Activated water molecular dissociation enhances nitrate electrochemical reduction activity by rational design of binary CoCu-Pi catalyst

Abstract

Electrochemical reduction nitrate reaction (NO₃RR) to ammonia presents a promising yet challenging route for treating high-concentration wastewater and recovering nitrogen. However, its efficiency is limited by a complex reaction pathway involving multiple proton-electron transfers and stringent competition from side reactions. Herein, we developed a series of binary CoCu phosphates with precisely tailored Co/Cu ratios to investigate their synergistic catalytic effects. A volcano-shaped relationship exists between the Co/Cu ratio and the electrocatalytic activity, with Co_0.5Cu_1.5(OH)PO₄ exhibiting optimal performance by facilitating electron transfer and enriching active sites. In 1 M nitrate electrolyte at a high current density of 200 mA cm⁻², the Co_0.5Cu_1.5(OH)PO₄ achieves a remarkable Faradaic efficiency (FE) of 99.0% for ammonia, simultaneously delivering a high production rate of 9.18 mg h⁻¹ cm⁻², while maintaining stable performance over continuous electrolysis for more than 200 h. DFT calculations attribute the superior performance to the optimized Co/Cu ratio. Specifically, the Co sites promote water dissociation to ensure a sufficient supply of active hydrogen, while the adjacent Cu sites utilize this hydrogen to drive the deoxygenation and hydrogenation steps. This effective division of labor significantly lowers the reaction energy barrier, thereby enhancing the intrinsic kinetics of the NO₃RR process. This work demonstrates that precise regulation of dual-site functionality in transition metal phosphates provides a novel strategy to break the activity-selectivity trade-off in electrocatalytic nitrate-to-ammonia conversion.