Efficient Tandem Electrocatalytic Nitrate Reduction to Ammonia on Bimodal Nanoporous Ag/Ag–Co across Broad Nitrate Concentrations

Electrocatalytic nitrate (NO₃^-) reduction reaction (NO₃^-RR) represents a promising strategy for both wastewater treatment and ammonia (NH₃) synthesis. However, it is difficult to achieve efficient NO₃^-RR on a single-component catalyst due to NO₃^-RR involving multiple reaction steps that rely on distinct catalyst properties. Here we report a facile alloying/dealloying-driven phase-separation strategy to construct a bimodal nanoporous Ag/Ag-Co tandem catalyst that exhibits a remarkable NO₃^-RR performance in a broad NO₃^- concentration range from 5 to 500 mM. In 10 and 50 mM NO₃^- electrolytes, the NH₃ yield rates reach 3.4 and 25.1 mg h^-1 mg_cat.^-1 with corresponding NH₃ Faradaic efficiencies of 94.0% and 97.1%, respectively, outperforming most of the reported catalysts under the same NO₃^- concentration. The experimental results and density functional theory calculations demonstrate that Ag ligaments preferentially reduce NO₃^- to NO₂^-, while bimetallic Ag-Co ligaments catalyze the reduction of NO₂^- to NH₃.