Trainable hydrogen sensing of palladium nanoparticles on polyvinylidene fluoride nanofibers: Effects of dynamic mechanics

Abstract

Palladium-based hydrogen sensors have been studied for decades owing to the extensive demand for hydrogen sensing. However, the dislocation of palladium induced by volumetric expansion is the main reason for the deterioration of the sensing performance. Polymer support was suggested to accommodate the volumetric expansion. However, the impact of the mechanical properties of polymers is unclear. In this study, palladium nanoparticles were mixed with carbon nanotubes (CNTs) and attached to polyvinylidene fluoride (PVDF) nanofibers. The comparative experimental results indicate that CNTs were used as conductors for modifying the conductivities of the sensors. For initial exposure, 3% H2 can significantly enhance sensor sensitivity with a detection limit of 25 ppm. Based on characterization and simulation, the elasto-viscoplastic PVDF is essential to the sensitivity of the sensor. The hardening process of PVDF is induced by initial hydrogen exposure. The hardened PVDF dampens the femtoscale oscillations of palladium nanoparticles and resists their deformation. Initial 3% H2 exposure obtains the most stable palladium nanoparticles, which contributes to stabilizing the conducting paths. Thus, the highest sensitivity is obtained through immobilized palladium nanoparticles. This study shows the impact of mechanical properties of the polymer substrate, which cannot be overlooked while designing a palladium-based hydrogen sensor.