Light-Driven Ammonia Synthesis Beyond Scaling Relations over LiH-Mediated Ru/TiN

Photothermal catalysis offers a promising route for ammonia synthesis under mild conditions, yet its performance is fundamentally limited by intrinsic scaling relations between dinitrogen activation and subsequent hydrogenation steps. Here, we overcome this longstanding constraint by introducing lithium hydride (LiH) as a dynamic “nitrogen mediator” in a Ru-LiH/TiN catalyst. Under ambient pressure and 3.3 W·cm-2 light irradiation, the Ru-LiH/TiN achieves an unprecedented ammonia production rate of 5574.3 μmol·g-1·h-1 (428.8 mmol·gRu-1·h-1), representing a 52-fold enhancement over the LiH-free Ru/TiN benchmark under illumination and 30.5 times higher than its thermal performance at 400 °C. Notably, Ru-LiH/TiN exhibits exceptional stability over 50 hours of continuous photothermal operation, in sharp contrast to its rapid deactivation observed under purely thermal conditions due to NHx poisoning. Mechanistic studies reveal that light excitation unlocks a distinct pathway: photo-generated hot electrons promote N2 activation on Ru, while simultaneously enabling LiH to act as a redox-active mediator that facilitates the hydrogenation of nitrogen intermediates (NHx, x=1-3) into NH3. This synergistic mechanism decouples N2 dissociation from hydrogenation, thereby circumventing the conventional scaling relations that limit thermal catalysis. Moreover, the light-driven process enhances NH3 desorption, collectively ensuring high activity and long-term stability under mild conditions.