Sensing characteristics of an optical fiber sensor for hydrogen leak

A fiber-optic hydrogen gas sensor using catalyst-supported tungsten trioxide (WO3) was characterized. This sensor utilizes the absorption of the evanescent field interaction in the clad of WO3 thin film which was prepared by sol–gel process, coated on a silica core. The sensor using platinic acid as precursor and calcined at 500 °C showed fast response to hydrogen. The sensitivity was quite high even at room temperature. More than 75% reduction in optical power propagating through the fiber was attained by the exposure to 1 vol.% H2/99 vol.% N2. This resulted from the color change in cladding WO3 region with the formation of tungsten bronze. The recovery of the sensor was achieved not in inert but in oxidizing atmosphere. The humidity strongly influenced the sensor responses. In both processes of the response to hydrogen and recovery with air, the reaction rate was accelerated by humidity. The sensitivity became smaller and the response speed got slower as ambient temperature lowered, but response of 4% decrease after 15 min, exposure to 1 vol.% H2/air was obtained at −30 °C. The observation guarantees the operations of wide temperature range. The high sensitivity in the low temperature range together with the line-sensing feature is very promising for the continuous monitoring of hydrogen leak for fuel-cell cars and other equipments utilizing hydrogen.