| Summary: | Composite chitosan/phosphotungstic acid (CS/PTA) with the addition of TiO<sub>2</sub> and Al<sub>2</sub>O<sub>3</sub> 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<sub>2</sub> 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<sub>2</sub>O<sub>3</sub> 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<sup>2</sup> 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<sub>2</sub> (5 wt.%) particles, i.e., a power density of 40 mW cm<sup>−2</sup>, almost doubling the performance reached by using pristine CS/PTA membrane (i.e., 24 mW cm<sup>−2</sup>).
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