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

Simultaneous promotion of N-2 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 N-2 adsorption and NH3 desorption, respectively. The combination of in situ characterization and DFT calculation reveals that the strong interaction between N-2 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 mu molg(-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 mu molg(-1)h(-1), respectively. This study opens an avenue for a catalytic reaction with scaling relationship.