Techniques for favoring carbon oxides electroreduction into ethylene

Abstract

The present disclosure relates to a sequential electroreduction process to convert CO2 into multicarbon products including ethylene, the process comprising (a) electroreducing CO2 in presence of a metallic CO2R catalyst in a first CO2RR stage to produce CO; and electroreducing CO in presence of a metallic COR catalyst in a second COR stage to produce multicarbon products comprising ethylene, wherein the metallic CO2R catalyst and the metallic COR catalyst are a metal-Sb compound comprising a metal and antimony, the antimony being atomically dispersed in a lattice formed by a crystalline structure of the metal.

Description

TECHNIQUES FOR FAVORING CARBON OXIDES ELECTROREDUCTION INTO ETHYLENETECHNICAL FIELD

[0001] The present techniques generally relate to the carbon oxides electroreduction into carbon products including ethylene, and more particularly to favoring carbon oxides electroreduction into ethylene based on at least one of a cation effect in an electrolyte and antimony doping in a catalytic system. The present disclosure also relates to a sequential electroreduction process to convert C02 into multicarbon products including ethylene.BACKGROUND

[0002] Renewable electricity powered CO2reduction (CO2R) opens a promising route to upgrade CO2to ethylene, an industrial feedstock in high demand. Compared with direct transformation from CO2to ethylene, the two-step CO2-CO-C2H tandem electrolysis is more efficient and sustainable, by circumventing issues such as CO2crossover and carbonate formation. However, the selectivity and activity of CO reduction (COR) to ethylene are not satisfying, and the underlying mechanism remains elusive.

[0003] Electrochemical CO reduction (COR) is an attractive technique to achieve carbon neutrality. However, this reaction usually generates a mixture of multicarbon products, and the underlying mechanism of such dispersive selectivity remains unclear. As a result, the selective and efficient production of a single product has yet to be achieved.

[0004] In addition, catalysts that are known to achieve satisfactory CO2conversion efficiency do not show promising results for CO conversion efficiency.

[0005] There is still a need for techniques that would overcome the lack of selectivity towards ethylene known in the field of COR.SUMMARY

[0006] The present techniques respond to the above-mentioned need by providing a metallic catalyst and a method for carbon oxides (CO2and / or CO) electroreduction into at least ethylene. Aspects of a related electroreduction system and method to prepare the metallic catalyst are further provided. In addition, the developed metallic catalyst canadvantageously be used as a metallic CO2R catalyst or a metallic COR catalyst to perform single-step C02to-ethylene, single-step CO-to-ethylene, or sequential C02-to-ethylene (via consecutive CO2RR stage and CORR stage) electroreduction. More particularly, aspects of the present techniques are as follows:

[0007] In a first aspect, the present disclosure relates to a sequential electroreduction process to convert CO2into multicarbon products including ethylene, the process comprising: a) electroreducing CO2in presence of a metallic CO2R catalyst in a first CO2RR stage to produce CO; and b) electroreducing CO in presence of a metallic COR catalyst in a second COR stage to produce multicarbon products comprising ethylene, wherein the metallic CO2R catalyst and the metallic COR catalyst are a metal-Sb compound comprising a metal and antimony, the antimony being atomically dispersed in a lattice formed by a crystalline structure of the metal.

[0008] Advantageously, the metallic CO2R catalyst and the metallic COR catalyst are a metal-Sb compound consisting of a metal and antimony, the antimony being atomically dispersed in a lattice formed by a crystalline structure of the metal.

[0009] Advantageously, the metal is Cu, Ag, Ni, Ga, or any combinations thereof, preferably Cu.

[0010] Advantageously, the metal Sb-compound of both metallic CO2R catalyst and metallic COR catalyst is a Cu-Sb compound that is made in situ with a step of providing a CuO-Sb compound followed by a step of reducing in situ said CuO-Sb compound into the Cu-Sb compound, said step of reducing being carried out with the reduction current provided at the electroreducing steps (a) and / or (b).

[0011] Advantageously, the crystalline structure has Cu(100) facets.

[0012] Advantageously, the metallic CO2R catalyst has a first Cu:Sb ratio ranging between 9 / 1 and 200 / 1 , preferably between 19 / 1 and 200 / 1 , more preferably between 49 / 1 and 200 / 1 , as determined by Inductive Coupled Plasma mass spectrometry.

[0013] Advantageously, the metallic COR catalyst has a second Cu:Sb ratio ranging between 49 / 1 and 200 / 1 as determined by Inductive Coupled Plasma mass spectrometry.

[0014] Advantageously, the metallic CO2R catalyst includes a first doping amount of Sb that is between 0.5 at. % and 10 at. %, optionally between 0.5 at.% and 5 at.%, based on a total number of atoms in said metallic CO2R catalyst as determined by Inductive Coupled Plasma mass spectrometry, or between 1 at.% and 9 at.%, or between 2 at.% and 8 at.%.

[0015] Advantageously, the metallic COR catalyst includes a second doping amount of Sb that is between 0.5 at.% and 2 at.% based on a total number of atoms in said metallic COR catalyst as determined by Inductive Coupled Plasma mass spectrometry, or between 0.6 at.% and 1 .5 at.%.

[0016] Advantageously, the metallic CO2R catalyst includes a first doping amount of Sb and the metallic COR catalyst includes a second doping amount of Sb, the first doping amount of Sb being higher than the second doping amount of Sb.

[0017] Advantageously, the step (b) of electroreducing CO is performed according to the following sub-steps: i. providing a COR system including an electrode comprising the metallic COR catalyst favouring reduction of CO; ii. supplying an electrolyte to the COR system, the electrolyte comprising a lithium cation source and a proton source to respectively provide lithium cations and protons at an electrical double layer (EDL) formed between the metallic COR catalyst and the electrolyte, iii. supplying a gaseous stream comprising CO to the COR system for contacting the metallic COR catalyst in presence of the lithium cations at the EDL; and iv. generating a reduction current through the COR system to cause electroreduction of CO into a product mixture including ethylene.

[0018] Advantageously, the proton source comprises a protic solvent.

[0019] Advantageously, the protic solvent is selected from water, acid, alcohol, another protic solvent or any combinations thereof.

[0020] Advantageously, the lithium cation source comprises LiOH, LiCIO4, LiCI, Li2SO4, LiHCO3, Li2CO3or any combinations thereof.

[0021] Advantageously, the electrolyte has a molar concentration in the cation source between 0.5 M and 3 M, or between 1 M and 2M; or between 1.2 M and 1.8 M.

[0022] Advantageously, the gaseous stream supplied at sub-step (iii) comprises CO in an amount of at least 80 vol.% of the total volume of the gaseous stream, more preferably of at least 85 vol.%, even more preferably of at least 90 vol.%, most preferably of at least 95 vol.%, even most preferably of at least 99 vol.%. For example, the gaseous stream consists of CO.

[0023] Advantageously, the step (iv) of generating the reduction current through the COR system comprises applying a current density between 100 mA.cnr2and 800 mA.cm-2, or between 150 mA.cnr2and 750 mA. cm-2, or between 200 mA.cnr2and 700 mA.cnr2.

[0024] Advantageously, the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 1 .0, or of at least 1 .2, or of at least 1 .5, or of at least 1 .8, or of at least 2.0.

[0025] Advantageously, the step (b) of electroreducing CO comprises the following substeps: i. providing a COR system including an electrode comprising the metallic COR catalyst favouring reduction of CO; ii. supplying an electrolyte to the COR system for providing ions at an electrical double layer (EDL) formed between the metallic COR catalyst and the electrolyte, iii. supplying a gaseous stream comprising CO to the COR system for contacting the metallic COR catalyst at the EDL; and iv. generating a reduction current through the COR system to cause electroreduction of CO into a product mixture including ethylene.

[0026] Advantageously, the electrolyte comprises a lithium cation source and a proton source to respectively provide lithium cations and protons at the electrical double layer (EDL).

[0027] Advantageously, the lithium cation source comprises LiOH, LiCIO4, LiCI, Li2SO4, LiHCO3, Li2CO3or any combinations thereof.

[0028] Advantageously, the electrolyte comprises a cation source and has a molar concentration in the cation source between 0.5 M and 3 M, or between 1 M and 2M, or between 1.2 M and 1.8 M.

[0029] Advantageously, the electrolyte comprises a proton source and the proton source comprises a protic solvent.

[0030] Advantageously, the protic solvent is selected from water, acid, alcohol, another protic solvent or any combinations thereof.

[0031] Advantageously, the gaseous stream supplied at sub-step (iii) comprises CO in an amount of at least 80 vol.% of the total volume of the gaseous stream, more preferably of at least 85 vol.%, even more preferably of at least 90 vol.%, most preferably of at least 95 vol.%, even most preferably of at least 99 vol.%. For example, the gaseous stream consists of CO.

[0032] Advantageously, the step (iv) of generating the reduction current through the COR system comprises applying a current density between 100 mA.cnr2and 800 mA.cm-2, or between 150 mA.cnr2and 750 mA. cm-2, or between 200 mA.cnr2and 700 mA.cnr2.

[0033] Advantageously, the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 1 .0, or at least 1 .2, or at least 1 .5, or at least 1 .8, or at least 2.0.

[0034] In a second aspect, the present disclosure relates to the use of a metallic catalyst under the form of a Cu-Sb compound in each stage of a sequential electroreduction operation including consecutive CO2RR and CORR to convert CO2into ethylene, wherein the Cu-Sb compound comprises copper and antimony, the antimony being atomically dispersed in a lattice formed by a crystalline structure of the copper.

[0035] Advantageously, the Cu-Sb compound consists of copper and antimony, the antimony being atomically dispersed in a lattice formed by a crystalline structure of the copper

[0036] Advantageously, the antimony is present in an amount of between 0.5 at.% and 10 at.% with respect to a total number of atoms in the metallic catalyst as determined byInductive Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), or between 1 at.% and 9 at.%, or between 2 at.% and 8 at.%.

[0037] Advantageously, the metallic catalyst comprises nanoparticles, said nanoparticles having a size ranging between 5 nm and 20 nm as determined by scanning transmission electron microscopy, or between 10 nm and 15 nm, or between 7.5 nm and 12.5 nm.

[0038] In a third aspect, the disclosure relates to a sequential electroreduction assembly to convert CO2into multicarbon products including ethylene, the assembly comprising: a CO2R system receiving a CO2flowstream and producing a CO flowstream via CO2RR, and a COR system fluidly connected to the CO2RR system to receive the CO flowstream and produce a multicarbon product stream including ethylene; wherein the CO2R system includes a metallic CO2R catalyst and the COR system includes a metallic COR catalyst, and both the metallic CO2R catalyst and the metallic COR catalyst include a metal-Sb compound comprising a metal and antimony, the antimony being atomically dispersed in a lattice formed by a crystalline structure of the metal.

[0039] Advantageously, each of the COR system and the CO2R system is at least one of a zero-gap electrolyzer, a one-gap electrolyzer and a two-gap electrolyzer.

[0040] Advantageously, the CO2R system is a zero-gap electrolyzer.

[0041] Advantageously, the COR system is a zero-gap electrolyzer.

[0042] Advantageously, the metal-Sb compound of the metallic CO2R catalyst and / or the metallic COR catalyst is as defined in the first aspect.

[0043] Advantageously, the assembly further comprises a separator being positioned between the CO2R system and the COR system, the separator being fed with a product stream from the CO2R system and removing unconverted CO2, when present, from the product stream to produce the CO flowstream that is supplied to the COR system.

[0044] In a fourth aspect, there is provided a method for carbon oxide (CO) electroreduction into at least ethylene. The method comprises:a) providing a COR system including an electrode comprising a metal-based catalyst favouring reduction of CO; b) supplying an electrolyte to the COR system, the electrolyte comprising lithium cation source and a proton source to respectively provide lithium cations and protons at an electrical double layer (EDL) formed between the metal-based catalyst and the electrolyte, c) supplying a gaseous stream comprising CO and being exempt of CO2to the COR system for contacting the metal-based catalyst in presence of the lithium cations at the EDL; and d) generating a reduction current through the COR system to cause electroreduction of CO into a product mixture including ethylene.

[0045] For example, the proton source comprises a protic solvent. With preference, said protic solvent is selected from water, acid, alcohol, another protic solvent or any combinations thereof.

[0046] For example, the alkali metal cation source is a lithium cation source. The lithium cation source can optionally comprise LiOH, LiCIO4, LiCI, Li2SO4, LiHCO3, Li2CO3or any combinations thereof.

[0047] For example, the electrolyte has a molar concentration in the cation source between 0.5 M and 3 M, or between 1 M and 2M, or between 1.2 M and 1.8 M.

[0048] For example, the gaseous stream comprises CO in an amount of at least 80 vol.% of the total volume of the gaseous stream, more preferably of at least 85 vol.%, even more preferably of at least 90 vol.%, most preferably of at least 95 vol.%, even most preferably of at least 99 vol.%. For example, the gaseous stream consists of CO.

[0049] For example, the step (d) of generating the reduction current through the COR system comprises applying a current density between 100 mA.cnr2and 800 mA.cm-2, or between 150 mA.cnr2and 750 mA. cm-2, or between 200 mA.cnr2and 700 mA.cnr2.

[0050] For example, the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 1 .0, or of at least 1 .2. Optionally, the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 1.5. Further optionally, the ratio of FE(ethylene) toFE(oxygenates) of the product mixture is of at least 1.8. Yet further optionally, the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 2.0.

[0051] For example, the metal-based catalyst can include Cu, Ag, Ni, Ga or any combinations thereof, preferably copper.

[0052] For example, the metal-based catalyst can be a metallic COR catalyst under the form of a Cu-Sb compound, the antimony being atomically dispersed in a lattice of a copper crystalline structure. Optionally, the metallic COR catalyst under the form of a Cu- Sb compound is made in situ with a step of providing a CuO-Sb compound followed by a step of reducing in situ said CuO-Sb compound into the Cu-Sb compound, said step of reducing being carried out with the reduction current provided at step (d). Further optionally, the copper crystalline structure has Cu(100) facets. Yet further optionally, the metallic COR catalyst under the form of a Cu-Sb compound has a Cu:Sb ratio ranging between 9 / 1 and 200 / 1 , preferably between 19 / 1 and 200 / 1 , more preferably between 49 / 1 and 200 / 1 as determined by Inductive Coupled Plasma mass spectrometry. The metallic COR catalyst under the form of a Cu-Sb compound can for example include a doping amount of Sb that is between 0.5 at.% and 2 at.% based on a total number of atoms of said metallic COR catalyst as determined by Inductive Coupled Plasma mass spectrometry.

