Materials, device and process for reduction of carbon oxides

Abstract

The present invention is related to a process for reduction of carbon oxides and to materials and devices for performing the said process. In particular, the present invention is related etched electrochemically active particles and a method of production thereof, an electrode comprising the etched electrochemically active particles, a method of production of the electrode, a flow cell electrolyzer including the electrode and the process for reduction of carbon oxides using the flow cell electrolyzer.

Description

MATERIALS, DEVICE AND PROCESS FOR REDUCTION OF CARBON OXIDESTechnical field

[0001] The present invention is related to a process for reduction of carbon oxides and to materials and devices for performing the said process. In particular, the present invention is related etched electrochemically active particles and a method of production thereof, an electrode comprising the etched electrochemically active particles, a method of production of the electrode, a flow cell electrolyzer including the electrode and the process for reduction of carbon oxides using the flow cell electrolyzer.Background

[0002] Electroreduction of carbon dioxide into carbon-based products as an alternative to traditional energy sources has garnered significant attention from scientists. However, the industrial application of CO2 electrolysers is not yet feasible due to significant challenges, such as salt precipitation during prolonged electrolysis and the high energy input required. Consequently, there has been a growing interest among researchers in the electroreduction of carbon monoxide (which can be produced from CO2 reduction) into hydrocarbons and / or oxygenates products. In the context herein, the term “hydrocarbons” products or molecules refers to organic molecules comprising at least one carbon, and hydrogen. The term “oxygenates” refers to hydrocarbons further comprising at least one oxygen. Non-limiting examples of such hydrocarbons and / or oxygenates molecules may comprise formic acid, methanol, methane, ethylene, ethanol, propanol, acetic acid or acetaldehydes.

[0003] Document US patent No 11,959,184 B2 discloses a method of electroreduction in a flow electrolyzer with a working electrode and a counter electrode comprising steps of streaming carbon monoxide into the flowelectrolyzer, and electrocatalyzing carbon monoxide in the presence of one or more nucleophilic co-reactants in contact with a catalytically active material present on the working electrode thereby forming one or more carbon-containing products electrocatalytically. The catalytically active material is comprised of at least one of copper, copper oxide or a copper containing material and the counter electrode is an anode comprising an anodic catalytically active material comprised of Irridium oxide.

[0004] Copper-based catalysts are predominantly nanoparticles which are commercially expensive.

[0005] Document CN114635153 discloses the preparation of copperbased nano-catalysts, using a one-step chemical etching method to dealloy crushed Dewey alloy particles containing aluminium copper and zinc, in presence of a corrosion inhibitor selected from benzotriazole, methylbenzotriazole and mercaptobenzotriazole, and in presence of a strong acid selected from hydrochloric acid, sulfuric acid, phosphoric acid or perchloric acid at 80°C for three hours. The nano-catalyst was used in an electrode for electrocatalytic reduction of carbon dioxide and the Faradaic efficiency for hydrogen was not below 20 %.

[0006] Document CN11346313 discloses the preparation of copper catalyst obtained from a process comprising the steps of dissolution of CUCI2.2H2O in water in presence of glucose, and with XC-72 carbon powder in the same mass ratio as copper. The mixture was stirred for five hours and a capping agent (hexadecylamine) was slowly added during this step. After a light blue emulsion was formed, it was poured into a high-pressure reactor and heated in an oil bath at 120°C for two hours. After cooling at room temperature, a copper nanocrystalline carbon material was obtained (Cu / C) and was heated and stirred at 60°C for four hours in presence of various concentrations of acetic acid for etching. The catalysts thereby obtained were used in an electrode of a flow electrolytic cell for electrocatalytic reduction of carbon dioxide and the Faradaic efficiency for hydrogen was not below 20%.

[0007] Document W02020056507 discloses metal nano-catalyst materials having nanocavities shaped and configured to promote formation of C3+ compounds from CO gas in electroreduction conditions. The nanocrystals were obtained by first growing CU2O. Sodium dodecyl sulphate was dissolved in water, followed by the addition of CuC , a hydroxylamine hydrochloride solution and HCI solution into a reactor. Next, NaOH was quickly added into the solution. The solution was aged at room temperature for various times of aging in presence of HCI to obtain different sizes of cavities in spherical particles. The derived Cu nano-catalyst electrodes were then prepared via in-situ CO electroreduction from the corresponding initial CU2O electrode. CO electroreduction using such electrodes including a nanocatalyst with a relatively wide cavity provided as desired more propanol than ethanol. However, the conversion of CO into combined hydrocarbons and oxygenates does not exceed 70%.

[0008] Up to now, no process has been reported that achieves high efficiency with low energy input. No electrochemical process of carbon oxide reduction achieving a high single-pass conversion rate of CO up to 90% has been reported. Furthermore, the present cell voltage for CO electrolysis at high current densities remains too high for industrial applications.

[0009] Another issue in electrocatalytic process for reduction of carbon oxides into hydrocarbons and / or oxygenates is the competing hydrogen evolution reaction.

[0010] Additionally, selectivity for hydrocarbons and / or oxygenates production remains an area needing improvement.Summary of the invention

[0011] The present invention aims to provide a process for the electrocatalytic reduction of carbon oxides to hydrocarbons and / or oxygenates products, achieving a high single-pass conversion rate and a good selectivity.

[0012] One objective of the present invention is to reduce the competing hydrogen evolution reaction (HER) in carbon oxide electrocatalytic reduction processes. It is particularly aimed to provide a process wherein the carbon oxide conversion rate can reach up to 95%, with H2 faradaic efficiency remaining around 10% or less at a high current density (250-350 mA / cm2).

[0013] Another objective of the present invention is to be able to tune the selectivity for carbon-based products from carbon monoxide in function of the reaction conditions in the electrolysis process.

[0014] Another objective of the present invention is to provide a carbon oxide electrocatalysis process which can achieve more than 90% faradaic efficiency for hydrocarbons and / or oxygenates products, with a relatively low voltage.

[0015] To achieve at least those objectives, the present invention is described here below and in reference to the appended claims.

[0016] In a first aspect, the present invention is related to a method for producing etched particles comprising an electrochemically active material. According to the method, the etched particles are obtained by:Providing particles comprising an electrochemically active material, the said particles having a particle size distribution comprised between 1 nm and 1 mm, preferably between 10 nm and 500 pm, more preferably between 100 nm and 500 pm, preferably expressed in number and measured by SEM in combination with an imaging treatment software such as a Phenom user interface from Thermo Fischer Scientific; Etching the said particles with an aqueous solution comprising a weak acid, during a time comprised between 30 minutes to 6 hours.

[0017] Preferably, the concentration of the weak acid in the aqueous solution is comprised between 0,1 and 3 mol / l, preferably between 0,1 and 1 mol / l.

[0018] Preferably, the weak acid is an organic acid, preferably having a pKa (in water under normal conditions of temperature and pressure) superior or equal to 3, preferably superior or equal to 3.1 , preferably superior or equal to 3.2, more preferably superior or equal to 3.3, more preferably superior or equal to 3.4, and preferably inferior or equal to 7.

[0019] Preferably, the method further comprises a step of pre-etching the particles before the step of etching, wherein the particles are pre-etched in an aqueous solution comprising a strong acid, during a time comprised between 10 seconds and 5 minutes.

[0020] Preferably, the concentration of the strong acid in the aqueous solution is comprised between 0,1 and 3 mol / l, preferably between 0,1 and 1 mol / l.

[0021] Preferably, the strong acid is an inorganic acid, preferably having a pKa (in water under normal conditions of temperature and pressure) below 3, more preferably below 2.

[0022] It is well accepted in the field of chemistry that a strong acid fully dissociates in aqueous solutions, while weak acids do not fully dissociate in aqueous solutions. It is well understood in the field of chemistry that the terms “strong acid” and “weak acid” are not related to their dilution in aqueous solutions.

[0023] In some embodiments, the particles before etching or pre-etching are blended with a polymeric binder material.

[0024] In some embodiments, the etched particles obtained after the etching are blended with a polymeric binder material. Preferred polymeric binder materials are presented in the description here below.

[0025] In some other embodiments, the method of producing etched electrochemically active particles is applied on particles comprising an electrochemically active material which are dispersed in a porous electrode.

[0026] Preferably, the particles comprising an electrochemically active material comprise at least an oxidable metallic element, and the method further comprises an oxidation step to provide at least a layer of oxide of the metallic element on the etched electrochemically active particles.

[0027] Preferably, before etching and before the optional pre-etching, the particles comprising electrochemically active material have:a particle size distribution with a D90 comprised between 1 nm and 1 pm, preferably between 10 nm and 1 pm, more preferably between 100 nm and 1 pm; ora particle size distribution with a D90 comprised between 1 pm and 1mm, preferably between 1 pm and 500 pm, more preferably between 10 pm and 100 pm; ora particle size distribution witha first fraction of particles having a D90 comprised between 1 nm and 1 pm, preferably between 10 nm and 1 pm, more preferably between 100 nm and 1 pm, and; a second fraction of particles having a D90 comprised between 1 pm and 1 mm, preferably between 1 pm and 500 pm, more preferably between 10 pm and 100 pm.

