Phosphotungstic acid supported on a nanopowdered ZrO2 as a filler in Nafion-based membranes for polymer electrolyte fuel cells

An inorganic filler prepared by impregnation of phosphotungstic heteropolyacid on zirconia (HPW/Zr) was developed to be inserted into a perfluorosulphonic polymer matrix for a polymer electrolyte fuel cell (PEFC) operating at a medium temperature (80-120 C) and low relative humidity (RH). Two different phosphotungstic acid (PWA) loadings (30 and 45% w/w) were anchored on a nanopowdered ZrO2. Such compounds were characterised by different techniques: differential scanning calorimetry (DSC), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX) and porosity and surface area by Brunauer-Emmett-Teller (BET), to verify the introduction and anchorage of PWA on ZrO2. Two composite Nafion membranes were prepared and characterised in terms of chemical-physical characteristics and electrochemical tests. Thermogravimetric analysis (TGA) provided evidence that HPW/Zr had been incorporated into composite membranes and it was not eluted. A good proton conductivity of about 6x10-3 S cm-1 at 120° C and 25% RH was recorded. Accelerated in situ ageing tests highlighted a good electrochemical stability (more than 150 cycles at 90°C with dry gases) of the composite membranes with a slow decay and a reasonable integrity of the analysed membrane-electrodes assembly (MEA). Finally, a post-mortem SEM-EDX analysis on MEAs confirmed the presence of HPW/Zr in the membrane after the in situ testing.