Possible Electrocatalytic N–N Coupling for the Green Synthesis of Nitramide (NH₂NO₂) via Nitrate Reduction Reaction on Nitrogen-Doped Graphene Supported Dual-Nickel Atoms (Ni₂–NC)

The conversion and removal of nitrate are critical challenges for restoring the globally perturbed nitrogen cycle. However, current catalytic systems predominantly yield ammonia (NH₃), and strategies for constructing high-value N–N coupling products remain largely unexplored. In this work, first-principles calculations were employed to systematically investigate dual-atom catalysts (DACs, M₂-NC) anchored on nitrogen-doped graphene, evaluating their structural stability and reaction selectivity. Nine dual-atom systems with potential NO₃RR activity were identified, including Cr, Mn, Fe, Co, Ni, Zn, Ru, Rh, and Ir. Among these catalysts, Ni₂–NC exhibits a reaction selectivity distinct from the conventional NH₃ pathway and is the only system capable of selectively producing the N–N coupling product nitramide (NH₂NO₂). It contains both a reductive amino group and a high oxidation state nitro group and is a valuable platform molecule with important applications in energetic materials. Electronic-structure analyses based on PDOS and pCOHP reveal that the relatively weaker Ni–N bonding strength underlies this selectivity by simultaneously enabling N–N coupling, nitro group protection, and desorption of the final NH₂NO₂ product. This study demonstrates that rational design of dual-metal active sites can redirect NO₃RR from traditional NH₃ synthesis toward high-value N–N coupling products. These findings provide new theoretical insights and design principles for developing next-generation catalysts for the electrochemical synthesis of specialty nitrogen chemicals.