Controlled Selectivity of CO2 Reduction on Copper by Pulsing the Electrochemical Potential.

We demonstrate a simple strategy to enhance the CO2 reduction reaction (CO2 RR) selectivity by applying a pulsed electrochemical potential to a polycrystalline copper electrode. By controlling the pulse duration, we show that the hydrogen evolution reaction (HER) is highly suppressed to a fraction of the original value (<5 % faradaic efficiency) and selectivity for the CO2 RR dramatically improves (>75 % CH4 and >50 % CO faradaic efficiency). We attribute the improved CO2 RR selectivity to a dynamically rearranging surface coverage of hydrogen and intermediate species during the pulsing. Our finding provides new insights into the interplay of transport and reaction processes as well as timescales of competing pathways to enable new opportunities to tune CO2 RR selectivity by adjusting the pulse profile. Additionally, the pulsed potential method we describe can be easily applied to other catalysts materials to improve their CO2 RR selectivity.