“…Therefore, hydrogen sensors are crucially needed to detect any hydrogen leakage; as well as, precisely measure the hydrogen concentration in the hydrogen fuel cell system during all stages of hydrogen production, transportation and storage [6,7] Page 3 of 34 A c c e p t e d M a n u s c r i p t 3 Many types of hydrogen sensors, such as, electrochemical [8], optical [9], catalytic [10,11], thermally conductive [12] and metal oxide semiconductor sensors [13,14], have been studied and commercialized. Metal oxide gas sensors have been widely used for hydrogen gas sensor applications because of their high sensitivity, fast response, long lifespan and feasibility to be miniaturized for use in the microelectronic devices.…”