Tackling the scaling relations in ammonia synthesis through light-driven catalysis over LiH-mediated Ru/TiN

Photothermal catalysis offers promise for ammonia synthesis under mild conditions, but its performance is constrained by intrinsic scaling relations between dinitrogen activation and subsequent hydrogenation. Here, we overcome this long-standing limitations by introducing lithium hydride (LiH) as a dynamic “nitrogen mediator” within a Ru-LiH/TiN catalyst. Under ambient pressure and illumination at 3.3 W·cm-2, the Ru-LiH/TiN catalyst achieves an unprecedented ammonia production rate of 5574.3 μmol·g-1·h-1 (equivalent to 428.8 mmol·gRu-1·h-1), representing a 31-fold increase over its thermal-catalytic counterpart and a 52-fold enhancement compared to the bare Ru/TiN photothermal catalyst. Notably, the Ru-LiH/TiN exhibits robust catalytic stability over 50 hours, a stark contrast to the rapid deactivation (< 1 hour) observed under thermal catalysis due to NHx (x=1–3) accumulation-induced poisoning. Mechanistic studies reveal the unique photothermal catalytic pathway on Ru-LiH/TiN: photo-generated hot electrons facilitate N2 activation on Ru sites, followed by nitrogen transfer to the LiH-TiN interface to form [Li-Ti-N-H] species. This process destabilizes the strong adsorption of NHx at the nitrogen vacancies of TiN. On the other hand, photoexcited LiH releases reactive hydrogen species that participate in nitrogen hydrogenation, substantially reducing its energy barrier from 0.90 to 0.22 eV. This work provides a strategy to decouple N2 dissociation from hydrogenation, enabling accelerated and stable ammonia synthesis.