Electrochemical carbon dioxide reduction catalyst for formate production

Abstract

The disclosure relates to a gas diffusion electrode—GDE—suitable for carbon dioxide electrolysis, said gas diffusion electrode having a gas diffusion membrane, the gas diffusion electrode further comprising an ink (19) deposited on the gas diffusion membrane; wherein the ink comprises an ion-conducting polymer and copper nanoparticles functionalized with one or more pyridine-containing ligands, wherein the one or more pyridine-containing ligands have an anchoring group comprising one sulphur atom tethered to the copper nanoparticles. The disclosure also relates to a gas-fed flow cell comprising such gas diffusion electrode and to a method for producing such GDE as well to the electrolysis of carbon dioxide using such GDE.

1 . Gas diffusion electrode ( 7 ) suitable for carbon dioxide electrolysis, said gas diffusion electrode ( 7 ) having a gas diffusion membrane ( 17 ), the gas diffusion electrode ( 7 ) further comprising an ink ( 19 ) deposited on the gas diffusion membrane ( 17 ); wherein the ink ( 19 ) comprises an ion-conducting polymer, said gas diffusion electrode ( 7 ) is characterized in that the ink ( 19 ) further comprises a catalyst comprising copper nanoparticles functionalized with one or more pyridine-containing ligands, wherein the one or more pyridine-containing ligands have an anchoring group comprising a sulphur atom tethered to the copper nanoparticles. 
     
     
         2 . The gas-diffusion electrode according to  claim 1  is characterized in that the one or more pyridine-containing ligands are selected from 4-pyridylethylmercaptan, 4-mercaptopyridine, 2,6-dimethyl-4-mercaptopyridine, 2-mercaptopyridine and any mixture thereof. 
     
     
         3 . The gas-diffusion electrode according to  claim 1  characterized in that the one or more pyridine-containing ligands are present in a surface concentration ranging from 5 nmol cm −2  to 40 nmol cm −2  as determined by reductive desorption and UV-visible spectroscopy as set out in the description: preferably ranging from 8 nmol cm −2  to 20 nmol cm −2 . 
     
     
         4 . The gas-diffusion electrode according to  claim 1  characterized in that, the copper nanoparticles comprise facets selected from Cu(200) facets, Cu(111) facets and any mixture thereof. 
     
     
         5 . The gas-diffusion electrode according to  claim 1  characterized in that the copper nanoparticles have an average diameter ranging from 5 nm to 200 nm as measured by transmission electron microscopy, preferably from 20 nm to 100 nm. 
     
     
         6 . The gas-diffusion electrode according to  claim 1  characterized in that the ink ( 19 ) has a weight ratio of the copper nanoparticles functionalized with one or more pyridine-containing ligands over the ion-conducting polymer ranging from 10 to 40. 
     
     
         7 . Gas-fed flow cell suitable for carbon dioxide electrolysis, said gas-fed flow cell ( 1 ) comprising a gas chamber ( 3 ), a catholyte chamber ( 9 ) and an anolyte chamber ( 13 ), wherein said gas chamber ( 3 ) is separated from the catholyte chamber ( 9 ) by a gas diffusion electrode ( 7 ) which is attached to the catholyte chamber ( 9 ) by an electrically conductive connection, said gas diffusion electrode ( 7 ) having a gas diffusion membrane ( 17 ) being comprised within said gas chamber ( 3 ),
 wherein said catholyte chamber ( 9 ) and said anolyte chamber ( 13 ) are separated by an anion exchange membrane ( 11 ), and   wherein said catholyte chamber ( 9 ) and said anolyte chamber ( 13 ) comprise respectively a cathode and an anode ( 15 ),   said gas-fed flow cell ( 1 ) is characterized in that the gas diffusion electrode ( 7 ) is according to  claim 1 .   
     
