Abstract
Hydrogen is one of the most important gases that can potentially replace fossil fuels in the future. Nevertheless, it is highly explosive, and its leakage should be detected by reliable gas sensors for safe operation during storage and usage. Most hydrogen gas sensors operate at high temperatures, which introduces the risk of hydrogen explosion. Gasochromic WO3 sensors work based on changes in their optical properties and color variation when exposed to hydrogen gas. They can work at low or room temperatures and, therefore, are good candidates for the detection of hydrogen leakage with low risk of explosion. Once their morphology and chemical composition are carefully designed, they can be used for the realization of sensitive, selective, low-cost, and flexible hydrogen sensors. In this review, for the first time, we discuss different aspects of gasochromic WO3 gas sensor-based hydrogen detection. Pristine, heterojunction, and noble metal-decorated WO3 nanostructures are discussed for the detection of hydrogen gas in terms of changes in their optical properties or visible color. This review is expected to provide a good background for research work in the field of gas sensors.
Highlights
Hydrogen is one of the most important gases that can potentially replace fossil fuels in the future
Gasochromic sensors have the advantage of working at low temperatures, which can significantly decrease the risk of hydrogen explosion
There are four models related to the gasochromic coloration of WO3 sensors, namely charge transfer of electrons between (i) W6+ /W5+ states, (ii) W5+ /W4+ states, (iii) W6+ /W5+ and W5+ /W4+
Summary
Hydrogen is a gas with no color, odor, or taste and cannot be detected by human senses [1,2]. Several gas sensors based on different mechanisms have been reported for sensing hydrogen, including fiber-optic [6], catalytic [7], electrochemical [8], acoustic [9], resistive [10], thermoelectric [11], and gasochromic gas sensors [12] Each of these sensors has its own merits and shortages [13]. Resistive gas sensors are inexpensive, simple in design and operation, highly responsive, and exhibit good stability [14,15,16] They can only work efficiently at high temperatures [17], which increases the risk of hydrogen explosion during detection. Inouye et al [33] reported crystal structure transition from in RF-sputtered WO3 films upon exposure to hydrogen gas.
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