Resistive-type hydrogen gas sensor based on TiO2: A review

Owing to its high energy density and environmentally friendly nature, hydrogen has already been regarded as the ultimate energy of the 21st century and gained significant attention from the worldwide researchers. Meanwhile, there are increasing concerns about its safe use, storage and transport as, despite being colorless and odorless, after certain concentration level it becomes flammable and explosive in air. Therefore, it is imperative to develop H₂ sensors for real-time monitoring of the H₂ leakage for an early warning. This paper firstly introduces the general hydrogen gas sensing mechanism of TiO₂-based hydrogen sensors. Then we summarize and comment on the current hydrogen gas sensor based on various TiO₂ materials, which include pristine TiO₂, metal-assisted TiO₂, organic-TiO₂ composites, carbon-TiO₂ composites, MOX-TiO₂ composites and novel sensor concept with effective top-bottom electrode configuration. Finally, we briefly discuss the obstacles that TiO₂-based H₂ sensors have to overcome in the progress of the systematically practical application, possible solutions, and future research perspectives that can be focused in this area.