EP4522784A1

EP4522784A1 - Functionnalised copper electrochemical catalysts for conversion of co2 to small molecules

Info

Publication number: EP4522784A1
Application number: EP23726080.7A
Authority: EP
Inventors: Damien Voiry; Huali WU
Original assignee: Centre National de la Recherche Scientifique CNRS; Ecole Nationale Superieure de Chimie de Montpellier ENSCM; Universite de Montpellier
Current assignee: Centre National de la Recherche Scientifique CNRS; Ecole Nationale Superieure de Chimie de Montpellier ENSCM; Universite de Montpellier
Priority date: 2022-05-13
Filing date: 2023-05-10
Publication date: 2025-03-19
Also published as: US20250313971A1; WO2023217917A1; CA3252307A1; EP4276224A1

Abstract

The present invention belongs to the field of catalytic chemistry, and more specifically to catalysed reduction chemical reactions, preferably of CO₂ into small molecules. The present invention relates to a new catalyst compound comprising at least a copper (Cu) layer, wherein the copper layer is functionalized with at least one aryl group and its use thereof in a reduction chemical reaction, preferably in reduction of CO₂ into CO, ethylene and other small molecules such as gaseous hydrocarbons (methane, propane) or liquid molecules (ethanol, formic acid, propanol). The invention relates to the process of manufacture of said catalyst compound and to a process electrochemical conversion of CO₂ to small molecules and in particular ethylene.

Description

FUNCTIONNALISED COPPER ELECTROCHEMICAL CATALYSTS FOR CONVERSION OF CO₂ TO SMALL MOLECULES

Technical field

The present invention belongs to the field of catalytic chemistry, and more specifically to catalysed reduction chemical reactions, preferably of CO2 into small molecules.

The present invention relates to a new catalyst compound comprising at least a copper (Cu) layer, wherein the copper layer is functionalized with at least one aryl functional group and its use thereof in a reduction chemical reaction, preferably in reduction of CO2 into CO, ethylene and other small molecules such as gaseous hydrocarbons (methane, propane) or liquid molecules (ethanol, formic acid, propanol). The invention relates to the process of manufacture of said catalyst compound and to a process electrochemical conversion of CO2 to small molecules and in particular ethylene.

In the description below, references between [1-4] refer to the list of references at the end of the examples.

Technical background

The release of carbon dioxide (CO2) is a major concern for the environment. Its capture and recycling into small organic bricks such as carbon monoxide (CO), formic acid (HCOOH), methane (CH4) or methanol (CH3OH), ethanol (C2H5OH) and ethylene (C2H4) could prove to be very advantageous.

Particularly, the electrochemical conversion of CO2 into small molecules such as gaseous hydrocarbons (methane, ethylene) or liquid molecules (ethanol, formic acid) is an attractive method as these molecules can be used as fuels or organic bricks to produce longer hydrocarbon molecules [1-3], Currently only copper-based catalysts (Cu) can convert CO₂ in small organic molecules, but their efficiency is still limited - preventing its use in industrial process [4],

Therefore, there is a critical necessity to explore for an easier and cheaper way to produce small molecules such as ethylene and gaseous hydrocarbons (methane, ethylene) or liquid molecules (ethanol, formic acid) from CO₂ in a cheap and environmentally friendly procedure.

Detailed description of the invention

Applicant has developed a new process and a new catalyst compound that solves all of the problems listed above.

The present invention deals with a new process and a new catalyst compound, and its applications, such as a method to convert CO2 into small molecules, more preferably ethylene, at room temperature and atmospheric pressure. Being able to produce such small molecules at room temperature and atmospheric pressure in large quantities is, to the knowledge of Applicant, something that was not observed in the art.

Applicant surprisingly found out that using a functionalized Cu catalyst made according to process of the invention gives very good yields in conversion of CO2 into small molecules such as ethylene and gaseous hydrocarbons (methane, ethylene) or liquid molecules (ethanol, formic acid). Specifically, it was identified that the performance is considerably improved by grafting specific functional groups on the surface of inorganic electrocatalysts. These functional groups, substituted aryl groups, allow increasing the current density and improving the Faradaic efficiency of the reaction towards the production of ethylene up to about 83% at -3.55 V in a membrane-electrode-assembly cell (MEA).

