Fabrication of Heterostructured TiO2 Nanorods for Enhanced Solar Water Splitting

Abstract

As global population growth and energy demand keep to ramp up, green and sustainable energy production with environmental concerns has become as one of the most serious challenges over the past years. Photocatalysis is a promising approach and can be regarded as a green and efficient energy source. Up to date, TiO2 has been demonstrated as one of the most used photocatalytic materials for photoelectrochemical (PEC) water splitting due to its low-cost, non-toxicity, high chemical and physical stabilities, and the excellent photocatalytic properties. However, TiO2 exhibits drawbacks such as high rate of electron-hole recombination and wide band gap, which means only 4% of the solar spectrum can be absorbed to promote charge carrier generation in the material. In order to overcome these limitations, various strategies have been developed to improve its photocatalytic activity toward the solar-driven water splitting including nanostructured morphology engineering, and construction of heterostructures. One-dimensional (1D), 2D TiO2 nanostructures exhibit unique PEC properties due to the faster charges transfer, and lower charges recombination rate. Oxynitrides are class of semiconducting materials that exhibits a good photocatalytic activity. However, the fast rate of the charges recombination and the bandgap edges can limit their usage as an efficient photocatalysts. Fabrication of heterostructure can be efficient approach to enhance the PEC water splitting. The novel LaMo(ON)x/TiO2 heterostructure (is not reported in the literature before) was synthesized via two-step procedure. In the first step, TiO2 nanorods (NRs) were prepared using hydrothermal synthesis. After that, LaMo(ON)x was deposited on the as-fabricated TiO2 NRs by electrophoretic deposition. The characterization techniques signified that heterojunction structure of LaMo(ON)x deposited on TiO2 NRs arrays were formed. The various characterization techniques revealed that the heterojunction preserved the nanorods morphology of pristine TiO2 NRs. The fabricated heterostructure was characterized using scanning electron microscope (SEM), X-Ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The photoelectrochemical measurements showed more than doubled enhancement in the photocurrent density of the heterostructure compared to the pristine TiO2 NRs. This was attributed to the efficient electron-hole (e--h+) charge separation at the interface of heterojunction which increases the life time of the photoinduced e--h+ pairs, and enhance the PEC activity.