PCS members publish article in Journal of Physical Chemistry In Situ X-ray Absorption Spectroscopy Study of the Deactivation Mechanism of a Ni-SrTiO3 Photocatalyst Slurry Active in Water Splitting

Several members of the PhotoCatalytic Synthesis group have published an article on In Situ X-ray Absorption Spectroscopy Study of the Deactivation Mechanism of a Ni-SrTiO₃ Photocatalyst Slurry Active in Water Splitting in the Journal of Catalysis, Volume 128, Issue 38.

Memet Tursun, Guido Mul, Marco Altomare [PCS] [Chemical Engineering Department], and others investigated the deactivation mechanism of a Ni-SrTiO3 photocatalyst for water splitting. They devised a liquid-phase spectroscopic cell for in situ X-ray absorption spectroscopy (XAS) in fluorescence mode to monitor changes in the Ni cocatalyst oxidation state during photocatalytic H2 generation from photocatalyst suspensions in plain water. The catalyst degradation was accelerated by high intensity UV light irradiation.

It was found that:
- Continuous exposure of the photocatalyst suspension to the X-ray beam, and simultaneously to UV irradiation, does not reveal significant changes in the Ni oxidation state.
- However, by minimizing the X-ray exposure, it was observed thatUV light-induced composition and structural changes of the Ni-SrTiO3 photocatalyst: In particular, they reveal oxidation and reconstruction of the metallic Ni phase, within a few hours of high intensity UV illumination, to Ni(II) species, namely, NiO and Ni(OH)2 solid phases, which cause a gradual loss of activity.
- Given the concurrent decrease in H2 evolution rate, it is infered that metallic nickel (Ni(0)) is the cocatalyst phase active for H2 generation.
-The dissolution of Ni in the form of solvated Ni(II) species as well as photodeposition of solvated Ni(II) ions (via photoreduction) onto the photocatalyst surface was ruled out.

The findings shed light on the root cause of the poor stability of Ni-SrTiO3 water splitting photocatalysts and can help design more stable photocatalyst materials.