Polar atom-pair catalysts for electrochemical C–N coupling

Abstract

The challenge of activating the inert dinitrogen molecule has greatly hindered the development of efficient catalysts for electrochemical C–N coupling. Herein, we propose a novel design idea of a polar B–V atom-pair catalyst (APC) embedded into two-dimensional (2D) g-CN (B–V@g-CN) for activating and polarizing the inert NN bond and accelerating the electrochemical C–N coupling process. Our work shows that B–V@g-CN is a promising electrocatalyst for the urea synthesis reaction with an ultra-low limiting potential (U_L) of −0.21 V. The synergistic side-on adsorption configuration of N₂ at the polar B–V dual-site triggers unbalanced electron transfer via a two-channel pathway, i.e., the σ donation–π backdonation of electron transfer through B–N and V–N bonds, which results in sufficient activation of the NN bond. The electronegativity difference between B and V atoms enables the polarization of non-polar N₂. Protonation of *N₂ to a *NH*NH intermediate further weakens the NN bond, which leads to a lower energy barrier for *NH*NH dissociation to 2*NH species (0.75 eV) than for the direct dissociation of *N₂ (1.45 eV). Subsequently, the coupling of CO and 2*NH species generates the key urea precursor *NHCO*NH with a low barrier of 0.45 eV. Furthermore, the B–V@g-CN APC demonstrates good thermodynamic and electrochemical stability, as well as excellent dispersibility of its dual-active sites. The construction of polar non-metal/metal APCs in this work provides a new avenue for designing high-performance catalysts in energy conversion reactions.