Roles of Ag redox reaction and water absorption inducing the Selemion bending

The dehydrated ion exchange polymer membranes plated with silver were found to bend under the low voltage by the two of the authors of this paper, H.T. and F.N., before (J. Membr. Sci. 243 (2004) 229). They speculated that the shift of silver layer on one surface of the ion exchange polymer membrane onto the opposite surface of it by the imposed applied voltage induced its bending. However, our latest investigation suggests that such a phenomenon of silver layer shift does not occur. Instead, the silver layer exhibits the reversible redox reaction of 4Ag + O2 = 2Ag2O by the polarity change of applied voltage, and it appears to be heavily involved in the bending induction. Furthermore, our investigation strongly suggested that the dehydrated ion exchange polymer membrane is actually in the not so completely dehydrated state, namely, a minute quantity of water is still contained in the ion exchange polymer membrane that has undergone the dehydration treatment. In this study, we concluded that a minute quantity of water inside ion exchange polymer membrane and the occurrence of redox reaction of silver on its surface play the critical roles for its bending induction.