Adsorption Configuration and H* Flux Modulation Enable Electrocatalytic Semihydrogenation of Alkynes with Group Tolerance in a Palladium Membrane Reactor

Ineffective control of alkene adsorption on a palladium membrane (PM) and the flux of active hydrogen (H*) diffusing from the aqueous side to the organic side through the PM cause low selectivity and Faradaic efficiency (FE) of alkynes to alkenes in a PM reactor. Here, a PM with a phenylthiolate-modified palladium sulfide thin layer coupled with pulsed electrolysis is reported to enable alkyne-to-alkene electrosynthesis with up to 98% selectivity and 80% FE. Electrochemical in situ Raman spectra reveal weak alkene adsorption and specific σ-alkynyl adsorption rather than flat adsorption of alkynes on the modified PM, accounting for the high alkene selectivity and functional group tolerance. Pulsed electrolysis causes reduced H* generation and restricted H* diffusion to the organic side, which better balances the generation and utilization of H*, suppresses H₂ evolution, and improves the FE. The high alkene selectivity and FE in a wide potential and current range, over 50 examples of (deuterated) alkenes with functional group tolerance and deuterated drug applications (<i>d</i>₂-<i>naftifine</i>, <i>d</i>₂-<i>cinarizine</i>, <i>d</i>₂-<i>bucinnazine</i>, <i>d</i>₂<i>-artemisinin derivative</i>, and <i>d</i>₂<i>-estradiol derivative</i>), and scalable electrosynthesis of deuterated styrene for deuterated polystyrene with improved thermal stability demonstrate potential utility.