The recent development of metal oxide heterostructures based gas sensor, their future opportunities and challenges: A review

Recently, atmospheric pollution has become a critical problem for modern society. The detection and monitoring of gases are the major problems nowadays. Metal oxides play a crucial role in the detection of different gases owing to their change in electrical or optical parameters relative to the adsorption/desorption of gas. The sensitivity and selectivity of the metal oxide-based gas sensor can be improved by the incorporation of heterostructures. The heterostructures-based gas sensor may improve the sensing performance due to their facilitating catalytic activity, increasing adsorption rate, and creating a charge carrier depletion layer that produces a larger modulation in resistance. In this article, various fabrication methods to synthesize metal-oxide-based heterostructure with different morphologies and dimensions have been reviewed. Also, different types of mechanisms that improved the gas sensing performance, have been discussed. The heterostructures have different types of structures such as mixed heterostructure, multilayered heterostructure, core-shell, decorated heterostructure, hollow heterostructure, and one-dimensional, two dimensional, or three-dimensional hierarchical heterostructures; hence improvement in important sensing parameters of the sensor can be obtained. A compositional contribution of an individual metal oxide within a composite exhibits the capability to tune the response and selectivity of the composite towards a particular gas.