Sulfur-Vacancy-Enabled Dual-Site MoS2 Enhances H* Utilization for Mo–H-Mediated Deep Dechlorination

Electrochemical dechlorination using molybdenum disulfide (MoS2) offers a cost-effective solution for treating chlorinated organic contaminants, yet its catalytic potential remains limited by the unclear roles of Mo and S sites in mediating hydrogen utilization and C–Cl bond cleavage. Herein, we engineer sulfur-vacancy-rich MoS2 (Sv-MoS2) electrodes to expose coordinatively unsaturated Mo sites and enable an efficient Mo–H*-mediated dechlorination pathway. Using florfenicol as a model chlorinated antibiotic, Sv-MoS2 achieved near-complete dechlorination with ∼15-fold faster kinetics than pristine MoS2, reaching a rate constant of 9.26 h–1 at low energy consumption (0.0083 kWh g–1). Mechanistic analyses combining CV, EPR, in situ Raman spectroscopy, kinetic isotope effects, and DFT calculations reveal a dual-site H* utilization mechanism: S sites primarily generate H*, while vacancy-exposed Mo sites stabilize Mo–H* species that selectively drive C–Cl bond cleavage. In contrast, pristine MoS2 follows a direct electron transfer-dominated pathway and shows limited deep dechlorination. The Mo–H*-mediated pathway on Sv-MoS2 substantially lowers the energy barriers for sequential C–Cl cleavage while promoting productive H* utilization over H2 formation. The Sv-MoS2 electrode further exhibits robust performance under variable pH, natural organic matter, coexisting anions, and repeated cycling. This work clarifies Mo/S site synergy in MoS2 electrocatalysts and establishes a dual-site design framework for efficient, selective, and sustainable electrochemical hydrodechlorination.