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.