Activated water molecular dissociation enhances nitrate electrochemical reduction activity by rational design of binary CoCu-Pi catalyst
Electrochemical nitrate reduction (NO3RR) to ammonia offers a sustainable route for nitrogen recovery from wastewater, yet its efficiency is constrained by complex multi-step proton-electron transfers and competitive hydrogen evolution. Here, we report a series of binary cobalt-copper phosphates with precisely tuned Co/Cu ratios, revealing a volcano-type relationship between composition and catalytic activity. The optimized Co0.5Cu1.5(OH)PO4 catalyst, supported on a Ni3Co1OxHy/Ni foam substrate, achieves a Faradaic efficiency of 99.0% for ammonia at a high current density of 200 mA cm−2 in 1 M nitrate electrolyte, with a production rate of 9.18 mg h−1 cm−2 and sustained stability over 200 hours. In-situ ATR-FTIR spectroscopy and density functional theory calculations elucidate a tandem mechanism: Co sites promote water dissociation to generate active hydrogen (H*), while adjacent Cu sites facilitate nitrate adsorption and subsequent hydrogenation steps. This synergistic division of labor lowers the energy barrier for the rate-determining step, effectively suppressing HER and enhancing intrinsic kinetics. The work demonstrates that precise atomic-ratio engineering in dual-site transition metal phosphates provides a viable strategy to overcome activity-selectivity trade-offs in electrocatalytic nitrate-to-ammonia conversion.