Oxygen Functionalized Copper Nanoparticles for Solar-Driven Conversion of Carbon Dioxide to Methane.

Solar conversion of carbon dioxide (CO2) into hydrocarbon fuels offers a promising approach to fulfill the world's ever-increasing energy demands in a sustainable way. However, a highly active catalyst that can also tune the selectivity toward desired products must be developed for an effective process. Here, we present oxygen functionalized copper (OFn-Cu) nanoparticles as a highly active and methane (CH4) selective catalyst for the electrocatalytic CO2 reduction reaction. Our electrochemical results indicate that OFn-Cu (5 nm) nanoparticles with an oxidized layer at the surface reach a maximum CH4 formation current density and turnover frequency of 36.24 mA/cm2 and of 0.17 s-1 at the potential of -1.05 V vs RHE, respectively, exceeding the performance of existing Cu and Cu-based catalysts. Characterization results indicate that the surface of the OFn-Cu nanoparticles consists of an oxygen functionalized layer in the form of Cu2+ (CuO) separated from the underneath elemental Cu by a Cu+ (Cu2O) sublayer. Density functional theory calculations also confirm that presence of the O site at the CuO (101) surface is the main reason for the enhanced activity and selectivity. Using this catalyst, we have demonstrated a flow cell with an active area of 25 cm2 that utilizes solar energy to produce 7.24 L of CH4 after 10 h of continuous process at a cell power density of 30 mW/cm2.