[0028] According to a second aspect, the present invention is related to etched particles comprising an electrochemically active material, herein after also referred to as “etched particles” for conciseness, preferably obtained by the method described herein.

[0029] Preferably, the etched particles have a particle size distribution comprised between 1 nm and 1 mm, preferably between 10 nm and 500 pm,more preferably between 100 nm and 500 pm, preferably expressed in number and measured by SEM in combination with an imaging treatment software such as a Phenom user interface from Thermo Fischer Scientific, and have an increased specific surface area relative to the particles before etching.

[0030] Preferably, the etched particles are blended with a polymeric binder material.

[0031] Preferably, the etched particles comprise a layer of a metal oxide of a metallic element comprised in the etched particles.

[0032] The etched particles described herein, when used in a porous electrode of a flow cell electrolyzer, advantageously allows to meet the objectives mentioned herein above.

[0033] In a third aspect, the present invention is related to a process for manufacturing a porous electrode comprising the steps of:shaping a blend comprising a polymeric binder material and particles comprising an electrochemically active material into an electrode body; andproducing etched electrochemically active particles by the method described herein;wherein the step of producing etched electrochemically active particles is realized before shaping the electrode body or after shaping the electrode body.

[0034] The manufacturing of the porous electrode can be made according to any method in the art. Some preferred methods of manufacturing a porous electrode are described in the description here below.

[0035] In a fourth aspect, the present invention is related to a porous electrode comprising a porous matrix comprising a polymeric binder material and etched electrochemically active particles.

[0036] The etched electrochemically active particles are preferably obtained according to a method of producing etched electrochemically active particles such as described herein.

[0037] In a fifth aspect, the present invention is related to a flow cell electrolyzer comprising an electrode according to the fourth aspect of the invention.

[0038] Preferably the flow cell electrolyzer comprises:a first cell adapted for flowing a first flow of electrolyte and comprising a porous electrode according to the fourth aspect, used as a cathode;a second cell adapted for flowing a second flow of electrolyte and comprising an anode;a generator electrically connected to the cathode and the anode and configured to provide a current between the cathode and the anode;wherein the flow cell is configured for receiving a flow of carbon oxide passing through the cathode or through the first flow of electrolyte.

[0039] In a sixth aspect, the present invention is related to a process of electrocatalytic reduction of carbon oxides to hydrocarbons and / or oxygenates products, using a flow cell electrolyzer as described in relation with the fifth aspect.

[0040] Preferably, the electrolysis process is realized with at least one of the following conditions:a current density comprised between 50mA / cm2to 650 mA / cm2, preferably between 50 mA / cm2to 400 mA / cm2;an electrolyte concentration comprised between 2 to 5 mol / l, preferably between 2.5 to 4mol / l, more preferably between 2.5 to 3.5 mol / l;an electrolyte flow rate comprised between 10 ml / min and 50 ml / min, preferably between 20 ml / min and 40 ml / min, more preferably between 25 ml / min and 35 ml / min;a carbon oxide flow rate comprised between 10 and 20 ml / min, preferably between 11 and 16 ml / min, more preferably between 11 and 14 ml / min.

[0041] Preferably, the electrolysis process is realized in ambient conditions of temperature and pressure.Brief description of the drawings

[0042] Aspects of the invention will now be described in more detail with reference to the appended drawings, wherein same reference numerals illustrate same features and wherein:

[0043] Figures 1A and 1B shows SEM images of starting materials including copper particles without any treatment process.

[0044] Figures 2A and 2B shows SEM images of materials comprising pre-etched copper particles.

[0045] Figures 3A and 3B shows SEM images of materials comprising etched copper particles after pre-etching and after 1 hour of etching according to an embodiment of the present invention.

[0046] Figures 4A and 4B shows SEM images of materials comprising etched copper particles after pre-etching and after 2 hours of etching according to an embodiment of the present invention.

[0047] Figures 5A and 5B shows SEM images of materials comprising etched copper particles after pre-etching and after 3 hours of etching according to an embodiment of the present invention.

[0048] Figure 6 shows a schematic embodiment of a flow cell electrolyzer according to an embodiment of the present invention.

[0049] Figure 7 shows a graph including the faradaic efficiency and the CO conversion rate in a CO electrolysis process for comparative gas diffusion electrodes and for gas diffusion electrodes according to some embodiments of the present invention.

[0050] Figure 8 shows various SEM images of comparative materials including copper particles and of materials including copper particles etched by contacting with various acidic compositions.

[0051] Figure 9 shows a graph presenting the faradaic efficiency in a CO electrolysis process for comparative gas diffusion electrodes and for gas diffusion electrodes including copper particles etched by different acidic compositions according to some embodiments of the present invention.

[0052] Figure 10 shows a graph presenting the CO conversion rate in a CO electrolysis process for comparative gas diffusion electrodes and for gas diffusion electrodes including copper particles etched by different acidic compositions according to some embodiments of the present invention.

[0053] Figures 11A and 11 B show SEM images of a surface of a gas diffusion electrode according to an embodiment of the invention wherein the copper particles included in the electrode have been etched after formation of the electrode.

[0054] Figures 12A and 12B show SEM images of a surface of a gas diffusion electrode according to an embodiment of the invention wherein the copper particles included in the electrode have been etched before the formation of the electrode.

[0055] Figure 13 shows a graph presenting the faradaic efficiency in a CO electrolysis process for a comparative gas diffusion electrode and for gas diffusion electrodes related to the embodiments of Figures 11 A, 11 B and Figures 12A, 12B.

[0056] Figure 14 shows a graph presenting the CO conversion rate in a CO electrolysis process for a comparative gas diffusion electrode and for gasdiffusion electrodes related to the embodiments of Figures 11 A, 11 B and Figures 12A, 12B.

[0057] Figure 15 shows a graph presenting the CO reaction rate in a CO electrolysis process for a comparative gas diffusion electrode and for gas diffusion electrodes related to the embodiments of Figures 11 A, 11 B and Figures 12A, 12B.

[0058] Figure 16A shows a graph of the evolution in time of the working potential of electrodes vs. Ag / AgCI in a CO electrolysis process for a comparative gas diffusion electrode and for gas diffusion electrodes related to the embodiments of Figures 11 A, 11B and Figures 12A, 12B.

[0059] Figure 16B shows a graph of the evolution in time of the cell voltage in a CO electrolysis process fora comparative gas diffusion electrode and for gas diffusion electrodes related to the embodiments of Figures 11 A, 11 B and Figures 12A, 12B.

[0060] Figures 17A, 17B and 17C shows respectively graphs of faradaic efficiency, CO conversion rate and CO reaction rate in a CO electrolysis process using an electrode according to an embodiment of the invention, wherein the concentration of electrolyte in the electrolyte solution is varied.

[0061] Figures 18A, 18B and 18C shows respectively graphs of faradaic efficiency, CO conversion rate and CO reaction rate in a CO electrolysis process using an electrode according to an embodiment of the invention, wherein the current density is varied.

[0062] Fig. 19 presents a SEM image of copper particles before any etching or pre-etching step.

[0063] Fig. 20 presents the measured system resistance of the flow cells comprising comparative bismuth containing gas diffusion electrodes and treated bismuth containing gas diffusion electrodes according to an embodiment of the present invention.

[0064] Fig. 21 A shows a graph of the evolution in time of the working potential of electrodes vs. Ag / AgCI in a CO electrolysis process for a comparative bismuth containing gas diffusion electrode and for treated bismuth containing gas diffusion electrodes according to an embodiment of the present invention.

[0065] Fig. 21 B shows a graph of the evolution in time of the cell voltage in a CO electrolysis process for a comparative bismuth containing gas diffusion electrode and for treated bismuth containing gas diffusion electrodes according to an embodiment of the present invention.

[0066] Fig. 22 shows the Faradaic efficiency of formic acid in a CO electrolysis process using a comparative bismuth containing gas diffusion electrode and using treated bismuth containing gas diffusion electrodes according to an embodiment of the present invention.Detailed description of the invention

[0067] According to a first aspect, the present invention is related to a method of producing etched particles. The etched particles according to the present invention are advantageously part of an electrode used in a flow cell electrolyzer.

[0068] According to a first embodiment of the method of producing etched particles, the method of producing comprises the steps of:Providing particles comprising an electrochemically active material, the particles having a particle size distribution comprised between 1 nm and 1mm, preferably between 10 nm and 500 pm, preferably between 100 nm and 500 pm, preferably expressed in number and measured by SEM in combination with imaging treatment software such as a Phenom user interface, from Thermo Fischer Scientific;Etching the particles with an aqueous solution of a weak acid, preferably having a pKa superior or equal to 3.0, during a time comprised between 30 minutes to 6 hours; andObtaining etched electrochemically active particles.

[0069] In the context of the present invention, the term “electrochemically active material” refers to any metallic compound or alloy commonly used in flow cell electrolyzers. Preferably the metallic compound or alloy is oxidable. Preferred metallic compounds include transition metals and post-transition metals and alloys of these transition metals and / or post-transition metals. In some preferred embodiments, electrochemically active particles comprise copper or bismuth.

