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.