Atomic‐Level Elucidation of Lattice‐Hydrogens in Copper Catalysts for Selective CO2 Electrochemical Conversion Toward C2 Products

Copper is the most efficient and practical electrocatalyst for the electrochemical reduction of carbon dioxide (ECR) to give multicarbon (C2+) products, but the mechanism by which such products are formed — though known to involve lattice‐hydrogens — remains elusive, and the selectivity of the reaction is poor. Herein, we report the synthesis of [AuCu24(dppp)6H22]+, a copper hydride nanocluster bearing exposed Cu3H3 units in specific surface cavities, and our use of it to study the mechansim and selectivity of the reduction of CO2 to C2+ products. Results of in situ infrared spectroscopy and theoretical calculations showed that these Cu3H3 units can effectively lower the energy barrier to the formation of the *COCOH intermediate, which allowed te competition between the C1 and C2 pathways to be elucidated. Isotope labeling experiments and catalyst recrystallization studies corroborated the theoretical simulations, identifying the lattice‐hydrogen (H‐) in the Cu3H3 active unit as being indispensable for the formation of C2H4. The molecular design guidelines which this work has facilitated constitute a new approach towards the of copper‐based catalysts that convert CO2 to C2+ products based on lattice‐hydrogen engineering.