[0070] In an embodiment the particles comprising an electrochemically active material are particles comprising a metallic compound or alloy commonly used in flow cell electrolyzers. Preferably the metallic compound or alloy is oxidable. Preferred metallic compounds include transition metals and post-transition metals and alloys of these transition metals and / or posttransition metals. In some preferred embodiments the metallic compound or alloy comprise copper or bismuth.

[0071] When referring to a particle size distribution having a particular range and without any further precision on the particle size distribution, it is considered that 100% of the particles have a size comprised within the said range.

[0072] The particles before etching can have a particle size distribution D90 expressed in number comprised between 1 nm and 1pm, preferably between 10 nm and 1 pm, more preferably between 100 nm and 1 pm, measured by SEM in combination with an image treatment software such as a Phenom user interface, from Thermo Fischer Scientific. The term “D90 expressed in number”, abbreviated “D90”, employed herein in combination with a particular range of particles indicates that 90 % of the particles observed in a bi-dimensional SEM image have their greater dimension, in thebi-dimensional image, with a size comprised within the particular range. Unless stated otherwise, the D90 of particles is measured by SEM in combination with an image treatment software such as a Phenom user interface, from Thermo Fischer Scientific. An average particle size of the particles and a particle size distribution can be determined by measuring the greater dimension viewed in a 2D image of a representative number of particles, for example at least 10 particles, more preferably at least 50 particles distributed over the whole surface of the 2D image wherein the dimensions (x,y) of the 2D image is at least 5 times greater than the average size of the particles, and wherein the 2D image has a minimum resolution of for example 1 to 20 nm or from 20 nm to 200 nm.

[0073] Preferably, the particles before etching can have a particle size distribution with a D90 comprised between 1 pm and 1mm, preferably between 1 pm and 500 pm, more preferably between 10 pm and 100 pm. Advantageously, such particles are less expensive.

[0074] Alternatively, the particles before etching can have a particle size distribution witha first fraction of particles having a D90 comprised between 1 nm and 1 pm, preferably between 10 nm and 1 pm, more preferably between 100 nm and 1 pm; anda second fraction of particles having a D90 comprised between 1 pm and 1 mm, preferably between 1 pm and 500 pm, more preferably between 10 pm and 100 pm;wherein the first fraction and the second fraction are initially separated from each other, their D90 measured separately, and then the fractions are mixed.

[0075] Advantageously, for cost reasons, particles having a particle size distribution with a D90 comprised between 1 pm and 1mm, preferably between 1 pm and 500 pm, more preferably between 10 pm and 100 pm are utilized alone or as a main fraction, e.g. more than 50 wt% in weight ofparticles, with a smaller fraction of particles having a D90 comprised between 1 nm and 1 pm, preferably between 100 nm and 1 pm, more preferably between 200 nm and 1 pm.

[0076] After the etching, the etched particles may have a substantially similar particle size distribution as before etching, or a particle size distribution inferior from 5% to 50%, preferably from 5% to 25% of the initial particle size distribution of the particles before etching. The etched particles have however an increased surface area compared to the particles before etching.

[0077] Preferably, the weak acid has a pKa superior or equal to 3.1 , more preferably superior or equal to 3.2, more preferably superior or equal to 3.3, even more preferably superior or equal to 3.4. Preferably, the pKa of the weak acid is also inferior or equal to 7.

[0078] Preferably, the weak acid is an organic acid. Particularly suitable weak acids include acetic acid, levulinic acid, lactic acid, or formic acid.

[0079] Preferably, the concentration of the weak acid is comprised between 0.1 mol / l and 3 mol / l.

[0080] In some embodiment, a polymeric binder material, preferably a non-ion conductive polymer, preferably in a pulverulent form can be blended with the particles in a blender before etching. Alternatively, the polymeric binder material is blended with the etched particles. Non-limiting polymeric binder materials include, PTFE, PEEK, polysulfone (PSU), polyethersulfone, polyvinylidene fluoride, poly(acrylonitrile), polyethylene-co-vinylalcohol, polycarbonate, polyimide, polyamide, polyamide-imide, polyether imide, ionomers, N-ionomers, cellulose acetate, and copolymers thereof. In preferred embodiments, the polymeric binder materials comprise PTFE and / or PEEK.

[0081] It has been observed that when the etched electrochemically active particles obtained by the process disclosed herein are present in a porous electrode of a flow cell electrolyzer used for electrolyisis of carbonoxides, the undesired production of hydrogen can be decreased at the profit of generation of hydrocarbons and / or oxygenates molecules.

[0082] In the context of the present invention, the term “carbon oxides” refers to carbon monoxide, carbon dioxide or the combination thereof.

[0083] In one embodiment, the etched electrochemically active particles are submitted to oxidation to provide an oxide layer of the metal oxide comprised in the electrochemically active particles. The oxide layer may cover partially or completely the outer surface of the etched particles. The oxidation step can comprise exposure of the etched electrochemically active particles to ambient air or to oxygen. The oxidation step can be alternatively performed by contacting the etched electrochemically active particles with other oxidants such as ozone, oxygen peroxide, permanganate compounds or any other oxidant known by the skilled person.

[0084] It has been observed that in use in an electrode of a flow cell electrolyzer, the etched particles comprising an oxide layer can provide additional or alternative benefits in a carbon oxide reduction process.

[0085] According to a second embodiment of the method of producing etched electrochemically active particles, the method comprises the steps of:Providing particles comprising an electrochemically active material, the particles having a particle size distribution comprised between 1 nm and 1mm, preferably between 10 nm and 500 pm, preferably between 100 nm and 500 pm measured by SEM as described above;Etching the particles with an aqueous solution of a weak acid, preferably having a pKa superior or equal to 3.0, during a time comprised between 30 minutes to 6 hours;such as described above, wherein the method further comprises, prior to the etching step, a pre-etching step of the particles with an aqueous solution of astrong acid having a pKa inferior to 3.0, during a time comprised between 10 seconds to 5 minutes.

[0086] The invention accordingly provides a method of producing etched electrochemically active particles, the method comprises the steps of:Providing particles comprising an electrochemically active material, the particles having a particle size distribution comprised between 1 nm and 1mm, preferably between 10 nm and 500 pm, preferably between 100 nm and 500 pm measured by SEM as described above;Pre-etching the particles with an aqueous solution of a strong acid having a pKa inferior to 3.0, during a time comprised between 10 seconds to 5 minutes; andEtching the particles with an aqueous solution of a weak acid, preferably having a pKa superior or equal to 3.0, during a time comprised between 30 minutes to 6 hours.

[0087] In embodiments, prior to the step of etching and if present, prior to the optional pre-etching step, the particles comprising an electrochemically active material can be provided as a porous electrode comprising said particles. In said embodiment the method of producing etched electrochemically active particles comprises the steps of;Providing a porous electrode comprising particles comprising an electrochemically active material, the particles having a particle size distribution comprised between 1 nm and 1mm, preferably between 10 nm and 500 pm, preferably between 100 nm and 500 pm measured by SEM as described above;Optionally pre-etching the particles with an aqueous solution of a strong acid having a pKa inferior to 3.0, during a time comprised between 10 seconds to 5 minutes; andEtching the particles with an aqueous solution of a weak acid, preferably having a pKa superior or equal to 3.0, during a time comprised between 30 minutes to 6 hours.

[0088] The porous electrode comprising the particles comprising an electrochemically active material can be prepared using any art known method to obtain a porous electrode, such as for example by blending the particles with a polymeric binder material, and an optional pore forming agent. Shaping and curing the blend to obtain the porous electrode comprising the particles comprising an electrochemically active material.

[0089] Hence in some embodiments, prior to the step of pre-etching, the particles are blended with a polymeric binder material. The polymeric binder material can be in a pulverulent form and can be mixed with the particles in a blender preferably during a time of at least 10 seconds, more preferably at least 30 seconds, even more preferably at least 1 minute and the blend is preferably pressed and optionally rolled into a calenderer to obtain a sheet of 20 to 500 pm, herein also referred to as the electrode body. The electrode body is cured to obtain the porous electrode. When the particles are blended with the binder or are part of a porous electrode, the step of pre-etching with a strong acid advantageously facilitates the initiation of the etching of the particles. The polymeric binder material preferably comprises a non-ion conductive polymer, preferably in a pulverulent form, and can be mixed in a blender with the particles before etching or alternatively with the etched particles. Non-limiting polymeric binder materials have been presented herein above.

[0090] Preferably, a step of washing the pre-etched particles with neutral water is applied before the step of etching.

[0091] In some embodiments, the strong acid may have a pKa inferior or equal to 3.1, inferior or equal to 3.2, inferior or equal to 3.3, or up to 3.4. Preferably, the pKa of the strong acid is inferior to 2.9, more preferably inferior or equal to 2.

[0092] Preferably, the strong acid is an inorganic acid. Particularly suitable strong acids include for example HCI, HNO3, H2SO4, HBr, HI, HCIO4, or HCIO3.

[0093] Preferably, the concentration of the strong acid is comprised between 0.1 mol / l and 3 mol / l. More preferably, the concentration of the strong acid is inferior or equal to 1 mol / l, more preferably inferior or equal to 0.5 mol / l.

