Influence of Ce doping on morphology, crystallinity and photoelectrochemical charge transfer characteristics of TiO<inf>2</inf> nanorod arrays grown on conductive glass substrate

Doping of rare earth elements into TiO2 nanorods allows tailoring of the electrical and optical properties, which in turn, modifies the photoelectrochemical behavior. This study presents hydrothermal synthesis of Ce doped TiO2 nanorod arrays on FTO coated glass substrate. XRD pattern confirms the rutile phase in both pristine and Ce doped samples; however, Ce doping results in an enhancement of peak intensity compared to that of pristine TiO2 nanorods. FESEM shows a significant change in the growth rate and the surface morphology of the nanorods with an apparent clustering of grains caused by Ce doping. HRTEM of the Ce doped sample shows regions of different crystallographic orientations. EDX data also confirms a uniform presence of Ce in the TiO2 nanorods. The optical absorption spectra show a slight redshift in the band gap from 3.08 eV for the pristine sample to 3.02 eV for the Ce doped nanorods that is attributed to the presence of shallow energy states within the band gap. Photoelectrochemical measurements indicate a negative shift in the flat-band potential from −0.80 V (for pristine) to −0.94 V (for Ce doped nanorods), resulting in a lower charge transfer resistance at the semiconductor/electrolyte interface, which is also corroborated by impedance spectroscopy. Although there is a reduction in the charge density, Ce doping facilitates better interfacial charge transport at the semiconductor/electrolyte interface.