Highly dispersed Cu/WO3 heterojunctions featuring a promoted hydrogen radical-mediated pathway for efficient nitrate reduction to ammonia
Electrochemical nitrate reduction to ammonia (NRA) offers a sustainable route for wastewater denitrification and decentralized ammonia synthesis, but its practical deployment is constrained by sluggish reaction kinetics and the competing hydrogen evolution reaction (HER). Monometallic Cu electrocatalysts, despite favorable nitrate adsorption and tunable electronic structure, exhibit weak H* adsorption, limiting the hydrogen radical-mediated pathway that suppresses HER at low overpotentials. Here, highly dispersed Cu/WO3 heterojunctions supported on carbon fiber were synthesized via carbothermal shock reduction, which reaches ultra-high temperatures within seconds and prevents active-site accumulation. The optimal Cu/WO3 heterojunction achieves an ammonia yield rate of 158.66 μmol h−1 cm−2 and a Faradaic efficiency of 98.27%. Electron paramagnetic resonance and density functional theory calculations reveal a synergistic mechanism: Cu sites preferentially adsorb NO3−, while adjacent WO3 sites accelerate water dissociation to generate hydrogen radicals (H*), which drive the continuous hydrogenation of nitrate to ammonia. This spatial separation of functions promotes the H*-mediated pathway and suppresses HER. The work establishes a heterojunction design strategy for non-precious-metal NRA electrocatalysts, enabling high-rate, high-selectivity ammonia production under mild conditions.