Tackling the Scaling Relations in Ammonia Synthesis through Light-Driven Catalysis over LiH-Mediated Ru/TiN.

Photothermal catalysis offers a promising pathway for sustainable ammonia synthesis under mild conditions. However, its performance is constrained by intrinsic scaling relations between dinitrogen activation and subsequent hydrogenation steps. To overcome this long-standing bottleneck, we design a Ru-LiH/TiN catalyst that enables a light-driven reaction cascade, wherein lithium hydride (LiH) serves as a dynamic "nitrogen mediator". Under ambient pressure and illumination at 3.3 W·cm-2, the catalyst achieves an unprecedented NH3 production rate of 5574.3 μmol·g-1·h-1 (equivalent to 428.8 mmol·gRu -1·h-1), representing a 31-fold improvement over its thermal-catalytic counterpart and a 52-fold enhancement relative to Ru/TiN. Notably, the Ru-LiH/TiN exhibits robust catalytic stability over 50 h, in stark contrast to the rapid deactivation (<1 h) commonly observed in thermal catalysis due to NH x (x = 1-3) accumulation-induced adsorbate poisoning. Mechanistic studies reveal a relayed photothermal catalysis mechanism: photogenerated hot electrons facilitate N2 activation on Ru sites, followed by nitrogen transfer to the LiH-TiN interface to form destabilized [Li-Ti-N-H] intermediates; subsequently, photoexcited LiH liberates reactive hydrogen species that participate in nitrogen hydrogenation. This work presents a new strategy that simultaneously weakens the strong adsorption of NH x on the catalyst and enables efficient NH3 production under mild conditions.