Synthesis and characterization of cross-linked chitosan membranes for application as alternative proton exchange membrane materials in fuel cells

Chitosan membranes cross-linked in sulfuric acid are evaluated for their thermal stability, water absorption and proton conductivity properties as alternative proton exchange membrane (PEM) material for application in fuel cells. Chitosan membranes are found to be more hydrophilic than Nafion 117 in water uptake experiments. Chitosan membranes absorb about 60% water on average compared with about 30% for Nafion 117. Preliminary TGA/DSC thermal stability studies show that after the initial weight loss due to water, chitosan membranes decompose in three stages with the final stage beginning at about 300 °C. Chitosan membrane proton conductivities under various temperature and humidity conditions are reported and compared with that for the commercial membrane Nafion 117. Partially-hydrated chitosan membranes at ambient temperature display a proton conductivity of about 0.005 S cm−1 as opposed to 0.08 S cm−1 for Nafion 117 under the same conditions. At 60 °C (full hydration) Nafion 117 membranes have a conductivity of about 0.12 S cm−1 and chitosan membranes have 0.02 S cm−1.