Mechanism Insight into Protonated N≡N Bond Breaking Promoting C–N Coupling on Synergistic Hybrid Dual-Atom Catalysts of Metal–Boron Anchored on g-C ₂ N for Efficient Urea Electrosynthesis

A design strategy of metal-boron (M-B) hybrid dual-atom catalysts (HDACs) anchored on g-C₂N (M-B@C₂N) and a mechanism of protonated N≡N bond breaking promoting C-N coupling has been proposed for electrocatalytic reduction of N₂ to urea with CO (NCR). Using density functional theory calculations, the stability, activity, and selectivity of 13 M-B@C₂N HDACs are systematically evaluated. V-B@C₂N has been screened as an excellent HDAC using a four-step screening strategy. N₂ can be adsorbed on V and B atoms of V-B@C₂N with a side-on configuration, and it can be activated by reversible dynamic evolution of the interatomic distance between the V and B atoms and by charge transport differences between the two N atoms and V-B sites. The inert N≡N bond is gradually weakened by two successive protonation steps until broken to form 2*NH with a kinetic energy barrier of 0.72 eV, further promoting two-step C-N coupling of 2*NH and *CO coadsorbed on V-B sites to form *NHCONH with kinetic energy barriers of 0.08 and 0.03 eV. V-B@C₂N not only exhibits excellent activity and selectivity for urea electrosynthesis with a limiting potential of only -0.44 V but also suppresses the competitive N₂ reduction (NRR) and hydrogen evolution reactions.