Effect of TiO₂ and Al₂O₃ Addition on the Performance of Chitosan/Phosphotungstic Composite Membranes for Direct...

Composite chitosan/phosphotungstic acid (CS/PTA) with the addition of TiO₂ and Al₂O₃ particles were synthesized to be used as proton exchange membranes in direct methanol fuel cells (DMFCs). The influence of fillers was assessed through X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, liquid uptake, ion exchange capacity and methanol permeability measurements. The addition of TiO₂ particles into proton exchange membranes led to an increase in crystallinity and a decrease in liquid uptake and methanol permeability with respect to pristine CS/PTA membranes, whilst the effect of the introduction of Al₂O₃ particles on the characteristics of membranes is almost the opposite. Membranes were successfully tested as proton conductors in a single module DMFC of 1 cm² as active area, operating at 50 °C fed with 2 M methanol aqueous solution at the anode and oxygen at the cathode. Highest performance was reached by using a membrane with TiO₂ (5 wt.%) particles, i.e., a power density of 40 mW cm^-2, almost doubling the performance reached by using pristine CS/PTA membrane (i.e., 24 mW cm^-2).