Water Transport during Ion Conduction in Anion-Exchange and Cation-Exchange Membranes

Water transport during ion conduction through an anion-exchange membrane (AEM) immersed in an aqueous solution of HNO3 and KOH was investigated. We have developed an apparatus to accurately measure small changes in volumes of the aqueous solution at each side of the membrane by capillary tubes during the passage of an electronic current through the membrane. In contrast to the previously reported apparatus, the present apparatus can be applied to an AEM in various aqueous solutions of electrolytes, and measurements under conditions close to those in actual solid alkaline fuel cells are therefore possible by using alkaline solutions. The water-transport number for AEM in HNO3 was larger than that in KOH, indicating the importance of selecting the appropriate aqueous solution of electrolytes. It is possible to determine whether anions or cations are conductors in electrolyte membranes with unknown properties. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3129618] All rights reserved.