Carbon-Doped Lattice Interstitial Sites Enable Water-Driven Electrocatalytic Alkyne Semihydrogenation by Suppressing Subsurface Hydrogen

While electrochemical semihydrogenation (ESH) of alkynes using water-derived hydrogen presents an eco-friendly alternative to traditional thermocatalytic methods, achieving high alkene selectivity remains fundamentally constrained by subsurface hydrogen accumulation in palladium (Pd)-based electrocatalysts. To address this challenge, we developed a class of carbon-doped Pd nanocubes (PdC x NCs) with precisely modulated interstitial carbon occupancy in lattice interstitial sites. The optimized PdC 0.15 NCs achieved high catalytic performance with 95.4% alkene selectivity at −1.0 V (vs Hg/HgO) and full conversion, representing a 3-fold selectivity enhancement over pure Pd counterparts without activity compromise. Through comprehensive structural and electrochemical characterization, we identified two critical mechanistic advantages: (1) carbon intercalation effectively suppresses subsurface hydrogen formation through lattice occupation effects, and (2) strategically weakened intermediate adsorption energetics prevent overhydrogenation pathways. In situ spectroscopic analysis and deuterium isotope tracing elucidated water-derived H* as the active hydrogen species, facilitating radical-mediated hydrogenation that preserves sensitive functional groups (e.g., C–Cl bonds) while achieving complete Z-selectivity for challenging internal alkynes. This interstitial doping strategy fundamentally resolves the inherent selectivity limitations of Pd catalysts, establishing an energy-efficient platform for ambient-condition synthesis of high-yield alkenes with preserved functionality.