Effect of seed layers on TiO2 nanorod growth on FTO for solar hydrogen generation

Abstract

Rutile titanium dioxide (TiO2) nanorods with an average length of 1–2 μm were grown vertically on fluorine-doped tin oxide (FTO, F:SnO2) alone and on seed layers/FTO using a hydrothermal method. The crystallographic microstructures and photoelectrochemical properties of the nanorods were then compared. Analysis of the microstructures shows that the nanorods on the seed layers were grown mainly in the [002] crystallographic orientation with (110) side planes. However, the nanorods grown directly on the FTO had both [101] and [002] orientations. Photocurrent densities measured for the nanorods primarily grown in the [002] orientation were larger. However, their incident photon to current efficiency (IPCE) and applied bias photon to current efficiency (ABPE) were lower. Furthermore, transient time measurements under a constant bias and pulsed light irradiation reveal that the charge carrier recombination rate in the nanorods on the seed layers was faster. Hydrogen was generated in quantities over 1000 μmol/cm2min for the TiO2 nanorod/FTO and 600 μmol/cm2min for the TiO2 nanorod/seed layer/FTO under white light irradiation. While the TiO2 nanorods grown on seed layers showed superior photocatalytic properties, resulting from their efficient light absorption in the (110) side planes having a high surface energy, the crystal defects in the seed layers caused a higher recombination rate during the charge transfer process.