodes described and claimed in the present patent application is carried out with CV measurements: in the CV scans, an anodic peak with onset about 0V vs Ref. and a cathodic peak with onset about -0.1V vs Ref. must be present.
  • the current intensity must reach 400mA (8.5“10 6 mA/m 2 ) .
  • Such a position and shape of the peaks is a diriment and surprising characteristic for establishing a priori whether an efficient catalyst has been formed during the oxidation stages .
  • the methodology allows to understand a priori whether a good copper oxide catalyst for CO2 reduction is present on the electrode.
  • the pre-testing of the electrode by means of voltammetry cycles allows to avoid lengthy reduction tests by establishing a priori whether the oxide formed is an efficient catalyst.
  • copper-containing electrodes are prepared with the state-of-the-art techniques, they are not very stable during the electrochemical reduction of carbon dioxide.
  • the electrodes according described and claimed in the present patent application appear to be particularly stable with respect to what is known in the state of the art; indeed, it has been observed that said electrodes show stable performance during the electrochemical reduction of carbon dioxide. The results so far show a working stability of 6 hours of the electrode in CO2 reduction with tests carried out on several consecutive days.
  • one of the advantages of the electrodes and processes described an claimed in the present patent application lies in the fact that if, during the operation of the electrodes in CO2 reduction, the current performance decreases, it is sufficient to proceed with a few voltammetry cycles to restore or even improve the initial performance of the electrode .
  • Said analysis method comprises the following stages: -providing an electrochemical cell containing an aqueous solution (electrolytic solution) in which the electrode described and claimed in the present patent application is positioned;
  • the carbon dioxide oxidation time can vary from
  • the applied current can vary from 50mA (l.l“10 6 mA/m 2 ) to 200mA (4.2“10 6 mA/m 2 ) , more preferably from 100mA (2.1 “IO 6 mA/m 2 ) to 150mA (3.2 “IO 6 mA/m 2 ) .
  • Gas-phase reduction products were determined by gas chromatography and liquid-phase reduction products were determined and quantified by NMR spectroscopy.
  • the hydrogen derives from a parasitic hydrolysis reaction.
  • the electrode described and claimed can be used to reduce carbon dioxide according to a process described below with which gas phase products such as carbon monoxide and liquid phase products such as ethanol, n-propanol, acetate and formate can be obtained. Said process comprises several stages .
  • an electrochemical cell which includes:
  • a counter-electrode acting as an anode containing metals which must not oxidize, preferably selected from the metals belonging to Group VIIIB of the Periodic Table of Elements, or steels, most preferably platinum;
  • the membrane creates two separate compartments, a cathode compartment in which the electrode and reference electrode are immersed, and an anode compartment in which the counter-electrode is immersed.
  • the electrodes containing copper and copper oxides in the Cu ( I ) and Cu (II) oxidation state, the counter-electrode and the membrane are immersed in an aqueous solution containing alkali metals (known in the text as electrolytic solution) .
  • Carbon dioxide is flushed into the cathode compartment until saturation; an inert is flushed into the anode compartment, preferably the inert is nitrogen.
  • a potential difference is applied and controlled between anode and cathode until at least part of the copper oxide Cu (II) is reduced (pre-reduct ion stage) and until the CO2 is reduced.
  • the reduction process can be carried out at a temperature of at least 25°C and preferably not more than 30°C.
  • aqueous solutions can be the same or different in the anode and cathode compartments.
  • the purpose of a different solution is to have a higher conductivity in the compartment where water oxidation occurs.
  • the aqueous alkaline solutions can contain oxides or carbonates of alkali metals.
  • the latter can preferably be selected from lithium (Li) , sodium (Na) , potassium (K) , rubidium (Rb) , caesium (Cs) and francium (Fr) ; more preferably potassium. More preferably, they can be selected from KHCO3 or KOH.
  • the preferred metals are those belonging to Group VIIIB of the Periodic Table of Elements, preferably selected from Fe, Rb, Os, Co. Rh, Ir, Ni, Pd, Pt; even more preferred is platinum.
  • the anodizing and CO2 electrochemical reduction tests were carried out in an H-type cell with two compartments separated by a membrane as shown in Figure 1.
  • the cell contains an aqueous solution of KHCO3 at a concentration of IM.
