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In Situ X-ray Absorption Spectroscopy Study of the Deactivation Mechanism of a Ni-SrTiO3 Photocatalyst Slurry Active in Water Splitting

Year: 2024

Type: article

Abstract: High Resolution Image Download MS PowerPoint Slide We used in situ X-ray absorption spectroscopy (XAS) to investigate the composition–performance correlation of Ni-SrTiO 3 photocatalysts active for water splitting. After preparation and exposure to ambient conditions, the Ni particles on SrTiO 3 consist of Ni(0) and Ni(II) phases, with a 4:1 at % ratio, in a metal/oxide core/shell configuration, as confirmed by XPS and TEM-EDX. In situ XAS experiments using an aqueous slurry of the Ni-SrTiO 3 photocatalyst and simultaneous continuous exposure to 365 nm light with a power density of 100 mW cm –2 and the X-rays do not reveal significant changes in oxidation state of the Ni particles. Contrarily, when the X-rays are discontinuously applied, UV excitation leads to oxidation of a significant fraction of Ni(0) to Ni(II), specifically to NiO and Ni(OH) 2 phases, along with cocatalyst restructuring. Ni dissolution or oxidation to higher valence states (e.g., Ni(III)) was not observed. The UV light-induced oxidation of Ni(0) causes the hydrogen evolution rate to drop to similar rates as observed for pristine SrTiO 3, suggesting that Ni(0) is the active phase for H 2 generation. Our results underscore the importance of assessing the effects of (continuous) X-ray exposure to (photo)catalyst-containing aqueous slurries during in situ XAS experiments, which can significantly influence the observation of compositional and structural changes in the (photo)catalysts. We ascribe this to X-ray induced water photolysis and formation of free electrons, which in this study quench SrTiO 3 photoholes and prevent Ni oxidation.

Source: The Journal of Physical Chemistry C

DOI: 10.1021/acs.jpcc.4c04688