The catalyst compound of the invention is based on copper (Cu) and optionally Ag, Bi, Zn and/or Sn crystal grown on a porous gas diffusion layer (typically a commercial carbon support such as a gas diffusion electrode or a porous polymer substrate such as PTFE, nylon or PVDF) via electrodeposition and then functionalization with various substituted aryl groups. The catalyst compound obtained by the process of the invention may present a raspberry-like morphology.

A first object of the invention is a process of manufacture of a catalyst compound comprising the steps of: a) depositing or coating copper on a porous gas diffusion layer, the porous gas diffusion layer being optionally pre-treated, preferably by electrodepositing copper, coating of copper particles and/or depositing of copper particles using physical vapour deposition process such as metal evaporation or sputtering; b) functionalisation of the metal catalyst obtained in step a) by contacting with a diazonium salt of formula I:

(Formula I) wherein,

- X’ represents an anion,

- a is an integer from 1 to 3,

- Ar^A represents an aryl group, substituted by at least one -R^A group,

- -R^A represents at least one substituent chosen from a halo group, - R¹, -NO2, -OR¹, -NR²R³ and a group of formula II: (Formula II), in which, o -R¹ represents a Ci to C3 alkyl group, o -R² and R³ independently represent H or a Ci to C3 alkyl group, o b is an integer from 0 to 3, o F^B is a functional group chosen from -N=N- and -NH-, o Ar^B represents an aryl group, optionally substituted by at least one -R^B group, o -R^B represents at least one substituent chosen from a halo group, -R¹, -OR¹ and -NR²R³, v^Z represent the point of attachment to Ar^A.

Advantageously, the process according to the invention is a process of manufacture of a catalyst compound comprising the steps of: a) electrodepositing copper on a porous gas diffusion layer, the porous gas diffusion layer being optionally pre-treated; b) functionalisation of the metal catalyst obtained in step a) by contacting with a diazonium salt of formula I:

(Formula I) wherein,

- X’ represents an anion,

- a is an integer from 1 to 3,

- Ar^A represents an aryl group, substituted by at least one -R^A group,

- -R^A represents at least one substituent chosen from a halo group, -

R¹, -NO2, -OR¹, -NR²R³ and a group of formula II: (Formula II), in which, o -R¹ represents a Ci to C3 alkyl group, o -R² and R³ independently represent H or a Ci to C3 alkyl group, o b is an integer from 1 to 3, o F^B is a functional group chosen from -N=N- and -NH-, o Ar^B represents an aryl group, substituted by at least one -R^B group, o -R^B represents at least one substituent chosen from a halo group, -R¹, -OR¹ and -NR²R³, v^Z represent the point of attachment to Ar^A.

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein X’ is chosen from BF , Cl’ and HSO4.

It is meant by “aryl”, a group derived from arenes by removal of a hydrogen atom from a ring carbon atom; arenes being monoyclic and polycyclic aromatic hydrocarbons (IIIPAC). According to the invention aryl groups may comprise from 4 to 10 carbon atoms, preferably 6 carbon atoms. According to the invention, aryl groups Ar^A and Ar^B do not comprise, heteroatoms besides the heteroatoms comprised in R^A, F^B and R^B.

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein Ar^A and/or Ar^B are aryl groups comprising 6 carbon atoms and are phenyl groups. Preferably, Ar^A and/or Ar^B are phenyl groups substituted by at least one -R^A group in ortho, meta and/or para position.

Advantageously, when Ar^A is substituted by more than one R^A group (i.e, a = 2 or 3), the R^A groups may be identical or different from each other.

Advantageously, when Ar^B is substituted by more than one R^B group (i.e, b = 2 or 3), the R^B groups may be identical or different from each other.

