Fundamental studies on a novel series of bipolar membranes prepared from poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) - II. Effect of functional group type of anion-exchange layers on I-V curves of bipolar membranes

In this paper, the water splitting properties of bipolar membranes with different types of functional groups are discussed. To do this, the anionexchange layers with different ammonium groups were prepared in advance which can be controlled by reacting the bromomethylated poly(2,6dimethyl- 1,4-phenylene oxide) (BPPO) base membrane with different amines such as methylamine (MA), dimethylamine (DMA), trimethylamine (TMA), triethylamine (TEA), tri-n-propylamine (TPA), tri-n-butylamine (TBA) and dimethyethanolarnine (DMEA) to form the corresponding secondary, tertiary and different quaternary ammonium groups. And then the corresponding bipolar membranes were prepared by casting the sulphonated PPO solution on these anion-exchange layers. The fundamental characteristics of bipolar membranes, current-voltage curves, are fully discussed based on the functional group type of anion-exchange layers. The results demonstrate that the bipolar membrane with strongly basic groups has larger water dissociation ability than those with weakly basic groups. For membranes with weakly basic groups (secondary or tertiary ammonium groups) or strongly basic groups (quaternary ammonium groups), water dissociation mainly depend on the pKb value of amines to form the anion-exchange layers if the mono-polar ion-exchange layers processes the close intrinsic properties such as water uptake and conductivity: voltage at a given current density roughly decreases with an increase in pKb values. (c) 2005 Elsevier B.V. All rights reserved.