Roles of Copper in Nitrate Reduction at Copper-Modified Ru/C Catalysts

Abstract

Electrochemical reduction is a potential solution to eliminate nitrate in wastewater; however, the poor activity and product selectivity of traditional electrocatalysts impede its large-scale application. Herein, we report a new catalyst of Cu-modified Ru nanoparticles (Cu-modified Ru/C NPs) prepared by underpotential deposition (UPD) of Cu atoms onto Ru NPs, which shows good nitrate reduction kinetics and NH3 selectivity. To unravel the enhancing mechanism, the impact of Cu coverage on nitrate reduction and the formation of possible products/intermediates as well as the competition of side products H2 have been investigated systematically by tracking the reverse oxidation of such species using rotation ring disk electrode (RRDE) combined with cyclic voltammetry. Our results reveal that the Cu-modified Ru/C NPs perform NH3 yield of 23.7 μmol h–1 cm–2 and 95% Faradaic efficiency, which is better than Ru/C NPs (6.0 μmol h–1 cm–2 with Faradaic efficiency of 66%); This enhancement of modified Cu atoms toward nitrate reduction results from synergetic effects: (i) Cu blocks the hydrogen evolution reaction (HER) sites on Ru surface; (ii) Cu accelerates the rate of nitrate reduction to nitrite; (iii) the enhanced nitrite reduction activity of Cu sites on Ru substrate is probably a result of changes in electronic structure of Cu.