Efficient Nitrate Synthesis via Ambient Nitrogen Oxidation with Ru‐Doped TiO2/RuO2 Electrocatalysts

Abstract A facile pathway of the electrocatalytic nitrogen oxidation reaction (NOR) to nitrate is proposed, and Ru‐doped TiO 2 /RuO 2 (abbreviated as Ru/TiO 2 ) as a proof‐of‐concept catalyst is employed accordingly. Density functional theory (DFT) calculations suggest that Ru δ + can function as the main active center for the NOR process. Remarkably doping Ru into the TiO 2 lattice can induce an upshift of the d‐band center of the Ru site, resulting in enhanced activity for accelerating electrochemical conversion of inert N 2 to active NO*. Overdoping of Ru ions will lead to the formation of additional RuO 2 on the TiO 2 surface, which provides oxygen evolution reaction (OER) active sites for promoting the redox transformation of the NO* intermediate to nitrate. However, too much RuO 2 in the catalyst is detrimental to both the selectivity of the NOR and the Faradaic efficiency due to the dominant OER process. Experimentally, a considerable nitrate yield rate of 161.9 µmol h −1 g cat −1 (besides, a total nitrate yield of 47.9 µg during 50 h) and a highest nitrate Faradaic efficiency of 26.1% are achieved by the Ru/TiO 2 catalyst (with the hybrid composition of Ru x Ti y O 2 and extra RuO 2 by 2.79 wt% Ru addition amount) in 0.1 m Na 2 SO 4 electrolyte.