Synergistic Ru/RuO₂ Nano-Islands and Satellite Ru-N₄ Sites for Efficient Nitrogen Photofixation via Dual Pathways

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/RuO₂ nanoparticles (NPs, as nano-islands) and densely dispersed satellite-like Ru-N₄ single-atom sites (as the sea) anchored on mesoporous carbon nitride. This photocatalyst delivers a high NO₃ ^- 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-N₄ sites and Ru NPs preferentially capture photogenerated electrons to activate N₂ and O₂, producing *N₂ and ·OH, respectively. RuO₂ NPs trap photogenerated holes to promote interfacial H₂O 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 NO₃ ^- through dual pathways: (1) direct oxidation of *NO to NO₃ ^- by ·OH radicals, (2) *NO → NO₂ oxidation by O₂ and subsequent spontaneous NO₂ → NO₃ ^-. The latter pathway dominates under O₂-enriched ambient conditions. This study provides a promising strategy for designing efficient catalysts for nitrogen photofixation.