Pressure dependence in aqueous-based electrochemical CO 2 reduction

Electrochemical CO 2 reduction (CO 2 R) is an approach to closing the carbon cycle for chemical synthesis. To date, the field has focused on the electrolysis of ambient pressure CO 2 . However, industrial CO 2 is pressurized—in capture, transport and storage—and is often in dissolved form. Here, we find that pressurization to 50 bar steers CO 2 R pathways toward formate, something seen across widely-employed CO 2 R catalysts. By developing operando methods compatible with high pressures, including quantitative operando Raman spectroscopy, we link the high formate selectivity to increased CO 2 coverage 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 proton-resistant layer to further the pressure-mediated selectivity effect. This work illustrates the value of industrial CO 2 sources as the starting feedstock for sustainable chemical synthesis.