In other terms, when there is more than one R^A substituent, the R^A substituents may be identical or different from each other and/or when there is more than one R^B substituent, the R^B substituents may be identical or different from each other. Also, when there is R^A and R^B groups, the R^A and R^B groups may be identical or different. For example, when there are two R^A, they may both be R¹, and yet be identical or different (e.g. one may be -Me and the other may be -Et or they may both be -Me). Also, for example, when one R^A substituent and one R^B substituent are both R¹, they may be identical or different (e.g. one may be -Me and the other may be -Et or they may both be -Me).

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein a = 1 or 2. Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein b = 1 or 2, more preferably 1 .

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein b = 0.

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein at least one R^A is a halo group, preferably chosen from Br, Cl and I.

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein at least one R^A is -NO2.

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein at least one R^A is -R¹, preferably chosen from - Me, -Et and -Pr (Pr being either isopropyl or n-propyl).

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein at least one R^A is -OR¹, preferably chosen from - OMe, -OEt and -OPr (Pr being either isopropyl or n-propyl).

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein at least one R^A is -NR²R³, preferably chosen from -NEt2, -NMe2, -NPr2, -NMeEt and -NMePr (Pr being either isopropyl or n- propyl). Advantageously, the diazonium salt may be chosen from diazonium salt of formula I, wherein at least one R^A group is a group of formula II.

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein at least one R^B is a halo group, preferably chosen from Br, Cl and I.

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein at least one R^B is -NO2.

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein at least one R^B is -R¹, preferably chosen from - Me, -Et and -Pr (Pr being either isopropyl or n-propyl).

Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein at least one R^B is -OR¹, preferably chosen from - OMe, -OEt and -OPr (Pr being either isopropyl or n-propyl). Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein at least one R^B is -NR²R³, preferably chosen from -NEt2, -NMe2, -NPr2, -NMeEt and -NMePr (Pr being either isopropyl or n- propyl). Advantageously, the diazonium salt may be chosen from diazonium salts of formula I, wherein at least one R^A group is a group of formula II and Ar^A and Ar^B are each substituted by one -R¹ group, preferably -Me. The diazonium salt may be chosen from diazonium salts of formula I, wherein at least one R^A group is a group of formula II and Ar^A is substituted by two - OR¹ groups, preferably -OMe and Ar^B is substituted by one -NO2 group. The diazonium salt may be chosen from diazonium salts of formula I, wherein at least one R^A group is a group of formula II and Ar^B is substituted by one - OR¹ group, preferably -OMe.

Advantageously, the diazonium salt may be chosen from the following salts:

Table 1 : example of salts

The different anions in the table above may be used independently to the nature of the cations. For example, “2-methyl-4-[(2- methylphenyl)diazenyl]benzenediazonium”, “4-[(4- methoxyphenyl)amino]benzene-1 -diazonium chloride” or “dichlorozinc;2,5- dimethoxy-4-[(4-nitrophenyl)diazenyl]benzenediazonium;dichloride” may have BF as counter anion.

Advantageously, the diazonium salt of formula I may be chosen from the following salts:

Preferably, the diazonium salt of formula I may be chosen from the following salts:

Advantageously, step a) of the process according to the invention may be depositing or coating copper on a porous gas diffusion layer, the porous gas diffusion layer being optionally pre-treated. Preferably, step a) of the process according to the invention may be electrodepositing copper on the porous gas diffusion layer, the porous gas diffusion layer being optionally pre-treated. Alternatively, step a) of the process according to the invention may be coating of copper particles on the porous gas diffusion layer, the porous gas diffusion layer being optionally pre-treated. Alternatively, step a) of the process according to the invention may be depositing of copper particles using physical vapour deposition process such as metal evaporation or sputtering. Step a) of the process according to the invention may also be a combination of previously cited deposition or coating methods. Advantageously, step a) and/or step b) of the process according to the invention may be conducted using a potentiostat.

