Carbon-Bifunctionalized Mo₂N Coupled Atomic Pb Sites for Efficient Nitrogen Reduction

The electrocatalytic nitrogen reduction reaction (ENRR) offers a sustainable pathway for ambient ammonia (NH₃) synthesis but suffers from kinetic limitations and competing hydrogen evolution (HER). Herein, a new type of ENRR catalyst is designed consisting of carbon-bifunctionalized Mo₂N nanoparticles (NPs) embedded in a hierarchical porous carbon matrix with atomic Pb sites (PbNC) through a one-step carbonitridation strategy. The carbon-bifunctionalization effect not only creates nitrogen vacancies through interstitial carbon doping to form molybdenum carbonitride (Mo₂CN) phase that enhances N₂ adsorption and activation, but also stabilizes active sites via nanoconfinement of the in situ formed carbon layer on Mo₂CN NPs. Concurrently, the atomically dispersed Pb within the PbNC matrix suppresses HER due to its weak H^* affinity. The optimized catalyst demonstrates 38.7 µg h^-1 mg^-1 NH₃ yield at a low potential of -0.1 V with 50 h operational stability. Density functional theory calculations reveal that carbon-induced nitrogen vacancies modulate the Mo d-band center, which facilitates electron back-donation to N₂ and thus shifts the potential-determining step from initial protonation to the NH₃ desorption step via the Mars-van Krevelen mechanism with a lower energy barrier for ENRR. This study proposes an integrated approach involving vacancy engineering, atomic-level HER suppression, and nanoconfinement toward efficient ENRR catalysis.