Regulating atomic hydrogen stabilization enables selective hydrodechlorination of trichloroethylene to ethylene

Reductive remediation of trichloroethylene (TCE) is often limited by low utilization of interfacial atomic hydrogen (H*) and poor pathway control in complex groundwater matrices. Here, a noble-metal-free Fe(OH)₂/nitrogen-doped graphene (Fe(OH)₂/NG) composite is developed to regulate H* generated in-situ via the Schikorr reaction and thereby steer TCE transformation pathways. By stabilizing and buffering the in-situ generated H*, the reaction network of TCE is effectively shifted from an acetylene-dominated route to an ethylene-dominated hydrodechlorination network, with ethylene formed predominantly via enhanced hydrodechlorination and secondarily via acetylene hydrogenation. As a result, near-complete TCE conversion is achieved with ethylene selectivity increased to approximately 70%, while over-hydrogenation to ethane remains negligible. Mechanistic investigations combining quenching experiments, kinetic isotope effects, electrochemical characterization, and probe reactions consistently support H* as the key reactive species governing pathway evolution. Density functional theory calculations further reveal that different nitrogen configurations exhibit intrinsically distinct hydrogen adsorption thermodynamics, among which pyridinic N provides an optimal balance between H* stabilization and availability, thereby lowering the energy barriers of key hydrodechlorination steps. The Fe(OH)₂/NG system maintains high activity and selectivity in real groundwater matrices, demonstrating strong resistance to common background constituents. This study elucidates how controlled stabilization of atomic hydrogen can redirect dechlorination pathways and improve product selectivity, offering a practical and scalable approach for selective remediation of chlorinated hydrocarbons in groundwater.