The currentevoltage (IeV) characteristics of the Pd/WO3/Si
and Pd/WO3/ZnO/Si Schottky diodes were measured under
exposure to synthetic air and hydrogen gas and shown in
Fig. 4. Different hydrogen concentrations were allowed to flow
by balancing 10,000-ppm hydrogen with synthetic air at
temperatures of 300 K, 373 K and 423 K, respectively.