  • the Nafion 115 membrane separates the cell into two compartments in each of which are immersed in the aqueous alkaline solution respectively copper-containing working electrode and silver-silver chloride (Ag/AgCl) reference electrode, and counter-electrode which is a platinum or steel filament.
  • a 3-electrode configuration was therefore used .
  • the working electrode acts as an anode during the preparation or anodizing stage, and as a cathode during the carbon dioxide reduction process.
  • the counter-electrode acts as a cathode during the electrode preparation stage and as an anode during the carbon dioxide reduction process.
  • CO2 is flushed in the cathode compartment to saturate the solution
  • N2 is flushed in the anode compartment to degas the solution and dilute any oxygen formed during the process.
  • the carbon dioxide reduction process is carried out in KHCO3 electrolyte at IM concentration applying a potential in the range 1.2-2V vs Ag/AgCl for a time in the range 10- 13 minutes.
  • the desired potential value is reached by applying a potential ramp with a scanning rate of O .OlV/s starting at -0.15V vs Ag/AgCl and maintaining the final potential for at least 10 minutes to achieve complete oxidation of the surface.
  • the graphs of the anodizing curves are shown in Figure 2.
  • the reduction products were evaluated as a function of the anodizing potential, and it was established that working electrodes obtained at high potential values ranging from 1.8V to 2V demonstrate greater selectivity towards alcohols. However, when the working electrodes are prepared at low potentials below 1.8V, the main product is formic acid.
  • the current reached in the voltammetric cycles was monitored: a higher current corresponds to a greater number of active sites on the electrode surface. Furthermore, an anodic peak with onset approximately OV vs Ag/AgCl and a cathodic peak with onset approximately -0.1V vs Ag/AgCl must be present in the cyclic voltammetry CV scans. The current intensity must reach 400mA (8.5“10 6 mA/m 2 ) . Such a position and shape of the peaks is a diriment and surprising characteristic for establishing a priori whether an efficient catalyst has been formed during the oxidation stages.
  • the electrodes were tested as catalysts for CO2 reduction in galvanostat ic mode for a time of 6 hours continuously.
  • the currents applied were 50, 100 and 150 mA (l.l“10 6 , 2.1 “IO 6 and 3.2 “IO 6 mA/m 2 ) .
  • the reduction products in the gas phase were determined by gas chromatography and are mainly H2 (from the parasitic hydrolysis reaction) and, to a much lesser extent, CO, ethylene and ethane.
  • the liquid phase products were determined and quantified by NMR spectroscopy and found to be formate, ethanol, propanol and acetate.
  • the percentage faradic efficiencies for products obtained with 50mA applied current after 6 hours of reduction were 4.7% for formate, 4.1% for acetate, 2.4% for ethanol and 2.4% for n-propanol. The efficiencies decrease linearly as the applied current increases.
  • Example 1 experimental set up Figure 1.
  • the anodizing and CO2 electrochemical reduction tests were carried out in an H-type cell with two compartments separated by a Nafion 115 membrane.
  • a 3-electrode configuration was used, with the silver/silver chloride (Ag/AgCl) reference electrode and the copper-containing working electrode inserted into the cathode compartment and immersed in a 0.5M KHCO3 aqueous solution.
  • the working electrodes used consist of wires (4 wires 150mm long and 0.025mm in diameter) or thin sheets (5*30mm 2 ) of copper which is oxidized using the described and claimed process.
  • the counter-electrode consisting of a platinum or, alternatively, steel filament immersed in a IM KOH aqueous solution, is placed in the anode compartment.
  • CO2 is flushed in at a flow rate of approximately 20 ml/min.
  • the pH of the solution is initially 9 and drops to about 7 after saturation with CO2.
  • N2 is flushed to degas the solution and to dilute any oxygen formed during the process. Measurements were made with an Autolab PGSTAT 20 potentiostat /galvanostat using the Nova program.
  • the continuous monitoring of the potential difference between anode and cathode was carried out using an externally connected tester. All the measurements are carried out at temperatures above 25°C. The same cell used for this test will be used for subsequent carbon dioxide reduction tests.
  • Example 2 preparation of working electrode by means of anodizing .
  • the anodizing of the copper filament /laminate is carried out in the same cell ( Figure 1) used in example 1 and also used for the subsequent reduction tests.
  • a copper filament is washed with dilute hydrochloric acid and then immersed in compartment 4 of the cell.
  • the anodizing occurs in two stages: the first stage is a ramp of potential from -0.15V vs Ag/AgCl at a scanning rate of 0.01 V/s.
