Abstract: Highly selective electrocatalytic semihydrogenation of alkynes to alkenes with water as the hydrogen source over palladium-based electrocatalysts is significant but remains a great challenge because of the excessive hydrogenation capacity of palladium. Here, we propose that an ideal palladium catalyst should possess weak alkene adsorption and inhibit subsurface hydrogen formation to stimulate the high selectivity of alkyne semihydrogenation. Therefore, sulfur-modified Pd nanowires (Pd-S NWs) are designedly prepared by a solid-solution interface sulfuration method with KSCN as the sulfur source. The introduction of S weakens the alkene adsorption and prevents the diffusion of active hydrogen (H*) into the Pd lattice to form unfavorable subsurface H*. As a result, electrocatalytic alkyne semihydrogenation is achieved over a Pd-S NWs cathode with wide substrate scopes, potential-independent up to 99% alkene selectivity, good fragile groups compatibility, and easily synthesized deuterated alkenes. An adsorbed hydrogen addition mechanism of this semihydrogenation reaction is proposed. Importantly, an easy modification of commercial Pd/C by in situ addition of SCN^- enabling the gram-scale synthesis of an alkene with 99% selectivity and 95% conversion highlights the promising potential of our method.

Key words: Electrocatalysis, Alkyne semihydrogenation, Selectivity, Hydrogen adsorption, Interface sulfuration