Unlocking Green Ammonia Production from Nitrate through NO Spillover in a Dual-Site Relay Catalyst

Abstract

The electrocatalytic nitrate reduction reaction (NO3RR) provides a sustainable and environmentally benign route for nitrate remediation and green ammonia synthesis. The intrinsic multi-electron character of NO3RR complicates intermediate hydrogenation, while the competing hydrogen evolution reaction (HER) consumes surface-active hydrogen, collectively limiting selective ammonia formation. Addressing these challenges requires catalysts that can spatially separate active sites to efficiently guide nitrogen intermediates toward selective ammonia formation. Here, we report a relay Fe2O3/SnO2 catalyst with spatially decoupled Sn–Fe dual active sites that facilitate stepwise nitrate reduction and selective ammonia formation. A portion of nitrate is activated at Sn sites to form *NO, which then migrates via a surface-mediated spillover pathway to Fe sites, where stepwise hydrogenation converts it to NH3. In situ attenuated total reflection–surface-enhanced infrared absorption spectroscopy (ATR–SEIRAS) and DFT calculations (–1.34 eV at Fe site vs. –0.55 eV at distal Sn site) confirm the energetically favorable *NO spillover from Sn to Fe. This dual-site relay mechanism results in a high NH3 production rate of 6.43 mol h–1 gcat.–1 at –0.8 V vs. RHE with a Faradaic efficiency of 93.05%. Our results highlight surface-mediated *NO spillover as a design principle for selective dual-site catalysts, offering a green and efficient strategy for electrochemical nitrate-to-ammonia conversion.