In situ constructed Cu@Co2P/NF heterojunctions with interfacial electronic coupling for selective nitrate electroreduction

The electrochemical nitrate reduction reaction (NO 3 RR) has emerged as a promising strategy for sustainable ammonia synthesis, offering high efficiency under mild conditions. However, its eight-electron transfer pathway and the competing hydrogen evolution reaction (HER) often limit NH 3 selectivity. Developing cost-effective electrocatalysts with high activity and selectivity is therefore of great significance. Herein, we report a Cu@Co 2 P heterojunction catalyst grown on nickel foam (Cu@Co 2 P/NF) through a sequential hydrothermal, phosphorization, and electrodeposition process. The intimate Cu–Co 2 P interface induces electronic coupling, modulates intermediate adsorption energies, lowers energy barriers, and creates highly efficient active sites for NO 3 − reduction. Benefiting from this synergy, the catalyst delivers an outstanding NH 3 production rate of 17267.51 μg h −1 cm −2 and a Faradaic efficiency of 98.3% at −0.5 V vs. RHE, surpassing most reported NO 3 RR electrocatalysts. Combined experimental studies and density functional theory (DFT) calculations reveal that Co2P serves as an efficient ∗H generation site by activating H2O and continuously supplying hydrogen to Cu through a surface spillover mechanism. Cu selectively adsorbs and stabilizes key nitrogen intermediates (∗NO3⁻, ∗NO2⁻, ∗NH2OH), enabling a smooth and highly selective eight-electron transfer pathway from NO3⁻ to NH3 while suppressing side reactions. Furthermore, the built-in electric field at the Cu–Co2P junction accelerates electron transfer, thereby enhancing reaction kinetics and maintaining high Faradaic efficiency. This work provides fundamental insight into the NO3RR mechanism and demonstrates a rational design strategy for constructing high-performance heterojunction catalysts with simultaneously high activity, selectivity, and stability. The Cu@Co 2 P/NF heterojunction catalyst leverages strong interfacial electronic coupling to enable an efficient dual-site synergistic mechanism. The Co 2 P domains facilitate ∗H generation via water dissociation, while the Cu sites preferentially adsorb and activate NO 3 − , collectively delivering enhanced nitrate reduction activity and high product selectivity. • The Cu@Co 2 P/NF heterojunction forms an intimate Cu–Co 2 P interface that induces strong electronic coupling, optimizes intermediate adsorption energies, and generates highly efficient active sites for NO 3 − reduction. • Interfacial electron redistribution in the heterojunction tailors the catalytic electronic structure, enabling Co 2 P to act as an efficient H donor that continuously supplies hydrogen to Cu sites via reverse spillover, thereby synergistically promoting the NO 3 − -to-NH 3 pathway while suppressing intermediate accumulation. • The Cu@Co 2 P/NF catalyst delivers an outstanding NH 3 production rate of 17267.51 μg h −1 ·cm −2 and a Faradaic efficiency of 98.3% at −0.5 V vs. RHE, surpassing most reported NO 3 RR electrocatalysts. • This study clearly elucidates the reaction mechanism of NO 3 RR, providing a feasible strategy for developing high-performance catalysts with high selectivity and activity.