Interfacial Ligand Engineering Breaks the Activity-Selectivity Trade-Off in Electrochemical Alkynol Semihydrogenation and -Deuteration

Electrochemical alkynol semihydrogenation and -deuteration uses water as the hydrogen source, offering a green alternative to thermocatalytic routes. However, its potential is constrained by an inherent activity-selectivity trade-off. Here, we demonstrate an interfacial ligand engineering strategy to break this seesaw effect. Through theoretical and experimental screening, cysteine, featuring both a thiol group and hydrophilic moieties, is identified as the optimal ligand. The cysteine-modified Cu (Cu-Cys) interface achieves concurrent gains in selectivity, conversion rate, and energy efficiency in electrochemical alkynol semihydrogenation and -deuteration. Using the electrochemical semihydrogenation of 2-methyl-3-butyn-2-ol (MBY) to 2-methyl-3-buten-2-ol (MBE) as a representative case, mechanistic studies reveal that the adsorbed cysteine ligands promote interfacial water transfer and dissociation to generate reactive hydrogen for boosting MBY semihydrogenation, while the thiol-mediated Cu surface facilitates MBE desorption and inhibits overhydrogenation, collectively accounting for the simultaneous enhancement in both conversion and selectivity. To demonstrate the practical potential, a flow cell incorporating the Cu-Cys catalyst exhibits stable performance for over 1000 h. The Cu-Cys catalyst compared to bare Cu reduces the power consumption for MBE electrosynthesis from ∼4.55 to ∼3.63 kWh kg –1 . Furthermore, a customized scaled-up electrolysis system equipped with a 400 cm 2 Cu-Cys electrode delivers near-complete MBY conversion while maintaining over 90% MBE selectivity at an applied current of 40 A.