Deformation mechanism of hydrogen-assisted ionic polymer metal composite actuator

Hydrogen power sources are expected to be the main power source for a sustainable society in the future. Therefore, the development of mechanical parts or systems to adapt to the usage of hydrogen is a key issue. Ionic polymer metal composite (IPMC) actuators are composed of an electrolyte polymer membrane coated with electrodes. Owing to their light weight, flexibility, and ease of miniaturization, IPMC actuators are promising candidates for use as micro-actuators in small robots, microvalves, or artificial muscles. In this study, a hydrogen-assisted IPMC actuator is developed, and its deformation mechanism is investigated. The hydrogen absorption produced by water splitting and the hydrated cation movement in the electrolyte are the driving forces involved in this actuator. The effects of applied voltage, thickness of palladium electrodes, and length of the actuators are studied. Moreover, the contributions of bending moments by a hydrated cation movement and those by hydrogen absorption to the bending deformation are separately clarified. The results indicate that the deformation mechanism of the hydrogen-assisted IPMC actuator depends on the applied voltage, palladium-electrode thickness, and actuator length. The contribution of the hydrogen assistance decreases with the applied voltage, while that of the hydrated cation movement increases. In addition, the specimen with a shorter length exhibits a larger hydrogen-induced moment ratio. These results suggest that the hydrogen assistance to the bending deformation is more effective in IPMC actuators with a shorter and thinner palladium electrode.