Synthesis and characterization of composite membrane with three-dimensionally ordered macroporous polyimide matrix for DMFC

A composite membrane consisting of three-dimensionally ordered macroporous (3DOM) polyimide matrix and a proton-conducting gel polymer was prepared for direct methanol fuel cells (DMFCs). The matrix effect on the physico-electrochemical properties of the composite membrane was investigated in order to compare 3DOM silica composite membrane containing the same proton-conducting polymer. From the comparison of 3DOM polyimide matrix with the 3DOM silica matrix reported in our previous paper, it was confirmed that the polyimide matrix has some structural advantages. In particular, the high uniformity of 3DOM structure provides fairly continuous proton-conducting pathways in the composite membrane, resulting in considerably high proton conductivity of 1.7 x 10(-1) S cm(-1) at 60 degrees C under 90% relative humidity, which is about three times greater than that obtained with the 3DOM silica composite membrane. Furthermore, high mechanical strength of 3DOM polyimide suppressed polymer swelling in the composite membrane, which resulted in low methanol permeability of 9.4 x 10(-7) cm(2) s(-1) in 20 mol dm(-3) methanol solution. Consequently, 1.3 x 10(5) S cm(-3) s was obtained as transfer selectivity of the composite membrane, which was about ten times larger than that of Nation membrane. (C) 2008 The Electrochemical Society.