  • the final ramp value is in the range 1.2-2V vs Ag/AgCl.
  • the second anodizing stage is a potent iostat ic stage in which the maximum potential is applied for a period of 10-13 min. At this stage the cathode solution turns blue due to the Cu 2+ passed in solution.
  • Figure 2 shows the trend of the current anodizing curves towards time, where the copper oxidation peak is present.
  • the curves vary considerably as the maximum potential is reached.
  • the current after the oxidation peak increases. It can be assumed that the initial oxide layer develops rapidly and then there is the formation of further oxidized low-resistive surfaces.
  • Example 3 electrode morphology
  • the morphology of the electrodes is assessed by scanning electron microscopy with a secondary electron detector. From a morphological point of view, it can be observed that as the potential increases, the specific surface area and the anchoring of the oxide layer to the metal bulk increases .
  • the morphology of the electrode shows an oxide layer composed of spherical nanoparticles ranging in size from 2 to 60 nm, distributed throughout the sample. Spherical aggregates of sub-micrometric-dimension nanoparticles form on this layer and more or less uniformly cover the entire sample. Such formations appear to be nucleation centers of needle-shaped dendritic structures, which are around pm in size and develop mainly in one dimension. Such structures unevenly cover the electrode surface.
  • figures 3 and 11 show the morphology of the CU2O sample obtained at 2V vs Ag/AgCl, while figure 12 shows that of the sample obtained at 1.8V vs Ag/ag/Cl.
  • Example 4 Chemical and physical characterization of the electrodes prepared in Example 2.
  • X-ray diffraction analysis (XRD)
  • micro-Raman spectroscopy and hemispherical reflectance measurements (DRS) with a UV-Vis-NIR spectrophotometer were used to determine the composition of the electrodes in Example 2.
  • DRS hemispherical reflectance measurements
  • Example 5 carbon dioxide reduction using the working electrodes produced in Example 2.
  • the CO2 reduction is carried out in situ, without changing the configuration of the electrochemical cell, using the same cell, experimental set up and working electrodes as in Examples 1 and 2.
  • the tests are carried out in galvanostat ic mode, applying a current value in the range 25-150 mA ( 5.3 ⁇ 10 5 -3.2 ⁇ 10 6 mA/m 2 ) for a period of 6 hours.
  • Figure 4 shows the potential versus time curve of a reduction test carried out at 25 mA (5.3“10 5 mA/m 2 ) for the anodized electrode at 2V vs Ag/AgCl.
  • the electrolyte in the cathode compartment is discharged for analysis.
  • the reduction products in the gas phase were determined by gas chromatography and are mainly H2 (from the parasitic hydrolysis reaction) and, to a much lesser extent, CO, ethylene and ethane.
  • the liquid phase products were determined and quantified by NMR spectroscopy and found to be formate, ethanol, propanol and acetate.
  • the solution is discolored and the Cu 2+ passed in solution (as described in example 2) is deposited on the surface of the electrode, helping to form the high surface area morphology.
  • Example 6 NMR characterization of liquid CO2 reduction products .
  • reaction products in the liquid phase were characterized by GC gas chromatography and 1 H-NMR spectroscopy in solution.
  • a standard pre-saturat ion sequence centered on the H2O signal and power of 57.7 dB was used to optimize the spectra.
  • a glass capillary containing a ImM solution of phenol in deuterated dimethyl sulfoxide was also inserted into the NMR tube in order to calibrate the intensity of the signals in the different spectra against the same reference signal.
  • the NMR spectra are shown as an example in Figure 5.
  • Figure 6 shows the graph of the formation efficiencies of the CO2 reduction products as a function of the anodizing potential with which the electrode was prepared.
  • Galvanostat ic tests were carried out for a time of 6 hours at 25 mA (5.3“10 5 mA/m 2 ) , with the electrodes prepared according to example 2.
  • the highest faradic efficiency towards alcohols is obtained using an electrode prepared at 2.0V vs Ag/AgCl: the resulting efficiencies of 2.09% for ethanol and 3.83% for n-propanol respectively
  • Example 7 electrode testing stage
  • An efficient electrode is characterized by an adequate number of active sites and must therefore be covered by an efficient oxide.
  • the current reached in voltammetric cycles GV was monitored: it is assumed that a higher current corresponds to a greater number of active sites.
