Enhancing the Catalytic Activity of Co Sites by the Synergistic Effect of Vacancy and Heterojunction Engineering for Efficient Electroreduction Nitrate to Ammonia

ABSTRACT Electrocatalytic nitrate reduction reaction (NO ₃ ⁻ RR) for ammonia synthesis is extremely compatible with the concept of green development as it enables both low carbon emission and low energy consumption ammonia (NH ₃ ) production, as well as the treatment of pollution in wastewater. However, the unavoidable competing reactions present in the NO ₃ ⁻ RR process and adsorption limitations of the reactants on the surface hinder the effective activation of nitrate and affect the efficient NH ₃ synthesis. Herein, the high‐performance V _P ‐ CoP/Co(OH) ₂ heterojunction catalysts for enhancing NO ₃ ⁻ RR competition in the NO ₃ ⁻ to NH ₃ conversion process was skillfully constructed by successfully growing Co(OH) ₂ nanosheets on P vacancy‐rich CoP via an electrochemical in situ reconfiguration strategy. The optimized V _P ‐CoP/Co(OH) ₂ exhibits excellent electrocatalytic performance of NO ₃ ⁻ RR at −0.1 V vs. RHE, corresponding to an NH ₃ Faraday efficiency of 96.60% and an NH ₃ yield of 0.091 mmol h ⁻¹ cm ⁻² , with a favorable stability. Combination of experimental studies and theoretical calculations demonstrates that P vacancies modify the coordination environment of the Co sites, which in turn modulates the electronic structure and accelerates the charge transfer rate. Heterojunctions, on the other hand, lead to a reconfiguration of the electronic structure at the interface, inducing a further accumulation of charge at the Co active sites. The synergy of both further activates the electronic states around the Co sites, which causes the d‐band center moving toward the Fermi energy level, further enhancing the adsorption of NO ₃ ⁻ and promoting the reduction of NO ₃ ⁻ . This work focuses on modulating the electronic structure of the Co active sites to enhance its NO ₃ ⁻ RR electrocatalytic performance, thus delivering a viable pathway for NO ₃ ⁻ to NH ₃ high‐efficiency conversion.