Precise location and regulation of active sites for highly efficient photocatalytic synthesis of ammonia by facet-dependent BiVO4 single crystals

Abstract

Based on the characterizations of photo-deposition experiment, environmental transmission electron microscopy (ETEM) and scanning fluorescence X-ray microscopy (SFXM) for the in-situ photocatalytic nitrogen reduction reaction (pNRR) on different facets as well as theoretical calculation, we confirmed that the cycle of oxygen vacancy-V4+/V5+ (OV-V4+/V5+) on (040) facet is the exact active site for the photocatalytic NRR (pNRR) by bismuth vanadate (BiVO4) single crystal. V4+ plays the role of chemisorption of N2, V5+ is electron transfer bridge, and the photogenerated electrons trapped in OV provide the driving force for ammonia synthesis. (110) facet has only V5+, which can not produce the start-up step of chemisorption of N2, so it is the inert facet of pNRR. Thus, NRR activity increases linearly with the increase of (040)/(110) facet ratio by adjusting the active sites on (040) facet, and the highest activity can reach 103.4 μmol g−1 h−1 without sacrifice reagent. Based on the discussion of real active sites and their transformation in photocatalytic NRR by facet-dependent BiVO4, we not only analyze the essential reason why exposing specific facets can greatly improve the photocatalytic activity, but also put forward a new viewpoint on the activity control of photocatalytic ammonia synthesis.