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 μgNH3 h–1 mgcat–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 NOx– 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.