Hydrothermal temperature-controlled size and distribution of CeO2 nanoparticles over TiO2 nanorods: Heterojunction characteristics and photoelectrochemical performance

Abstract

The search for a suitable photoelectrode material remains the most challenging problem in photoelectrochemical applications. Metal oxides are favorable for their chemical stability under an aqueous environment. This work presents size and distribution controlled CeO2 nanoparticles on TiO2 nanorod arrays achieved through a systematic variation of the hydrothermal process temperature. In a two-step hydrothermal process, single crystalline TiO2 nanorods are first grown on fluorine doped tin oxide (FTO) coated glass substrate using titanium (IV) butoxide precursor followed by a treatment with cerium nitrate to obtain CeO2 nanoparticles over TiO2. Variation of the hydrothermal process temperature in the second step from 80 °C to 150 °C results in CeO2 nanoparticles with a systematic variation of size and distribution over TiO2 nanorods. We demonstrate that an effective heterojunction between the CeO2 nanoparticles and TiO2 nanorod forms at a process temperature of 120 °C, which is manifested by improved photoelectrochemical performance. The CeO2–TiO2 heterojunction photoanode shows a photocurrent density of 3.77 mA/cm2 (at 1.23 V vs. RHE) in 1 M KOH solution under one Sun (100 mW/cm2) illumination, which is approximately three times higher than that of bare TiO2 nanorod arrays. Further, Applied Bias Photon-to-current Efficiency (ABPE) is estimated to be 2.01%. Diffuse Reflectance Spectra (DRS) shows a redshift of ~0.1 eV in CeO2–TiO2 heterojunction that signifies the contribution of CeO2 towards visible light absorption. The Electrochemical Impedance Spectroscopy (EIS) shows a lower value for charge transfer resistance in samples processed at 120 °C. The superior photoelectrochemical performance of CeO2–TiO2 heterojunction is attributed to the collective contributions of visible light absorption and efficient charge transfer at the CeO2–TiO2 interface.