[0094] The particles are preferably mixed with the polymeric binder material in a weight ratio of polymeric binder material to the particles between 2:98 and 50:50, preferably between 10:90 and 50:50.

[0095] When particles are mixed with the polymeric binder material, the pre-etching step wherein the particles are contacted with an aqueous solution of a strong acid advantageously facilitates the initiation of etching of the particles to obtain partially etched particles. The contact of the particles with the aqueous solution of the strong acid must be however limited in time and in concentration of the strong acid such as to prevent a too important dissolution or even a complete dissolution of the particles.

[0096] In some embodiments, the etched particles, optionally in presence of the polymeric binder material or as part of a porous electrode, are further submitted to oxidation to provide an oxide layer of the metal oxide comprised in the electrochemically active particles.

[0097] According to a second aspect, the present invention is related to etched particles comprising an electrochemically active material. The etched particles are preferably obtained by one of the embodiments of the methods described herein above. The term “electrochemically active material” refers to any metallic compound or alloy commonly used in flow cell electrolyzers such as presented herein above.

[0098] Preferably, the etched particles according to the invention have a particle size distribution similar to the initial particle size distribution of theinitial particles before etching, or inferior from 5% to 50%, preferably inferior from 5% to 30% compared to their initial particle size distribution.

[0099] The etched particles according to the invention comprises etched surfaces which are visible by SEM as seen in images of figures 3B; 4B and 5B. A change of morphology from particles before etching and after etching according to the process of production of etched particles as described above is visible by SEM for example on an image of 15 p x 15 pm to 100 pm x 100 pm.

[0100] In one embodiment, the etched particles are blended with a polymeric binder material. The polymeric binder material preferably comprises a non-ion conductive polymer such as described above.

[0101] The polymeric binder material may come from the process of producing the etched particles, so that the term “etched particles blended with a polymeric binder” may refer to polymeric binder material particles attached to the etched particles or etched particles partially embedded within polymeric binder material particles, or free particles of polymeric binder material and free etched particles or a combination thereof.

[0102] Preferably, at least a part of the etched electrochemically active particles comprises an oxidable metallic element and comprise an oxidized layer of said oxidable metallic element. The oxidized layer may cover partially or completely the outer surface of the etched electrochemically active particles.

[0103] When etched particles according to the invention, with or without an oxidized layer, are blended with a polymeric binder material, the particle size distribution of the etched particles can be measured by SEM combined with EDS and a treatment image software to distinguish etched particles comprising the electrochemically active material from binder particles.

[0104] The etched particles according to the present invention are advantageously used in an electrode of a flow cell electrolyzer for reductionof carbon oxides and generation of hydrocarbons and / or oxygenates molecules. Benefits of such etched particles compared to non-etched particles in an electroreduction process of carbon oxides includes reduction of hydrogen generation at the profit of higher conversion of CO and / or CO2 into molecules of interest such as C2H4, acetate (or acetic acid), ethanol or propanol.

[0105] According to a third aspect, the present invention is related to a method of manufacturing a porous electrode comprising etched particles such as described herein above.

[0106] The method of manufacturing a porous electrode comprising etched electrochemically active particles, comprising the steps of:shaping a blend comprising a polymeric binder material and particles comprising an electrochemically active material into an electrode body, and;producing etched electrochemically active particles;wherein the step of producing etched electrochemically active particles is realized before shaping the electrode body or after shaping the electrode body.

[0107] Various methods known in the art can be applied to manufacture a porous electrode comprising a matrix of polymeric binder material with particles dispersed therein.

[0108] In a first embodiment of the method of manufacturing a porous electrode, etched particles comprising an electrochemically active material according to the invention are mixed with a polymeric binder material, for example PTFE or PEEK and optionally a pore forming agent to form a blend and the blend is shaped as an electrode body which can be optionally cured, to obtain a porous electrode including etched particles dispersed therein.

[0109] The polymeric binder material preferably comprises a non-ion conductive polymer, preferably in a pulverulent form can be mixed in ablender with the particles before etching or alternatively with the etched particles. Non-limiting polymeric binder materials have been presented herein above.

[0110] The weight ratio of the polymeric binder material to the etched particles is preferably comprised between 2:98 and 50:50, preferably between 10:90 and 50:50.

[0111] Advantageously, the blend comprises up to 30 wt % of pore forming agent based on the total weight of the blend. Preferred pore forming agents can be polyvinylpyrrolidone (PVP), ammonium bicarbonate, or any other suitable pore forming agent known in the art.

[0112] In one embodiment, the electrode body can be obtained by compressing a blend into a mold wherein the blend comprises:etched particles comprising an electrochemically active material according to the invention;a polymeric binder material, and;optionally a pore forming agent.

[0113] In some embodiments, the blend comprises between 40 wt% to 80 wt% of etched particles, between 5 wt% to 30wt% of polymeric binder material and between 15 wt% to 30 wt% of pore forming agent, relative to the total weight of the blend. The blend can be pressed for example at 15*10A6 N / m2and then calendered with a calender machine to obtain an electrode sheet with a relatively uniform thickness of at least 100 pm, preferably inferior to 2 mm, more preferably inferior to 1 mm. Preferably, a second blend comprising from 50 wt% to 80 wt% of pore forming agent and 20 wt% to 50 wt% of polymeric binder material is pressed and calendered to obtain a second sheet with a relatively uniform thickness of at least 100 pm, preferably inferior to 2 mm, more preferably inferior to 1 mm, and then, the electrode sheet and the second sheet are calendered together and let in an oven at a temperature of at least 50°C, for example 70°C, for at least 12 hours.

[0114] The electrode body can be cured at an elevated temperature, preferably inferior to the temperature of fusion of the polymeric binder but sufficiently high such as to create porosity in the electrode body.

[0115] The porous electrode can be obtained according to any other alternative methods known by the skilled person. For example, one alternative method comprises the steps of:preparing a slurry comprising a solvent, between 1 % and 25 % by weight of a polymeric binder material and between 10 % and 80 % by weight of etched particles comprising an electrochemically active material, based on the total weight of the slurry, wherein the polymeric binder material is at least partially dissolved in the solvent;shaping the slurry, thereby obtaining a green body also referred as preformed electrode body;subjecting the preformed electrode body to phase inversion, thereby forming the porous electrode, wherein the porous electrode comprises a porous matrix comprising the polymeric binder material and the etched particles comprising the electrochemically active material dispersed therein.

[0116] Preferably, the weight ratio of the polymeric binder material to the etched particles in the slurry is between 2:98 and 50:50, and a total amount of the polymeric binder material and the etched particles in the slurry is comprised between 32 % and 80 % by weight, based on the total weight of the slurry.

[0117] Preferably, the solvent utilized for the preparation of the slurry comprise a polar aprotic solvent. The polar aprotic solvent is preferably selected from the group of dialkyl carbonates, cyclic carbonate esters, cycloaliphatic ethers, liquid pyrrolidones, aliphatic ketones, liquid piperidines, or a combination thereof. Dialkyl carbonates can be linear or branched. Non-limiting examples of dialkyl carbonates include diethyl carbonate, diallylcarbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, methyl isobutyl carbonate, methyl pentyl carbonate and methyl hexyl carbonate. Non-limiting examples of cyclic carbonate esters include ethylene carbonate or propylene carbonate or trimethylene carbonate. Non-limiting examples of cycloaliphatic ethers include oxirane, tetrahydrofuran, dioxane, dioxolane and dioxepane. Non-limiting examples of liquid pyrrolidones include N-methyl-pyrrolidinone (NMP), N-ethyl-pyrrolidinone (NEP) and 2-pyrrolidone. Non-limiting examples of aliphatic ketones include acetone, methyl ethyl ketone, diethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl butyl ketone, methyl isobutyl ketone, methyl sec-butyl ketone and methyl tert-butyl ketone. Non-limiting examples of liquid piperidines include formyl piperidine, N-methylpiperidine, N-ethylpiperidine and N-propylpiperidine.

[0118] Preferably, the phase inversion of the green body, or preformed electrode body, comprises contacting or immersing the green body or preformed electrode body with a non-solvent for the polymeric binder material so as to precipitate the polymeric binder material, thereby obtaining the porous electrode.

[0119] The non-solvent for the polymeric binder material preferably comprises a polar protic solvent. Non-limiting examples of suitable nonsolvents for the polymeric binder materials of the invention include water, an alcohol, an acid, or combinations thereof. Particularly preferred non-solvents include water and mixtures of N-Methyl-2-pyrrolidone (NMP) and water, for example having a volume ratio of NMP to water comprised between 0:100 (100% water) and 75:25, for example 50:50.

[0120] In some embodiments, the etched particles can be submitted to oxidation indifferently before or after shaping the preformed electrode. The oxidation step can comprise exposure of the etched electrochemically active particles to air or to oxygen. The oxidation step can be alternatively performedby contacting the etched electrochemically active particles with other oxidants such as ozone, oxygen peroxide, permanganate compounds or any other oxidant known by the skilled person.

[0121] In another embodiment of the method of manufacturing a porous electrode, particles comprising electroactive material are etched according to the first aspect of the invention after shaping of the electrode body.

[0122] Particles comprising electrochemically active material are mixed with a polymeric binder material and optionally a pore forming agent to form a blend which is then and shaped as an electrode body.

