Stabilizing Hydrogen Radicals in Two-Dimensional Cobalt-Copper Mesoporous Nanoplates for Complete Nitrate Reduction Electrocatalysis to Ammonia.

Ambient electrochemical reduction of waste nitrate (NO ) represents an alternative green route for sustainable ammonia (NH) electrosynthesis in water. Despites some encouraged achievements, sluggish eight electron and nine proton reduction routes that involve multi-step hydrogenation pathways have severely hindered their NH Faradaic efficiency (FE) and yield rate. Herein, we develop a robust two-dimensional mesoporous cobalt-copper (meso-CoCu) nanoplate electrocatalyst that delivers excellent performance of complete NO reduction reaction (NORR), including superior FE of 98.8 %, high NH yield rate of 3.39 mol h g and energy efficiency of 49.8 %, and good cycling stability. Mechanism investigations unveil that active hydrogen (*H) radicals produced from water splitting on Co sites spillover to adjacent Cu sites and further stabilize within confined mesopores, which kinetically promote its coupling hydrogenation reactions of nitrogen intermediates and thus facilitate complete NORR for favorable NH electrosynthesis. Moreover, meso-CoCu nanoplates perform well as a bifunctional electrocatalyst in the two-electrode coupling system that concurrently synthesizes NH from NO at cathode and 2,5-furanedicarboxylic acid from 5-hydroxymethylfurfural at anode. This work in stabilizing *H radicals in mesoporous microenvironment provides some insights applied to various hydrogenation reactions for selective electrosynthesis of high value-added chemicals in water.