Modified Nafion®-based membranes for use in direct methanol fuel cells

Commercially available Nafion® membranes at present do not meet the requirements for high power density direct methanol fuel cell (DMFC) applications, amongst others factors because of their high methanol permeability. With the aim of improving the membrane properties with respect to this application, a modification procedure has been applied to recast Nafion®-based membranes. Membranes, containing different additives namely silicon dioxide particles (Aerosil®) and molybdophosphoric acid, are assessed with regard to their conductivity and methanol permeation rate. The preparation of the samples involves the introduction of a small amount of a high boiling point solvent to the as-received Nafion® solution and then shaping the membranes by a recast procedure. An enhancement of the conductivity of the thermally treated membranes in comparison to Nafion® 117 is found. The combined parameter of methanol permeation rate and conductivity of the samples, containing inorganic additives (Aerosil and molybdophosphoric acid), decreases compared with the pure recast and as-received Nafion® membranes. The observed results are discussed in terms of the membrane structure and preparation.