  • an anodic peak with onset approximately OV vs Ag/AgCl and a cathodic peak with onset approximately -0.1V vs Ag/AgCl must be present in the CV scans.
  • the current intensity must reach 400mA (8.5“10 6 mA/m 2 ) .
  • An example of such volt ammograms is shown in figure 7. Such a position and shape of the peaks is a diriment and surprising characteristic for establishing a priori whether an efficient catalyst has been formed during the oxidation stages .
  • Such testing methodology can be used to test electrodes obtained by applying other different preparation methods, such as thermal oxidation.
  • Example 8 stability tests of the electrodes of Example 2. Two different stability tests were carried out on the electrodes prepared in Examples 1 and 2 in order to test their service life. The results can be seen in Figure 9 and 10.
  • Duration tests were carried out to verify the stability over time of the 2V anodized electrodes prepared in Examples 1 and 2.
  • the tests consisted of daily CO2 reduction tests in galvanostat ic mode at 50 mA (l.l“10 6 mA/m 2 ) by applying the current for a time of 6 hours each day; the tests were repeated for 4 consecutive days for a total of 24 hours of electrode work.
  • the tests showed that the system activates with time: cyclic voltammetry tests in the range -0.2V -1.5V vs Ag/AgCl (figure 9) showed an increase over time in the current carried by the electrodes.
  • Table 1 specifies the current values reached by the CV curves in Figure 9 at potential 1.2V and 1.5V vs. Ag/AgCl, further highlighting the increase in current over the following days.
  • the electrodes prepared with examples 1 and 2 were subjected to a daily stress test with duration tests for 6 hours each at increasing current. A different current was applied each day and kept constant for 6 hours. The currents tested were 25 mA, 50 mA, 75 mA, 100 mA and 150 mA. (5.3 - 10 5 , 1-10 6 , 1.6 - 10 6 , 2.1 - 10 6 , 3.2 - 10 6 , mA/m 2 ) .
  • the electrodes are stable and catalytically active towards CO2 reduction.
  • Example 9 anodizing with alternative preparation
  • This example describes an alternative anodizing process, secondary to that described in example 2.
  • the anodizing of the copper filament /laminate is carried out in the same cell (figure 1) used in example 1 and also used for the subsequent reduction tests.
  • a copper filament is washed with diluted hydrochloric acid and then immersed in compartment 4 of the cell by means of one or more voltammetric cycles starting from a minimum value of -IV vs Ag/AgCl and increasing the maximum value up to 2.5V vs Ag/AgCl until a current of at least 400 mA (8.5“10 6 mA/m 2 ) is reached.
  • the SEM images of the electrodes obtained with the procedure described are shown in image 14.
  • the electrode consists of an oxide layer consisting of spherical nanoparticles ranging in size from 2 to 60 nm; the spherical nanoparticles aggregate into cluster structures consisting of spheroidal aggregates of sub-micrometric dimensions.

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Abstract

La présente invention concerne une électrode contenant du cuivre et des oxydes de cuivre avec un état d'oxydation du Cu(I) et Cu(II), lesdits oxydes formant une couche de nanoparticules sphériques ayant un diamètre allant de 20 nm à 60 nm et étant des centres de nucléation de structures dendritiques de type aiguille qui se développent principalement suivant une direction.
PCT/IB2021/058681 2020-09-25 2021-09-23 Électrodes contenant du cuivre et des oxydes de cuivre et leur procédé de préparation WO2022064414A1 (fr)

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CN115247269A (zh) * 2022-05-16 2022-10-28 山东大学 集成化光阳极器件、电池及其制备方法与应用

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WO2018210515A1 (fr) * 2017-05-19 2018-11-22 Siemens Aktiengesellschaft Fabrication d'électrocatalyseurs dendritiques pour la réduction de co2 et/ou co
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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115094461A (zh) * 2022-05-13 2022-09-23 山东大学 一种原位自选择性铜纳米枝晶材料及其制备方法和应用
CN115094461B (zh) * 2022-05-13 2023-11-28 山东大学 一种原位自选择性铜纳米枝晶材料及其制备方法和应用
CN115247269A (zh) * 2022-05-16 2022-10-28 山东大学 集成化光阳极器件、电池及其制备方法与应用
CN115247269B (zh) * 2022-05-16 2024-05-10 山东大学 集成化光阳极器件、电池及其制备方法与应用

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