[0053] In some implementations, the electrolyte can be a catholyte and wherein the COR system is a catholyte-containing one-gap electrolyzer.

[0054] In other implementations, the COR system can be a two-gap electrolyzer.

[0055] In other implementations, the COR system can be a zero-gap electrolyzer. For example, the COR system is a membrane electrode assembly and the electrolyte is an anolyte, with the alkali metal cations migrating to the electrode in a cathodic compartment via an anion exchange membrane with cation crossover.

[0056] In a fifth aspect, there is provided a method for carbon oxides electroreduction into at least ethylene. The method comprises: a) providing a metallic catalyst under the form of a Cu-Sb compound to favour reduction of CO2 and / or CO into ethylene, wherein the antimony is atomicallydispersed in a lattice of a copper crystalline structure, the metallic catalyst being provided within a system; b) supplying an electrolyte to the system for providing ions at an electrical double layer (EDL) formed between the catalyst and the electrolyte; c) supplying a gaseous stream comprising CO2and / or CO to the system for contacting the metal-based catalyst at the EDL; and d) generating a reduction current through the system to cause electroreduction of CO2and / or CO into a product mixture including ethylene.

[0057] For example, the step (a) comprises a step of providing a CuO-Sb compound followed by a step of reducing in situ said CuO-Sb compound into the Cu-Sb compound, said step of reducing being carried out with the reduction current provided at step (d).

[0058] For example, the copper crystalline structure has facets being Cu(100).

[0059] For example, the metallic catalyst under the form of a Cu-Sb compound has a Cu:Sb ratio ranging between 49 / 1 and 200 / 1 as determined by ICP mass spectrometry.

[0060] For example, the metallic catalyst under the form of a Cu-Sb compound includes a doping amount of Sb that is between 0.5 at.% and 10 at.% based on a total number of atoms of said metallic catalyst as determined by ICP mass spectrometry, or between 1 at.% and 1.5 at.%.

[0061] For example, the electrolyte comprises an alkali metal cation source to provide alkali metal cations at the EDL. Optionally, the alkali metal cation source can be a lithium cation source; with preference, said lithium cation source is one or more selected from LiOH, LiCIO4, LiCI, Li2SO4, LiHCO3, Li2CO3, or a mixture thereof.

[0062] For example, the electrolyte further comprises a proton source; with preference, said proton source is one or more selected from water, acid, alcohol, another protic solvent or any combinations thereof. Optionally, the lithium cation is lithium hydroxide, the proton source is water, and the electrolyte is an aqueous solution of lithium hydroxide.

[0063] For example, the electrolyte has a molar concentration in the lithium cation source between 0.5 M and 3 M, or between 1 M and 2M, or between 1.2 M and 1.8 M.

[0064] For example, the gaseous stream comprises CO2and / or CO in an amount of at least 80 vol.% of the total volume of the gaseous stream; preferably of at least 85 vol.%, more preferably of at least 90 vol.%, even more preferably of at least 95 vol.%, most preferably of at least 99 vol.%. With preference, the gaseous stream consists of CO2and / or CO.

[0065] For example, the step (d) of generating the reduction current through the COR system comprises applying a current density between 100 mA.cnr2and 800 mA.cm-2, or between 150 mA.cnr2and 750 mA. cm-2, or between 200 mA.cnr2and 700 mA.cnr2.

[0066] For example, the ratio of FE(ethylene) to FE(oxygenates) of the product mixture can be of at least 1.0, or of at least 1.2. Optionally, the ratio of FE(ethylene) to FE(oxygenates) of the product mixture can be of at least 1.5. For example, the ratio of FE(ethylene) to FE(oxygenates) of the product mixture can be of at least 1.8. For example, the ratio of FE(ethylene) to FE(oxygenates) of the product mixture can be of at least 2.0.

[0067] In some implementations, the system can be a catholyte-containing one-gap electrolyzer. In other implementations, the system can be a two-gap electrolyzer. In yet other implementations, the system can be a zero-gap electrolyzer.

[0068] In a sixth aspect, there is provided a metallic catalyst under the form of a metal- Sb compound. The metallic catalyst comprises a metal and antimony, the antimony being atomically dispersed in a lattice formed by a crystalline structure of the metal and being present in a doping amount of between 0.5 at.% and 2 at.% with respect to a total number of atoms of said metallic catalyst as determined by Inductive Coupled Plasma (ICP)- Optical Emission Spectroscopy (OES).

[0069] With preference, the metallic catalyst consists of a metal and antimony, the antimony being atomically dispersed in a lattice formed by a crystalline structure of the metal and being present in a doping amount of between 0.5 at. % and 2 at.% with respect to a total number of atoms of said metallic catalyst as determined by Inductive Coupled Plasma (ICP)- Optical Emission Spectroscopy (OES).

[0070] For example, the catalyst can comprise nanoparticles, said nanoparticles having a size ranging between 5 nm and 20 nm as determined by scanning transmission electron microscopy, or between 10 nm and 15 nm, or between 7.5 nm and 12.5 nm.

[0071] For example, the metal-Sb ratio can be ranging between 9 / 1 and 200 / 1 , preferably between 19 / 1 and 200 / 1 , more preferably between 49 / 1 and 200 / 1 as determined by ICP mass spectrometry.

[0072] For example, the metal can be Cu, Ag, Ni, Ga, or any combinations thereof, preferably Cu.

[0073] For example, the catalyst can have an increased oxyphilicity characterized by an OH binding strength that is higher than for a non Sb-doped catalyst.

[0074] For example, the metallic catalyst is a metallic COR catalyst.

[0075] For example, the metallic catalyst is a metallic CO2R catalyst.

[0076] In a seventh aspect, there is provided a cathode / system comprising the metallic catalyst as defined in the sixth aspect.

[0077] In an eighth aspect, there is provided a method to synthesize a metallic catalyst as defined herein. The method includes the following steps: a) preparation of a first solution comprising antimony; b) preparation of a second solution comprising copper; c) addition of water in the second solution to form an aqueous second solution; d) combining the first solution and the aqueous second solution of step (c) to obtain a mixture; e) heating the mixture obtained at step (d) at a temperature ranging between 90°C and 150°C; f) cooling the mixture to room temperature so that a solid is precipitated; g) optionally, washing the solid obtained at step (f); h) lyophilizing the solid to produce a lyophilized solid; i) heating the lyophilized solid from room temperature up to at most 400°C so that a CuO-Sb compound is obtained; and applying a reduction current to the CuO-Sb compound obtained in step (i) for reduction thereof into the metallic catalyst under the form of a Cu-Sb compound.

[0078] For example, the heating of step (i) is performed at a rate comprised between 5°C / minutes and 15°C / minute, preferably between 7°C / minutes and 13°C / minute. For example, the heating of step (i) is performed during at least 1 hour, or during at least 1 .5 hours, or during at least 2 hours.

[0079] For example, the first solution comprises at least one of SbCI3, Sb2O3, and SbCI5, at least one of NaOH, LiOH, and KOH, and water.

[0080] For example, the second solution comprises at least one of Cu(NO3)2-3H2O, CU(NO3)2-2.5H2O, CU(NO3)2-XH2O, CUSO and CuSO4-5H2O, and ethanol.

[0081] For example, urea is further added along with the water in step (c).

[0082] For example, the aqueous second solution is added dropwise to the first solution to obtain the mixture of step (d).

[0083] While the invention will be described in conjunction with example embodiments, it will be understood that it is not intended to limit the scope of the invention to such embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included as defined by the present description. The objects, advantages and other features of the present invention will become more apparent and be better understood upon reading of the following non-restrictive description of the invention, given with reference to the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0084] Figure 1 shows CORR performance of 25 nm Cu NPs in three different electrolytes LiOH, NaOH, and KOH, including graph (1A) showing the FE of C2H4 (solid line) and H2 (dash line) at different applied current density (in mA. cm-2), graph (1 B) showing a ratio of FE(C2H4) to FE(oxygenates) at different applied current densities (in mA. cm-2); and graph (1 C) showing Tafel slopes of ethylene.

[0085] Figure 2 shows measurements conducted in a flow cell, with CO flow through a gas chamber that was on the back side of a gas diffusion electrode, including graph (2A) being a radial pair distribution function g(r) of OCo-M+in Molecular Dynamics (MD) simulations, graph (2B) being a radial pair distribution function g(r) of OCo-H2O in MD simulations, graph (2C) showing Operando shell-isolated nanoparticles-enhanced Raman spectra in 1 M LiOH, graph (2D) showing Operando shell-isolated nanoparticles-enhanced Raman spectra in 1 M NaOH, graph (2E) showing Operando shell-isolated nanoparticles- enhanced Raman spectra in 1 M KOH, and graph (2F) showing comparative Raman spectra at -1.01 VSHE among different cations of the electrolyte.

[0086] Figure 3 includes a schematic (3A) of a snapshot of MD simulation results of 0.15 ML of CHCO* on Cu in LiOH and KOH, a graph (3B) of radial pair distribution function g(r) of OCHCO-M+, graph (3C) of radial pair distribution function g(r) of OCHCO-H2O, a schematic (3D) showing protonation of CHCO* to form CHCOH* and CHCHO* with the transition states of two protonation reactions in KOH and LiOH being illustrated, graphs (3E) show calculated activation energies AG of protonation process for Li cation and K cation, schematic (3F) shows interfacial structures in KOH (left) and LiOH (right) based on MD and Raman results with carbon being in black, oxygen in grey, hydrogen in white, and the Oco-M+interactions and OCo-HWater interactions being represented by dash lines.

[0087] Figure 4 includes graph (4A) showing COR performance of Cu-Sb in LiOH, NaOH, and KOH in flow cell, graph (4B) showing comparative FE for H2and C2H4at different applied current densities (mA. cm-2) between Cu-Sb and Cu-Ref and being measured in 1 M LiOH in a flow cell, graph (4C) showing comparative polarization curves of Cu-Sb and Cu-Ref measured in 1 M LiOH in a flow cell, graph (4D) shows COR performance of Cu- Sb in a MEA including an anode catalyst being a NiFe-based OER catalyst, and an anolyte being 2 M LiOH; graph (4E) being a summary of COR performance in MEA includingprevious reports. (F) Stability test of Cu-Sb in MEA. A PTFE sputtered with Cu was used as gas-diffusion electrode to prevent flooding.

[0088] Figure 5 includes an HAADF-STEM image (5A) of Cu-Sb and its corresponding elemental maps of Cu and Sb, AC-HAADF-STEM image (5B) of Cu-Sb, Operando XANES spectra of Cu K-edge (graph 5C) and of Sb K-edge (graph 5D), graph (5E) showing OH chemisorption / desorption of Cu-Sb and Cu-Ref in 1 M NaOH (5F) DFT, and schematic (5G) illustrating Sb’s promoting effect on ethylene pathway.

[0089] Figure 6 includes two graphs showing Faradaic efficiency (FE) of COR products on 25 nm Cu nanoparticles in 1 M LiOH (graph 6A), 1 M NaOH (graph 6B), 1 M KOH (graph 6C).

[0090] Figure 7 is a graph showing polarization curves of CORR in different electrolytes using 25 nm Cu nanoparticles as catalyst with a scan rate of 100 mV / s.

[0091] Figure 8 includes two graphs showing comparison of COR performance in LiOH, NaOH, and KOH, with graph (8A) showing FE(C2H4) and FE(H2), and graph (8B) showing a ratio of FE(C2H4) to FE(oxygenates).

[0092] Figure 9 includes three graphs showing COR performance in acidic (0.005 M H2SO4+ 0.495 M Na2SO4) electrolyte (graph 9A), in neutral (0.5 M Na2SO4) electrolyte (graph 9B), and a summary of COR at different pH (graph 9C).

[0093] Figure 10 is a graph of a Kinetic isotope effect (KIE) of COR to ethylene according to E in V vs RHE.

[0094] Figure 11 relates to COR in water-in-salt electrolytes and includes graph (1 1 A) showing jC2H4 vs. V curves of COR in NaCIO4solution with a concentration 9 m m is molarity, or mole of NaCIO4in 1 kg of H2O), 12 m, and 15 m, respectively, with the inset being the water activity (aw) at each concentration; graph (11 B) showing ethylene partial current densities at -0.986 V vs SHE in electrolytes with different water activities; and graph (11C) showing the corresponding Tafel slopes using data in graph (11A).

[0095] Figure 12 provides MD results in 1 M LiOH and 1 M KOH without CO and includes snapshots (12A), (12B) of simulations of Cu electrode in 1 M LiOH; snapshots (12C), (12D)of simulations of Cu electrode in 1 M KOH; and graph (12E) showing distribution of Li and K cations along the z axis.

[0096] Figure 13 provides MD results in 1 M LiOH and 1 M KOH with 0.15 monolayer (ML) of CO and includes snapshots (13A), (13B) of simulations of Cu electrode in 1 M LiOH; snapshots (13C), (13D) of simulations of Cu electrode in 1 M KOH; and graph (13E) showing distribution of Li and K cations along the z axis.

[0097] Figure 14 shows optimized geometries of adsorbed CO* (schematic 14A) and of adsorbed CHCO* (schematic 14B) on Cu3s in DFT calculations.

[0098] Figure 15 shows geometries of CHCO* protonation to form CHCOH* on Cu(100) with Li+including side and top views of an initial state (schematic 15A), a transition state (schematic 15B), and a final state (schematic 15C). The Li+, H2O, *CHCO, and *COCOH are indicated.

[0099] Figure 16 shows geometries of CHCO* protonation to form CHCOH* on Cu(100) with K+including side and top views of an initial state (schematic 16A), a transition state (schematic 16B), and a final state (schematic 16C). The K+, H2O, *CHCO, and *COCOH are indicated.

[0100] Figure 17 shows geometries of CHCO* protonation to form CHCHO* on Cu(100) with Li+including side and top views of an initial state (schematic 17A), a transition state (schematic 17B), and a final state (schematic 17C. The Li+, H2O, *CHCO, and *COCOH are indicated.

