Ronglan Pan, Shuai Cheng, Heng Guo, Jili Yuan, Z K Li
ABSTRACT Solar‐driven nitrogen oxidation reactions for nitrate production are a promising alternative to the traditional energy‐intensive nitrate synthesis industry. Nevertheless, its performance is fundamentally hampered by inefficient charge carrier utilization, the intrinsic inertness of nitrogen molecules, and insufficient mechanistic insights into the reaction pathway. Here, we report a synergistic nano‐island/sea catalyst composed of Ru/RuO 2 nanoparticles (NPs, as nano‐islands) and densely dispersed satellite‐like Ru−N 4 single‐atom sites (as the sea) anchored on mesoporous carbon nitride. This photocatalyst delivers a high NO 3 − production rate of 14.34 mg g cat −1 h −1 , together with an apparent quantum yield of 5.2% at 420 nm. The Ru−N 4 sites and Ru NPs preferentially capture photogenerated electrons to activate N 2 and O 2 , producing *N 2 and ·OH, respectively. RuO 2 NPs trap photogenerated holes to promote interfacial H 2 O dissociation, generating additional ·OH radicals. We further revealed that ·OH facilitates the rapid cleavage of the N≡N bond to form *NO intermediates, which are subsequently converted to NO 3 − through dual pathways: (1) direct oxidation of *NO to NO 3 − by ·OH radicals, (2) *NO → NO 2 oxidation by O 2 and subsequent spontaneous NO 2 → NO 3 − . The latter pathway dominates under O 2 ‐enriched ambient conditions. This study provides a promising strategy for designing efficient catalysts for nitrogen photofixation.