The design of higher temperature composite proton-exchange membranes (PEMs) with adequate performance under low relative humidity (RH) is discussed here based on experimental and theoretical considerations. The approach is based on enhancing the acidity and water sorption of a conventional polymer electrolyte membrane by incorporating in it a solid acidic inorganic material. A systematic investigation of the composite Nafion/inorganic additive PEMs based on characterization of water uptake, ion-exchange capacity (IEC), conductivity, and fuel cell polarization is presented. The effects of particle size, chemical treatment, additive loading, and alternate processing methodologies are investigated. The most promising candidate investigated thus far is the nanostructured ZrO2/Nafion PEM exhibiting an increase of similar to10% in IEC, similar to40% increase in water sorbed, and similar to5% enhancement in conductivity vs. unmodified Nafion 112 at 120degreesC and 40% RH. This appears to be an attractive candidate for incorporation into a membrane-electrode assembly for improved performance under these hot and dry conditions. (C) 2004 The Electrochemical Society. All rights reserved.
