Hygro-thermal and mechanical behavior of carbon based thin film materials for advanced energy and actuator application

Abstract

Carbon based thin film materials are widely used in advanced energy and actuator. Using ionomer binder, such thin film materials are applying to polymer electrolyte membrane fuel cell and electro-active polymer actuator as electrode materials of them. In order to improve the device’s performance and reliability, it should be preferred to understand the intrinsic physical properties. In this research, hygro-thermal and mechanical behavior of the electrodes are investigated in free-standing. New electrode separation method from coating substrates is proposed for quantitative analysis of the intrinsic behavior. Improvement of mechanical property is obtained through the flawless separation method with the maximum improvement of mechanical elongation of ~ 100 % compared with conventional electrode separation method. Moreover, the intrinsic hygro-thermal behavior is examined in consideration of operating environments. In-plane swelling strain and electron transport property are measured in-situ under variety of relative humidity and temperature. Differences of such behaviors depending on the weight fraction of ionomer are analyzed through theoretical modeling of swelling expansion. In contrast to previous works, the thin film electrodes have 1 ~ 4 % of in-plane swelling strain depending on the weight fraction of ionomer. Ten times increment of electrical resistance is showed via four-wire measurement using a digital multimeter. Transmission electron microscope analysis provides the structural alteration of ionomer binder as the containing ionomer increases, and hence the electrodes show structural transition from decoupling to coupling between the electrical resistance and the macroscopic swelling depending on the structure. This research may provide positive insights for the improvement of the mechanical performance and the robustness of electrodes. Furthermore, beneficial contributions are expected by spanning this research to the intrinsic electrical and chemical properties.