Active Hydrogen-Switchable Dynamic Oxygen Vacancies in MoO_3–x upon Ru Nanoparticle Decoration for Boosting Photocatalytic Ammonia Synthesis Performance

Simultaneous promotion of N₂ adsorption and NH₃ desorption, which is referred to as breaking the scaling relationship, is a major challenge in the photocatalytic ammonia synthesis reaction. Herein, we have successfully developed an active hydrogen (H*)-switchable dynamic oxygen vacancy (OV) evolution strategy for solving this problem on MoO_3–x decorated by Ru nanoparticles (Ru/MoO_3–x). In this strategy, H* drives the cyclic dynamic evolution of the OVs between the initial state Ru/MoO_3–x and intermediate state Ru/MoO_3–xN_y, which exhibit strong capabilities for N₂ adsorption and NH₃ desorption, respectively. The combination of in situ characterization and DFT calculation reveals that the strong interaction between N₂ and OVs in Ru/MoO_3–x induces the spontaneous formation of Ru/MoO_3–xN_y, whereas this nitrogen species filling the OVs promotes the H* spillover from Ru to MoO_3–x, thereby accelerating the hydrogenation of lattice N and the desorption of NH₃. As a result, the 6.5 wt % Ru/MoO_3–x achieves an ammonia production rate of 192.38 μmol·g^–1·h^–1, 2.68-fold higher than that of pristine MoO_3–x. Besides, nitrate reduction and nitric oxide reduction to synthesize NH₃ further verified this strategy, which exhibited a performance of 370 and 220 μmol·g^–1·h^–1, respectively. This study opens an avenue for a catalytic reaction with scaling relationship.