Strong electric field effects on proton transfer between membrane-bound amines and water

Abstract

DURING water demineralisation by electrodialysis much of the current is carried by hydrogen and hydroxyl ions1,2. This is attributed to an effect known as water splitting, which occurs near those surfaces of the ion exchange membranes which are depleted of ions during current flow (see Fig. 1). I have found3 that water splitting only occurs in sulphonic acid membranes if certain impurities are present. But in contrast, it is an intrinsic property of anion exchange membranes in which the functional group is a tertiary alkyl amine. It is also intrinsic to membranes with quaternary ammonium ions if the surface groups have been converted to the tertiary form. An investigation of water splitting for the latter type of membrane (Negev Institute A)4 is described here. It will be shown that the effect could be due to a 1,000-fold increase in the forward rate constant for reaction (2), caused by the strong external electric field (107–108 V m−1) at the interface.