Solid-state gas sensors: sensing mechanisms and materials

Rapid population growth and industrial development are the major reasons for rapid consumption of our natural resources and increase in pollution. Monitoring of such pollutants and their control is peremptory to avoid any kind of environmental disasters. For this purpose, conventional analytical instruments were used till date, but as per their size, cost, processing and measurement time point of view, they are not the suitable candidates to be used on the forefront. In recent years, with the advancements in the field of material sciences, improvements in the processing and miniaturization techniques, solid-state gas sensors are presenting themselves as an effective alternative for the targeted functionalities in real time. Though they are not capable of giving such precise analysis like analytic instruments, they prove themselves to be the next generation state-of-the-art gas sensors when compared with respect to their cost, compactness, robustness, versatility, etc. The current review article is based on few chemical sensors that measure the concentration of targeted gas using ‘solid state platforms’. Specifically, this paper concentrates on electrochemical-, capacitance- and heterojunction-based solid state sensors explaining their detection principle, mechanism and structure. Over the past few years, the growth and advancement in the area of porous metal oxide (PMO)-based sensors has shown great potential in the field of gas sensing. Owing to the current developments in synthesis methods, numerous porous metal oxides with well-defined surface modification are possible. Therefore, this review article summarizes the different PMO materials employed to enhance the unique properties like increasing surface area, tunable pore sizes, high pore volume, etc. to address the advancements in the field of solid-state gas sensors.