Integrated Cascade Catalysts for Electrochemical Nitrate Reduction to Ammonia

Electrocatalytic nitrate reduction reaction (NO 3 – RR) powered by renewable energy sources offers a promising approach to achieve ammonia (NH 3 ) synthesis with zero-carbon emission. However, sluggish proton-coupled electron transfer and byproduct formation challenge efficient NH 3 synthesis. Here, we construct an integrated cascade catalytic system to elucidate the governing principles of active hydrogen (*H) generation and utilization during NO 3 – RR. A representative catalyst, composed of atomically dispersed Fe sites anchored on an N-doped carbon matrix and encapsulated Ru nanoparticles, exhibits an NH 3 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 x – 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 NH 3 electrosynthesis and wastewater treatment.