Gas sensing oxide materials and methods - past, present and future

Metal oxides in different length scales have been used as sensing materials for designing gas sensors for several years. A number of sensor architectures have been explored for developing selective gas sensors that are capable of discriminating between reducing and oxidising gases as well as amongst the gases that are either reducing or oxidising. There is an immense drive towards developing highly selective gas sensors for continuous environmental monitoring and in-line process control in both benign and hostile conditions. Some of the desirable essential features of a typical gas sensor are (1) the ability to discriminate between gases in a real mixture of gases at all temperatures, (2) fast response, (3) rapid recovery, (4) high sensitivity, (5) size, (6) manufacturability, (7) cost effectiveness, (8) signal reproducibility, (9) robustness of signal, (10) compatibility with data logging system and (11) wireless communication. Many of these aspects strongly depend on the synthetic chemistry, crystal structure, film thickness, particle size, porosity, morphology, composition and catalytic properties of the sensing material.This paper will attempt to illustrate how gas sensors research has evolved over the number of years with the advancement in physics and chemistry of materials and what does the future holds for the technology.