DMFC Membranes Based On Polymer-Modified Silica Colloidal Crystals

We report hybrid organic-inorganic materials that meet all the requirements for the successful proton conductive membranes used in direct methanol fuel cells. In these membranes, mechanically and chemically stable silica colloidal crystal serves as rigid matrix containing a continuous network of nanopores, providing mechanical and thermal stability, non-swelling and water retaining properties, while the polymer brushes grown on the surface of the nanopores and carrying sulfonic groups provide proton conductivity. Proton conductivity of the prepared membranes as well as their fuel cell open circuit potential and current were studied as function of the degree of polymer sulfonation. We found an S-shaped dependence of the proton conductivity on the amount of sulfonic groups, while the open circuit current showed a more complex dependence on sulfonation. The proton conductivity of the membrane and fuel cell performance do not significantly improve after reaching the 60% degree of sulfonation. The fuel cell performance can be improved by the addition of a certain amount of alkyl side-chains to the polymer brushes.