Advantageously, the porous gas diffusion layer may be a commercial conducting carbon-based gas diffusion electrode or a porous polymer substrate such as (PTFE, nylon, PVDF). Advantageously, step a) and/or step b) of the process according to the invention may be conducted under a current density from 5 mA. cm^-2 to 50 mA. cm^-2, preferably from 10 mA.crrr² to 20 mA. cm^-2, and more preferably at 15 mA. cm^-2.

Advantageously, in step a) of the process according to the invention, the quantity of deposited Cu may be from 0.5 C.crrr² to 50 C.crrr², preferably between 15 C.crrr² to 35 C.crrr², more preferably at 15 mA. cm^-2.

Advantageously, step a) and/or step b) of the process according to the invention may be done under pulse deposition or galvanostatic method. Preferably, the applied current density for electrodepositing copper is 15 mA. cm^-2, and the electrodepositing time is 5 minutes.

Advantageously, in the step a) of the process according to the invention, the source of copper (Cu) may be chosen in the group comprising CuBr2, CuCI₂ and CuSCU. The source of copper may be an electrolyte comprising CuBr2, sodium tartrate dibasic dihydrate and KOH.

Advantageously, in the step a) of the process according to the invention, the electrodeposition of copper may be done using a carbon based-gas diffusion layer (GDL), a Pt plate, and Ag/AgCI (saturated with KCI) respectively as the working, counter, and reference electrodes, respectively. Alternatively, the process can be done using a 2-electrode configuration using a carbon based-gas diffusion layer (GDL) and a Pt plate respectively as the working and counter electrodes, respectively.

Advantageously, in step a) of the process according to the invention, the copper may be electrodeposited in a raspberry-like morphology.

Advantageously, the process according to the invention may further comprise a pre-treatment step a’) (prior to step a)) of electrodepositing Ag, Bi, Zn and/or Sn on the porous gas diffusion layer. In the pre-treatment step a’) of the process according to the invention, the source of Ag, Bi, Zn and/or Sn may be chosen in the group comprising -NO3, CH3COO-, and/or -Cl. The source of Ag, Bi, Zn and/or Sn may be an electrolyte comprising AgNOs, CHsCOOAg, Bi(NO3)3-5H2O, ZnC and/or SnCL, sodium tartrate dibasic dihydrate and KOH. The pre-treatment step a’) may be done under the same conditions as step a) in terms of current density, quantity of deposited metal and pulse deposition or galvanostatic method.

Advantageously, the step b) of the process according to the invention may be performed in water, organic solvent(s) and mixtures thereof. The organic solvents may be chosen from ethanol, acetonitrile, methanol, acetone, propanol, tetrahydrofuran and mixtures thereof. The concentration of the diazonium salt of formula I in the water and/or an organic solvent may be from 1 to 100 mM, preferably from 2 to 10 mM. For example, when the diazonium salt is 4, 2-methyl-4-([2- methylphenyl]azo)benzenediazonium salt, the preferred concentration is 3 mM.

Advantageously, the step b) of the process according to the invention may be done under galvanostatic method with a current density from 0.1 to 5 mA. cm^-2, preferably from 0.2 to 2.5 mA.crrr², and more preferably at 0.75 mA. cm^-2.

Advantageously, the step b) of the process according to the invention may have a duration from 5 seconds to 30 minutes, preferably from 30 seconds to 10 minutes and more preferably 100 seconds. Step b) may be performed at a temperature from 5°C to 80 °C, preferably at room temperature (i.e., from 15 to 30 °C).

Advantageously, the process according to the invention may further comprise a step c) of spray coating an ionomer of formula III:

(Formula III) wherein, m and n are integers from 1 to 50,000.

Advantageously, the process according to the invention may further comprise a step d) of washing the obtained catalyst compound with deionized water.

The invention also relates to a catalyst compound obtained by the process according to the invention.

The invention relates to a catalyst compound comprising a porous gas diffusion layer, said porous gas diffusion layer being at least partially coated by copper atoms, wherein at least one copper atom is functionalised by a substituent of formula I’: (Formula I’) wherein Ar^A, R^A and a are defined as above and ^l/ ' represents the point of attachment to copper.

