Selective Mass Accumulation at the Metal-Polymer Bridging Interface for Efficient Nitrate Electroreduction to Ammonia and Zn-Nitrate Batteries.

The electrochemical conversion of nitrate (NO), a common nitrogen source in industrial wastewater and contaminated groundwater, into ammonia (NH), signifies an approach to wastewater treatment and NH production. Nevertheless, its selectivity and activity at low NO concentrations and industrial current densities are constrained by limited mass transfer around the electrode. Here, we report a metal-polymer bridging interface constructed by anchoring Cu/CuO nanoparticles onto a two-dimensional (2D) Cu-based benzene dicarboxylate (CuBDC) coordination polymer via in situ electroreduction (denoted as E-CuBDC). This interface weakens the electrostatic repulsion and regulates the distribution/migration of NO and HO, creating a Janus NO-rich and HO-poor domain near the catalyst surface. Operando characterizations and theoretical simulations indicate that the metal-polymer bridging interface selectively accumulates NO and reduces the energy barrier toward the reduction of *NHOH to *NH, overcoming the mass transfer limitations at a low NO concentration. E-CuBDC exhibits a high Faradaic efficiency (FE) of over 90% across wide NO concentrations (7.1-100 mM NO) and high applied voltages. Additionally, it achieved stable NH production over 100 h at ampere-level current densities. When applied in a Zn-NO system, this newly developed E-CuBDC catalyst demonstrates an outstanding power density and FE for NH production, showcasing its great potential for large-scale electrochemical conversion and storage systems. This study presents a generalizable strategy for constructing metal-polymer interfaces to regulate interfacial mass transport.