Enhanced Electrocatalytic Activity for Nitrate Reduction to Ammonia by Tuning a Ruthenium Oxidation State of Ruthenium-Based Nanotubes

Electrocatalytic nitrate reduction to ammonia (NRA) seriously suffers from slow kinetics and low selectivity due to its eight-electron transfer process and complex reaction intermediates. Herein, Ru-based nanotubes (NTs) were designed to enhance the electrocatalytic activity of NRA. Significantly, the metallic Ru NTs endowed remarkable ammonia (NH3) yield rate (v NH3) of 40.6 mg h(-1) mg(cat.)(-1) at -1.20 V vs SCE and the highest NH3 Faradaic efficiency (FE NH3) of 98.4% at -1.10 V vs SCE under ambient conditions, which are superior to those of RuO2 NTs (v NH3 : 0.52 mg h(-1) mg(cat.)(-1), FE NH3 : 18.2%). Both experimental and theoretical results have proved that the Ru metallic state is more beneficial to N-O bond breaking and hydrogenation than the oxidized state, improving the kinetics and selectivity of NRA.