Integrated Cascade Catalysts for Electrochemical Nitrate Reduction to Ammonia

Electrocatalytic nitrate reduction reaction (NO₃^-RR) powered by renewable energy sources offers a promising approach to achieve ammonia (NH₃) synthesis with zero-carbon emission. However, sluggish proton-coupled electron transfer and byproduct formation challenge efficient NH₃ synthesis. Here, we construct an integrated cascade catalytic system to elucidate the governing principles of active hydrogen (*H) generation and utilization during NO₃^-RR. A representative catalyst, composed of atomically dispersed Fe sites anchored on an N-doped carbon matrix and encapsulated Ru nanoparticles, exhibits an NH₃ yield up to 2336.43 μg_NH3 h^-1 mg_cat^-1 while maintaining a Faradaic efficiency of 96.03% at a low potential of 0 V vs RHE. In addition, operando SR-FTIR spectroscopy and DFT calculations reveal that electron transfer from Fe atom to Ru particle not only enhances the affinity of Fe sites for NO_<i>x</i>^- species but also enriches H coverage on Ru sites, thereby accelerating hydrogenation steps and sustaining a steady *H generation-consumption cycle. This work reveals the mechanistic origin of active hydrogen in tandem catalytic structures and provides fundamental insights for advancing highly selective, energy efficient, and durable NH₃ electrosynthesis and wastewater treatment.