Promoting Water Dissociation and Weakening Active Hydrogen Adsorption to Boost the Hydrogen Transfer Reaction over a Cu−Ag Superlattice Electrocatalyst

The prerequisite for electrocatalytic hydrogenation reactions (EHRs) is H₂O splitting to form surface hydrogen species (*H), which occupy catalytic sites and lead to mismatched coverage of *H and reactants, resulting in unsatisfactory activity and selectivity. Thus, modulating the splitting pathway of H₂O is significant for optimizing the EHR process. Herein, a Cu-Ag alloy with a superlattice structure of staggered-ordered Cu and Ag is theoretically predicted and experimentally proven to undergo a pathway for H₂O splitting called the hydrogen transfer reaction (HTR) in the water layer, which involves the formation of *H, the capture of *H by a water cluster to form H*(H₂O)_x and subsequent hydrogenation reactions by H*(H₂O)_x. Taking acetylene hydrogenation as a model case, the as-proposed HTR pathway could lead to a relaxation hydrogenation process to modulate the matching degree of C₂H₂ and *H, thus enabling a 91.2 % C₂H₄ Faradaic efficiency at a partial current density of 0.38 A cm^-2, greatly outperforming its counterpart without a superlattice structure.