Advantageously, the compound according to the invention may be chosen from catalyst compounds comprising a porous gas diffusion layer, said porous support being at least partially coated by copper atoms, wherein at least one copper atom is functionalised by a substituent of one or more of the following formulas:

Table 2: example of substituents wherein ^1/ ' represents the point of attachment to copper.

Advantageously, the compound according to the invention may further comprise a Ag, Bi, Zn and/or Sn atom layer in between the porous gas diffusion layer and the copper layer. Advantageously, in the compound according to the invention, the copper may be in a raspberry-like morphology, while higher deposition currents will form dendritic fern-like structure.

Advantageously, the compound according to the invention, may comprise from 70 to 100 at.% of copper atoms, preferably 85 at.%, with regards to the total number of metal atoms in the compound.

Advantageously, the compound according to the invention, may have an Ar^A/Cu atomic surface ratio from 1 to 3, preferably from 1 and 2. The Ar^A/Cu atomic surface ratio, in number of atoms, is estimated from the top 5 nm of the surface of the compound and measured by X-ray photoelectron spectroscopy.

Advantageously, the compound according to the invention, may comprise from 0.5 to 50 at.% of Ag, Bi, Zn and/or Sn atoms, preferably 6 at.%, with regards to the total number of metal atoms in the compound. Advantageously, the compound according to the invention, may have an Ar^A/(Ag, Bi, Zn and/or Sn) atomic surface ratio from 1 to 3, preferably from 1 and 2. The Ar^A/(Ag, Bi, Zn and/or Sn) atomic surface ratio, in number of atoms, is estimated from the top 5 nm of the surface of the compound and measured by X-ray photoelectron spectroscopy.

Advantageously, the compound according to the invention, may comprise a porous gas diffusion layer, preferably a commercial carbonbased gas diffusion electrode. The structure of the catalyst compound according to the invention is such as the porous gas diffusion layer is coated by a functionalized copper layer and may optionally comprise an in-between layer of Ag, Bi, Zn and/or Sn atom layer in between the porous gas diffusion layer and the copper layer.

Some advantages of the catalyst compound according to the invention are listed below:

- the catalyst compound according to the invention has an increased current density and an improved selectivity of the reaction towards the production of C2 molecules (mainly ethylene) up to -213 mA.crrr² and a Faradaic efficiency > 80 % at a full cell potential (V_cathode-Vanode) of -3.55 V compared to -122 mA. cm^-2 and ~40 % for pristine non-functionalized Cu- based electrocatalyst at -3.80 V when measured in a 2-electrode configuration;

- the catalyst compound according to the invention can be easily obtained by electrodepositing Cu and optionally Ag, Bi, Zn and/or Sn metals in the form of a flower structure for larger active surface;

- the functionalization step b) is easy and cheap as the molecules needed are very common and easily obtainable;

- the catalyst compound according to the invention allows the production of high concentrated gaseous product, notably C2 products and more specifically ethylene molecule with high added values - the catalyst compound according to the invention have a total current density over 683 mA rrr² at -3.9 V in a 2-electrode configuration;

- the catalyst compound according to the invention have a specific current density over 536 mA rrr² for ethylene for CO2RR at -3.9 V, which means 461 g m’²h’¹ of ethylene.

The invention further relates to the use of the catalyst compound according to the invention as a catalyst, preferably to convert CO2 into small molecules. It is meant by small molecules, molecules such as gaseous hydrocarbons (methane, ethylene) or liquid molecules (ethanol, formic acid). H2 may be formed from the electrolysis of water (side-reaction). According to the invention, the conversion of CO2 mainly leads to C2H4. Ethylene may represent up to ~82.4 % (volume ratio) of the gas products (the normalized concentration of CO and ethylene are 5.1 and 24 in GC) of the conversion of CO₂.

