Date of this Version
United States Cornelius Patent Patent No.: US 7,022,810 B1
A new class of hybrid organic-inorganic materials, and methods of synthesis, that can be used as a proton exchange membrane in a direct methanol fuel cell. In contrast with Nafion PEM materials, which have random sulfonation, the new class materials have ordered sulfonation achieved through self-assembly of alternating polyimide segments of different molecular weights comprising, for example, highly sulfonated hydrophilic PDA-DASA polyimide segments alternating with an unsulfonated hydrophodic 6FDA-DAS polymide segment. An inorganic phase, e.g., 0.5-5 wt % TEOS, can be incorporated in the sulfonated. The new materials exhibit reduced swelling when exposed to water, increased thermal stability, and decreased 02 and H2 gas permeability, while retaining proton conductivities similar to Nafion. These improved properties may allow direct methanol fuel cells to operate at higher temperatures and with higher efficiencies due to reduced methanol crossover.