Enhancing the Electrochemical Nitrate-to-Ammonia Performance on Co3O4 via 4f-2p-3d Orbital Hybridization Engineering

Abstract

Co3O4-based nanomaterials have been widely applied as electrocatalysts for nitrate reduction (NO3‒RR) to ammonia (NH3); however, their performance is still unsatisfactory. Here, an attempt is made to increase the NO3‒RR performance of Co3O4 via rare-earth (denoted RE) metal-induced 4f-2p-3d orbital hybridization. By introducing various single-atom RE metals (i.e., Y, La, Pr, and Sm) into the octahedral location, the 4f-2p-3d orbital hybridization can be well regulated to optimize the 3d orbital configuration of Co3O4. Consequently, optimum Pr-doped Co3O4 displays a 3.2-fold increase in activity for NO3‒RR to NH3 compared with its counterpart without Pr. Mechanistic studies combining operando experiments and theoretical calculations reveal that the Pr not only assists Co in adsorbing NO3‒ but also induces 4f-2p-3d orbital hybridization to increase the *NO adsorption strength and promote electron transfer from Co to *NO, thereby markedly boosting the rate-determining step of NO3−RR. This study provides a new pathway to improve the performance of NO3−RR to NH3 by using the f-p-d orbital hybridization.