Hierarchical NiO/TiO2 heterojuntion-based conductometric hydrogen sensor with anti-CO-interference

Constructing a heterojunction is an effective way to improve the gas sensing properties of metal oxide semiconductors. In this work, a hydrogen sensor containing hierarchical and porous NiO/TiO2 heterojunction bilayer structure was designed. The top layer is formed by the NiO nanowalls grown along the [220] direction with exposed (111) facets, and the bottom layer is formed by the [002] oriented TiO2 nanorod arrays. The exposed high energy crystal surfaces of NiO and TiO2, together with the adapted surface depletion region, induced by the formation of the heterojunction, enable the hydrogen sensor to have both a wide detection range and a much higher response to hydrogen than single layer materials. With the optimized size of the pores existing between the walls, the hydrogen sensor shows excellent prevention to interference from CO. Both the gas diffusion regulated by the porous structure and the surface interaction between H2/CO and O2- controlled by the heterojunction barrier contribute to the distinctive detection of H2 and CO at room temperature (25 ℃ ± 2 ℃).