[0101] Figure 18 shows geometries of CHCO* protonation to form CHCHO* on Cu(100) with K+including side and top views of an initial state (schematic 18A), a transition state (schematic 18B), and a final state (schematic 18C). The K+, H2O, *CHCO, and *COCOH are indicated.

[0102] Figure 19 relates to microscopic characterization of CuO-Sb and includes a Scanning electron microscopy (SEM) image (19A); a Transmission electron microscopy (TEM) image (19B); and aberration-corrected high angle-annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) images (19C) and (19D).

[0103] Figure 20 is a graph of an X-ray diffraction (XRD) pattern of CuO-Sb.

[0104] Figure 21 provides a summary graph (21A) and related graphs (21 B), (21C) and (21 D) of COR FE of ethylene and H2for Cu-Sb in 1 M LiOH, 1 M NaOH, and 1 M KOH, respectively.

[0105] Figure 22 is a graph showing COR FE(C2H4) and FE(H2) of Cu-Sb in 2 M LiOH with the FE(C2H4) being generally larger than 75% from 50 mA / cm2to 175 mA / cm2.

[0106] Figure 23 relates to MEA performance of Cu-Sb in 2 M LiOH and is a graph showing the FE(C2H4) and corresponding energy efficiency (EE) at different applied current densities (mA / cm2).

[0107] Figure 24 is a graph of single-pass utilization (SPU) (%) and FE(C2H4) of Cu-Sb catalyst with respect to inlet flow rate (mL / min) in a MEA being operated at 150 mA / cm2, with 2 M LiOH as the anolyte. The electrode surface area was 4 cm2, so the overall working current was 600 mA. The FE(C2H4) increased to 81 .6 % at a CO flow rate of 5.5 mL / cm2, due to the decreased CO concentration.

[0108] Figure 25 provides a microscopic characterization of Cu-Sb and includes STEMs images (25A) and (25B), a TEM image (25C) and a graph (25D) showing size distribution of Cu-Sb.

[0109] Figure 26 includes two graphs showing underpotential deposition of Pb on Cu-Sb (graph (26A)) and on Cu NPs (graph (26B)), with the electrolyte being N2-saturated 1 M NaCIO4+ 2 mM Pb(CIO4)2at a scan rate of 50 mV / s, wherein a dashed area is ascribed to the desorption of Pb underpotential deposition (Pbupo), and the corresponding charge is calculated and used to estimate the electrochemical surface area (ECSA) of the catalyst with a conversion rate of 0.31 mC / cm2cu. Before tests, both catalysts were activated by applying a current density of 100 mA / cm2first, and then increased with an increment of 100 mA / cm2every 5 minutes to 600 mA / cm2.

[0110] Figure 27 is a graph of the Energy dispersive spectroscopy (EDS) of Cu- Sb and showing that the existence of Sb in CuO-Sb catalyst precursor is confirmed.

[0111] Figure 28 provides Operando Raman spectroscopy results for Cu-Sb and Cu-Ref catalysts.

[0112] Figure 29 includes two graphs of X-ray photoelectron spectroscopy (XPS) of CuO-Sb and CuO-Ref showing Cu 2p3 / 2. (graph (29A)) and O 1s and Sb 3d (graph (29B)).

[0113] Figure 30 includes two graphs of a Fourier transform of2-weighted EXAFS spectra at Cu K-edge (graph (30A)), and Sb K-edge (graph (30B)).

[0114] Figure 31 provides Extended X-ray adsorption fine-structure (EXAFS) spectroscopy at Cu K-edge and includes graphs of Fourier-transform (FT)-EXAFS fitting of Cu-Sb and Cu-Ref at R space (graph (31 A)) and k space (graph (31 B)).

[0115] Figure 32 is a graph of Operando X-ray adsorption near-edge structure (XANES) of Cu K-edge for CuO-Sb.

[0116] Figure 33 is a graph of Operando X-ray adsorption near-edge structure (XANES) of Sb K-edge for CuO-Sb.

[0117] Figure 34 is a graph of a Bader charge analysis of the Sb-containing surface of the metallic COR catalyst showing charge transfer from Sb to surrounding Cu atoms.

[0118] Figure 35 is a schematized process flow diagram of a sequential electroreduction of CO2into multicarbon products including ethylene using a Cu-Sb compound as a CO2R catalyst and as a COR catalyst.

[0119] Figure 36 includes two graphs showing Faradaic efficiency (FE) of CO2RR products and COR products using a Cu-Sb compound in 0.5 M KHCO3and 0.1 M K2SO4(graph 36 A) and in 1 M LiOH (graph 36B).

[0120] Figure 37 includes two TEM images of CuO-Sb (image A) and CuO-Ref (image B).DETAILED DESCRIPTION

[0121] Unlike other multi-carbon products of carbon oxides reduction (CO2R or COR) (such as ethanol, acetate, and propanol), the generation of ethylene (C2H4) requires complete removal of oxygen atoms in carbon oxides. The techniques proposed herein allow destabilizing of the intermediate oxygen in CO2or CO to favour a reaction pathway towards ethylene production. More particularly, the tuning of the properties of at least oneof an electrode catalyst or an electrolyte is proposed to effectively destabilize the intermediate oxygen atoms, thereby promoting ethylene generation.

[0122] Thus, the present techniques relate to electrolyte engineering, catalyst development and a combination thereof to boost ethylene production from CO2and / or CO. For example, there is proposed herein a lithium(Li)-containing electrolyte that can be supplied to an electrolyzer for sustaining CO electroreduction having an enhanced Faradaic Efficiency towards ethylene in comparison to conventional electrolytes used for CO electroreduction. For example, there is further provided an antimony(Sb)-doped Cu catalyst that can be implemented in the cathode of an electrolyzer for sustaining CO2and / or CO electroreduction having an enhanced Faradaic Efficiency towards ethylene in comparison to conventional catalysts used for CO2and / or CO electroreduction. For example, a single step CO2R performance was characterized by an ethylene Faradaic Efficiency of 53% when using the metal-Sb catalyst described herein. For example, there is further proposed a combined use of the lithium-containing electrolyte and antimony- doped Cu catalyst for electroreduction of CO in an electrolyzer to achieve, for example, an ethylene Faradaic Efficiency of 79% and a corresponding record CO-to-ethylene energy efficiency of 37% at an applied current density of 150 mA / cm2. Spectroscopic characterization and computational analysis that were performed experimentally demonstrate that the hydrated Li+on the electrode surface favour production of reaction intermediates that lead to carbon-carbon bonds forming ethylene rather than intermediates leading to oxygenates ( / .e., favouring H2O-Ointermediate interaction and not cation-Ointermediate interaction), while Sb-doping of the catalyst increases a carbon binding strength and decreases an oxygen binding strength. The electrolyte and the catalyst implementations described herein, either alone or in combination, destabilize the intermediate oxygen and hence favour ethylene reaction pathway over oxygenates reaction pathway. Further details are provided as follows.Modification of the microenvironment on electrode surface

[0123] In one aspect, there is provided a method for enhancing carbon oxide (CO) electroreduction into ethylene by modifying a microenvironment at an electrode-electrolyte interface with cations having a low surface charge, such as Li+, Na+, K+or Cs+. The electrode-electrolyte interface is characterized as being the electrical double layer (EDL) at the surface of the metal-based catalyst. For example, the method can include supplyingan electrolyte to a COR electrolyzer, with the electrolyte comprising a lithium cation source and being referred to as a lithium-containing electrolyte.

[0124] More particularly, the method can include providing a COR system including an electrode comprising a metal-based catalyst favouring reduction of CO into ethylene; supplying an electrolyte to the system, the electrolyte comprising a lithium cation source; supplying a gaseous stream comprising CO to the system for contacting the metalbased catalyst in presence of the lithium cations at the EDL; and generating a reduction current through the system to cause electroreduction of CO into a product mixture including ethylene and having a ratio of FE(ethylene) to FE(oxygenates) of at least 1. In some implementations, a current density between 50 mA.cnr2and 800 mA. cm-2can be applied in the COR system, or between 100 mA.cnr2and 800 mA.cnr2, or between 150 mA.cnr2and 750 mA. cm-2, or between 200 mA. cm-2and 700 mA. cm-2. It is noted that the current density can reach an optimal value in accordance with the nature / concentration of the catalyst and of the cations in the electrolyte. For example, for 1 M LiOH, a benchmark 25 nm Cu NPs used as catalyst can reach a current density of 200 mA.cnr2.

[0125] In another aspect, there is provided a use of the lithium-containing electrolyte in a COR system to favour a reaction pathway from CO to ethylene rather than from CO to oxygenates.

[0126] Due to high electronegativity, oxygen atoms can bring considerable polarity to COR reaction intermediates, which are thus stabilized by cations present within the electrochemical double layer (EDL) that is formed at an electrode-electrolyte interface. The strategies described herein weaken such cation-Ointermediate interaction. Since the interfacial environment (being the environment of the EDL) can be greatly modulated by cations, the electrolyte includes a source of at least one monovalent cation, such as an alkali metal cation having a low surface charge, for example Li+, Na+, K+or Cs+, which bounds the intermediate O atoms weakly and hence favours ethylene generation over oxygenates. For example, the at least one cation can be the Li+cation which is shown herein to favour ethylene production with respect to oxygenates production from CO2. For example, the at least one cation can be Na+which was found as demonstrating slightly lower FE(C2H ) than in Li+, but the current density in Na+is much higher than in Li+, which might be of interest to certain industrial applications. It is noted that multivalent cations,such as Ca2+, Ba2+, Al3+or analogs thereof could be considered as the at least one cation for COR reactions in non-alkaline medium.

[0127] Referring to Figures 2 and 6, COR performance was experimentally tested with three different cations in EDL by using three different 1 M alkaline electrolytes (MOH, M = Li, Na, K) in a flow cell, with CO flow through a gas chamber that was on the back side of a gas diffusion electrode. A benchmark catalyst made of 25 nm copper nanoparticles (Cu NPs) was used as the catalyst of the gas diffusion electrode. Referring to graph 1A of Figure 1 and Table 1 , it was shown that the Faradaic Efficiency of ethylene [FE(C2H4)] in the different electrolytes followed the order of LiOH > NaOH > KOH. The overall C2+ FE for all the cations fell in the range between 80%~90%, and the FE of methane was negligible (< 0.1 %). The FE(C2H4) in LiOH reached its maximum of 56% at -250 mA / cm2. Referring to Figure 8, although the FEs(C2H4) in NaOH and KOH increased further at higher current densities, their maxima still follow the same trend and remain smaller than the one in LiOH. Referring to graph 1 B of Figure 1 , the Faradaic Efficiency of liquid products [FE(oxygenates)] in said electrolytes was also measured and compared with the corresponding FE(C2H4). The variations in the ratio of FE(C2H4) to FE(oxygenates)can be related to the nature and hydration state of the low surface charge cations specifically suppressing the production of oxygenates and promoting ethylene generation. More details are provided in sections related to Raman experiment, MD and DFT simulation.

[0128] Table 1. Summary of the Faradaic efficiencies for the COR using benchmark 25 nm Cu NPs in 1 M LiOH, NaOH, and KOH.

[0129] The FE results shown in Table 1 illustrate that application of the present techniques leads to promoting the formation of ethylene over side products, such as oxygenates.

[0130] The reaction mechanism was further studied to understand the variation of selectivity in different electrolytes. Referring to graph 1 C of Figure 1 , Tafel slopes of COR in the three above-detailed electrolytes were all around 120 mV / dec, indicating a rate determining step (RDS) of irreversible single electron transfer without proton or hydroxide involved in RDS or prior quasi-equilibrium step. Similarly, graphs 9A to 9C of Figure 9 show current densities recorded at different pH and overlapping at the SHE scale, thereby confirming that the CO-to-ethylene conversion is pH-independent, hence no proton or hydroxide appear to be involved in the RDS. The Tafel slopes were also close to 120 mV / dec. Referring to Figure 10, the partial current density of ethylene jC2H4 in deuterated electrolyte was also shown to be lower than its counterpart in H2O (the ethylene partial current density in H2O being 1.5-1.7 times faster than its counterpart in D2O, being equivalent to a kinetic isotopic effect (KIE) of 1.5-1.7), suggesting hydrogen atom is involved in the bond forming / breaking event in RDS.

[0131] Further experimentation was performed to determine a reaction order of water ROH2O in water-in-salt electrolyte. In order to measure the water reaction order ROH2O, the salt concentration was increased to suppress the water activity and data was collected at high salt concentrations to prevent the promotional effect of cations on COR because cations were saturated on electrode surface. NaCIO4 was chosen as theelectrolyte, and used in three concentrations: 9 m (m is molarity, or mole of NaCIO in 1 kg of H2O), 12 m, and 15 m. Referring to graph 11A of Figure 1 1 , the corresponding water activities (aw) were listed on the table in the inset of the graph. The partial current density of ethylene JC2H4 is found increased with higher aw. The water reaction order (ROH2O) was calculated according to equation 3 below:where n is the number of electrons transferred during the reaction (8 for ethylene, 6 for methane, 2 for hydrogen), F is the Faraday constant (96485 C / mol), v is the flow rate of CO, c is the concentration of the product in the outlet in parts-per-million (ppm), / is the total current, Vmis the unit molar volume of gas.

[0132] Referring to graph 11 B of Figure 11 , the calculated ROH2O was close to 1 at -0.986 V vs SHE, thereby suggesting that one water molecule was involved in RDS. Referring to graph 11C of Figure 11 , the Tafel slopes in all conditions are close to 120 mV / dec.

[0133] In summary, experimentation demonstrated that the cations do not appear to influence the COR selectivity by changing the reaction mechanism, and that water, as the proton source, appears to be involved in COR. Thus, the interfacial water environment induced by different cations contributes to the selectivity trend in COR. In addition to the cation source, such as Li+, the electrolyte includes a proton source which can be water or another protonated solvent.

[0134] Referring to Figures 12 and 13, molecular dynamics (MD) simulation was further used to assist in understanding the interfacial environment of the electrode without CO and with a model that contained 0.15 monolayer (ML) of CO on the Cu surface to imitate the experimental condition during COR.