[0123] In some embodiments, the blend comprises between 40 wt% to 80 wt% of particles (non-etched particles), between 5 wt% to 30wt% of polymeric binder material and between 15 wt% to 30 wt% of pore forming agent, relative to the total weight of the blend. The blend can be pressed for example at 15*10A6 N / m2and then calendered with a calender machine to obtain an electrode sheet with a relatively uniform thickness of at least 100 pm, preferably inferior to 2 mm, more preferably inferior to 1 mm. Preferably, a second blend comprising from 50 wt% to 80 wt% of pore forming agent and 20 wt% to 50 wt% of polymeric binder material is pressed and calendered to obtain a second sheet sheet with a relatively uniform thickness of at least 100 pm, preferably inferior to 2 mm, more preferably inferior to 1 mm, and then, the electrode sheet and the second sheet are calendered together and cured in an oven at a temperature of at least 50°C, for example 70°C, for at least 12 hours.

[0124] The electrode body thereby obtained comprises a porous matrix comprising a polymeric binder material wherein particles comprising an electrochemically active material are dispersed into the porous matrix. The particles comprise exposed surfaces within pore cavities of the preformed electrode.

[0125] The particles in the electrode body are then pre-etched with an aqueous solution of a strong acid during a time comprised between 10seconds to 5 minutes, the electrode body is optionally washed with neutral water, then a further step of etching of the particles dispersed in the electrode body is realized by contacting the electrode body with an aqueous solution of a weak acid during a time comprised between 30 minutes to 6 hours. The concentrations of the strong acid and of the weak acid in the aqueous solutions are the same as described herein above in relation with the first aspect of the invention. A porous electrode comprising etched particles comprising electrochemically active material dispersed in a binder matrix is thereby obtained.

[0126] Alternatively, the shaping of the electrode body can be obtained by preparing a slurry comprising a solvent, between 1 % and 25 % by weight of a polymeric binder material and between 10 % and 80 % by weight of particles comprising an electrochemically active material, based on the total weight of the slurry, wherein the polymeric binder material is at least partially dissolved in the solvent;shaping the slurry, thereby obtaining a green body also referred as preformed electrode body;subjecting the preformed electrode body to phase inversion, thereby forming the porous electrode, wherein the porous electrode comprises a porous matrix comprising the polymeric binder material and the particles comprising the electrochemically active material dispersed therein.

[0127] The slurry is preferably prepared with at least one of the polar aprotic solvents described herein above. The phase inversion of the green body, or electrode body, preferably comprises contacting or immersing the green body or electrode body with a non-solvent for the polymeric binder material so as to precipitate the polymeric binder material, thereby obtaining the porous electrode. The non-solvent for the polymeric binder materialpreferably comprises at least one of the polar protic solvents as described herein above.

[0128] The same steps of pre-etching, optionally washing and etching the particles dispersed in the electrode body as described above is applied to obtain a porous electrode comprising etched particles comprising an electrochemically active material.

[0129] A fourth aspect of the invention is related to a porous electrode comprising etched particles comprising electrochemically active material. Preferably, the electrode is obtained from a method according to the third aspect of the present invention.

[0130] A fifth aspect of the invention is related to a flow cell electrolyzer. The flow cell electrolyzer comprises a porous electrode as described herein above. A schematic view of a flow cell electrolyzer 100 according to the invention is presented in Fig. 6.

[0131] Preferably, the flow cell electrolyzer comprises:a first cell 101 adapted for flowing a first flow of electrolyte 114 and comprising the porous electrode 110 according to the fourth aspect of the invention as a cathode; anda second cell 102 adapted for flowing a second flow of electrolyte 115 and comprising an anode 111;an anion exchange membrane 103 separating the first cell 101 from the second cell 102 while allowing the passage of ions from the first cell to the second cell and;a generator 112 electrically connected to the cathode 110 and to the anode 111 and configured to provide a current between the cathode and the anode;wherein the flow cell is configured for receiving a flow of carbon oxide passing through the cathode or through the first flow of electrolyte.

[0132] An embodiment of a flow cell electrolyzer is presented in Fig. 6. The flow cell electrolyzer comprises a first cell 101 and a second cell 102 separated from each other by an anion exchange membrane 103, preferably reinforced, and having a thickness comprised for example between 20 pm and 200 pm. The first cell 101 comprises the porous electrode 110 as a cathode, also referred herein as gas diffusion electrode (GDE). The cathode is separated from the anion exchange membrane by a volume of the first cell adapted for flowing a first electrolyte 114, also referred herein as a catholyte solution. The second cell 102 comprises an anode 111 which is separated from the anion exchange membrane 103 by a volume of the second cell adapted for flowing a second electrolyte 115, also referred herein as an anolyte solution. The anode 111 of the second cell 102 can be made of any electrochemically active material. In one embodiment, the anode 111 is a Nickel felt / Pt anode. In another embodiment, the anode 111 can be an IrOx / Ru-coated Pt anode. The cathode 110 and the anode 111 are electrically connected to a generator 112 for providing the electrolysis current from the cathode 110 to the anode 111. A gas supply 113 is arranged at a side of the cathode 110 opposite to the side of the cathode in contact with the catholyte solution, such as to allow the flow of a gas through the cathode, also referred as a gas diffusion electrode. The gas to be electrolyzed and flowing through the cathode is preferably a carbon oxide such as CO or CO2 or a mixture thereof. Preferably, the first cell 101 and the second cell 102 comprise inlets 116, 117 for supplying respectively the catholyte 114 and the anolyte 115. The first cell 101 further comprises an outlet 118 for evacuating the catholyte 114 and optionally any element or gas formed during an electroreduction process. The second cell 102 also preferably comprises an outlet 119 for evacuating the anolyte 115 and any molecule or gas formed during an electroreduction process. Preferably, a flow of catholyte solution is circulated through the first cell and a flow of anolyte solution is circulated through the second cell. In one embodiment, the catholyte and the anolyte comprise thesame electrolyte, for example KOH. In another embodiment, the catholyte and the anolyte are different.

[0133] A sixth aspect of the present invention is related to a process of reduction of carbon oxides, using a flow cell electrolyzer as described above. In the context herein, the term “carbon oxides” refers to carbon monoxide, or carbon dioxide or a combination thereof.

[0134] Preferably, the flow cell electrolyzer is operated with at least one of the following conditions:A current density comprised between 50mA / cm2to 650 mA / cm2, preferably between 50 mA / cm2to 400 mA / cm2;An electrolyte concentration comprised between 2 to 5 mol / l, preferably between 2.5 to 4 mol / l, more preferably between 2.5 to 3.5 mol / l;An electrolyte flow rate comprised between 10 ml / min and 50 ml / min, preferably between 20 ml / min and 40 ml / min, more preferably between 25 ml / min and 35 ml / min;A carbon oxide flow rate comprised between 10 and 20 ml / min, preferably between 11 and 16 ml / min, more preferably between 11 and 14 ml / min.

[0135] The inventors have provided herein a durable metal-based electrode and successfully applied it to CO electrolysis in a flow cell configuration, which can also be adapted for use in a zero-gap cell.

[0136] The etched particles comprising electrochemically active material which are dispersed in a porous electrode and used for CO electrolysis, have shown significant improvements in catalytic performance, including enhanced faradaic efficiency for hydrocarbons and / or oxygenates products, increased single-pass conversion rates, reduced working potentials, and lower cell voltage.

[0137] It has been found that by providing etched particles according to the invention in a porous electrode for a flow cell electrolyzer, the use of such porous electrode in a process for the electrocatalytic reduction of CO to hydrocarbons and / or oxygenates products allows achieving a high singlepass conversion rate and exceptional selectivity.

[0138] The process can reduce the competing hydrogen evolution reaction to less than 20%, preferably to 15% or less. In some embodiments, the process effectively suppresses the competing hydrogen evolution reaction to less than 10%. CO is converted into a gaseous product (ethylene) and a mixture of liquid products (e.g. acetate or acetic acid, ethanol, and propanol, in some embodiments formic acid). The CO conversion rate can reach up to 95%, with H2 faradaic efficiency remaining around 10% at a high current density (250-350 mA / cm2).

[0139] The CO conversion rate can be determined by quantifying gasphase and liquid-phase products by gas chromatography (GC) and proton nuclear magnetic resonance (NMR) spectroscopy, respectively.

[0140] GC measurements were obtained using a CompactGC40apparatus from Global Analyser Solutions, equipped with:A first set of consecutive columns ShinCarbon 1m*0.53mm + ShinCarbon 0.5m*0.53mm run with N2 for H2 detection; A second set of consecutive columns Havesep N, 60-80, 1 m ‘1 / 16’ 1mm ID; Molsieve 5A, 60-80, 2m ‘1 / 16’ 1mm ID, run in parallel to the first set of columns with He for detection of hydrocarbons, oxygenates and carbon oxides;With a thermal conductivity detector for quantifying H2;With a flame ionization detector for quantifying the hydrocarbons, oxygenates and carbon oxides; andWherein N2 and He as a carrier gas were introduced at an injection pressure of 2 bar.

