Atomic‐Level Elucidation of Lattice‐Hydrogens in Copper Catalysts for Selective CO ₂ Electrochemical Conversion toward C ₂ 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 the 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.