[0135] Compared to Li+, K+is shown to easily dehydrate under a negative bias due to a weak hydration energy thereof. Accordingly, K+has a much higher local concentration close to the electrode than Li+, which results in stronger local electric field and more cation- CO interactions. Two structural properties were also specifically studied: the distance between the oxygen atom in CO and cations in solution (OCo-M+) and the distancebetween the oxygen atom in CO and the hydrogen in water (OCo-HWater). Referring to graph 2A of Figure 2, the radial distribution function (RDF) of OCo-M+(gOco-M+ r)) revealed that the population density of K+around the Oco was much higher than Li+. Referring to graph 2B of Figure 2, the RDF of Oco-Hwater goCo-nwater^r^ indicated more water was around the oxygen atom in CO (Oco) in LiOH than in KOH. The MD simulation thus identified a structural difference at the EDL that originates from the nature of the cations in the electrolyte.

[0136] Operando shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) was further performed to confirm the differences in the structure of the EDL at the EDL when using different cations. Referring to graphs 2C to 2F of Figure 2, the local water environment was probed during COR by stimulation at the Raman bandwidth from 3000 cm-1to 3800 cm'1that corresponds to the O-H stretching mode in a water molecule. Two types of bands were identified: the one at c.a. 3500 cm-1corresponding to the water in the hydration shell of cations (H2O...M+), and the other at c.a. 3600 cm'1corresponding to the H2O at interfaces containing hydrophobic species and which could be assigned to the H2O interacting with CO through hydrogen bonds (CO...H-OH). Referring to the comparative data of graph 2F, the H2O...M+band was most prominent in KOH, consistent with the prediction of dominant Oco-K+from the MD results; while the CO...H-OH band prevailed in LiOH, in accordance with a stronger Oco-H2O peak in LiOH observed in MD simulation. It is noted that, in NaOH, the water environment was in an intermediate state where both bands could be clearly observed. The results suggest the interplay of CO-H2O- cations varies significantly with different cations, which may dictate the selectivity of COR.

[0137] MD simulation was also used to model the interfacial structure in the presence of a CHCO* intermediate. Referring to graph 3A of Figure 3, 0.15 mL of CHCO* on Cu in LiOH and KOH was modeled with the CHCO* intermediate being proposed as the trifurcating point of COR, and the next hydrogenation on the oxygen atom (CHCOH*) directing the reaction pathway to ethylene, while hydrogenation on either one of the carbon atoms (CHCHO* / CH2CO*) direct to oxygenates pathway. Referring to graphs 3B and 3C of Figure 3, the RDF of OCHCO-M+and RDF of OCHco-HWater in KOH and LiOH had the same trend as the above discussed simulations on CO. Graph 3B shows the oxygen in CHCO* having more cations around KOH than in LiOH, and graph 3C shows the oxygen in CHCO* had more H2O around in LiOH than in KOH. Referring to schematic 3D of Figure 3 andFigures 14 to 18, using the established MD results as models, a density functional theory (DFT) was applied to evaluate the activation energy and Gibbs free energy change of each reaction pathway (CHCOH* towards ethylene vs. CHCHO* towards oxygenates) in LiOH and KOH. Referring to graphs 3E of Figure 3, in the presence of Li+in the electrolyte, the activation energy barrier for the CHCHO* pathway is 0.34 eV higher than the CHCOH* pathway, while in the presence of K+, the value decreased to 0.19 eV. The results suggest that cations Li+suppress the CHCHO* (oxygenates) pathway more than K+does.

[0138] Referring to the schematic 3F of Figure 3, the above conclusions can be explained by the fact that structure-breaking cations such as K+tend to pack densely within the EDL and dehydrate under COR-relevant potentials. Both the strong electric field and undercoordination status promote the K+cations to interact directly with the oxygen atoms (of CO or other reaction intermediates) through ion-dipole interactions, which preserve the carbon-oxygen bond and yield oxygenates in the end. Still referring to the schematic 3F of Figure 3, on the other hand, structure-making cations such as lithium have their hydration shell preserved and are less populated within the EDL. Consequently, the Oco- H2O interactions prevail as suggested by the Raman results in graph 2C of Figure 2. Due to the lack of stabilization from cations, the oxygen atoms are removed by hydrodeoxygenation process and ethylene becomes the main product. Preservation of the hydration shell and the size of the hydrated cation are key parameters which render the Li+cation a suitable candidate for the electrolyte as further explained herein.

[0139] It should be noted that the cation effect trend that has been found herein in COR is opposite to the cation effect trend known to favour ethylene in CO2R, where larger cations promote not only Ci , but also C2+ products, including ethylene. It is believed that the difference lies in the surface coverage of CO, which is the reactant in COR, but an intermediate in CO2R. Although small cations favour ethylene in COR, they can suppress CO production from CO2and cannot stabilize them as the big cations do, hence the subsequent C-C coupling being restrained. A fundamental difference between COR and CO2R is thus shown herein by suggesting that C02-to-CO and CO-to-C2+are not governed by the same reaction descriptor.

[0140] The lithium-containing electrolyte that was developed is tailored to favour the reaction pathway from CO to ethylene when used during COR in a COR system by providing lithium cations in the EDL.

[0141] In some implementations, the lithium cation source can be or include lithium hydroxide (LiOH), LiCIO4, LiCI, Li2SO4, LiHCO3, Li2CO3, or any combinations thereof. The electrolyte is further defined as including a proton source with the proton source being or including water, acid, alcohol or another protic solvent. For example, the proton source can be ethanol, glycol, propanol, phenol, or any combinations thereof.

[0142] It is noted that the Li cation concentration can be maximized in order to achieve the highest FE(ethylene) possible, while avoiding flooding at lower current densities. For example, the lithium-containing electrolyte can have a molar concentration in the lithium cation source between 0.5 M and 3M, optionally between 1 M and 2M, or between 1.2 M and 1.8 M.

[0143] The electrolyte described herein is tailored to obtain a ratio of FE(ethylene) to FE(oxygenates) of at least 1 , for example between 1 and 2. Optionally, the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 1.2. Further optionally, the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 1 .5. Yet further optionally, the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 1.8. Yet further optionally, the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 2. These values can for example be applied to using standard copper nanoparticles as catalyst. However, the ratio resulting from application of the present techniques can differ from this range in accordance with the nature and structure of the used catalyst. However, experimentation has demonstrated that, for a same catalyst, the ratio will decrease in accordance with the cation present in the electrolyte and following this order: Li > Na > K > Cs.

[0144] Referring to Figure 7, since the FE(H2) among the three electrolytes didn’t vary too much, the current densities recorded here can roughly represent the activity of COR, which followed the trend LiOH < NaOH < KOH, consistent with previous literature.Catalyst development

[0145] The techniques described herein provide for another solution to destabilize the intermediate oxygen atoms, and to promote ethylene generation from CO2and / or CO via electroreduction. There is further proposed a metallic catalyst under the form of a metal-Sb compound, including metal and a doping amount of antimony (Sb) that favours the formation of metal-C bonds over metal-O-C bonds, thus suppressing the formation ofoxygenates. The metallic catalyst can be used for single-step C02-to-ethylene, single-step CO-to-ethylene or sequential C02-to-ethylene conversion.

[0146] Although a growing number of ethylene-production catalysts have been reported in recent years, such catalysts target CO2R and focus on increasing local CO concentration or promoting C-C coupling step by surface modification, which is not the key to enhance ethylene production in COR because the FE of C2+is generally > 80%. On the other hand, COR catalysts with ethylene selectivity are scarcely reported.

[0147] For example, the metal can be copper (Cu). The metallic catalyst can be a metallic COR catalyst that is designed to regulate the electronic structure of Cu, which destabilizes the intermediate oxygen atom in CO and modifies its reactivity. For example, it has been found that an antimony-doped Cu (Cu-Sb) catalyst surface significantly improves the formation of ethylene.

[0148] Antimony refers herein to the chemical element Sb that typically occurs in oxidation state of +3 Sb (III) or +5 Sb(V). Antimony compounds including Sb(lll), for example SbCI3, can be used as starting material to form the catalyst, Sb (III) being further oxidized to oxidation state of Sb(V) upon reacting.

[0149] As further discussed below, the antimony of the metallic catalyst is atomically dispersed in the lattice of the copper crystalline structure. In some implementations, the metallic COR catalyst includes a doping amount of Sb that is between 0.5 at.% and 2 at.% with respect to a total number of atoms of the metallic COR catalyst as determined by Inductive Coupled Plasma (ICP) - Optical Emission Spectroscopy (OES). For example, the metal-based catalyst has a Cu:Sb ratio between 49 / 1 and 200 / 1 as determined by ICP spectroscopy. For example, the copper crystalline structure has Cu(100) facets. In some implementations, the metallic CO2R catalyst can include a doping amount of Sb that is between 0.5 at. % and 10 at. %, optionally between 0.5 at.% and 5 at.%, based on a total number of atoms in said metallic CO2R catalyst as determined by Inductive Coupled Plasma mass spectrometry.

[0150] The metallic catalyst has been shown to be formed as a porous material comprising or consisting of nanoparticles, said nanoparticles having a size ranging for example between 5 nm and 20 nm as determined by scanning transmission electron microscopy, or between 10 nm and 15 nm, or between 7.5 nm and 12.5 nm.

[0151] There is further provided a method to synthesize the metallic catalyst. In some implementations, the metallic catalyst can be prepared by electroreduction of a catalyst precursor during CO2R or COR, with the catalyst precursor including the doping amount of Sb. For example, the catalyst precursor can be prepared from copper oxide CuO which is modified with a Sb content (doping amount) that can be controlled between 0.5 at.% and 2 a.% based on the total number of atoms of the catalyst precursor as determined by ICP mass spectrometry.

[0152] For example, referring to Figures 19 and 20, fixing the Sb in the lattice of CuO to produce CuO-Sb can be performed by combining the copper oxide precursor CuO and antimony Sb through solvothermal method, thereby achieving atomic dispersion where oxygen atoms act as anionic bridges that interconnect Sb and Cu. For example, the antimony content can be controlled to be 1 mol.% based on the total molar content of CuO-Sb. The active form, Cu-Sb, can thus be obtained by electrochemical reduction of CuO-Sb during CO2R or COR in a corresponding electrolyzer.

[0153] An example method for the synthesis of the catalyst precursor CuO-Sb and metallic catalyst Cu-Sb that was used for the COR experimentation discussed herein is provided as follows. To synthesize the catalyst precursor CuO-Sb, 2.3 mg of SbCI3(0.01 mmol) was first dissolved in 15 mL 1 M NaOH solution with the aid of sonication, denoted as Solution A. In a separate beaker, 0.2392 g of Cu(NO3)2-3H2O (0.99 mmol) was dissolved in 10 mL of ethanol under vigorous agitation, followed by a dropwise addition of 10 mL of a solution of water and 0.21 g urea (3.5 mmol) in 1 minute. The obtained solution is denoted as Solution B. Solution A was added dropwise to Solution B in 2 to 3 minutes under vigorous stirring. The resulting solution was transferred into a 45 mL autoclave under continuous stirring for another 10 minutes. Then, the autoclave was placed in a preheated oven at 100 °C for 20 h. After cooling down to room temperature, the solid was collected and washed with a mixture of methanol and water (1 :1 , v / v) for 5 times and pure water for 1 time by centrifugation. After lyophilized overnight, the product was placed in a Muffle oven, heated to 400 °C with a ramp rate of 10 °C / min, and hold at this temperature for 3 hours. The CuO-Sb catalyst precursor was obtained after naturally cooling down the reaction to room temperature and stored in a dry, dark environment. It is noted that the synthesis of the CuO-Ref catalyst precursor was similar to CuO-Sb, with the sole difference being that no SbCI3was added when preparing the Solution A. Then, synthesis of the COR catalyst Cu-Sb from the formed CuO-Sb precursor (or catalyst Cu-Ref fromCuO-Ref) includes applying a reduction current to the CuO-Sb catalyst precursor to produce the Cu-Sb catalyst during COR.

[0154] Referring to graph 5A of Figure 5 and Figure 25, electron microscopy images suggested Cu-Sb had a general morphology of porous nano-rod / needle (porous material) that was inherited from CuO-Sb (the Sb single atom and the lattice plane of CuO(111 ) were marked by dashed circles and solid lines in image 19D of Figure 19), and each nano-rod / needle comprised interconnected nanoparticles with a size of c.a. 10 nm. The Cu-Sb compound is thus highly porous and comprises copper nanoparticles with a size of 2-10 nm, which enables a high surface area, with antimony being homogeneously dispersed in the copper catalyst as seen in Figure 5A.

[0155] Referring to Figure 26, the small particle size enabled a larger electrochemical surface area (ECSA), which was confirmed by Pb underpotential deposition (PbuDp). Pb(ll) can be deposited onto Cu at potentials higher than its reduction potential. Indeed, since the amount of PbupD is proportional to the amount of Cu, an electrochemical active surface area of Cu can be determined by measuring the amount of PbupD (i.e., desorption charge in this case).

[0156] Referring to images 5A and 5B of Figure 5 and Figure 27, the incorporation of Sb atoms into the lattice of the copper was confirmed by elemental mapping and aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM). It is noted that the atomic resolution HAADF-STEM images were taken from Thermo Fisher Scientific (TFS) Titan Themis scanning transmission microscope equipped with a high-brightness field emission gun (X-FEG) operated at an acceleration voltage of 300 kV. A probe convergence angle of 20 mrad was used.

[0157] There is further provided a method for carbon oxides (CO2and / or CO) electroreduction into ethylene based on the metallic catalyst described herein. More particularly, the method includes providing a CO2R or COR system including an electrode comprising a metallic catalyst comprising a Cu-Sb compound comprising antimony and copper to favour reduction of CO2and / or CO into ethylene, wherein the antimony is atomically dispersed in a lattice of a copper crystalline structure. The method further includes supplying an electrolyte to the CO2R or COR electrolyzer system for providingions at the EDL, supplying a gaseous stream comprising CO2and / or CO to the system for contacting the metal-based catalyst at the EDL; and generating a reduction current through the electrolyzer system to cause electroreduction of CO2and / or CO into a product mixture including ethylene and having a ratio of FE(ethylene) to FE(oxygenates) of at least 1.

