Early-Stage Deactivation of Platinum-Loaded TiO₂ Using In Situ Photodeposition during Photocatalytic Hydrogen Evolution

Abstract

This work unravels a sudden deactivation of Pt/TiO 2 (P25) during the initial stages of photocatalytic H 2 evolution from aqueous solution that, until now, has gone unnoticed, using a unique combination of in situ photodeposition of Pt with an on-line gas detector system. Utilizing a set of techniques, including highresolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), UV-visible diffuse reflectance spectroscopy (DRS-UV-vis), X-ray powder diffraction (XRD), Raman spectroscopy, and physisorption, we were able to attribute this deactivation to a shift in mechanism, accompanied by an increase in CO concentration. Key to this phenomenon is the ratio of Pt atoms to oxygen vacancies, which were created through ultrasonic pretreatment and in situ UV irradiation in the bulk and surface, respectively. We also observed a potential additional contribution to the deactivation by encapsulation of the Pt nanoparticles, indicating that strong metal−support interaction (SMSI) may indeed happen in aqueous and ambient conditions. Furthermore, we encourage implementing the concept of a "dynamic" catalyst to photochemistry that opens up a new approach toward understanding the complex mechanisms and kinetics in heterogeneous photocatalysis.

Ordered Mesoporous TiO2 Gyroids: Effects of Pore Architecture and Nb‐Doping on Photocatalytic Hydrogen Evolution under UV and Visible Irradiation

“…Note that the initial activity for P25 was considerably higher but had dropped after minutes, leading to the values reported in literature. This recently discovered early‐stage deactivation is supposed to originate from a complex interplay of UV‐induced oxygen vacancies and the Pt cocatalyst active sites, which induces a change in reaction mechanism associated with CO formation . Importantly, a calcination treatment prior to the reaction to anneal oxygen vacancies can minimize this deactivation process, thus highlighting the impact of defects.…”

Photocatalytic overall water splitting using modified SrTiO3

“…This certainly highlights that post-catalysis-characterization is required to fully describe the composition of a working photocatalyst. Haselmann et al 43 recently reported for Pt-loaded TiO2 an early stage deactivation after ultrasound pre-treatment. The fast deactivation (within approximately one hour of illumination) was primarily observed for composites with low Pt-loading ( Figure 6.3A).…”

“…In contrast, some metal oxides (e.g. IrOx, MnOx, and CoOx) [40][41][42][43] and metal hydroxides (e.g. NiOOH, FeOOH) 44,45 often serve as the water oxidation catalysts.…”

“…Such strong metal-support interactions (SMSI) are frequently reported in heterogeneous catalysis, however, for heterogeneous photocatalysis the phenomenon is hardly discussed. 43,44 Finally, it is worth noting that Haselmann et al 43 compared low (= deactivating) and high (= non-deactivating) Pt loading using similar Pt particle size distributions and Pt leaching or particle migration and growth were excluded as causes of deactivation.…”

“…Deactivation is observed at low Pt loadings independent of the pretreatment with ultrasound (US) (e.g., 0.25 wt %), but not at high Pt loadings (≥0.75 wt %). Reproduced from ref43 . Copyright 2017 American Chemical Society.…”