Effect of TiO 2 and Al 2 O 3 Addition on the Performance of Chitosan/Phosphotungstic Composite Membranes for Direct Methanol Fuel Cells.

Composite chitosan/phosphotungstic acid (CS/PTA) with the addition of TiO ₂ and Al ₂ O ₃ 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 TiO ₂ 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 Al ₂ O ₃ particles on the characteristics of membranes is almost the opposite. Membranes were successfully tested as proton conductors in a single module DMFC of 1 cm ² 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 TiO ₂ (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 ).