[0158] In some implementations, the proposed metallic catalyst can be integrated in the cathode of a flow cell to enhance selectivity towards ethylene. Experiments were performed to test the COR performance of the Cu-Sb catalyst in 1 M alkaline electrolytes in a flow cell. Referring to graph 4A of Figure 4 and Figure 21 , the maximum FE(C2H4) that was observed in 1 M LiOH, NaOH, and KOH was 77%, 72%, and 65%, respectively, which is higher than maximum FE(C2H4) typically reported for benchmark catalyst made of copper nanoparticles (Cu NPs). The FE(C2+) was higher than 90% across the measured current range. A control group (denoted as CuO-Ref) was also electroreduced as a Sb- free sample by a similar method. Referring to graph 4B of Figure 4, its activated form, Cu- Ref, only had a maximum FE(C2H4) of 58 % in the same condition at -225 mA. cm-2. Referring to Figure 22, the effect of varying the concentration of the electrolyte on the COR performance was studied by increasing for example the concentration of the lithium cation source LiOH from 1 M to 2M in a flow cell. The FE(C2H4) was found to be higher than 70 % across the applied current density range. The maximum FE(C2H4) was 79% at the applied current density of 125 mA / cm2, which is the highest value that has been reported in the field. These results confirm the promoting effect of Sb for COR-to-ethylene.

[0159] In addition, Cu-Sb is shown to possess improved activity in comparison to benchmark 25 nm Cu NPs. Referring to graph 4C of Figure 4, the Cu-Sb required 260 mV less overpotential to reach 200 mA / cm2. Referring to graph 1 C of Figure 1 , given that the Tafel slope for COR-to-ethylene was about 120 mV / dec, the Cu-Sb catalyst is determined as being at least 100 times more active than Cu NPs catalyst.

[0160] Operando Raman spectroscopy confirmed that Cu-Sb had a CO adsorption configuration that favoured less oxygenates production (Fig. 27). The measurement was carried out in 1 M NaOH in a modified flow cell. CO was purged through the back of the electrode. The peak(s) locate between 2000 cm-1and 2100 cm-1can be ascribed to the stretching mode of atop C=O (COatop). The COatoPcan be further divided into high frequency band (COHFB) and low frequency band (COLFB), which are generally attributedto the CO adsorbed at terrace site and step site, respectively. Here Cu-Sb only exhibited a single peak corresponding to COHFB, while Cu-Ref had an extra, large COLFB peak. Although COLFB is usually considered to be responsible for C-C coupling in CO2R, this is not verified herein because the COR FE(C2+) of Cu-Sb and Cu-Ref were similar, which cannot explain the huge difference of selectivity within C2+products between Cu-Sb and Cu-Ref. However, assuming that the intensity of COLFB relative to the intensity of COHFB is positively correlated with the FE of oxygenates, it is noted that Cu-Sb with negligible COLFB, has minimum selectivity toward oxygenates.

[0161] Referring to Figure 29, further X-ray photoelectron spectroscopy (XPS) results suggested the oxidation state of Cu and Sb in CuO-Sb were +2 and +5, respectively. The Cu 2p XPS spectra of both CuO-Sb and CuO-Ref had a singlet peak at 933.7 eV, corresponding to Cu(ll) 2p3 / 2. The characteristic intense satellite peaks of Cu(ll) could be also observed from 938 eV to 946 eV, which originated from the 2p^3d9final state, where the complicated shape was due to the multiplet splitting in the final state. The existence of Sb in CuO-Sb can be also confirmed by XPS. Although the energy range of Sb 3d5 / 2 overlapped with the one of O 1s, the Sb 3c / 3 / 2peak was clearly seen at 539.8 eV, corresponding to Sb(V). Operando X-ray adsorption spectroscopy (XAS) was also used to probe the evolution of the oxidation states of Cu and Sb during COR. Both the Cu K- edge X-ray adsorption near-edge structure (XANES) spectroscopy and the extended X- ray adsorption fine-structure (EXAFS) spectroscopy suggested Cu was quickly reduced from Cu(ll) to metallic Cu at the beginning of electrolysis (graph 4C of Figure 4, Figure 25) and remain stable after prolonged electrolysis at higher current densities (Figs. 30 and 31 , due to the excessively low concentration of Sb, the Cu-Sb path cannot be identified in Cu- Sb - and the fitting results are shown in Table 1). When comparing the XANES spectra of Cu-Sb and Cu-Ref, the energy of Cu in Cu-Sb was found to be negatively shifted, indicating the existence of negatively charged Cu (Cu5-) that was induced by Sb. In contrast, referring to graph 4D of Figure 4, Sb K-edge XANES spectra suggested the oxidation state of Sb during COR was constantly higher than metallic Sb and close to Sb(lll). Referring to Figure 32, the XANES of Cu K-edge for CuO-Sb, being conducted in a modified flow cell with CO being purged through the back of GDL and LiOH being used as the catholyte and anolyte, shows that this higher oxidation state persisted throughout the course of electrolysis. In addition, referring to Figure 33 providing XANES of Sb K- edge for CuO-Sb measured in the same conditions, other than the Sb-Cu path, a smallshoulder was identified that could be assigned to a Sb-0 path from the Sb K-edge EXAFS spectrum of Cu-Sb. The XAS results indicate that Cu5'-Sb5+is the COR-active state. The Cu5-, which was uncommonly reported, can be the origin of a superior ethylene selectivity in COR.

[0162] In other implementations, the proposed metallic catalyst can be integrated in the cathode of a membrane electrode assembly (MEA) to enhance selectivity towards ethylene. An anion exchange membrane (AEM) is known to have cations from the anolyte to cross-over to the catholyte, so cations from the anolyte can still exert their influence in the MEA as they do in a flow cell. Referring to graph 4D of Figure 4 related to COR, it was shown that using 2 M LiOH as anolyte and a NiFe-based material as anode catalyst in the MEA, the FE(C2H4) and FE(C2+) was around 79% and 90 % respectively, for an applied current density from 150 mA / cm2to 200 mA / cm2. It is noted that C2+ compounds refer to compounds having at least 2 carbon atoms, and mainly include herein ethylene. Details regarding the method used to assemble the MEA and prepare the NiFe-based material are provided further below. Referring to Figure 23, the CO-to-ethylene energy efficiency, EE(C2H4), was found above 35 % across the measured potential range, with the highest at EE(C2H4) of 38.4% at 75 mA / cm2. The highest EE(C2H4) at an industrial-relevant current densities ( / .e., > 100 mA / cm2) was 37.1 %, which was obtained at 150 mA / cm2. Referring to graph 4E, the maximal EE(C2H4) marked a 28% improvement on previous record (29%). The catalyst also exhibited outstanding COR stability in MEA (Fig. 4F). The catalyst was stably operated over continuous electrolysis of 118 hours at 150 mA / cm2 with negligible selectivity decay.

[0163] Referring to Figure 24, it was observed that FE(C2H4) increases to 81 .6 % at a CO flow rate of 5.5 mL / cm2, due to the decreased CO concentration when the MEA was operated at 150 mA / cm2, with 2 M LiOH as the anolyte (electrode surface area being 4 cm2and the overall working current being 600 mA).DFT session

[0164] The present catalyst has been developed with a strong carbon binding strength and weak oxygen binding strength that favour CHCOH* pathway over CHCHO* pathway. Considering the polar nature of C-0 bond, in COR intermediates the carbon usually carries positive charge (6+) while the oxygen carries negative charge (6 ). Lewisbasic Cu sites (Cu6-) are believed herein to interact more weakly with the nucleophilic oxygen in CHCHO* compared to Cu(0), thus suppressing the formation of O-terminated intermediates. On the other hand, the Cu6-is more likely to bond with electrophilic C5+next to the O6; promoting the formation of C-terminated intermediates, directing COR selectivity along the ethylene pathway. Sb thus transfers electrons to Cu and induce Cu6-, as seen in the DFT with Bader Charge analysis provided by Fig. 34. Activation energies of the protonation step of CHCO* on Cu-Sb and Cu surface were also calculated as seen in graph 5F of Fig. 5. The activation energy for CHCO*-to-CHCHO* was 0.68 eV higher than CHCO*-to-CHCOH* step on the Cu-Sb surface, while such value was 0.41 eV on pure Cu. These calculations confirm that the Sb-doped Cu has the potential to selectively reduce CO to ethylene.Cathode and system

[0165] In some aspects, there is provided a cathode / system including the Cu-Sb catalyst as described herein to perform single-step C02-to-ethylene, single-step CO-to- ethylene or sequential C02-to-ethylene conversion. In other aspects, there is provided a COR system having an electrolyte inlet configured to receive the lithium-containing electrolyte as described herein. In yet other aspects, there is provided a COR system including the Cu-Sb catalyst as described herein and having an electrolyte inlet configured to receive the lithium-containing electrolyte as described herein.

[0166] The system can be a flow cell, such as a catholyte-containing one-gap electrolyzer or a two-gap electrolyzer, preferably a catholyte-containing one-gap electrolyzer; or a zero-gap electrolyzer, such as a membrane electrode assembly (MEA).Flow cell

[0167] The flow cell can be defined as including a gas chamber, a cathode, a catholyte chamber, an ion exchange membrane, an anode, an anolyte chamber, a counter electrode and a reference electrode.

[0168] For example, for the purpose of the experimentation discussed herein, a flow cell was assembled according to the following example method. All the windows in th chambers had a size of 1 cm x 1 cm. The cathode was placed between the gas chamber and the catholyte chamber, with the catalyst side of the cathode facing the catholytechamber. The reference electrode (Ag / AgCI soaked in saturated KCI, CHI instrument, Inc.) was inserted into the catholyte chamber through a pre-drilled hole. A piece of nickel foam or Pt mesh with a size of 0.6 cm x 1 cm were used as the counter electrode, which was placed between catholyte chamber and anolyte chamber. The catholyte and anolyte chambers were separated by a piece of 1.5 cm x 1.5 cm anion exchange membrane (Sustainion® X37-50 Grade RT Membrane). During operation, the CO-containing gas stream (e.g., pure CO) was flowed through the gas chamber, with a flow rate of 20 s.c.c.m, for example, that was controlled by a digital mass flow controller (SmartT rack 100, Sierra). The catholyte and anolyte were supplied separately by two peristaltic pumps in fluid communication with the catholyte chamber and anolyte chamber, respectively.

[0169] For example, the cathode of the flow cell can include the metal-Sb catalyst (e.g., Cu-Sb) as described herein or prepared by the synthesis method as described herein. It is noted that when the flow cell includes the metallic catalyst (or metallic catalyst precursor) as described herein, a negative bias can be applied first before flowing the catholyte to prevent the dissolution of antimony oxide in alkaline solution.

[0170] For example, the catholyte chamber of the flow cell can be supplied with the lithium-containing electrolyte as described herein.Membrane electrode assembly (MEA)

[0171] The MEA can be defined as a zero-gap electrolyzer including, a cathode, an ion exchange membrane, an anode, in which the ion exchange membrane is in contact with both the cathode and the anode.

[0172] In order to assemble the MEA, both electrodes were cut into 1 cm x 1 cm pieces. The cathode was placed on a cathodic plate (stainless steel) with catalyst size facing upward. A piece of 3 cm x 3 cm Sustainion® X37-50 Grade RT membrane and an anode were put on top of the cathode successively and assembled together. To prevent leakage, two silicone rubber gaskets with a thickness of 0.01 inch were placed between cathodic plate and membrane, membrane and anodic plate, respectively. During operation, the humidified CO was supplied to the cathode, its flow rate was controlled by a digital mass flow controller (SmartT rack 100, Sierra). The electrolyte was pumped to the anode through a peristaltic pump.

[0173] For example, the cathode of the MEA can include the metal-Sb catalyst (e.g., Cu-Sb) as described herein or prepared by the synthesis method as described herein.

[0174] For example, the anolyte chamber of the MEA can be supplied with the lithium-containing electrolyte as described herein, with cations crossing over the ion exchange membrane to the cathodic side.

[0175] Known C02-to-CO electrocatalysts having a satisfactory to high conversion efficiency cannot be further used to reduce CO to ethylene. Advantageously, it was found that the metallic COR catalyst as described herein can also be used as a metallic CO2R catalyst favoring reduction of CO2into CO. It is noted that all aspects / embodiments / implementations described herein with respect to or involving the metallic COR catalyst can be applied to the metallic CO2R catalyst.

[0176] The two CO2R and COR reactions are advantageously coupled to produce multicarbon products via sequential electroreduction of CO2using the Cu-Sb compound or the CuO-Sb compound as described herein. The Cu-Sb compound can have distinct selectivity toward CO2RR and CORR when used as metallic CO2R catalyst and metallic COR catalyst respectively.

[0177] It is noted that the metallic catalyst as encompassed herein is under the form of a metal-Sb compound, wherein the metallic catalyst consists of a metal and antimony, the antimony being atomically dispersed in a lattice formed by a crystalline structure of the metal and being present in a doping amount of between 0.5 at.% and 10 at.% with respect to a total number of atoms in said metallic catalyst as determined by Inductive Coupled Plasma (ICP) - Optical Emission Spectroscopy (OES). The metallic catalyst can be under the form of porous nano-rod / needle consisting of nanoparticles, said nanoparticles having a size ranging between 5 nm and 20 nm as determined by scanning transmission electron microscopy, or between 10 nm and 15 nm, or between 7.5 nm and 12.5 nm. The metallic catalyst can have a Metal-Sb ratio ranging between 9 / 1 and 200 / 1 , preferably between 19 / 1 and 200 / 1 , more preferably between 49 / 1 and 200 / 1 as determined by ICP mass spectrometry.

[0178] The metallic catalyst can be referred to as a metallic COR catalyst when used to enhance the selectivity of the electroreduction of CO into C2+products, and to ametallic CO2R catalyst when used to enhance the selectivity of the electroreduction of CO2into CO in a sequential electroreduction process. Both metallic CO2R catalyst and metallic COR catalyst fall under the definition of the metallic catalyst being a metal-Sb compound. When used in sequential electroreduction, the metallic CO2R catalyst and metallic COR catalyst can be the same. However, certain characteristics of the metal-Sb compound can be tuned depending on its use as metallic CO2R catalyst or metallic COR catalyst. For example, the loading in antimony (also referred to as a doping amount of Sb) can differ in each stage of the sequential process. The metallic CO2R catalyst can thus have a first doping amount of Sb being different from a second doping amount of Sb of the metallic COR catalyst. In some implementations, the first doping amount of Sb can be higher than the second doping amount of Sb. In some implementations, the first doping amount of Sb can be between 0.5 at. % and 10 at. %, optionally between 0.5 at. % and 5 at. %, based on a total number of atoms in said metallic CO2R catalyst as determined by Inductive Coupled Plasma mass spectrometry. In some implementations, the second doping amount of Sb can be between 0.5 at. % and 2 at. % based on a total number of atoms in said metallic CO2R catalyst as determined by Inductive Coupled Plasma mass spectrometry.