     
         8 . Method for producing the gas diffusion electrode ( 7 ) suitable for carbon dioxide electrolysis according to  claim 1 , said method is characterized in that it comprises the following steps:
 a) providing copper nanoparticles;   b) obtaining a first dispersion by dispersing the copper nanoparticles into a solvent selected from water and/or a first organic solvent;   c) adding pyridine-containing ligands to the first dispersion to obtain a suspension with copper nanoparticles functionalized with one or more pyridine-containing ligands, wherein the one or more pyridine-containing ligands have an anchoring group comprising at least one sulphur atom;   d) obtaining a second dispersion by dispersing the copper nanoparticles functionalized with pyridine-containing ligands into a second organic solvent;   e) adding an ion-conducting polymer to the second dispersion to obtain an ink ( 19 );   f) providing a gas-diffusion membrane ( 17 ) and depositing said ink ( 19 ) onto said gas-diffusion membrane ( 17 ) to obtain the gas diffusion electrode.   
     
     
         9 . Process for electrolysing carbon dioxide, said process comprising the following steps:
 i) providing a gas-fed flow cell ( 1 );   ii) providing at least one electrolyte flow ( 21 ) into said gas-fed flow cell ( 1 ) wherein the at least one electrolyte flow is a catholyte flow and an optional anolyte flow;   iii) activating said gas-fed flow cell ( 1 );   iv) providing an input flow ( 23 ) of carbon dioxide to produce an output flow ( 25 ) of liquid components comprising at least formate;   v) recovering said output flow ( 25 ) comprising at least formate;   said process is characterized in that the gas-fed flow cell ( 1 ) provided at step (i) is as defined in  claim 7 , and in that said step (iii) is performed by injecting carbon dioxide at a potential gradient starting at −0.3 V versus a reference electrode and ending at −2.0 V versus said reference electrode at a sweep rate ranging from 15 mV s −1  to 35 mV s −1 , the reference electrode being preferably an Ag/AgCl electrode filled with 3.4 M of KCl.   
     
     
         10 . The process according to  claim 9 , is characterized in that the electrolyte flow ( 21 ) provided in step (ii) is a flow of an aqueous solution of one or more inorganic bases; with preference, the aqueous solution of one or more inorganic bases has a concentration ranging from 1 M to 10 M: preferably from 3 M to 7 M or from 5 M to 10 M. 
     
     
         11 . The process according to  claim 9 , is characterized in that the one or more inorganic bases are alkali selected from NaOH, KOH, Ca(OH) 2 , LiOH, Mg(OH) 2 , RbOH, CsOH and any mixture thereof. 
     
     
         12 . The process according to  claim 9 , is characterized in that it is operated with a cathodic voltage no lower than −0.5V vs. reversible hydrogen electrode. 
     
     
         13 . Use of a catalyst for electrochemical carbon dioxide reduction reactions to produce formate, the use is characterized in that the catalyst is comprising copper nanoparticles functionalized with one or more pyridine-containing ligands, wherein the one or more pyridine-containing ligands have an anchoring group comprising a sulphur atom tethered to the copper nanoparticles. 
     
     
         14 . The use according to  claim 13  is characterized in that the one or more pyridine-containing ligands are selected from 4-pyridylethylmercaptan, 4-mercaptopyridine, 2,6-dimethyl-4-mercaptopyridine, 2-mercaptopyridine and any mixture thereof. 
     
     
         15 . The use according to  claim 13  is characterized in that the one or more pyridine-containing ligands are present in a surface concentration ranging from 5 nmol cm −2  to 40 nmol cm −2  as determined by reductive desorption and UV-visible spectroscopy as et out in the description; preferably ranging from 8 nmol cm 2 to 20 nmol cm −2 . 
     
     
         16 . The use according to  claim 13  characterized in that, the copper nanoparticles comprise facets selected from Cu(200) facets, Cu(111) facets and any mixture thereof. 
     
     
         17 . The use according to  claim 13  characterized in that the copper nanoparticles have an average diameter ranging from 5 nm to 200 nm as measured by transmission electron microscopy, preferably from 20 nm to 100 nm.