Controlling Catalytic Selectivities during CO2 Electroreduction on Thin Cu Metal Overlayers

The catalytic activity and selectivity of the electrochemical CO2 reduction on Cu overlayers with varying atomic-scale thickness on Pt was investigated. Hydrogen, methane, and ethylene were the main products. Beyond an activity improvement with increasing copper layer thickness, we observed that the thickest 15 nm Cu layer behaved bulk-like and resulted in high relative faradaic selectivities for hydrocarbons. With decreasing Cu layer thickness, the formation of methane decreased much faster than that of ethylene. As a result, the relative faradaic selectivity of the technologically useful product ethylene increased sharply. The selectivity ratios between methane and ethylene were independent of electrode potential on a Cu monolayer. A combination of geometric tensile strain effects and electronic effects is believed to control the surface reactivity and product distribution on the copper surfaces. This study highlights the general strategy to tune product distributions on thin metal overlayers.