Microstructural Study on Heterostructures of TiO2 and Two-Dimensional Transition Metal Disulfides for Solar Water Splitting

Abstract

In order to achieve the superior performance photoelectrode, TiO2 nanorods were synthesized on F doped SnO2 (FTO) substrates

TiO2 single crystal with (001), (101), and (110) substrates

and p-type Si substrates by the hydrothermal method. The growth mechanism of TiO2 nanorods is proposed by the hydrothermal processes with various synthesis condition, such as the temperature and time, the concentration of the precursor and HCl, and the growth on the diverse substrates. During the hydrothermal synthesis, the morphology of the TiO2 nanorods are strongly depends on the surface energy of each lattice plane of the TiO2 and the chemistry of the synthesis solution. Most of all, those two parameters can be controlled by the concentration of HCl in the solution simultaneously. The morphological evolutions of the TiO2 nanorods with the HCl concentration were confirmed. In terms of the formation of the TiO2 nanorods, the rod shape can be constructed by the generation of four TiO2 {110} planes, which exhibit the lowest surface energy, and preferential growth on {001} planes, which possess the highest surface energy, resulting in growth along the [001] direction. It has been revealed that the HCl concentration is the most effective parameter to control the morphology of the TiO2 nanorods. The {110} planes of the TiO2 nanorods were stabilized by the selectively absorption of the Cl- ions on the {110} planes, resulting in the preferential growth along the [001] direction. Furthermore, TiO2 nanorods were grown on the p-Si by the hydrothermal method to reduce the disadvantages of p-Si as a photocathode on the photocorrosion and high reflectance. The photoelectrochemical (PEC) performances were effectively enhanced. It can be elucidated that the hydrothermally grown TiO2 nanorods can act both as the passivation and the antireflection layer. In addition, MoS¬2, which is known as one of the 2D-TMD materials with excellent photocatalytic properties, was decorated on TiO¬2 nanorods by the hydrothermal synthesis. Both the photocurrent and overpotential were further enhanced after the MoS2 decoration. By the high resolution-transmission electron microscope (HR-TEM), the fast furrier transformation (FFT), and X-ray photoelectron spectroscopy (XPS) analysis, the MoS2 synthesized by the hydrothermal method was confirmed. The formation of the MoS2/TiO2 heterojunction was verified by ultraviolet photoemission spectroscopy (UPS) analysis.