Atomic structural change of silver-plating layers on the surfaces of Selemion, resulting in its excellent bending controllability

One of the ion-exchange polymer membranes called Selemion, containing –SO3H groups in the largely dehydrated state, where its top and bottom surfaces are plated with silver, exhibits an excellent bending controllability for fairly a long while by the applied voltage control unlike the conventionally well-investigated hydrated ion-exchange polymer membranes, such as Nafion. The exact mechanism of such an excellent bending controllability of Selemion has not been elucidated yet. However, the involvement of silver redox reaction in this excellent bending controllability was strongly suggested before. XRD measurement in this study clearly suggests the occurrence of redox reaction, 4Ag + O2 = 2Ag2O. By the bending controllability testing and the current measurements along with this XRD measurement on Selemion and Nafion, we reached the conclusion that the atomic structural change of Ag and Ag2O on the top and bottom surfaces of Selemion caused by the redox reaction is responsible for the excellent Selemion bending controllability. This bending mechanism is totally different from the conventionally accepted mechanism for the bending of hydrated ion-exchange polymer membranes, which cannot exhibit a good bending controllability even for a short while.