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 (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.