Enhanced electrocatalytic activity for nitrobenzene reduction via p–d orbital hybridization in single- and dual-atom catalysis

Aniline (PhNH₂) is usually prepared via the hydrogenation of nitrobenzene (PhNO₂) under high-temperature and high-pressure conditions. Consequently, the development of electrocatalytic PhNO₂ hydrogenation catalysts with high activity under mild conditions is of great significance for the green preparation of PhNH₂ and for electrochemical energy storage applications. In this paper, a series of single-atom catalysts and the corresponding dual-atom catalysts were designed to explore the electrocatalytic reduction mechanism of PhNO₂ and to screen the optimal catalyst. First, 14 types of transition-metal single-atom catalysts (SACs; Co, Cu, Ni, Fe, Pd, Au, Ag, Cd, Ir, Mo, Rh, Mn, Zn, and Cr) were supported on nitrogen-doped graphene to theoretically screen their electrocatalytic performance for PhNO₂ hydrogenation using density functional theory (DFT). Among these, the Co SAC showed the highest catalytic activity and selectivity. Second, 10 kinds of N-doped graphene-supported Co-M-N₆V₄-G dual-atom catalysts [M = Al, Ga, Ge, In, Sn, Sb, Tl, Pb, Bi, and Co] were designed to explore the synergistic effect of the diatomic sites. The screened Co-Bi-N₆V₄-G catalyst exhibited the best catalytic activity and selectivity based on structural stability, free energy diagrams, limiting voltage, and the hydrogen evolution reaction. Third, electronic structure analysis of the dual-atom catalyst showed that the improved performance of the catalyst is due to the regulation of the interaction between nitrobenzene and the catalyst via the p-d orbital hybridization in Co-Bi-N₆V₄-G. This study provides a new theoretical method for the design of dual-atom catalysts at the atomic orbital level.