Conversion of Bicarbonate to Formate in an Electrochemical Flow Reactor

Electrochemical CO2 reduction studies typically supply CO2 to the cathode as a gas or dissolved in aqueous media. Both of these feedstocks present challenges when scaling a CO2 electrolyzer: gaseous CO2 feedstocks require significant energy to pressurize CO2, while the low solubility of CO2 in water precludes high current densities. Using a liquid bicarbonate feedstock bypasses the need for a gaseous CO2 feedstock while delivering higher concentrations of CO2 to the cathode than currently possible with CO2 dissolved in water. We show here that an electrochemical flow cell can be designed such that protons convert bicarbonate into CO2 (at the catalyst interface), which is then reduced to generate formate. Electrolysis of 3.0 M KHCO3(aq) solutions yield formate at partial current densities > 100 mA cm–2, which is nearly commensurate with electrolyzers fed with gaseous CO2. The use of bicarbonate as a feedstock presents an opportunity to efficiently integrate carbon capture with CO2 electrochemistry.