Grain boundary engineering on Cu-based electrocatalysts promotes nitrate reduction to ammonia production

Abstract

Cu-based electrocatalysts derived from copper oxide exhibit good electrocatalytic activity and selectivity in the electrocatalytic nitrate reduction reaction (NO₃ RR). However, the origin of the enhanced selectivity and activity of NO₃RR is unclear. Herein, we investigate the activity of three copper oxide/hydroxide-derived catalysts, and verify the phase changes during the reduction process through electrochemical in situ Raman spectroscopy. Our results show that all phases ultimately transform into metallic copper during the electrochemical synthesis process, supporting that the zero valent copper phase is the actual active phase. The high-density grain boundaries and defects are responsible for the activity of NO₃RR. By combining with the nickel oxide, the selectivity of the catalyst for NO₃RR can be further improved, achieving an ammonia Faradaic efficiency of ∼96% and an ammonia yield of 3.2 mmol cm⁻² h⁻¹ at −0.05 V_RHE. This experimental design of oxygen intercalation/elimination brings a more flexible electrode, which provides a new methodology for constructing the grain boundary toward NO₃RR.