Improved NH3-N conversion efficiency to N2 activated by BDD substrate on NiCu electrocatalysis process

Abstract We developed a novel boron-doped diamond (BDD) electrode by the modification of bimetallic NiCu catalysts via electrochemical co-deposition method for improving the NH3-N conversion efficiency and selectivity to N2 in aqueous solution. It shows that the N2 selectivity of ammonia oxidation reaction (AOR) reached 88.62% with the NH3-N oxidation efficiency of 44.8% in 6 h. The high current efficiency of 84.17% was achieved at 1.2 V (vs Ag/AgCl), and the energy consumption was 8.19 kW·h/(kgN). Furthermore, the reaction mechanism has been investigated by in-situ Raman spectra, X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) during the reaction. It is verified that the BDD substrate plays a crucial role not only in the improvement of electronic transmission rate and but also the generation of abundant hydroxyl radicals (·OH) which provide proper hydrogen acceptors for the N-H bond activation processes. Theoretical calculations further reveal the doping effect of Cu(OH)2 with NiOOH that constructs the Cu/Ni concerted metal-nitrogen interaction, which stabilizes the relative energies of the intermediates thus promoting the reaction. This work sheds new light on the mechanism of selective electrochemical oxidation of NH3-N and develops an innovative technology of catalytic anode design toward wastewater treatment.