[0179] In a further aspect, there is provided a process including sequential electroreduction of CO2to produce ethylene using the same catalyst compound. More particularly, referring to Figure 35, the same Cu-Sb compound (or CuO-Sb precursor compound) can be used to perform electroreduction of CO2to CO in a first CO2RR stage (e.g., in electrochemical cell 1) and further electroreduction of CO to ethylene in a second CORR stage (e.g., in electrochemical cell 2). The CO2RR stage and the CORR stage are operated consecutively, so as to efficiently convert CO2to ethylene while avoiding separation of CO2and CO in between the two stages.

[0180] In a further aspect, there is provided a sequential electroreduction assembly including a CO2R system receiving a CO2flowstream and producing a CO flowstream, and a COR system fluidly connected to the CO2R system so as to receive the CO flowstream and produce a multicarbon product stream including ethylene. The CO2R system includes a metallic CO2R catalyst and the COR systems includes a metallic COR catalyst. Both the metallic CO2R catalyst and the metallic COR catalyst include a Cu-Sb compound or a CuO-Sb compound as described herein. In some implementations, the metallic CO2R catalyst is the same as the metallic COR catalyst.

[0181] Referring to Figure 36, graph A provides the CO2RR performance of the Cu-Sb compound when used as the CO2R catalyst in an electrolyte solution containing 0.5 M KHCO3and 0.1 M K2SO . The Faradaic efficiencies (FEs) to H2were in the range of 3%-5% at current densities from 100 mA / cm2to 600 mA / cm2. CO is shown to be generated with high selectivity: the FEsCo were in the range of 64%~78%, with the maximum FEco achieved at 200 mA / cm2. Although the FEsCo decreased at higher current densities, it was converted to ethylene, which was the target final product. The FEs to liquid products were below 20 % and kept decreasing with the growth of current density.

[0182] Still referring to Figure 36, graph B provides the CORR performance of the Cu-Sb compound when tested in a 1 M LiOH electrolyte and receiving the CO flowstream produced in the CO2RR stage. The FESC2H4 for Cu-Sb increased from 66% at 50 mA / cm2to 76% at 225 mA / cm2. It is noted that conducting the COR in 2 M LiOH could further improve the FEC2H4 to 79% at 150 mA / cm2.

[0183] The distinct selectivity of the Cu-Sb compound under different gas reactants renders sequential CO2electrolysis possible with a single catalyst being the Cu- Sb compound as described herein. As shown in Figure 35, the CO2 is firstly reduced to CO in a CO2electrolyzer (Cell 1), the generated CO can then be subsequently directed to the second CO electrolyzer (Cell 2) and gets reduced to ethylene.

[0184] The CO2R system and the COR system can be chosen among zero-gap, one-gap, two-gap electrolyzer structures. In some implementations, the type of electrolyzer that is used for the CO2R system and the COR system can be different. For example, the CO2R system can include a zero-gap electrolyzer, such as a membrane electrode assembly (MEA), and the COR system can include a one-gap electrolyzer, In other implementations, the CO2R system and the COR system have the same electrolyzer structure. For example, both CO2R system and COR system can be a zero-gap electrolyzer.

[0185] In some implementations, to optimize the pH to alkaline conditions for CORR and stabilize cell voltage, the assembly can further include a separator that is positioned between the CO2R system and the COR system so as to remove any unconverted CO2from the product stream and produce a stream consisting of CO that is fed to the COR system.MATERIALS AND METHODS

[0186] Further details regarding materials and methods that were used to gather experimental results described or shown in the present description and accompanying Figures are provided below.Materials

[0187] Copper(ll) nitrate trihydrate (99.999%), antimony(lll) trichloride (99.95%), urea (99.5%), methanol (99.8%), sodium hydroxide (puriss, 98-100.5%), lithium hydroxide (98%), Nation® perfluorinated resin solution (5 wt.% in mixture of lower aliphatic alcohols and water, contains 45% water), potassium chloride (99.0%), sodium perchlorate (98%), silver nitrate (99%), sodium oxalate (99.5%), potassium permangate (99.0%), nickel(ll) chloride hexahydrate (99.9%), iron(lll) chloride anhydrous (99.99%), sodium borohydride (98%) trisodium citrate dihydrate (99.0-101 .0%), lead perchlorate (99.995%), Pt mesh and nickel foam used in flow cell as counter electrodes were all purchased from Sigma-Aldrich without further treatment. Copper nanoparticles (25 nm) was purchased from US Research nanomaterials, Inc. Potassium hydroxide (Reagent grade) and sulfuric acid (trace metal grade) were purchase from Caledon Laboratory Chemicals. Ethanol (USP / NF grade) was purchased from Commercial Alcohols. Sustainion® X37-50 Grade RT Membrane was purchased from Dioxide Materials. The membrane was cut into 3 cm x 3 cm pieces and stored in 1 M KOH solutions. Freudenberg H23C3, platinized titanium felt, and Pention-D18-5% were purchased from Fuel Cell Store. PTFE nanoparticles (20 nm) was purchased from AliExpress. The Ag / AgCI reference electrodes used in flow cell were purchased from CHI Instruments, Inc. Gaseous CO (99.99%) was purchased from Linde.Ultrapure water (18.2 MQ) was used to prepare all the solutions and electrolytes.CORR related experimentsElectrode preparation

[0188] For example, to prepare the cathodes that were used in flow cell and membrane-electrode assembly (MEA), 20 mg Cu-based catalysts, 1.9 mL methanol, 0.1 mL H2O, and 64 pL Nation solution were added into a 20 mL vial. The mixture was sealed and sonicated in a water bath for 2-4 hours (the temperature of the water bath was kept below 30 °C. The solution was then spray onto a 3 cm * 3 cm gas diffusion electrode(Freudenberg H23C3). The final catalyst loading was controlled to be ~ 1 mg / cm2. After drying at ambient environment overnight, the gas diffusion electrode was cut into 4 pieces for further use.

[0189] For example, the anode of the MEA can include a NiFeB OER catalyst as used for the experimentation discussed herein. The synthesis of NiFeB included dissolving 0.6656 g (2.8 mmol) NiCI2-6H2O and 0.4542 g (2.8 mmol) FeCI3into 4 mL ice-cold water, denoted as Solution A. In a separate vial, 0.7566 g NaBH (20 mmol) was dissolved in 4 mL ice-cold water, denoted as Solution B. Solution A was dropwise added into Solution B in 3 minutes in an ice-water bath under vigorous agitation, and the solution was continuously stirred for 15 minutes. The product was collected and washed with H2O for 3 times and acetone for 2 times by centrifugation. Final NiFeB product was stored in air. Then, to prepare the anode that was used in the MEA, 20 mg NiFeB, 1.6 mg PTFE nanoparticles, 100 pL Pention-D18-5%, 1.9 mL methanol, and 0.1 mL H2O were added into a 20 mL vial. The mixture was sealed and sonicated for 2 hours. It was then sprayed onto a 1 cm x 3.2 cm platinized titanium felt. The final loading was around 3-4 mg / cm2. The electrode was cut into 1 cm x 1 cm pieces for further use.Electrochemical measurement

[0190] All the electrochemical measurements were carried out using an electrochemical station (Metrohm Autolab) connected to a current booster.

[0191] The COR performance was evaluated under galvanostatic mode. Before recording the performance, all the catalysts were activated to ensure a stabilized activity. The activation methods depend on the identity of electrolyte: in LiOH, the catalysts were hold at 50 mA / cm2for 1 h; in NaOH, a 100 mA / cm2was applied first, the current density was then increased with an increment of 100 mA / cm2every 5 minutes to 600 mA / cm2; in KOH, the activation method was similar to the one in NaOH except the final current was stopped at 900 mA / cm2.

[0192] In flow cell, the applied potential was iR-corrected by Equation 1 :

[0193] Ecathode—Eapplied — 0.9 ‘ Itotai ' Rcatholyte (1)

[0194] Ecathode is the iR-corrected potential on the cathode, EaPPiied is the applied potential before iR-correction, itotai is the total current (itotai was a negative value at cathode),Rcathoiyte is the resistance between reference electrode and working electrode, which was determined using electrochemical impedance spectroscopy. The resistance in 1 M LiOH, NaOH, and KOH were 5.27 Q, 4.07 Q, and 3.02 Q, respectively. A factor of 0.9 was applied to the iR-correction to prevent over-compensation.

[0195] The iR-corrected potential was then converted to reversible hydrogen electrode (RHE) scale according to the Equation 2:

[0196] ERHE - Ag / AgCI + 0.0592xpH + 0.197(2)

[0197] ERHE is the cathodic potential in RHE scale, E g / Agci is the iR-corrected potential with respect to the reference electrode. For 1 M LiOH, NaOH, KOH, the solution pH was 13.7 (4). For 1 M LiOD in D2O, the solution pD was 14.6, because the ionic product pKwof D2O is smaller than H2O (pKw(D2O)=14.951 , pKw(H2O)=13.995) (5).COR products analysis

[0198] The gas phase products (H2, CH4, and C2H4) were analyzed by a gas chromatography (GO, Shimadzu, GC-2014) equipped with a thermal conductivity detector (TCD) for the detection of H2, CO, and a flame ionization detector (FID) for the detection of ethylene and methane. The Faradaic efficiency (FE) of a gas product can be calculated via Equation 3:FE = ^ (3) iV .v 7

[0199] where n is the number of electrons transferred during the reaction (8 for ethylene, 6 for methane, 2 for hydrogen), F is the Faraday constant (96485 C / mol), v is the flow rate of CO, c is the concentration of the product in the outlet in parts-per-million (ppm), Vmis the unit molar volume of gas.

[0200] Liquid products (ethanol, acetate, and n-propanol) were analyzed by1H nuclear magnetic resonance (NMR) spectroscopy (600 MHz, Aligent DD2 NMR spectrometer) with water suppression. Dimethyl sulfoxide (DMSO) was used as internal standard and D2O was used as lock solvent.

[0201] The energy efficiency (EE) was calculated according to Equation 4:

[0202] where Eco-to-ethyiene is the thermodynamic potential of the reaction 2CO + 2H2O — » C2H4 + 2O2, which is -1 .06 V. Efuii ceii is the measured full cell potential in MEA.Operando Raman spectroscopy

[0203] The operando Raman spectroscopy was carried out in a custom-made flow cell with an epi-illumination configuration. A 532 nm and a 785 nm laser were used as the excitation source for interfacial water structure studies and COR intermediate detection, respectively. The scattered Raman light was collected by a water immersion objective (Leica, HC APO L 63x / 0,90 W U-V-l). Each time prior to the measurement, the spectrometer was calibrated by a standard silicon sample. During operation, CO was flowed through the gas chamber that was located on the back of GDL.

[0204] For interfacial water structure study, the shell-isolated nanoparticles- enhanced Raman spectroscopy (SHINERS) that was developed in the last decades was used. Ag nanoparticles with a size around 50 nm were prepared, and a thin layer of MnO2was coated onto it as insulator as further detailed below.

[0205] To prepare the electrode for operando Raman experiments, an ink solution containing 10 mg Cu nanoparticles and 32 pL Nation solution was first sprayed onto a 3 cm x 3 cm carbon paper. Then a second ink solution with the same composition was mixed with 0.5 mL as-prepared Ag@MnO2solution and sprayed on top of the previous carbon paper.Synthesis of Ag nanoparticles solution

[0206] The Ag nanoparticles for surface-enhanced Raman spectroscopy was prepared through a reported method (2). 100 mL 0.08 mM AgNOs aqueous solution was added into a conical flask and boiled for 10 minutes on a heating plate. Then 2 mL 20 mM trisodium citrate aqueous solution was injected under agitation. The resulting solution was continuously heated for 30 minutes, and 30 mL 0.8 mM AgNO3solution was added. The solution was continuously stirred and boiled for 90 minutes. The solution containing ~50 nm Ag nanoparticles was obtained and stored in dark environment.Synthesis of Ag@MnO2nanoparticles

[0207] The Ag@MnO2nanoparticles was prepared by modifying a reported method (3). 10 mL solution containing Ag nanoparticles from above synthesis was placed in a cold-water bath, the solution pH was tuned to 9.5 by adding 75 pL 0.1 M NaOH. 1 .6 mL 10 mM K2C2O4was added into the above solution, followed by dropwise adding 0.32 mL 10 mM KMnO4solution under vigorous agitation. The color of resulting solution turned quickly from grey to brown in 1 minute, and further stirred for 9 minutes before placing it to a pre-heated water bath at 60 °C. After holding at the same temperature for 2 hours with agitation, the solution was cooled down and washed with water for 1 time. The product was collected and dispersed in 1.5 mL H2O and stored in dark environment.Operando XAS experiments

[0208] The XAS measurements were performed in Soft X-ray MicroCharacterization Beamline (SXRMB) at the Canadian Light Source (Saskatoon, Canada), which is equipped with a water-cooled Si (111) and InSn (111) double-crystal monochromator covering a photon energy range from 1.7 to 10.0 keV, and 20 BM in the Advanced Photon Source (Lemont, U.S.A.) with a Si(111) monochromator that covers a photon energy range from 2.7 to 35 keV. A modified flow cell was used. During measurement, 1 M LiOH was flowed through both catholyte and anolyte chamber, and CO was flowed through gas chamber. For the data shown in the main text, several scans were measured and averaged for each sample to gain a better signal-to-noise ratio. The XAS data were processed with Demeter (v.0.9.26) (7).Molecular Dynamics (MD) simulations

