High-Performance Gas Sensors Based on Nanostructured Metal Oxide Heterojunctions

Nanostructured metal oxide heterojunctions have been successfully assembled to be gas sensors with high sensor responses and fast response/recovery speeds, which was attributed to their advantages of the high specific surface areas and the adjustable highness of the potential barriers. A number of strategies have been used to assemble the nanostructured heterojunctions in the sensing materials, such as mixing the sensing nanopowders, preparing the multilayer films, synthesizing the core-shell or the decorated nanomaterials, and so on. The gas sensors based on the designed heterojunctions with the n–n, n–p, p–n, p–p, n–p–n, or p–n–p structures have been widely studied to improve their sensing performances to the typical reducing/oxidizing gases, which was confirmed by the researches on the most-studied materials including ZnO, SnO2, TiO2, WO3, In2O3, Fe2O3, MoO3, Co3O4, and CuO. Their enhanced mechanisms in the gas-sensing performances were mainly attributed to the essential improvement in the modification of band structures at the nanojunctions composed of the studied metal oxides. According to the overview of recent developments, the challenges and outlooks of the gas sensors based on the heterojunctions were also discussed. Our review further indicated that the materials based on the metal oxide heterostructures could be the promising candidates to exhibit outstanding gas-sensing performances.