Extending the detection range and response of TiO2 based hydrogen sensors by surface defect engineering

With the increasing usage of hydrogen energy, the requirements for hydrogen detection technology is increasingly crucial. In addition to bringing down the working temperature, further improvement in the response and broadening the detection range of hydrogen sensors in particular are still needed. TiO2 based sensors show great promise due to their stable physical and chemical properties as well as low cost and easy fabrication, but their detection range and low concentration response requires further improvement for practical applications. Here (002) oriented rutile TiO2 thin films are prepared by a hydrothermal method followed by annealing in either air, oxygen, vacuum or H2 and the hydrogen sensing performance are evaluated. Raman results show that TiO2 thin films annealed in vacuum and hydrogen have more oxygen vacancies, while those annealed in air and oxygen have a more stoichiometric surface. Annealing in an oxygen-rich atmosphere is shown to extend the detection range of the TiO2 sensors while annealing in anaerobic atmospheres increases their response. At high hydrogen concentrations surface adsorbed O2− is the dominant factor, while at low concentrations the Schottky barrier between Pt and TiO2 is key to achieving a high response. Here we show controlling the TiO2 surface properties is essential for optimizing hydrogen detection over specific concentration ranges. We demonstrate that adjusting the annealing conditions and ambient provides a simple method for tuning the performance of room temperature operating TiO2 based hydrogen sensors.