Lattice sulfur-induced disordered and electron-deficient Pd-based nanosheets enabling selective electrocatalytic semi-hydrogenation of alkynes

The semi-hydrogenation of alkynes to alkenes is of great significance in industrial production of pharmaceutical and fine chemicals. Electrochemical semi-hydrogenation (ECSH) has emerged as a promising alternative to conventional thermochemical hydrogenation. However, its practical application is hindered by low reaction rate and competing hydrogen evolution reaction (HER). In this work, the controllable incorporation of sulfur into the lattice of Pd nanostructures is proposed to develop disordered and electron-deficient Pd-based nanosheets on Ni foam and enhance their ECSH performance of alkynes. Mechanistic investigations demonstrate that the electronic and geometric structures of Pd sites are optimized by lattice sulfur, which tunes the competitive adsorption of H* and alkynes, inherently inhibits the H^* coupling and weakens alkene adsorption, thereby promotes the semi-hydrogenation of alkynes and prevents the over-hydrogenation of alkenes. The optimized Pd-based nanosheets exhibit efficient electrocatalytic semi-hydrogenation performance in an H-cell, achieving 97% alkene selectivity and 94% Faradaic efficiency, and a reaction rate of 303.7 μmol mg^-1 catal. h^-1 using 4-methoxyphenylacetylene as the model substrate. Even in a membrane electrode assembly (MEA) configuration, the optimized Pd-based nanosheets achieves a single-cycle alkyne conversion of 96% and an alkene selectivity of 97%, with continuous production of alkene at a rate of 1901.1 μmol mg_catal.^-1 h^-1. The potential- and time-independent selectivity, good substrate universality with excellent tolerance to active groups (C-Br/Cl/C=O, etc.) further highlight the potential of this strategy for advanced catalysts design and green chemistry.