Boosting electrocatalytic nitrate-to-ammonia of single Fe active sites via coordination engineering: From theory to...

Atomically dispersed iron-nitrogen-carbon (Fe-N₄-C) catalysts show great promises for the electrocatalytic nitrate (NO₃^-) reduction to ammonia (NH₃). Nevertheless, the microenvironmental engineering of the single Fe active sites for further optimizing the catalytic performance remains a challenge. Herein, we proposed to regulate the coordination environment of single Fe active sites to boost its intrinsic electrocatalytic activity for NO₃^- -to-NH₃ conversion by the incorporation of new heteroatoms, including B, C, O, Si, P, and S. Our results revealed that most of the candidates possess low formation energies, showing great potential for experimental synthesis. Moreover, incorporating heteroatoms effectively modulates the charge redistribution and the d-band center of single Fe active sites, enabling the regulation of the binding strength of nitrogenous intermediates. As a result, the N and C coordinated Fe active site (Fe-N₃C) exhibits superior catalytic performance for NO₃^- electroreduction with a relatively low limiting potential (-0.13 V) due to its optimal adsorption strength with nitrogenous intermediates induced by its moderate charge and d-band center. Importantly, our experimental measures confirmed such theoretical prediction: a maximum NH₃ yield rate of 21.07 mg h^-1 mg_cat.^-1 and 95.74 % Faradaic efficiency were achieved for NO₃^- electroreduction on Fe-N₃C catalyst. These findings not only suggest a highly efficient catalyst for nitrate reduction but also provide insight into how to design and prepare electrocatalysts with enhanced catalytic performance.