Production of C₂/C₃ Oxygenates from Planar Copper Nitride-Derived Mesoporous Copper via Electrochemical Reduction of CO₂

Electrochemical reduction of CO<sub>2</sub> provides an opportunity to produce fuels and chemicals in a carbon-neutral manner, assuming that CO<sub>2</sub> can be captured from the atmosphere. To do so requires efficient, selective, and stable catalysts. In this study, we report a highly mesoporous metallic Cu catalyst prepared by electrochemical reduction of thermally nitrided Cu foil. Under aqueous saturated CO<sub>2</sub> reduction conditions, the Cu<sub>3</sub>N-derived Cu electrocatalyst produces virtually no CH<sub>4</sub>, very little CO, and exhibits a faradaic efficiency of 68% in C<sub>2+</sub> products (C<sub>2</sub>H<sub>4</sub>, C<sub>2</sub>H<sub>5</sub>OH, and C<sub>3</sub>H<sub>7</sub>OH) at a current density of ~18.5 mA cm<sup>–2</sup> and a cathode potential of -1.0 V versus the reversible hydrogen electrode. Under these conditions, the catalyst produces more oxygenated products than hydrocarbons. We show that surface roughness is a good descriptor of catalytic performance. The roughest surface reached 98% CO utilization efficiency for C<sub>2+</sub> product formation from CO<sub>2</sub> reduction and the ratio of oxygenated to hydrocarbon products correlates with the degree of surface roughness. These effects of surface roughness are attributed to the high population of undercoordinated sites as well as a high pH environment within the mesopores and adjacent to the surface of the catalyst.