The invention further relates to a process of conversion of CO2 into small molecules comprising a step of contacting CO2 (gas) with a catalyst compound according to the invention. The conversion reaction of CO2 may be done under atmospheric pressure and at room temperature (i.e., from 15 to 30°C). According to invention, the conversion reaction of CO2 mainly leads to C2H4. Ethylene may represent up to ~82.4 % (volume ratio) of the gas products (the normalized concentration of CO and ethylene are 5.081 and 23.959 in GC) of the conversion of CO2.

The conversion of CO2 to products (mainly gas products, CO and ethylene) is conducted at room temperature and (25°C, 1 atm) with the periodic electrolyte of 0.5 M KHCO3. The reactant of CO2 is continuously flow into the membrane electrode assembly cell with the flow rate of 10 seem.

Brief description of the figures Figure 1. Low-magnification scanning electron microscopy (SEM) images for the pristine and functionalized Cu catalysts, (a) Precursor 1 (Cu), (bi) 1A and (b2) the cross-section of 1A.

Figure 2. Comparison of FEs for ethylene on different Cu electrodes measured at full-cell potentials ranging from -3.0 to -4.0 V and measured in 0.5 M KHCO3. Cu refers to Precursor 1 , unfunctionalized Cu catalyst; 1 A, 1 B, 1 C, 1 D, 1 E, 1 F and 1 G respectively refer to Cu modified with 2-methyl-4-[(2- methylphenyl)diazenyl]benzenediazonium; 4-[(4- methoxyphenyl)amino]benzene-1 -diazonium chloride; dichlorozinc;2,5- dimethoxy-4-[(4-nitrophenyl)diazenyl]benzenediazonium; dichloride; 4- methoxybenzenediazonium;tetrafluoroborate; 4-

Bromobenzenediazonium;tetrafluoroborate; 4- nitrobenzenediazonium;tetrafluoroborate and 4-

(diethylamino)benzenediazonium;tetrafluoroborate; and 11 refers to Cu modified with 2-methyl-4-[(2-methylphenyl)diazenyl]benzenediazonium and the ionomer.

Figure 3. The total current density from different functionalized electrodes in membrane-electrode-assembly reactor (MEA). Cu refers to Precursor 1 , unfunctionalized Cu catalyst; 1A, 1 B, 1 C, 1 D, 1 E, 1 F and 1 G respectively refer to Cu modified with 2-methyl-4-[(2- methylphenyl)diazenyl]benzenediazonium; 4-[(4- methoxyphenyl)amino]benzene-1 -diazonium chloride; dichlorozinc;2,5- dimethoxy-4-[(4-nitrophenyl)diazenyl]benzenediazonium; dichloride; 4- methoxybenzenediazonium;tetrafluoroborate; 4-

Figure 4. The C2H4 specific current density from different functionalized electrodes in membrane-electrode-assembly reactor (MEA). Cu refers to Precursor 1 , unfunctionalized Cu catalyst; 1A, 1 B, 1 C, 1 D, 1 E, 1 F and 1 G respectively refer to Cu modified with 2-methyl-4-[(2- methylphenyl)diazenyl]benzenediazonium; 4-[(4- methoxyphenyl)amino]benzene-1 -diazonium chloride; dichlorozinc;2,5- dimethoxy-4-[(4-nitrophenyl)diazenyl]benzenediazonium; dichloride; 4- methoxybenzenediazonium;tetrafluoroborate; 4-

(diethylamino)benzenediazonium;tetrafluoroborate; and 11 refers to Cu modified with 2-methyl-4-[(2-methylphenyl)diazenyl]benzenediazoniurn and the ionomer.

EXAMPLES

Example 1 : Preparation of a catalyst compound precursor 1

The electrodeposition of Cu was conducted on a potentiostat. Firstly, to electrodeposit Cu, an electrolyte composed of 0.1 M copper bromide (98%, Sigma-Aldrich), 0.2 M sodium tartrate dibasic dihydrate (purum pro analysis > 98.0% non-aqueous titration (NT), Sigma-Aldrich), and 1 M KOH was prepared. Acid-treated gas diffusion layer (GDL), Pt plate, and Ag/AgCI (saturated with KCI) were used as the working, counter, and reference electrodes, respectively. The Cu was electrodeposited galvanostatically on the GDL at a constant current density of 15 mA cm^-2. The loading amount of Cu is 4.5 C cm^-2 with electrodepositing time of 300 seconds.

