Photoelectrochemical Study on Charge Transfer Properties of TiO2−B Nanowires with an Application as Humidity Sensors

Abstract

One-dimensional (1-D) TiO₂−B nanowires have been synthesized via a facile solvothermal route. The morphology and crystalline structures of the nanowires were characterized by using powder X-ray diffraction, low/high-resolution transmission electron microscopy, and Brunauer−Emmett−Teller methods. It is important with the calcination treatment at 350 °C to maintain 1-D morphologies of the material in the form of single-crystalline TiO₂−B nanowires. In addition, a simple method was used to study the photogenerated charge transfer and photoelectrochemical properties of the TiO₂−B nanowires in comparison with commercial TiO₂ P25 nanoparticles based on the experimental data from the electric field-effected photocurrent action spectrum and Mott−Schottky measurements. It was revealed that TiO₂−B nanostructures played an important role in the photoelectrochemical processes. The synthetic TiO₂−B nanowire electrode exhibited unique electronic properties, e.g., favorable charge-transfer ability, negative-shifted appearing flat-band potential, existence of abundant surface states or oxygen vacancies, and high-level dopant density. Moreover, the obtained TiO₂−B nanowires were found to display excellent humidity sensing abilities as functional materials in the humidity sensor application. With relative humidity increased from 5% to 95%, about one and half orders of magnitude change in resistance was observed in the TiO₂−B nanowire-based surface-type humidity sensors.