[0141] Liquid products such as formic acid, acetic acid, ethanol and propanol were identified by proton nuclear magnetic resonance spectroscopy (NMR). 450 pL of final electrolyte solution was mixed with 50 pL of a D2O stock solution containing 10 mM of DMSO and 50 mM of phenol as the internal references.1H NMR spectra of samples were obtained from Spinsolve™ 60 (Magritek) spectrometer, with the initial program names as 1 D PRESAT OPTIONS with setting of parameters FREQ SEARCH [Auto]; SAT FREQ (pmm) [4.77]; SAT POWER(db) [-65]; SAT PERIOD (s) [3]; DUMMY SCANS [0], SCANS

[0064] , ACQUISATION TIMES [6.4s]; REPETITION TIME [15s],

[0142] Depending on the reaction conditions, the selectivity for carbonbased products from carbon monoxide can be tuned. The highest single-pass faradaic efficiency achieved was approximately 50%, the highest reported in the literature. At a certain high current density, the faradaic efficiency of ethylene can also reach up to 40%. The cell voltage is as low as 2.6 V under conditions where CO electroreduction achieves more than 90% faradaic efficiency for hydrocarbons and / or oxygenates products, with nearly 95% faradaic efficiency at a current density of 250 mA / cm2.

[0143] This invention, initially developed using a flow cell system, can also be adapted to a membrane electrode assembly (MEA) system for even better results.

[0144] Examples

[0145] Example 1: Preparation of electrodes comprising etched copper particles

[0146] Examples of electrodes comprising etched copper particles have been obtained according to the method of the invention, as described here below.

[0147] Copper powder with a particle size distribution D90 comprised between 20 pm and 50 pm were provided and measured by SEM as presented Fig. 19.

[0148] A first blend was prepared by mixing in a mass ratio:119 g of copper particles (non-etched particles);17 g of PTFE; and34 g of ammonium bicarbonate.

[0149] The first blend was be pressed at 150 kN in a 10 cm x 10 cm press, and the pressed blend was then calendered with a multi-step calender machine to obtain an electrode sheet with a relatively uniform thickness of 531 pm.

[0150] A second blend was prepared by mixing 70 g of ammonium bicarbonate with 30 g of PTFE. The second blend was pressed in the same press and calendered to obtain a second sheet with a relatively uniform thickness of 560 pm.

[0151] Then, the electrode sheet and the second sheet were calendered together in a multi-step calender machine adapted to receive the two sheets and to obtain joined sheets with a relatively uniform thickness of 700 pm. The joined sheets were cured at 70°C, for a night.

[0152] Five untreated electrodes obtained according to the process described herein above have been provided.

[0153] SEM images of the untreated electrode with the side comprising copper particles before etching treatment are presented in Fig. 1 A and in Fig.1 B with their respective magnifications. The surface of the copper particles appears relatively smooth.

[0154] The electrodes were then immersed in a diluted sulfuric acid aqueous solution (0.05 Mol / I) during 3 minutes for pre-etching the copper particles within the electrode. The pre-treated (pre-etched) electrode wasthen rinsed several times with neutral water. SEM images of the pre-etched particles in the electrode are provided in Fig. 2A with a and in Fig. 2B with their respective magnifications. Compared to the SEM image of Fig. 1B, the SEM image of Fig. 2B shows a few relatively narrow grooves on the surface of copper particles indicating the initiation of etching of the copper particles.

[0155] The pre-treated electrodes have been immersed in an aqueous solution of acetic acid (0.5 mol / l) under agitation for 6 hours. Three electrodes have been taken respectively after 2 hours, 4 hours and 6 hours and SEM images of these electrodes, with the side comprising the copper particles, were acquired.

[0156] SEM images of the electrode surface comprising copper particles etched for 2 hours are shown in Fig. 3A and 3B with their respective magnification. The SEM image of Fig. 3B shows a rugous surface of the copper particles, indicative of a higher specific surface area compared to the copper particles before pre-etching and after pre-etching.

[0157] SEM images of the electrode surface comprising copper particles etched for 4 hours are shown in Fig. 4A and 4B with respective magnification. The figure 4B shows a rugous surface of the copper particles with some deeper grooves.

[0158] SEM images of the electrode surface comprising copper particles etched for 6 hours are shown in Fig. 5A and 5B with respective magnification. The Fig. 5B shows a more rugous surface of the copper particles compared to the materials obtained after 2 hours and 4 hours. The specific surface area is also increased.

[0159] Example 2: Electrolysis of CO using GDE comprising copper particles submitted to different times of etching

[0160] A flow cell electrolyzer according to the embodiment described in the Fig. 6 was utilized for electrolysis of CO. The first cell and the second cell of the flow cell electrolyser were separated by a fumasep® FAS-PET-130anion exchange membrane from Fuelcell store. Five electrolysis process examples were performed with the five different electrodes obtained in example 1, with the same electrolysis conditions comprising:CO flow rate of 11.5 ml / min;KOH concentration of 2.M mol / l in the electrolyte (catholyte and anolyte) solution;An electrolyte flow rate of 30 ml / min;A galvanic electrolysis at a current density of -250 mA / cm2.

[0161] The Fig. 7 shows the CO conversion rate (cco), measured by a compact gas chromatography and the faradaic efficiency (FE) for CO electrolysis in the flow cell for the five different GDE utilized. The results shows a correlation between:the reduction of the faradaic efficiency of the competing hydrogen evolution reaction (HER) and;the time of exposure of the copper particles during the etching treatment in acetic acid solution.

[0162] This suggests that acid etching removes active sites favourable for HER while increasing the exposed surface area for CO electrolysis active sites. For electrodes comprising non-etched copper particles, the single-pass CO conversion rate was of 62%. For electrodes comprising copper particles that have been pre-etched during a brief exposure to diluted sulfuric acid, the single-pass CO conversion rate slightly increased from 62% to 65.9%. The electrodes that comprise copper particles that have been pre-etched followed by acetic acid etching for 2 hours, 4 hours and 6 hours further improved the CO conversion rate, gradually increasing it to respectively 72.1%, 73.6%, and 78.9%. The highest CO conversion rate achieved was nearly 10 ml / min, compared to 7 ml / min without Cu-GDE pretreatment. Additionally, the faradaic efficiency for hydrocarbons and / or oxygenates products increased from 69% (with fresh Cu-GDE without acid etching) to 80%.

[0163] Example 3: Pretreatment of copper powder with sulfuric acid, followed by etching with different organic acids followed by a natural oxidation process

[0164] Five electrode comprising untreated copper particles and obtained according to the process described in relation with example 1 were submitted to a pre-etching step for 3 minutes in presence of H2SO4 in a concentration of (0.05 mol / l). The pre-etched electrodes were filtrated and washed. The five pre-etched particle samples were then submitted to an etching step with different organic acid solutions having the same concentrations (0.5 mol / l). All the etching steps were realized during the same amount of time (3 hours) in order to evaluate the influence of different organic acids. The five different organic acids aqueous solutions were used for the five different etchings were comprising respectively citric acid, formic acid, lactic acid, levulinic acid and acetic acid. Each of the electrodes comprising the etched particles where then oxidized under ambient air conditions.

[0165] Figure 8 shows different SEM images with respective magnifications for electrode surfaces comprising etched copper particles that were etched using the different acids, from left to right: the untreated copper particles, copper particles etched with citric acid aqueous solution, copper particles etched with formic acid aqueous solution, copper particles etched with lactic acid aqueous solution, copper particles etched with levulinic acid aqueous solution, and copper particles etched with acetic acid aqueous solution.

[0166] When acetic acid was replaced with other organic acids, similar morphological changes occurred, except when using citric acid.

[0167] Example 4: Electrolysis of CO using GDE comprising copper particles submitted to etching by different acids

[0168] Each of the electrodes comprising copper particles etched with the different organic acids of example 3 were used in the flow cell electrolyser according to the embodiment described in relation with Fig. 6 for electrolysisof CO. Each of the CO electrolysis processes were realized with the five different electrodes with the same operating conditions comprising:CO flow rate of 11.5 ml / min;KOH concentration of 2.5 mol / l in the electrolyte (catholyte and anolyte) solution;An electrolyte flow rate of 30 ml / min;A galvanic electrolysis at a current density of -250 mA / cm2.

[0169] The Fig. 9 shows the faradaic efficiency (FE) for CO electrolysis in a flow cell setup using different gas diffusion electrodes comprising copper particles that have been submitted to an etching treatment according to the invention using different organic acids. The Fig. 10 shows the CO conversion rates for the CO electrolysis using such different electrodes.

[0170] When these electrodes comprising etched copper particles obtained from the example 3 were used for CO electrolysis under identical conditions, compared to the non-modified Cu-GDE electrode, the acid etching treatment with formic acid, lactic acid, levulinic acid, or acetic acid, followed by natural oxidation, resulted in a completely faceted copper morphology, which significantly suppressed the HER and improved the catalytic performance for CO electroreduction. However, copper particles etched with a citric acid solution, when used in the GDE electrode for CO electrolysis provided less good results in term of CO conversion and faradaic efficiency compared to the use of a non-modified Cu-GDE electrode. The pKa of citric acid is relatively low compared to the pKa of the other acids used.

