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. <i>Operando</i> 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.