Keiji Sasajima

Properties of Composite Membrane Consisting of 3DOM Silica Matrix Filled with Sulfonated Poly(1,4-phenylene ether ether sulfone) at Various Ratios

A composite membrane consisting of three-dimensionally ordered macroporous (3DOM) silica matrix and sulfonated poly (1,4-phenylene ether ether sulfone) (SPEES) was prepared. Both water uptake and methanol permeability of the composite membrane changed according to the filling ratio of SPEES in the 3DOM silica matrix. Proton conductivity of the composite membrane was hardly influenced by the filling ratio, which was 6.0-6.5 X 10 -2 S cm -1 at a filling ratio of 14-46%. This may be explained by the interface region between SPEES and silica having a high transfer of protons. Hence, the membrane having high proton conductivity and low methanol permeability was prepared by adjusting the filling ratio of SPEES. The prepared membrane has more than two times higher performance than Nafion as solid electrolyte membrane for direct methanol fuel cells.

Design of Filling Polymer Electrolytes for 3DOM Composite Membrane

Introduction Direct methanol fuel cell (DMFC) which can feed methanol directly to the anode without a reformer, has been expected as a portable power source for various kinds of mobile devices. However, it is necessary for the practical applications to restrain methanol cross-over through an electrolyte membrane that decreases not only fuel utilization but also cell voltage. This phenomenon is mainly attributable to swelling of an electrolyte membrane by water and methanol absorption. However, electrolyte membranes must be sulfonated at certain level to maintain proton conductivity enough for DMFC, so that the suppression of cross-over is practically difficult. In our previous study, we prepared a composite membrane composed of a three-dimensionally ordered macroporous (3DOM) silica matrix and two kinds of polymer electrolytes, and revealed that its proton conductivity was strongly influenced on characteristics of a polymer electrolyte on the silica surface. On the other hand, the methanol permeability depended on the polymer occupying the bulk of 3DOM pores. In this study, we tried to improve the performance of 3DOM composite membrane by appropriate selection of polymer electrolytes for the silica surface and the bulk of pores, respectively.