Comprehensively improved hydrogen sensing performance via constructing the facets homojunction in rutile TiO2 hierarchical structure

Development of advanced hydrogen sensors with high sensitivity, fast response speed, and long term stability is essential for safe utilization of hydrogen energy. In this work, a gas sensor with TiO2 hierarchical trunk/branch structure as the sensing material is prepared by hydrothermal and immersion method. The experimental results show that facet homojunctions are formed by the facet contacts at the trunk/branch interfaces. The optimized sensor works at room temperature with an excellent sensing performance of S= 31.6% when exposed to 1 ppm H2 concentration and a fast response and recovery time of about 10 s. The sensor also shows long-term stability, high sensing gas selectivity and high humidity resistance. It is found that the facet homojunction in the hierarchical structure of TiO2 results in a significantly increased density of the charged oxygen ions absorbed on the surface and an enhanced effective barrier height, which are responsible for the much promoted sensing performance. This work provides a new way for designing gas sensors with highly commercial competitiveness.