Constructing high activity Cu/Cu2O via nitrate-assisted directed evolution for enhanced electro catalytic nitrate-to-ammonia conversion

Abstract

The electrochemical reduction of nitrate (NO₃⁻RR) is a promising strategy for producing value-added ammonia while addressing water pollution and promoting sustainable nitrogen management. Inspired by the reduction process from CuO to Cu, we proposed a novel electrochemically driven NO₃⁻-assisted directed evolution strategy to construct Cu/Cu₂O heterojunctions for enhanced NO₃⁻RR performance. A copper foam-supported copper oxides (Cu_xO) catalyst was synthesized via an electrochemical reconstruction method in the presence of nitrate. Comprehensive characterization using SEM, XPS, and XRD demonstrated that nitrate concentration plays a crucial role in tuning the structure, surface chemistry, and oxidation state of Cu_xO/CF. In a 0.5 M Na₂SO₄ solution containing 0.01 M KNO₃, the optimized Cu-0.1 catalyst exhibited significantly enhanced NO₃⁻RR activity, achieving a high NH₄⁺ yield rate of 4.33 mg·h⁻¹·cm⁻² at –1.0 V vs. RHE and a Faradaic efficiency of 78.0 % at –0.8 V vs. RHE. Furthermore, DFT calculations revealed that nitrate concentration was the critical factor in regulating Cu₂O content and controlling its growth during the formation of Cu/Cu₂O heterojunctions. The enhanced NO₃⁻RR activity was attributed to the synergistic effect between NO₃⁻ adsorption on the Cu₂O(111) crystal plane and NH₃ desorption on the Cu(111) plane.