[0209] More particularly, all MD simulations discussed herein were conducted using a GROMACS 2019.3. Parameters for intermediates CO* and CHCO* were generated with an antechamber module of Amber18 using a general Amber force field (GAFF). The partial charges were obtained by fitting the electrostatic potential generated with a Cu38 model system by restrained electrostatic potential (RESP). Referring to Figure 14, the geometries of adsorbed CO and CHCO on Cu3s were optimized with Perdew- Burke-Ernzerhof (PBE) exchange-correlation functional. A 6-31 G(d) basis set was used for C H O atoms and a Lan2TZ basis set was used for Cu atoms. The potential parameters for Cu, Li+and K+are known in the art. The electrode surface consists of 8 layers of 32 X26 Cu (111) surface with 6656 atoms. Water molecules were represented by a three-point charge SPCE model. The CO* and CHCO* species were fixed on the Cu surface during MD simulations. The total system was energy minimized by a succession of steepest descent and conjugate gradient methods. Thereafter, it was equilibrated for 200 ns at constant temperature (298.15 K) and pressure (1 bar) (NPT). A V-rescale thermostat and a Parrinello-Rahman barostat were used to keep the temperature and pressure constant, respectively. The time step was set to 2 fs. The cutoff radius for neighbor searching and nonbonded interactions was taken to be 12 A, and all bonds were constrained using a LINCS algorithm. The last 100 ns-long MD trajectories were used for analysis. All computed structures in MD simulations were illustrated using Visual Molecular Dynamics (VMD).DFT Calculations

[0210] All density functional theory (DFT) calculations were carried out using the Vienna ab initio simulation package (VASP) (23-27). The generalized gradient approximation was used with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional (27). The projector-augmented wave method was used to describe the electronion interactions and the cut-of energy for the plane wave basis set was 450 eV. The D3 correction method was employed to illustrate the long-range dispersion interactions between the adsorbates and catalysts. Brillouin zone integration was accomplished using a 2x2x1 Monkhorst-Pack k-point mesh for all calculations. A vacuum region of more than 15 A thickness was included along the perpendicular direction to avoid artificial interactions. A periodic four-layer model and p(5x5) or p(6x6) super cell were chosen. Adsorption geometries of the different states were optimized by a force-based conjugate gradient algorithm, whereas the transition states were located using the climbing image- nudged elastic band method. During the calculations, the two lower layers were fixed and the two upper layers together with adsorbates were allowed to relax. The Gibbs free energy (AG) was calculated by converting the electronic energy using the equation: AG=AE+AZPE+fACpc / T-7'AS, where AE, AZPE, ACP, and AS are the differences in electronic energy, zero-point energy, heat capacity and entropy, respectively, and T was set to room temperature (298.15K). During the calculations, a HsO+was added as the hydrogen source for the protonation reaction of CHCO*. The procedure to obtain an alkaline barrier by an acidic barrier was the same as the previous work. All the activation energies AGawere calculated at URHE = 0 V and pH=7.sTable 2. Structural parameters of Cu-Sb and Cu-Ref extracted from Cu K-edge EXAFS spectra.;00211 ] Scanning electron microscopy (SEM) was performed in a high-resolution scanning electron microscope (HR-SEM, Hitachi S-5200).

[0212] X-ray photoelectron spectroscopy (XPS) were carried out in an ECSA device (PHI 5700) with Al Ka X-ray energy source (1486.6 eV) for excitation. Prior to measurements, the catalysts were rinsed sequentially with 1 M H3PO4and DI water to remove any potential residual salt from the surface.Sequential CO2RR and CORR related experimentsSynthesis of the catalysts

[0213] In order to homogeneously disperse Sb into Cu lattice, a Sb-doped CuO precursor (denoted as CuO-Sb) was prepared first through hydrothermal process, follow by annealing in air (see Figures 20 and 29) The catalyst was obtained by in situ reducing the Sb-doped CuO precursor to Cu. A reference sample without Sb was also prepared, denoted as CuO-Ref.

[0214] For the synthesis of the CuO-Sb precursor compound: 0.2392 g (0.99 mmol) Cu(NO3)2-3H2O was dissolved in 10 mL EtOH, to which 10 mL H2O containing 0.21 g (3.5 mmol) urea was dropwise added. Then 2.3 mg (0.01 mmol) SbCI3was dissolved in 15 mL 1 M NaOH, this solution was dropwise added into the as-prepared Cu(NO3)2-3H2O- urea solution. The solution was stirred at room temperature for 10 min, transferred into a 45 mL autoclave and heated at 100 °C for 20 h. The solid product was separated and washed by centrifugation with a mixed solution of H2O:MeOH 1 :1. After lyophilizationovernight, final product can be obtained by heating the powder at 400 °C for 3 h (ramp rate: 10 °C / min) in air.

[0215] The synthesis of CuO-Ref is similar to CuO-Sb compound, except the no SbCI3was added at the beginning. Then, synthesis of the Cu-Sb compound from the formed CuO-Sb precursor compound (or Cu-Ref from CuO-Ref) includes applying a reduction current to the CuO-Sb precursor compound to produce the Cu-Sb compound.

[0216] Referring to Figure 37, the CuO-Sb compound displays nanoneedle morphology (image A) while CuO-Ref has a less regular morphology (image B). Upon electroreduction under negative potentials, the CuO precursors were reduced to metallic copper (denoted as Cu-Sb and Cu-Ref, respectively), as revealed by operando XAS (see Figures 5C and 5D).

[0217] The Cu-Sb compound was used as the metallic CO2R catalyst and the metallic COR catalyst.Electrode preparation

[0218] To prepare the electrode ink, 20 mg Cu-based compound (either Cu-Sb or Cu-Ref), 2 mL methanol, 0.2 mL H2O, and 100 pL 5% Nation solution (sigma-Aldrich, SKU: 510211-25ML) were mixed in a 20 mL glass vial. The mixture was sonicated for 2 h and then spray coated onto a 3*3 cm2gas-diffusion layer (Freudenberg H23C3). The final loading of the electrode was controlled to be around 1.2 mg / cm2.CO2RR and CORR electrochemical measurement

[0219] In flow cell, the electrolysis was carried out in a three-electrode system. Ag / AgCI (with saturated KCI solution and Pt mesh were used as reference electrode and counter electrode, respectively. For CO2RR experiments, a piece of 2*2 Nation 117 was used as the membrane, and 0.5 M KHCO3+ 0.1 M K2SO was used as the electrolyte. For CORR experiments, a piece of 2*2 cm2Sustainion® X37-50 was used as the membrane and 1 M LiOH was used as the electrolyte. CO2and CO were respectively supplied to the gas chamber of one flow cell, the gas chamber being on the back side of the working electrode. The flow rate was controlled to be 20 mL / min by a mass-flow controller (MFC). Both anolyte and catholyte were supplied to the flow cell by a peristaltic pump with a flowrate of 20 mL / min. Before electrolysis, the catalyst was reduced at a current density of 50 mA / cm2.

[0220] For product detection and quantification, the gas products were analyzed using a gas chromatograph (PerkinElmer Clarus 600).

[0221] It should be noted that the same numerical references refer to similar elements. Furthermore, for the sake of simplicity and clarity, namely so as to not unduly burden the figures with several reference numbers, not all figures contain references to all the components and features, and references to some components and features may be found in only one figure, and components and features of the present disclosure which are illustrated in other figures can be easily inferred therefrom. The embodiments, geometrical configurations, materials mentioned and / or dimensions shown in the figures are optional, and are given for exemplification purposes only. Therefore, the descriptions, examples, methods and materials presented in the claims and the specification are not to be construed as limiting but rather as illustrative only.

[0222] It is worth mentioning that throughout the following description when the article “a” is used to introduce an element it does not have the meaning of “only one” it rather means of “one or more". It is to be understood that where the specification states that a component, feature, structure, or characteristic “may”, “might”, “can” or “could” be included, that particular component, feature, structure, or characteristic is not required to be included.

[0223] In the above description, the term “about” means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e. , the limitations of the measurement system. It is commonly accepted that a 10% precision measure is acceptable and encompasses the term “about”.

[0224] In the above description, an embodiment is an example or implementation of the inventions. The various appearances of “one embodiment,” “an embodiment” or “some embodiments” do not necessarily all refer to the same embodiments. Although various features of the invention may be described in the context of a single embodiment, the features may also be provided separately or in any suitable combination. Conversely,although the invention may be described herein in the context of separate embodiments for clarity, the invention may also be implemented in a single embodiment.

[0225] It should be understood that any one of the aspects methods, COR systems, lithium-containing electrolyte, COR catalyst and use thereof may be combined with any other of the aspects thereof, unless two aspects clearly cannot be combined due to their mutually exclusivity. For example, the various operational steps and / or structural elements described in relation to the method for facilitating carbon oxide (CO) electroreduction into ethylene including providing the lithium-containing electrolyte described herein, may be combined with any aspects of the method for facilitating carbon oxide (CO) electroreduction into ethylene including providing the COR Cu-Sb catalyst as described herein and / or in accordance with the appended claims / figures.All publications that are identified herein are incorporated herein by reference.X. Chang et al. , C-C Coupling Is Unlikely to Be the Rate-Determining Step in the Formation of C(2+) Products in the Copper-Catalyzed Electrochemical Reduction of CO. Angew. Chem. Int. Ed. 61 , e202111167 (2022).Y. H. Wang et al., In situ Raman spectroscopy reveals the structure and dissociation of interfacial water. Nature 600, 81-85 (2021).J. Li, X. Li, C. M. Gunathunge, M. M. Waegele, Hydrogen bonding steers the product selectivity of electrocatalytic CO reduction. Proc. Natl. Acad. Sci. 116, 9220-9229 (2019).H. J. Peng, M. T. Tang, J. Halldin Stenlid, X. Liu, F. Abild-Pedersen, Trends in oxygenate / hydrocarbon selectivity for electrochemical CO((2)) reduction to C(2) products. Nature communications 13, 1399 (2022).S. Chu et al., Single atom and defect engineering of CuO for efficient electrochemical reduction of CO2 to C2H4. SmartMat. 3, 194-202 (2022).Perez-Gallent, G. Marcandalli, M. C. Figueiredo, F. Calle-Vallejo, M. T. M. Koper, Structure- and Potential-Dependent Cation Effects on CO Reduction at Copper Single-Crystal Electrodes. Journal of the American Chemical Society 33, 16412-16419 (2017).

Claims

CLAIMS1 . A sequential electroreduction process to convert CO2into multicarbon products including ethylene, the process comprising: a) electroreducing CO2in presence of a metallic CO2R catalyst in a first CO2RR stage to produce CO; and b) electroreducing CO in presence of a metallic COR catalyst in a second COR stage to produce multicarbon products comprising ethylene, wherein the metallic CO2R catalyst and the metallic COR catalyst are a metal-Sb compound comprising a metal and antimony, the antimony being atomically dispersed in a lattice formed by a crystalline structure of the metal.

2. The process of claim 1 , wherein the metal is Cu, Ag, Ni, Ga, or any combinations thereof, preferably Cu.

3. The process of claim 2, wherein the metal Sb-compound of both metallic CO2R catalyst and metallic COR catalyst is a Cu-Sb compound that is made in situ with a step of providing a CuO-Sb compound followed by a step of reducing in situ said CuO-Sb compound into the Cu-Sb compound, said step of reducing being carried out with the reduction current provided at the electroreducing steps (a) and / or (b).

4. The process of claim 2 or 3, wherein the crystalline structure has Cu(100) facets.

5. The process of any one of claims 2 to 4, wherein the metallic CO2R catalyst has a first Cu:Sb ratio ranging between 9 / 1 and 200 / 1 , optionally between 19 / 1 and 200 / 1 , as determined by Inductive Coupled Plasma mass spectrometry.

6. The process of any one of claims 2 to 5, wherein the metallic COR catalyst has a second Cu:Sb ratio ranging between 49 / 1 and 200 / 1 as determined by Inductive Coupled Plasma mass spectrometry.

7. The process of any one of claims 1 to 6, wherein the metallic CO2R catalyst includes a first doping amount of Sb that is between 0.5 at. % and 10 at. %, optionally between 0.5 at.% and 5 at.%, based on a total number of atoms in said metallic CO2R catalyst as determined by Inductive Coupled Plasma mass spectrometry.

8. The process of any one of claims 1 to 7, wherein the metallic COR catalyst includes a second doping amount of Sb that is between 0.5 at.% and 2 at.% based on ta total number of atoms in said metallic COR catalyst as determined by Inductive Coupled Plasma mass spectrometry.

9. The process of any one of claims 1 to 6, wherein the metallic CO2R catalyst includes a first doping amount of Sb and the metallic COR catalyst includes a second doping amount of Sb, the first doping amount of Sb being higher than the second doping amount of Sb.

10. The process of any one of claims 1 to 9, wherein the step (b) of electroreducing CO is performed according to the following sub-steps: i. providing a COR system including an electrode comprising the metallic COR catalyst favouring reduction of CO; ii. supplying an electrolyte to the COR system, the electrolyte comprising a lithium cation source and a proton source to respectively provide lithium cations and protons at an electrical double layer (EDL) formed between the metallic COR catalyst and the electrolyte, iii. supplying a gaseous stream comprising CO to the COR system for contacting the metallic COR catalyst in presence of the lithium cations at the EDL; and iv. generating a reduction current through the COR system to cause electroreduction of CO into a product mixture including ethylene.11 . The process of claim 10, wherein the proton source comprises a protic solvent.

12. The process of claim 11 , wherein the protic solvent is selected from water, acid, alcohol, another protic solvent or any combinations thereof.

13. The process of any one of claims 10 to 12, wherein the lithium cation source comprises LiOH, LiCICU, LiCI, Li2SO4, LiHCOs, Li2COs or any combinations thereof.

14. The process of any one of claims 10 to 13, wherein the electrolyte has a molar concentration in the cation source between 1 M and 2M.

15. The process of any one of claims 10 to 14, wherein the gaseous stream supplied at substep (iii) comprises CO in an amount of at least 80 vol.% of the total volume of the gaseous stream; with preference, the gaseous stream consists of CO.

16. The process of any one of claims 10 to 15, wherein the step (iv) of generating the reduction current through the COR system comprises applying a current density between 100 mA.cm'2and 800 mA. cm-2.