Firstly, Cu is successively electrodeposited on the support by controlling the voltage or the current density in order to control the morphology of the deposited. Cu was successively electrodeposited using a current density of 15 mA cm^-2. The loading of Cu is comprised 4.5 C cm^-2. The best performance is obtained when the copper is grown in the form of a raspberry structure using a galvanostatic deposition method where the applied current density is 15 mA cm^-2 (Figure. 1 ). The source of Cu used for the electrodeposition at CuBr2 (CAS: 7789-45-9).

The catalyst compound precursor 1 was obtained.

Example 2: Synthesis of the catalyst compounds 1A-1G according to the invention

The raspberry structured copper gave the performance in term of Faradaic efficiency (FE) towards C2H4 of 40% at -3.8 V in a MEA electrolyzer (Table 1 ).

Different diazonium salts functional groups of formula I were attached on the catalyst compound precursor 1 by an electroreduction method. The different diazonium salts molecules that have been tested are shown in Figures 2, 3 and 4. The functionalization of the catalyst compound precursor 1 was performed in water. The concentration of the diazonium salt of formula I, and reaction conditions are detailed in table 3 below. The electrodes were functionalized using the same optimized conditions in order to compare the performance of the different functional groups and the performances were recorded under the exact same conditions (electrolyte, temperature, time). The obtained electrodes (catalyst compounds 1A-1 G) were washed with water and dried with Ar.

The catalyst compounds 1A-1 G were obtained. Table 3: reaction conditions

Example 3: Performances of the catalyst compounds 1A-1G according to the invention

The catalytic performance of compounds 1A to 1 G is presented in table 4 below:

Table 4: Summary of the electrocatalytic performance for pristine anc functionalized Cu electrodes.

The results shown in table 4 demonstrate that both the current density and the Faradaic efficiency are both strongly improved after functionalization. Compounds 1A and 11 groups gave the best results and the Faradaic efficiency towards the formation of C2H4 can reach 83% at - 3.55 V and 89% at -3.9 V compared to 40% for Precursor 1 (Fig. 2). By taking into account the current density, the results show that the specific current density for ethylene can be as high as 212 mA cm^-2 and 536 mA cm^-2 respectively from 1A and 11 (Figure. 4). These values correspond to a production of ~ 147.84 L and 369.6 L of ethylene per m² per hour of electrode for their applied potentials of -3.55 V and -3.9 V, respectively.

Importantly the functionalization of Cu to obtain compounds according to the invention translates into 1 ) high activity (higher current density), 2) higher efficiency towards the conversion of CO2, 2) High activity towards the production of C2H4 product (Table 1 ).

The catalysts according to the invention prepared and tested in the example allowed improving the performance towards the production of C2H4 molecule at room temperature and atmospheric pressure. Compared to traditional Cu electrocatalyst, the Faradaic efficiency towards ethylene are increased by 43% and 49% for 1 A and 11 groups modified Cu.

The new electrocatalysts according to the invention are more energy efficient.

Example 4: Preparation of a catalyst compound precursor 2

Commercial Cu particles (2-3.5 pm in size) was deposited on the GDL using spray coating. The commercial Cu particles were functionalized with 4, 2-Methyl-4-([2-methylphenyl]azo)benzenediazonium. The catalyst compounds 2 and 2A were obtained for commercial Cu particles and functionalized commercial Cu particles, respectively.

The loading amount of Cu is 1.0 mg cm^-2 and the catalysts was tested following the same methodology as in Example 2.

