Impact of crystalline core/amorphous shell structured black TiO2 nanoparticles on photoelectrochemical water splitting

Abstract

This work examined the influence of the annealing temperature on the preparation of crystalline core/amorphous shell structured black TiO2 nanoparticles in a vacuum. As the annealing temperature was increased from 200 to 500 °C, the visible light absorption increased, and the bandgap of the black TiO2 nanoparticles narrowed. The formation of oxygen vacancies was revealed by estimating the relative portion of Ti–O and Ti–OH species by XPS analysis. The growth of amorphous shell on the crystalline core of the black TiO2 nanoparticles was demonstrated by TEM micrographs. The photocurrent density was enhanced greatly by altering the band edge positions of valence and conduction bands to form a crystalline core/amorphous shell structure. The enhancement was ascribed to the efficient separation of photoinduced charge carriers. A possible mechanism for the enhanced photoelectrochemical water splitting activity was proposed based on the crystalline core/amorphous shell structure of the black TiO2 nanoparticles.