17. The process of any one of claims 10 to 16, wherein the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 1.0.

18. The process of any one of claims 10 to 17, wherein the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 1.2.

19. The process of any one of claims 10 to 18, wherein the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 1.5.

20. The process of any one of claims 10 to 19, wherein the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 1.8.

21. The process of any one of claims 10 to 20, wherein the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 2.

22. The process of any one of claims 1 to 9, wherein the step (b) of electroreducing CO comprises the following sub-steps: i. providing a COR system including an electrode comprising the metallic COR catalyst favouring reduction of CO; ii. supplying an electrolyte to the COR system for providing ions at an electrical double layer (EDL) formed between the metallic COR catalyst and the electrolyte, iii. supplying a gaseous stream comprising CO to the COR system for contacting the metallic COR catalyst at the EDL; and iv. generating a reduction current through the COR system to cause electroreduction of CO into a product mixture including ethylene.

23. The process of claim 22, wherein the electrolyte comprises a lithium cation source and a proton source to respectively provide lithium cations and protons at the electrical double layer (EDL).

24. The process of claim 23, wherein the lithium cation source comprises LiOH, LiCIO4, LiCI, Li2SO4, LiHCO3, Li2CO3or any combinations thereof.

25. The process of any one of claims 22 to 24, wherein the electrolyte comprises a cation source and has a molar concentration in the cation source between 1 M and 2M.

26. The process of any one of claims 22 to 25, wherein the electrolyte comprises a proton source and the proton source comprises a protic solvent.

27. The process of claim 26, wherein the protic solvent is selected from water, acid, alcohol, another protic solvent or any combinations thereof.

28. The process of any one of claims 22 to 27, wherein the gaseous stream supplied at substep (iii) comprises CO in an amount of at least 80 vol.% of the total volume of the gaseous stream; with preference, the gaseous stream consists of CO.

29. The process of any one of claims 22 to 28, wherein the step (iv) of generating the reduction current through the COR system comprises applying a current density between 100 mA.cm'2and 800 mA. cm-2.

30. The process of any one of claims 22 to 29, wherein the ratio of FE(ethylene) toFE(oxygenates) of the product mixture is of at least 1.0.

31. The process of any one of claims 22 to 30, wherein the ratio of FE(ethylene) toFE(oxygenates) of the product mixture is of at least 1.2.

32. The process of any one of claims 22 to 31 , wherein the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 1.5.

33. The process of any one of claims 22 to 32, wherein the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 1.8.

34. The process of any one of claims 22 to 33, wherein the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 2.

35. Use of a metallic catalyst under the form of a Cu-Sb compound in each stage of a sequential electroreduction operation including consecutive CO2RR and CORR to convert CO2into ethylene, wherein the Cu-Sb compound comprises copper and antimony, the antimony being atomically dispersed in a lattice formed by a crystalline structure of the copper.

36. The use of claim 35, wherein the antimony is present in an amount of between 0.5 at.% and 10 at.% with respect to a total number of atoms in the metallic catalyst as determined by Inductive Coupled Plasma-Optical Emission Spectroscopy (ICP-OES).

37. The use of claim 35 or 36, wherein the metallic catalyst comprises nanoparticles, said nanoparticles having a size ranging between 5 nm and 20 nm as determined by scanning transmission electron microscopy.

38. A sequential electroreduction assembly to convert CO2into multicarbon products including ethylene, the assembly comprising: a CO2R system receiving a CO2flowstream and producing a CO flowstream via CO2RR, and a COR system fluidly connected to the CO2RR system to receive the CO flowstream and produce a multicarbon product stream including ethylene; wherein the CO2R system includes a metallic CO2R catalyst and the COR system includes a metallic COR catalyst, and both the metallic CO2R catalyst and the metallic COR catalyst include a metal-Sb compound comprising a metal and antimony, the antimony being atomically dispersed in a lattice formed by a crystalline structure of the metal.

39. The assembly of claim 38, wherein each of the COR system and the CO2R system is at least one of a zero-gap electrolyzer, a one-gap electrolyzer and a two-gap electrolyzer.

40. The assembly of claim 39, wherein the CO2R system is a zero-gap electrolyzer.41 . The assembly of claim 39 or 40, wherein the COR system is a zero-gap electrolyzer.

42. The assembly of any one of claims 38 to 41 , wherein the metal-Sb compound of the metallic CO2R catalyst and / or the metallic COR catalyst is as defined in any one of claims 2 to 9.

43. The assembly of any one of claims 38 to 42, further comprising a separator being positioned between the CO2R system and the COR system, the separator being fed with a product stream from the CO2R system and removing unconverted CO2, when present, from the product stream to produce the CO flowstream that is supplied to the COR system.

44. A method for carbon oxide (CO) electroreduction into at least ethylene, the method comprising: a) providing a COR system including an electrode comprising a metal-based catalyst favouring reduction of CO; b) supplying an electrolyte to the COR system, the electrolyte comprising a lithium cation source and a proton source to respectively provide lithium cations and protons at an electrical double layer (EDL) formed between the metal-based catalyst and the electrolyte, c) supplying a gaseous stream comprising CO and being exempt of CO2to the COR system for contacting the metal-based catalyst in presence of the alkali metal cations at the EDL; and d) generating a reduction current through the COR system to cause electroreduction of CO into a product mixture including ethylene.

45. The method of claim 44, wherein the proton source comprises a protic solvent; with preference, said protic solvent is selected from water, acid, alcohol, another protic solvent or any combinations thereof.

46. The method of claim 44 or 45, wherein the lithium cation source comprises LiOH, LiCIO4, LiCI, Li2SO4, LiHCO3, Li2CO3or any combinations thereof.

47. The method of any one of claims 44 to 46, wherein the electrolyte has a molar concentration in the cation source between 1 M and 2M.

48. The method of any one of claims 44 to 47, wherein the gaseous stream comprises CO in an amount of at least 80 vol.% of the total volume of the gaseous stream, with preference, the gaseous stream consists of CO.

49. The method of any one of claims 44 to 48, wherein the step (d) of generating the reduction current through the COR system comprises applying a current density between 100 mA.cm'2and 800 mA. cm-2.

50. The method of any one of claims 44 to 49, wherein the ratio of FE(ethylene) toFE(oxygenates) of the product mixture is of at least 1.0.

51. The method of any one of claims 44 to 50, wherein the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 1.2.

52. The method of any one of claims 44 to 51 , wherein the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 1 .5.

53. The method of any one of claims 44 to 52, wherein the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 1.8.

54. The method of any one of claims 44 to 53, wherein the ratio of FE(ethylene) toFE(oxygenates) of the product mixture is of at least 2.0.

55. The method of any one of claims 44 to 54, wherein the metal-based catalyst comprises Cu, Ag, Ni, Ga or any combinations thereof, preferably copper.

56. The method of any one of claims 44 to 55, wherein the metal-based catalyst is a metallic COR catalyst under the form of a Cu-Sb compound, the antimony being atomically dispersed in a lattice of a copper crystalline structure.

57. The method of claim 56, wherein the metallic COR catalyst under the form of a Cu-Sb compound is made in situ with a step of providing a CuO-Sb compound followed by a step of reducing in situ said CuO-Sb compound into the Cu-Sb compound, said step of reducing being carried out with the reduction current provided at step (d).

58. The method of claim 56 or 57, wherein the copper crystalline structure has Cu(100) facets.

59. The method of any one of claims 56 to 58, wherein the metallic COR catalyst under the form of a Cu-Sb compound has a Cu:Sb ratio ranging between 49 / 1 and 200 / 1 as determined by Inductive Coupled Plasma mass spectrometry.

60. The method of any one of claims 56 to 59, wherein the metallic COR catalyst under the form of a Cu-Sb compound includes a doping amount of Sb that is between 0.5 at.% and 2 at.% based on the total number of atoms of said metallic COR catalyst as determined by Inductive Coupled Plasma mass spectrometry.61 . The method of any of claims 44 to 60, wherein the electrolyte is a catholyte and wherein the COR system is a catholyte-containing one-gap electrolyzer.

62. The method of any of claims 44 to 60, wherein the COR system is a two-gap electrolyzer.

63. The method of any one of claims 44 to 60, wherein the COR system is a zero-gap electrolyzer.

64. The method of claim 63, wherein the COR system is a membrane electrode assembly and the electrolyte is an anolyte, with the alkali metal cations migrating to the electrode in a cathodic compartment via an anion exchange membrane with cation crossover.

65. A method for carbon oxides electroreduction into at least ethylene, the method comprising: a) providing a metallic catalyst under the form of a Cu-Sb compound to favour reduction of CO2and / or CO into ethylene, wherein the antimony is atomically dispersed in a lattice of a copper crystalline structure, the metallic catalyst being provided within a system; b) supplying an electrolyte to the system for providing ions at an electrical double layer (EDL) formed between the catalyst and the electrolyte; c) supplying a gaseous stream comprising CO2and / or CO to the system for contacting the metal-based catalyst at the EDL; and d) generating a reduction current through the system to cause electroreduction of CO2and / or CO into a product mixture including ethylene.

66. The method of claim 65, wherein the step (a) comprises a step of providing a CuO-Sb compound followed by a step of reducing in situ said CuO-Sb compound into the Cu-Sb compound, said step of reducing being carried out with the reduction current provided at step (d).

67. The method of claim 65 or 66, wherein the copper crystalline structure has facets being Cu(100).

68. The method of any one of claims 65 to 67, wherein the metallic catalyst under the form of a Cu-Sb compound has a Cu:Sb ratio ranging between 49 / 1 and 200 / 1 as determined by ICP mass spectrometry.

69. The method of any one of claims 65 to 68, wherein the metallic catalyst under the form of a Cu-Sb compound includes a doping amount of Sb that is between 0.5 at.% and 10 at.% based on a total number of atoms in said metallic catalyst as determined by ICP mass spectrometry.

70. The method of any one of claims 65 to 69, wherein the electrolyte comprises an alkali metal cation source to provide alkali metal cations at the EDL.71 . The method of claim 70, wherein the alkali metal cation source is a lithium cation source; with preference, said lithium cation source is one or more selected from LiOH, LiCIO4, LiCI, Li2SO4, LiHCO3, Li2CO3, or a mixture thereof.

72. The method of claim 70 or 71 , wherein the electrolyte further comprises a proton source, with preference, said proton source is one or more selected from water, acid, alcohol, another protic solvent or any combinations thereof.

73. The method of claim 72, wherein the lithium cation source is lithium hydroxide, the proton source is water, and the electrolyte is an aqueous solution of lithium hydroxide.

74. The method of any one of claims 70 to 73, wherein the electrolyte has a molar concentration in the lithium cation source between 1 M and 2M.

75. The method of any one of claims 65 to 74, wherein the gaseous stream comprises CO2and / or CO in an amount of at least 80 vol.% of the total volume of the gaseous stream; with preference, the gaseous stream consists of CO2and / or CO.

76. The method of any one of claims 65 to 75, wherein the step (d) of generating the reduction current through the system comprises applying a current density between 100 mA.cnr2and 800 mA. cm-2.

77. The method of any one of claims 65 to 76, wherein the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 1.0.

78. The method of any one of claims 65 to 77, wherein the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 1.2.

79. The method of any one of claims 65 to 78, wherein the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 1.5.

80. The method of any one of claims 65 to 79, wherein the ratio of FE(ethylene) to FE(oxygenates) of the product mixture is of at least 1.8.

81. The method of any one of claims 65 to 80, wherein the ratio of FE(ethylene) toFE(oxygenates) of the product mixture is of at least 2.

082. The method of any one of claims 65 to 81 , wherein the system is a catholyte-containing one-gap electrolyzer.

83. The method of any one of claims 65 to 81 , wherein the system is a two-gap electrolyzer.

84. The method of any one of claims 65 to 81 , wherein the system is a zero-gap electrolyzer.

85. A metallic catalyst under the form of a metal-Sb compound, wherein the metallic catalyst comprises a metal and antimony, the antimony being atomically dispersed in a lattice formed by a crystalline structure of the metal and being present in a doping amount of between 0.5 at.% and 10 at.% with respect to a total number of atoms of said metallic catalyst as determined by Inductive Coupled Plasma (ICP)- Optical Emission Spectroscopy (OES).

86. The catalyst of claim 85, being under the form of porous nanoparticles, said porous nanoparticles having a size ranging between 5 nm and 20 nm as determined by scanning transmission electron microscopy.

87. The metallic catalyst of claim 85 or 86, wherein the Metal-Sb ratio is ranging between 9 / 1 and 200 / 1 , preferably between 19 / 1 and 200 / 1 , more preferably between 49 / 1 and 200 / 1 as determined by ICP mass spectrometry.

88. The metallic catalyst of any one of claims 85 to 87, wherein the metal is Cu, Ag, Ni, Ga, or any combinations thereof, preferably Cu.

89. The metallic catalyst of any one of claims 85 to 88, having an increased oxyphilicity characterized by an OH binding strength that is higher than for a non Sb-doped catalyst.

90. A cathode / system comprising the metallic catalyst as defined in any one of claims 85 to 89.

91. A method to synthesize a metallic catalyst as defined in any one of claims 85 to 89, wherein the method comprises the following steps: a) preparation of a first solution comprising antimony; b) preparation of a second solution comprising copper; c) addition of water in the second solution to form an aqueous second solution; d) combining the first solution and the aqueous second solution of step (c) to obtain a mixture; e) heating the mixture obtained at step (d) at a temperature ranging between 90°C and 150°C; f) cooling the mixture to room temperature so that a solid is precipitated; g) optionally, washing the solid obtained at step (f); h) lyophilizing the solid to produce a lyophilized solid; i) heating the lyophilized solid from room temperature up to at most 400°C so that a CuO-Sb compound is obtained; and applying a reduction current to the CuO-Sb compound obtained in step (i) for reduction thereof into the metallic catalyst under the form of a Cu-Sb compound.

92. The method of claim 91 , wherein the heating of step (i) is performed at a rate comprises between 5°C / minute and 15°C / minute.

93. The method of claim 91 or 92, wherein the heating of step (i) is performed during at least 1 hour.

94. The method of any one of claim 91 to 93, wherein the first solution comprises at least one of SbCh, Sb2O3, and SbCk, at least one of NaOH, LiOH, and KOH, and water.

95. The method of any one of claims 91 to 94, wherein the second solution comprises at least one of Cu(NO3)2-3H2O, CU(NO3)2-2.5H2O, CU(NO3)2-XH2O, CUSO4and CuSO4-5H2O, and ethanol.

96. The method of any one of claims 91 to 95, wherein urea is further added along with the water in step (c).

97. The method of any one of claims 91 to 96, wherein the aqueous second solution is added dropwise to the first solution to obtain the mixture of step (d).

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