Toward Rational Design of NRR Catalysts: Deciphering the Behavior of N x H y * Intermediates at the Electrocatalytic Interface

Despite extensive research on the nitrogen reduction reaction, its interfacial mechanism at the catalyst–electrolyte interface remains incompletely understood. Herein, we report theoretical studies of adsorbed N–H intermediates NxHy* (x = 1–2, y = 0–5) at the interface between N-doped graphene-supported diatomic metal catalysts and an electrolyte environment that explicitly accounts for coadsorption of hydroxyl (OH*) solvent species at dual active sites. Constant-potential calculations show that OH* coadsorption alters interfacial energetics and enables reaction pathways that differ from those obtained without OH* or from constant-charge calculations. Potential-dependent kinetics analysis identifies the preferred reaction pathways, and the principal kinetic bottlenecks are the initial hydrogenation step and desorption of adsorbed ammonia (NH3*), rather than N–N bond cleavage. Finally, the origin of catalytic activity is elucidated by potential-dependent shifts in the Fermi level and NxHy* orbital energies, with the resulting electronic reorganization providing a mechanistic basis for the potential-dependent behavior of key elementary steps.