Stable Pd/V2O5 optical H2 sensor

Thin films of Pd exhibit a change in their optical properties when exposed to hydrogen. A new sensor structure consisting of a combined Pd and V2O5 thin film stack has been developed for optical detection of hydrogen. Unlike a singular palladium thin film sensor, the new structure is durable and allows detection of hydrogen concentration in excess of 4%. The sensor exhibits a very fast response time and can be cycled for over 500 cycles without degradation of performance. It has been found that the stoichiometry of oxygen in the vanadium oxide layer is very critical for its reaction with hydrogen and greatly affects the overall sensor stability. A study of the operating mechanism reveals that the formation of palladium hydride is singularly responsible for the optical modulation while the vanadium oxide layer offers no contribution (after the initial irreversible color change from yellow to blue). Subsequent reversible hydrogen insertion into vanadium oxide does take place as evidenced by the Raman data even though no optical change in the visible spectrum is observed. (C) 2002 The Electrochemical Society.