Counter-ion and humidity effects on electromechanical properties of Nafion®/Pt composites

Ionomeric polymer/metal composites (IPMCs) are smart materials that deform in response to electrical stimuli and vice versa. Its electromechanical performance depends on several factors, such as the electrical stimulus, environment humidity, counterions, and the number of actuation cycles. For this reason, in this paper, the electromechanical response of Pt-Nafion (R) IPMC samples was evaluated using several counterion types (H+, Li+, Na+, K+ and Ionic Liquid) and relative humidities. Results showed that the electromechanical behaviour of the IPMC was strongly influenced by the counterion type and polymer matrix hydration level (RH). Blocking force, Electric Charge Storage and the Coulombic Efficiency of the devices increased with the reduction of counterion ionic radius and increase of the hydration level of the polymeric matrix. An atypical current response, associated with water electrolysis, was observed for samples incorporated with H+ counterion. The mechanical performance decreased with the number of cycles, showing a limited life cycle for the device. SEM images presented that Pt surface cracks density increases after several actuations, harming the performance of the IPMC. As the main conclusion, this work shows that the hydration level and the counterion type exert a great influence on IPMC electromechanical properties, being the hydration level more prevailing than counterion.