Active Hydrogen-Switchable Dynamic Oxygen Vacancies in MoO3–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 MoO3–x decorated by Ru nanoparticles (Ru/MoO3–x). In this strategy, H* drives the cyclic dynamic evolution of the OVs between the initial state Ru/MoO3–x and intermediate state Ru/MoO3–xNy, 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/MoO3–x induces the spontaneous formation of Ru/MoO3–xNy, whereas this nitrogen species filling the OVs promotes the H* spillover from Ru to MoO3–x, thereby accelerating the hydrogenation of lattice N and the desorption of NH3. As a result, the 6.5 wt % Ru/MoO3–x achieves an ammonia production rate of 192.38 μmol·g–1·h–1, 2.68-fold higher than that of pristine MoO3–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.