Formation of formic acid with the help of indium-containing catalytic electrode

Abstract

Electrochemical conversion of CO2 to formic acid or a salt thereof, using an indium containing catalytic electrode, comprising (a) electrochemically converting CO2 to formic acid or a salt thereof by applying a voltage to an electrochemical cell comprising the catalytic electrode as cathode and an anode, wherein the electrochemical cell is fed with an electrolyte comprising CO2; and (b) regenerating the catalytic electrode by lowering the voltage and subsequently washing the catalytic electrode with an aqueous liquid and exposing the catalytic electrode to air without applying voltage; and (c) optionally repeating steps (a) and (b).

1 . A process for the electrochemical conversion of carbon dioxide to formic acid or a salt thereof, using an indium-containing catalytic electrode, comprising:
 (a) electrochemically converting carbon dioxide to formic acid or a salt thereof by applying a voltage to an electrochemical cell comprising the catalytic electrode as cathode and an anode, wherein the electrochemical cell is fed with an electrolyte comprising carbon dioxide; and   (b) regenerating the catalytic electrode by lowering the voltage and subsequently washing the catalytic electrode with an aqueous liquid and exposing the catalytic electrode to air without applying voltage; and   (c) optionally repeating steps (a) and (b).   
     
     
         2 . The process according to  claim 1 , wherein the catalytic electrode is an indium-bismuth catalyst, indium-tin catalyst or an indium catalyst. 
     
     
         3 . The process according to  claim 1 , wherein the process is operated in cycles wherein step (c) is repeated at least 10 times. 
     
     
         4 . The process according to  claim 1 , wherein in each cycle the duration of step (b) is 0.1 50% of the duration of step (a); wherein the duration of step (a) in a single cycle is in the range of 1-100 h, and wherein the duration of step (b) in a single cycle is in the range of 0.1-2.5 h. 
     
     
         5 . The process according to  claim 1 , wherein the exposure of the electrode to air in step (b) is performed by feeding air to the electrochemical cell, wherein the electrochemical cell is equipped with air jets. 
     
     
         6 . The process according to  claim 1 , wherein the catalytic electrode is a gas diffusion electrode, wherein air is led through the gas diffusion electrode during step (b). 
     
     
         7 . The process according to  claim 1 , wherein a plurality of electrochemical cells are connected in parallel and wherein some of the cells are being subjected to the regeneration of step (b) while other cells are simultaneously used for the conversion of step (a). 
     
     
         8 . The process according to  claim 1 , wherein the aqueous liquid is deionized water or the electrolyte used during step (a). 
     
     
         9 . The process according to  claim 1 , wherein a control system is in place which determines the performance of the electrochemical cell, by determining the faradaic yield, and wherein step (a) is interrupted and step (b) is initiated in case the performance drops below a predetermined threshold value. 
     
     
         10 . The process according to  claim 1 , wherein feeding of the electrolyte comprising carbon dioxide of step (a) involves feeding a liquid and gas flow and step (b) involves:
 (1) ramping down the current, preferably with a decrease of 0.1-10 mA/min;   (2) stopping the liquid and gas flows;   (3) washing the catalytic electrode with the aqueous liquid;   (4) feeding air at a rate of 0.01 10 L/min;   (5) starting the liquid and gas flows;   (6) ramping up the current with an increase of 0.1 10 mA/min.   
     
     
         11 . (canceled) 
     
     
         12 . (canceled) 
     
     
         13 . An electrochemical cell assembly for reduction of carbon dioxide to formic acid, comprising a plurality of electrochemical cells, each cell comprising an anode and an indium-containing catalytic gas diffusion electrode as cathode, wherein the cathode is configured to receive either an electrolyte containing carbon dioxide or washing liquid or air, and wherein each cell further contains an outlet for discharging formic acid or a salt thereof, wherein the gas diffusion electrodes are equipped with an air jet stream to enable contacting of the electrode with air during regeneration. 
     
     
         14 . The electrochemical cell assembly according to  claim 13 , wherein the plurality of electrochemical cells are arranged in blocks each containing an equal amount of electrochemical cells, wherein each block alternates between a first position wherein it is used for conversion of carbon dioxide to formic acid or a salt thereof and a second position wherein it is regenerated. 
     
     
         15 . The electrochemical cell assembly according to  claim 13 , wherein each electrochemical cell contains a cathode compartment and an anode compartment separated by at least one membrane and wherein the cathode compartment contains an inlet for receiving either the electrolyte containing carbon dioxide or air and the anode compartment a separate inlet for receiving an anolyte.