Promoting Selective CO₂ Electroreduction to Formic Acid in Acidic Medium with Low Potassium Concentrations under High CO₂ Pressure

Electrocatalytic CO2 reduction reaction (CO2RR) offers a sustainable pathway for the production of chemicals and fuels. Acidic electrolysis has been shown to be a promising strategy in order to avoid CO2 loss via the formation (bi)carbonate during reaction. Previous studies have been carried out in ambient CO2 pressure systems and have stressed the importance of adding high concentration of alkali cation (K+) in the catholyte to inhibit the hydrogen evolution reaction (HER) and achieve higher selectivity of CO2RR. Herein, CO2 reduction to HCOOH was performed in strong acid (pH 1) using a dendritic bismuth catalyst in a home-designed high-pressure electrochemical cell. At a CO2 pressure of 30 bar, we could achieve a high Faradaic efficiency of 100 % at 100 mA cm(-2) at a KCl concentration of 3.0 M. With this first system that combines high pressure of CO2 and highly acidic catholyte, we show that pressurization offers an appropriate strategy to limit both HER and K+ dependence. Indeed we obtained a Faradaic efficiency of 34 % in the absence of K+ cations and 75-80 % in the presence of 1.0 M KCl under an applied current density of 100 mA cm(-2).