[0171] The acid treatment of copperparticles with formic acid, lactic acid, levulinic acid, or acetic acid, improved both the faradaic efficiency for hydrocarbons and / or oxygenates products and the single-pass CO conversion rate in all cases. Among these etched copper particles used in the GDE, those etched with acetic acid provided the best catalytic performance, achieving a single-pass CO conversion rate of nearly 90% with an inlet flowrate of 11.5 mL min-1. Additionally, the faradaic efficiency for hydrocarbons and / or oxygenates products was close to 90%, with ethanol accounting for nearly 40% of that efficiency. Also, as seen in figure 9, copper particles etched with levulinic acid, when used in the GDE for CO electrolysis provides a remarkable higher amount of ethanol, despite a less good reduction of HER compared to copper particles etched with acetic acid.

[0172] Example 5: manufacturing of GDE

[0173] In the present example, two electrodes have been produced according to different embodiments of the process for manufacturing the electrodes according to the invention.

[0174] A first electrode was produced according to the process presented in relation with example 1. The electrode comprising untreated copper particles was provided in an aqueous solution comprising H2SO4 in a concentration of 0.05 mol / l during 3 minutes, then the electrode was washed with neutral water and provided in an aqueous solution comprising acetic acid in a concentration of 0.5mol / l during 3 hours such as to obtain etched copper particles in the electrode. The electrode was then let under ambient air for oxidation of the etched copper particles. This electrode is referred herein after as “etched after GDE”.

[0175] Fig. 11A and Fig. 11 B presents SEM images of an electrode surface of the first electrode, with their respective magnifications. The very rugous surfaces of the etched copper particles included in the electrode are well visible.

[0176] A second electrode was produced according to the same process, but wherein prior to forming the second electrode, copper particles were first provided in an aqueous solution comprising H2SO4 in a concentration of 0.05 mol / l during 10 seconds , then the pre-etched copper particles were washed with neutral water and provided in an aqueous solution comprising acetic acid in a concentration of (0.5mol / l) during 30 minutes such as to obtain etched copper particles. The etched copper particles were let under ambient air foroxidizing the etched copper particles. This electrode is referred herein after as “etched before GDE”.

[0177] Fig. 12A and Fig. 12B presents SEM images of an electrode surface of the second electrode, with their respective magnifications. The very rugous surfaces of the etched copper particles included in the electrode are well visible. Compared to the first electrode wherein the copper particles were etched after the formation of the first electrode, the second electrode morphology appears similar, with all metallic copper on the Cu-GDE electrode becoming faceted and exhibiting a significant high specific surface area.

[0178] A comparative electrode was also made by providing a mixture of copper particles and PFTE particles and processing the mixture to form the GDE, without any etching of the copper particles before or after shaping of the electrode.

[0179] Example 6: electrolysis of CO using GDE comprising etched copper particles, wherein the etching of copper particles is performed before or after the manufacturing of the GDE

[0180] The comparative Cu-GDE, the GDE comprising the etched copper particles etched after the shaping of the GDE (referred herein after as “etched after GDE”), and the GDE comprising the etched copper particles etched before the shaping of the GDE (referred herein after as “Etched before GDE”) were used in a flow cell electrolyzer for CO electrolysis with the same electrolysis conditions as presented for example 2 and 4.

[0181] The figure 13 shows the faradaic efficiency for the comparative electrode, the etched after GDE and the etched before GDE. Both etched after GDE and etched before GDE have a better faradaic efficiency compared to the comparative Cu-GDE. The etched after GDE appears to provide a better faradaic efficiency when used in CO electrolysis, so it appears more advantageous to apply to process for etching the copper particles on an GDE body comprising copper particles.

[0182] As presented in Fig. 14, compared to the non-modified comparative Cu-GDE, both etched after GDE and etched before GDE provided an excellent catalytic performance for the production of hydrocarbons and / or oxygenates products from CO electrolysis, achieving nearly a 90% single-pass CO conversion rate, while suppressing the competing HER to around 10%.

[0183] Interestingly, as shown in Fig. 16A, CO electrolysis at -250 mA / cm2using the non-modified Cu-GDE electrode required a very negative potential of -2.0 V vs. Ag / AgCl. However, after modification through acid etching followed by oxidation, the working potential under the same conditions shifted by 500 mV to -1.5 V vs. Ag / AgCl. Additionally, the CO reaction rate improved from 7 mL min-1to 10 mL min-1, representing a nearly 50% increase. More importantly, as shown in Fig. 16B, the cell voltage decreased from 4.3 V to 2.5 V, significantly enhancing the economic energy efficiency.

[0184] Example 7: CO electrolysis with various electrolytes concentrations

[0185] The etched after GDE as described in example 5 and 6 was used in a flow cell for CO electrolysis under the following constant conditions:CO flow rate of 11.5 ml / min;An electrolyte flow rate of 30 ml / min;A galvanic electrolysis at a current density of -250 mA / cm2.

[0186] The KOH concentration of the electrolyte was varied from 2.5 to 3.5 and then 4.5 mol / l.

[0187] As shown in Figure 17B, increasing the electrolyte concentration to 3.5 M KOH at -250 mA / cm2further raised the single-pass CO conversion rate to approximately 93.5%, with a total faradaic efficiency of 90% as presented in Fig. 17A, and a CO reaction rate of 10.75 ml / min as shown in Fig. 17C. During this optimization process, it was found that galvanostatic electrolysis at -250 mA / cm2in 3.5 M KOH provided the optimal potential forCO electrolysis using the etched before Cu-GDE electrode, achieving -1.6 V vs Ag / AgCI with a cell voltage of 2.6 V.

[0188] Example 8: CO electrolysis with various current density conditions

[0189] The etched after GDE electrode as described for example 5 to 7 was used in a flow cell electrolyzer for CO electrolysis in the conditions comprising:CO flow rate of 11.5 ml / min for applied current densities between 50 and 250 mA / cm2;CO flow rate of 16 ml / min for applied current density of 350 mA / cm2;An electrolyte flow rate of 30 ml / min;A KOH concentration of 3.5 mol / l in the electrolyte solution.

[0190] The applied current density was varied from 50 mA / cm2to 350 mA / cm2.

[0191] As shown in Figure 18A, at a current density of 50 mA / cm2, acetic acid was the dominant product, achieving a faradaic efficiency of 47.5%, the highest reported in the literature or patents. Under these conditions, hydrogen evolution was completely suppressed, resulting in a single-pass CO conversion rate of 41.8%, with nearly pure CO as the outlet gas, which could be recycled as the initial CO electrolysis reactant. The working potential for galvanostatic electrolysis at -50 mA cm-2was -1.3 V vs. Ag / AgCI, with a cell voltage of 1.8 V, indicating that the modified Cu-GDE electrode under optimal conditions can fully suppress the competitive hydrogen evolution reaction and efficiently produce acetic acid.

[0192] When increasing the current, the faradaic efficiency for acetic acid gradually decreased, reaching only 18% at -350 mA / cm2, while the CO reaction rate increased to nearly 13.7 ml / min as presented in Fig. 18C.

[0193] The working potential for CO galvanostatic electrolysis increased with current density, from -1.3 V at -50 mA / cm2to -1.5 V at -150 mA / cm2and -1.6 V vs. Ag / AgCI at -250 mA / cm2and -350 mA / cm2. Meanwhile, the cell voltage gradually increased from 1.8 V at -50 mA / cm2to 2.3 V at -150 mA / cm2and 2.6 V at both -250 mA / cm2and -350 mA / cm2.

[0194] At increased applied current densities for CO electrolysis using the modified Cu GDE electrode, the CO reaction rate rises from 14 ml / min at -350 mA / cm2to 14.3 ml / min at -450 mA / cm2, reaching a peak of 15.3 ml / min at -550 mA / cm2. However, at a current density of 650 mA / cm2, the reaction rate declines to 14.7 ml / min.

[0195] Although the reaction rate initially increases with higher current density, the single-pass CO conversion rate gradually decreases, hitting a low of 29.3% at -650 mA cm-2, with a CO feed rate of 50 mL min-1and a working potential of -1.8 V vs Ag / AgCI. Additionally, the faradaic efficiency of the competing hydrogen evolution reaction increases with current density, reaching nearly 40%.

[0196] Example 9: Preparation of electrodes comprising etched bismuth particles

[0197] Two examples of electrodes comprising etched bismuth particles have been obtained according to the method of the invention, as described hereinbelow.

[0198] Bismuth powder (>99.5%, 325 mess, less than 40 pm) were obtained from VWR, CAS 7440-69-9.

[0199] A first blend was prepared by mixing in a mass ratio:119 g of bismuth powder (non-etched particles)17 g of PTFE; and34 g of ammonium bicarbonate.

[0200] The first blend was pressed at 150 kN in a 10 cm x 10 cm press, and the pressed blend was then calendered with a multi-step calender machine to obtain an electrode sheet with a relatively uniform thickness of 531 pm.

[0201] A second blend was prepared by mixing 70 g of ammonium bicarbonate with 30 g of PTFE. The second blend was pressed in the same press and calendered to obtain a second sheet with a relatively uniform thickness of 560 pm.

