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

Electrocatalytic nitrate (NO 3 - ) reduction reaction (NO 3 - RR) represents a promising strategy for both wastewater treatment and ammonia (NH 3 ) synthesis. However, it is difficult to achieve efficient NO 3 - RR on a single-component catalyst due to NO 3 - 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 NO 3 - RR performance in a broad NO 3 - concentration range from 5 to 500 mM. In 10 and 50 mM NO 3 - electrolytes, the NH 3 yield rates reach 3.4 and 25.1 mg h -1 mg cat. -1 with corresponding NH 3 Faradaic efficiencies of 94.0% and 97.1%, respectively, outperforming most of the reported catalysts under the same NO 3 - concentration. The experimental results and density functional theory calculations demonstrate that Ag ligaments preferentially reduce NO 3 - to NO 2 - , while bimetallic Ag-Co ligaments catalyze the reduction of NO 2 - to NH 3 .