Flame spray pyrolysis made Pt/TiO2 photocatalysts with ultralow platinum loading and high hydrogen production activity

Abstract

In this paper, flame spray pyrolysis (FSP) is used to synthesize Pt/TiO2 catalysts with surface-supported isolated Pt atoms through elaborate precursor/solvent formulation and flame temperature history control. It is a pivotal factor to this FSP process that there is a major distinction on saturated vapor pressure between two components (Pt species and Ti species), and thereby they exist as gas phase and particle phase at a certain temperature range, respectively. When the flame is quenched to ambient temperature with cold sheath gas, Pt species of gaseous PtO2 (being in the vapor phase above 723 K) condense into deposition state on the surface of TiO2 nanoparticles. Combined with X-ray photoelectron spectroscopy (XPS) analysis and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) detection, we identify that Pt atoms are dispersed and anchored on the catalyst surface. Single-atom Pt dispersed Pt/TiO2 catalysts can be well achieved by controlling the loading at a very low level, which offers an effective way to maximize the atom economy for surface catalysis of scarce noble metals. In this work, considering that Pt as the best co-catalyst of hydrogen evolution, the FSP-made Pt/TiO2 catalysts are tested in a photocatalysis water splitting system aiming to a simple and attractive means of renewable hydrogen production. The highest activity presents in 0.1Pt/TiO2 with 0.1% molar ratio of Pt to Ti, reaching 108.5 times of the benchmark sample from commercial flame-made TiO2 (P25). The high activity is attributed to the fact that the isolated Pt atom serves as the main active site for photocatalysis hydrogen evolution. Therefore, the performance and cost efficiency of catalysts are greatly improved by the FSP, mainly ascribed to engineering atomically dispersing Pt on the support surface.