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 HO 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 HO 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 HO 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*(HO) and subsequent hydrogenation reactions by H*(HO). 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 CH and *H, thus enabling a 91.2 % CH Faradaic efficiency at a partial current density of 0.38 A cm, greatly outperforming its counterpart without a superlattice structure.