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

Electrocatalytic nitrate reduction reaction (NO₃ ^-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 (NH₃) production, as well as the treatment of pollution in wastewater. However, the unavoidable competing reactions present in the NO₃ ^-RR process and adsorption limitations of the reactants on the surface hinder the effective activation of nitrate and affect the efficient NH₃ synthesis. Herein, the high-performance V_P- CoP/Co(OH)₂ heterojunction catalysts for enhancing NO₃ ^-RR competition in the NO₃ ^- to NH₃ 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 NO₃ ^-RR at -0.1 V vs. RHE, corresponding to an NH₃ Faraday efficiency of 96.60% and an NH₃ 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 NO₃ ^- and promoting the reduction of NO₃ ^-. This work focuses on modulating the electronic structure of the Co active sites to enhance its NO₃ ^-RR electrocatalytic performance, thus delivering a viable pathway for NO₃ ^- to NH₃ high-efficiency conversion.