Efficient Tandem\nElectrocatalytic Nitrate Reduction\nto Ammonia on Bimodal Nanoporous Ag/Ag–Co across Broad Nitrate\nConcentrations

Electrocatalytic nitrate (NO<sub>3</sub><sup>–</sup>) reduction\nreaction (NO<sub>3</sub><sup>–</sup>RR) represents a promising\nstrategy for both wastewater treatment and ammonia (NH<sub>3</sub>) synthesis. However, it is difficult to achieve efficient NO<sub>3</sub><sup>–</sup>RR on a single-component catalyst due to\nNO<sub>3</sub><sup>–</sup>RR involving multiple reaction steps\nthat rely on distinct catalyst properties. Here we report a facile\nalloying/dealloying-driven phase-separation strategy to construct\na bimodal nanoporous Ag/Ag–Co tandem catalyst that exhibits\na remarkable NO<sub>3</sub><sup>–</sup>RR performance in a\nbroad NO<sub>3</sub><sup>–</sup> concentration range from 5\nto 500 mM. In 10 and 50 mM NO<sub>3</sub><sup>–</sup> electrolytes,\nthe NH<sub>3</sub> yield rates reach 3.4 and 25.1 mg h<sup>–1</sup> mg<sub>cat.</sub><sup>–1</sup> with corresponding NH<sub>3</sub> Faradaic efficiencies of 94.0% and 97.1%, respectively, outperforming\nmost of the reported catalysts under the same NO<sub>3</sub><sup>–</sup> concentration. The experimental results and density functional theory\ncalculations demonstrate that Ag ligaments preferentially reduce NO<sub>3</sub><sup>–</sup> to NO<sub>2</sub><sup>–</sup>,\nwhile bimetallic Ag–Co ligaments catalyze the reduction of\nNO<sub>2</sub><sup>–</sup> to NH<sub>3</sub>.