Pressure dependence in aqueous-based electrochemical CO2 reduction

Abstract

Abstract Electrochemical CO2 reduction (CO2R) is an approach to closing the carbon cycle for chemical synthesis. To date, the field has focused on the electrolysis of ambient pressure CO2. However, industrial CO2 is pressurized – in capture, transport and storage – and is often in dissolved form. Here, we discover that pressurization up to 50 bar steers CO2R pathways toward formate, as universally exemplified on common CO2R catalysts. By developing operando methods compatible with high pressures, including quantitative operando Raman spectroscopy, we ascribe the pronounced formate selectivity to the higher CO2* coverages and lower hydronium ion concentrations on the cathode surface. The interplay of theory and experiments validates the mechanism, and guides us to functionalize the surface of a Cu cathode with a hydronium-repelling layer to further the pressure-mediated selectivity effect. This work illustrates the value of industrial CO2 sources as the starting feedstock for sustainable chemical synthesis.