Resistance-based H2S gas sensors using metal oxide nanostructures: A review of recent advances

Gas sensors play an undeniable role in most fields of technology in the modern world; they are broadly used for public safety, pollution monitoring, quality control, breath analysis, smart homes and automobiles, and so on. Due to their low cost, high sensitivity, compact size, online detection, ease of use, portability, and low power consumption, metal oxide (MO) gas sensors have exceptional potential for detection of more than 150 gases. This paper reviews the current state-of-the-art H2S conductometric MO gas sensors. In the first part, the H2S sensing mechanism for MOs is presented in detail. In the next part, the H2S sensing characteristics of the different MOs are presented, focusing on strategies such as metal doping, heterojunction composites, and different morphologies that are applied to enhance their sensing characteristics. In general, CuO, ZnO, and SnO2 show the highest sensitivity to H2S; therefore, most of this review is dedicated to these oxides. In the last part, some unusual and emerging MOs for H2S sensing are presented.