Response characteristics of hydrogen gas sensor with porous piezoelectric poly(vinylidene fluoride) film

Previously, we have proposed a new type of organic hydrogen gas sensor in which a β-phase poly(vinylidene fluoride) (PVDF) film is coated with thin films of palladium (Pd) on both sides. Volume expansion of the Pd thin film caused by uptake of hydrogen is monitored by a capacitance change of the piezoelectric PVDF thin film. The β-phase PVDF film was synthesized from α-phase PVDF powder by using a wet process that we developed. In this study, we have examined the microscopic structure of the β-phase PVDF films and investigated the response characteristics of the sensors: response at hydrogen exposure, detection sensitivity, recovery time and effect of humidity. We find that the PVDF film has the porous structure consisting of micro-scaled grains of PVDF and demonstrates that the response characteristics depend on the structure of the PVDF films. We propose a simple simulation model to get insight into the observed response characteristics. In the model, it is assumed that PVDF micro-grains expand and shrink one by one while exposing to hydrogen and air (or oxygen), respectively. The simulation explains the basic response characteristics of the sensor.