Strategies to improve the water splitting properties of bipolar membranes (BPMs) were discussed in this study. The BPMs with a composite anion-exchange layer and catalytic junction layer were prepared and the water splitting properties were evaluated. The results showed that the water splitting properties are highly depending on both the fixed charge density at the bipolar (BP) junction and the degree of cross-linking in the anion-exchange layer (AEL). Additionally, based on the chemical reaction theory, an alkali-treated polyacrylonitrile (PAN) layer was introduced as an active junction material using a spin coating method. The modified-PAN junction layer significantly enhanced water splitting of the BPM. It was concluded that the optimized ion-permselectivity of the AEL and charge density at the BP junction can improve the performance of BPMs. (C) 2003 Elsevier B.V. All rights reserved.