The synergistic catalysis effect on electrochemical nitrate reduction at the dual-function active sites of the heterostructure

Abstract

Advanced design concept of catalysts to drive the efficient electrochemical nitrate reduction reaction (NITRR) is highly desirable for converting the harmful nitrate (NO₃⁻) to ammonia (NH₃) as a hydrogen carrier. Herein, the string bead-like nanowire heterostructure derived from the Cu foam electrode (o-CoP/C@Cu₃P/CF) is designed to incorporate the advantages of dual-function active sites in the processes of water-splitting and nitrate reduction. In such heterostructures, the theoretical and experimental results confirm that the CoP sites function to accelerate water-splitting to release protons. Furthermore, the Cu₃P sites exhibit thermodynamic advantages during adsorption, deoxygenation, and hydrogenation steps of adsorbed intermediates (*NO_x). Attributed to the synergistic catalysis effect of the heterostructure, the self-supporting electrode displays an excellent NH₃ yield of 1.571 ± 0.046 mmol h⁻¹ cm⁻² at a low potential of −0.25 V vs. RHE in 1 M KOH containing of 100 mM NO₃⁻. As the NO₃⁻ concentration decreases to 50 mM and 20 mM, the NH₃-faradaic efficiency reached 96.23 ± 0.55% and 97.02 ± 1.64%, respectively. Thus, aqueous zinc–nitrate batteries could achieve three goals with one action for nitrate removal, ammonia synthesis, and electricity supply.