Single-Atom Cu and Zn Vacancy Synergy in NiFe-LDH Boosts Metal-Support Interaction for High-Efficiency Nitrate-to-Ammonia Electroreduction.

The electrochemical nitrate (NO3-)-to-ammonia conversion reaction (NO3RR) represents a transformative approach addressing dual challenges of environmental remediation and sustainable ammonia (NH3) synthesis. Despite its promise, practical implementation remains constrained by parasitic hydrogen evolution and inherent kinetic limitations. We propose an innovative dual-site architecture through atomic-scale metal-support engineering, constructing single copper (Cu) atoms anchored on zinc-deficient NiFe-layered double hydroxide (CuSA/V-LDH). This strategic design achieves exceptional NO3RR performance, delivering 95.2% Faradaic efficiency and 2.08 mg h-1 cm-2 NH3 yield at environmentally relevant NO3- levels (100 mg-N L-1), surpassing most reported catalysts in low-concentration scenarios. Operando spectroscopy and multiscale modeling uncover key synergistic effects that govern the system's enhanced performance. Vacancy-mediated charge redistribution strengthens metal-support interactions and structural durability, while LDH-derived atomic hydrogen species exhibit prolonged lifetimes through CuSA coordination, which facilitates efficient hydrogenation of nitrogen intermediates. Additionally, the flow-through reactor configuration optimizes mass transport, further boosting the overall reaction kinetics. System-level validation and life cycle assessment highlight the reduced environmental footprint of the proposed technology. This work establishes a paradigm for vacancy-engineered atomic interfaces in advanced electrocatalytic systems in circular water-energy nexus applications.