Selective Transfer Semihydrogenation of Alkynes with H 2 O (D 2 O) as the H (D) Source over a Pd‐P Cathode

We reported a selective semihydrogenation (deuteration) of numerous terminal and internal alkynes using H 2 O (D 2 O) as the H (D) source over a Pd‐P alloy cathode at a lower potential. P‐doping caused the enhanced specific adsorption of alkynes and the promoted intrinsic activity for producing adsorbed atomic hydrogen (H* ads ) from water electrolysis. The semihydrogenation of alkynes could be accomplished at a lower potential with up to 99 % selectivity and 78 % Faraday efficiency of alkene products, outperforming pure Pd and commercial Pd/C. This electrochemical semihydrogenation of alkynes might proceed via a H* ads addition pathway rather than a proton‐coupled electron transfer process. The decreased amount of H* ads at a lower potential and the more preferential adsorption of the Pd‐P to C≡C π bond than C=C moiety resulted in the excellent alkene selectivity. This method was capable of producing mono‐, di‐, and tri‐deuterated alkenes with up to 99 % deuterium incorporation.