Chitosan-based electrolyte composite membranes: II. Mechanical properties and ionic conductivity

Chitosan-based ion-immobilized electrolyte composite membranes have been prepared with a three-layer structure that has a porous intermediate layer and two solid surface layers using glutaraldehyde as crosslinking agent. Potassium hydroxide has been incorporated into the porous intermediate layer of the composite membranes as ionic functionality by using a two-step pathway. The ionic conductivity of these composite membranes is investigated using impedance spectroscopy. It is found that some dried composite membranes with a load of KOH between 5.5 and 8.5 wt.% can show a conductivity in the range of semi-conductors (around 10−6 S cm−1), and their conductivity can reach about 10−2 S cm−1 after being hydrated for 1 h at room temperature. Main mechanical properties: tensile strength, breaking elongation and modulus have been evaluated. The obtained results suggest that in order to ensure the composite membranes to have desired mechanical properties and higher conductivity, and to be possibly used in an alkaline fuel cell, the ratio of glutaraldehyde to chitosan should be selected between 4 and 5 wt.% and the content of potassium hydroxide loaded inside the inner layer should be controlled below 6 wt.%.