Preparation of Composite Membrane with Three-Dimensionally Ordered Polyimide Matrix and Proton Conductive Gel Polymer

Direct methanol fuel cells (DMFCs) using polymer electrolyte membranes have attracted considerable attention as promising power sources for mobile and stationary applications. Perfluorosulfonated polymer membranes (e.g., Nafion) have been studied due to high proton conductivity, high chemical stability, and so on. However, they are easily expanded by an immersion into water or methanol, which should result in methanol permeation through the membrane. Methanol cross-over to the oxygen cathode leads to lowering of cell voltage and fuel utilization. Therefore, alternative polymer materials have been investigated by many research groups. Among them, polyimide type polymers have been especially studied and expected as new proton conductive electrolyte membrane because of their good mechanical and chemical properties. On the other hand, a mechanical suppression of polymer expansion is studied as another approach. Some new classes of composite membranes such as pore-filling structure have been proposed. Recently, we developed the composite membrane consisting of gel electrolyte and threedimensionally ordered silica matrix, which exhibited both high proton conduction and a low methanol cross-over due to the suppression of polymer expansion by the silica matrix. In this study, ordered macroporous membrane of polyimide, which might work as proton conductor by itself, was fabricated and evaluated as a matrix of composite electrolyte for fuel cell.