Example 5: Performances of the catalyst compounds 2 and 2A according to the invention

The catalytic performance of compounds 2 to 2A is presented in table 5 below:

Table 5: Summary of the electrocatalytic performance for pristine and functionalized Cu electrodes. List of references

[1 ] Bushuyev, 0. S. et al. What should we make with CO2 and how can we make it? Joule 2, 825-832 (2018).

[2], Ager, J. W. & Lapkin, A. A. Chemical storage of renewable energy. Science 360, 707-708 (2018).

[3], Jouny, M., Luc, W. & Jiao, F. General techno-economic analysis of CO2 electrolysis systems. Industrial & Engineering Chemistry Research 57, 2165-2177 (2018).

[4], Verma, S., Lu, S. & Kenis, P. J. Co-electrolysis of CO2 and glycerol as a pathway to carbon chemicals with improved technoeconomics due to low electricity consumption. Nature Energy 4, 466-474 (2019).

Claims

1. A process of manufacture of a catalyst compound comprising the steps of: a) depositing or coating copper on a porous gas diffusion layer, the porous gas diffusion layer being optionally pre-treated, preferably by electrodepositing copper, coating of copper particles and/or depositing of Cu particles using physical vapour deposition process such as metal evaporation or sputtering; b) functionalization of the metal catalyst obtained in step a) by contacting with a diazonium salt of formula I: X (Formula I) wherein,

- X’ represents an anion,

- a is an integer from 1 to 3,

- Ar^A represents an aryl group, substituted by at least one -R^A group,

- -R^A represents at least one substituent chosen from a halo group, - R¹, -NO2, -OR¹, -NR²R³ and a group of formula II: (Formula II), in which, o -R¹ represents a Ci to C3 alkyl group, o -R² and R³ independently represent H or a Ci to C3 alkyl group, o b is an integer from 0 to 3, o F^B is a functional group chosen from -N=N- and -NH-, o Ar^B represents an aryl group, optionally substituted by at least one -R^B group, o -R^B represents at least one substituent chosen from a halo group, -R¹, -OR¹ and -NR²R³, o represent the point of attachment to Ar^A.

2. The process according to claim 1 , wherein the copper is electrodeposited in a raspberry-like morphology.

3. The process according to any of preceding claims, further comprising a pre-treatment step a’) of electrodepositing Ag, Bi, Zn and/or Sn on the porous gas diffusion layer.

4. The process according to any of preceding claims, wherein X’ is chosen from BF , Cl’ and HSO4.

5. The process according to any of preceding claims, wherein Ar^A and/or Ar^B are phenyl groups.

6. The process according to any of preceding claims, wherein the diazonium salt of formula I is chosen from the following salts:

7. The process according to any of preceding claims, further comprising

5 a step c) of spray coating an ionomer of formula III: (Formula III) wherein, m and n are integers from 1 to 50,000.

8. A catalyst compound obtained by the process according to any of the preceding claims.

9. A catalyst compound comprising a porous gas diffusion layer, said porous gas diffusion layer being at least partially coated by copper atoms, wherein at least one copper atom is functionalised by a substituent of formula I’: (Formula I’) wherein Ar^A, R^A and a are defined as in previous claims and ^1/ ' represents the point of attachment to copper.

10. The compound according to the preceding claim, further comprising a Ag, Bi, Zn and/or Sn atom layer in between the porous gas diffusion layer and the copper layer.

11 . The compound according to any of claims 8 to 10, wherein the copper is in a raspberry-like morphology.

12. The compound according to any of claims 8 to 11 , wherein the porous gas diffusion layer is a commercial conducting carbon-based gas diffusion electrode or a porous polymer substrate such as PTFE, nylon or PVDF.

13. Use of the compound according to any of claims 8 to 12 as a catalyst, preferably to convert CO2 into small molecules, preferably C2H4, C2H5OH, CO, formic acid, as well as small amount of H2.

14. A process of conversion of CO2 into small molecules comprising a step of contacting CO2 with a catalyst compound according to any of claims

8 to 12.

15. The process according to the preceding claim, wherein the conversion reaction of CO2 is done under atmospheric pressure and at room temperature.