Growth direction and exposed facets of Cu/Cu₂O nanostructures affect product selectivity in CO₂ electroreduction

The electrochemical reduction of CO₂ to fuels and value-added chemicals on metallic copper is an attractive strategy for valorizing CO₂ emissions. However, favoring the CO₂ reduction over hydrogen evolution and exclusive control of selectivity towards C₁ or C₂₊ products by restructuring the copper surface is a major challenge. Herein, we exploit the differential orientation of the exposed facets in copper nanostructures that can tune the product selectivity in CO₂ electroreduction. The Cu nanostructure with predominant {111} orientation produce C₁ products only upon CO₂ electroreduction at an applied potential of −1.3 V vs. reversible hydrogen electrodes (RHE), with 66.57% Faradaic efficiency (FE) for methane. Whereas the vertically grown copper nanostructures that are oriented in {110} direction have higher dislocation density and show greater CO₂ electroreduction activity (>95%) at the same applied potential, with FE towards ethylene 24.39% and that of oxygenates 41.31%. FIA-DEMS analysis provided experimental evidence of selectivity of methane over methanol at higher overpotentials indicating the mechanism of methane formation occurs via *COH intermediate. The ethylene formation at a potential −1.0 V vs. RHE or more negative to it suggests a common intermediate for methane and ethylene on the vertically grown copper nanostructures. This work advances the understanding between the product selectivity and the surface structure of the copper nanostructures in electrochemical CO₂ reduction.