[0202] The electrode sheet and the second sheet were then calendered together in a multi-step calender machine adapted to receive the two sheets and to obtain joined sheets with a relatively uniform thickness of 700 pm. The joined sheets were cured at 70°C for a night.

[0203] Three uncoated electrodes were obtained according to the process described hereinabove. A first electrode was left untreated (unmodified Bi GDE).

[0204] A second electrode was pre-etched by immersion during three minutes in a solution of 0.05 M H2SO4, followed by risning with water (H2SO4-treated Bi GDE).

[0205] A third electrode was pre-etched in the same way, followed by rinsing with water followed by an etching treatment by immersion in 0.5 M acetic acid for three hours (H2SO4 and acetic acid-treated Bi GDE).

[0206] Example 10: Electrolysis Set-up and Procedure

[0207] Three experimental electrochemical reductions of CO2 were conducted in a flow cell electrolyzer according to the embodiment described in Fig. 6, using the electrodes of Example 9. The first cell and the second cell of the flow cell electrolyzer were separated by a Nation™ N117 membrane.

[0208] In a first set-up, the first cell of the flow cell electrolyzer comprised the first untreated Bi GDE electrode of Example 9 as cathode. In a second set-up, the first cell of the flow cell electrolyzer comprised the second H2SO4-treated Bi GDE electrode of Example 9 as cathode. In a third set-up, the first cell of the flow cell electrolyzer comprised the third H2SO4 and acetic acid-treated Bi GDE electrode of Example 9 as cathode.

[0209] In each of these set-ups, the second cell of the flow cell electrolyzer comprised an IrOx / Ru-coated Pot plate as a second electrode.

[0210] In each of these set-ups, the first cell comprised a flowing catholyte comprising 0.5 M KHCO3 (saturated with CO2) and the second cell comprised a flowing anolyte comprising 0.5 H2SO4.

[0211] The cathode was a bismuth containing GDE with a 1 cm2geometric surface area. CO2 was fed to the back of the GDE at 30 mL / min, and the catholyte was circulated over the electrode front at 20 mL / min.

[0212] Example 11: System Resistance

[0213] The resistance for each set-up of the flow cell electrolyzers described in Example 10 was measured with a VMP-3e multichannel potentiostat from BioLogic. Electrochemical impedance spectroscopy (EIS) was applied for measuring the system resistance. EIS is an extension of the high frequency resistance (HFR) method known by the skilled person and differs from HFR in two ways. Whereas HFR employ a single frequency and only examines the real component of the impedance, EIS involves imposing the AC perturbation over a broad range of frequencies, typically 10 kHz to 1 Hz or lower, and monitoring the resulting variations in magnitude and phase of the cell voltage and current in order to determine the complex impedance (Z’, Z”, orZ-phase relation) of the electrochemical system being studied. This results in a rich dataset from which several parameters may be extracted via equivalent circuit modelling. These parameters include non-electrode ohmic resistance, electrode properties such as ohmic resistance and activation polarization resistance, double-layer capacitance, and transport properties. The real component of the impedance measured using SEI at the frequency used for a HFR measurement should be identical to the resistance obtained using HFR.

[0214] As shown in Figure 20, the cell’s system resistance was dependent on the cathode pretreatment. The resistance dropped from 10.4 Q for the unmodified Bi GDE to 7.9 Q for the FhSCU-treated Bi GDE, and decreased further to 6.1 Q for the H2SO4-treated Bi GDE.

[0215] Example 12: Electrochemical voltage data

[0216] Galvanostatic CO2 electrolysis at -100 mA / cm2revealed that while the working potential (ac. -2.6 V vs. Ag / AgCI) was largely unaffected by the electrode pretreatment (Fig. 21 A), the overall cell voltage was substantially lowered. The cell voltage decreased from 9.3 V with the unmodified Bi GDE to 6.4 V with the H2SO4-treated Bi GDE and 6.8 V with the H2SO4-treated Bi GDE (Fig. 21 B).

[0217] Example 13: Gas and Liquid Product Analysis

[0218] Analysis of the electrolysis products by GC and1H NMR demonstrated that acid pretreatment of the Bi GDE electrode effectively suppresses the hydrogen evolution reaction (HER). As presented in Fig. 22, the Faradaic efficiency of H2 (FE H2) was slightly reduced from 23% for the unmodified electrode to 21% after H2SO4 treatment. The combined H2SO4 and acetic acid treatment further suppressed the HER, lowering the FE H2 to 15%. This suppression correlated with an increase in the formic acid Faradaic efficiency from 77% to 85%.Nomenclature100 flow cell electrolyzer101 first cell102 second cell103 anion exchange membrane 110 gas diffusion electrode 111 anode112 generator113 CO feed114 catholyte115 anolye116 first cell inlet117 second cell inlet118 first cell outlet119 second cell outlet

Claims

46Claims1. Method of producing etched particles comprising an electrochemically active material, the method comprising the steps of:- Providing particles comprising an electrochemically active material, the particles having a particle size distribution D90 expressed in number comprised between 1 nm and 1mm, preferably between 10 nm and 500 pm measured by SEM in combination with an imaging treatment software;- Etching the particles with an aqueous solution of a weak acid during a time comprised between 30 minutes to 6 hours.

2. Method according to claim 1 , further comprising a step of pre-etching the particles with an aqueous solution of a strong acid during a time comprised between 10 seconds to 5 minutes, prior to the step of etching.

3. Method according to claim 1 or 2 wherein the particles before etching or pre-etching are blended with a polymeric binder material.

4. Method according to any one of the preceding claims, wherein the etched particles are blended with a polymeric binder material.

5. Method according to any one of the preceding claims, wherein the particles comprise at least an oxidable metallic element, preferably selected from copper or bismuth as the oxidable metallic element, the method further comprising an oxidation step to provide at least a layer of oxide of the metallic element on the etched electrochemically active particles.

6. Method according to any one of the preceding claims wherein the particles have:47- A particle size distribution with a D90 expressed in number and measured by SEM in combination with an imaging treatment software, comprised between 1 nm and 1pm, preferably between 10 nm and 1 pm, more preferably between 100 nm and 1 pm; or - a particle size distribution with a D90 expressed in number and measured by SEM in combination with an imaging treatment software, comprised between 1 pm and 1mm, preferably between 1 pm and 500 pm, more preferably between 10 pm and 100 pm; or - a particle size distribution witho a first fraction of particles having a D90 expressed in number and measured by SEM in combination with an imaging treatment software, comprised between 1 nm and 1 pm, preferably between 10 nm and 1 pm, more preferably between 100 nm and 1 pm, and;o a second fraction of particles having a D90 expressed in number and measured by SEM in combination with an imaging treatment software, comprised between 1 pm and 1 mm, preferably between 1 pm and 500 pm, more preferably between 10 pm and 100 pm.

7. Etched particles comprising electrochemically active material, obtained by the method according to any one of the claims 1 to 6, wherein the etched particles have a particle size distribution comprised between 1 nm and 1 mm measured by SEM preferably with an imaging treatment software.

8. Etched particles according to claim 7 further blended with a polymeric binder material.

489. Etched particles according to claim 7 or 8, wherein at least part of the etched particles comprises an oxidable metallic element and comprises an oxidized layer of said oxidable metallic element.

10. Method of manufacturing a porous electrode comprising etched electrochemically active particles, comprising the steps of:- shaping a blend comprising a polymeric binder material and particles comprising an electrochemically active material into an electrode body, and;- producing etched electrochemically active particles according to the method of any one of the claims 1 to 6;wherein the step of producing etched electrochemically active particles is realized before shaping the electrode body or after shaping the electrode body.

11. Electrode obtained from the process of claim 9, the electrode comprising a porous matrix comprising a particulate material according to claims 6 to 8.

12. Flow cell electrolyzer comprising an electrode according to claim 11.

13. Flow cell electrolyzer according to claim 12 comprising:- a first cell adapted for flowing a first flow of electrolyte and comprising the electrode of claim 10 as a cathode;- a second cell adapted for flowing a second flow of electrolyte and comprising an anodewherein the flow cell is configured for receiving a flow of carbon monoxide, or carbon dioxide, or a combination thereof passing through the cathode or through the first flow of electrolyte.

14. Process of electrocatalytic reduction of carbon oxides to hydrocarbon and / or oxygenate products using a flow cell electrolyzer according to any one of the claims 12 or 13.

15. Process of electrocatalytic reduction of carbon monoxide, or carbon dioxide, or a combination thereof to hydrocarbons and / or oxygenates products according to claim 14 wherein the flow electrolyzer is operated with at least one of the following conditions:- A current density comprised between 50mA / cm2to 650 mA / cm2, preferably between 50 mA / cm2to 400 mA / cm2;- An electrolyte concentration comprised between 2 to 5 mol / l, preferably between 2.5 to 4 mol / l, more preferably between 2.5 to 3.5 mol / l;- An electrolyte flow rate comprised between 10 ml / min and 50 ml / min, preferably between 20 ml / min and 40 ml / min, more preferably between 25 ml / min and 35 ml / min;- A carbon oxide flow rate comprised between 10 and 20 ml / min, preferably between 11 and 16 ml / min, more preferably between 11 and 14 ml / min.

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