Incorporation of nano-Al2O3 within the blend of sulfonated-PVdF-co-HFP and Nafion for high temperature application in DMFCs

Abstract

Nano-Al₂O₃ was incorporated into the blend of sulfonated-PVdF-co-HFP/Nafion using NMP (1-methyl-2-pyrrolidone) as a common solvent with the aim to develop an alternate membrane to be used in a single cell direct methanol fuel cell (DMFC). Furthermore, the synthesized nano-composite membranes were subjected to different tests such as FTIR, XRD, water uptake, swelling, IEC (ion exchange capacity), proton conductivity and methanol crossover. The water uptake results indicated that with an increase in the nano-Al₂O₃ content (up to 5% w/w) in the blend, the water uptake of the nanocomposite matrix rapidly increased up to 34.8%. Sample S-5 composed of 5% (w/w) Al₂O₃ exhibited comparable proton conductivity/IEC, low methanol permeability and high membrane selectivity over the corresponding Nafion-117 membrane. In addition, the prospective nanocomposite membrane also exhibited comparable mechanical stability. Moreover, the maximum current density at 0.2 V in a single cell DMFC, which was operated with atmospheric air (without preheating/humidification) at the cathode, was recorded as 285 mA cm⁻² and 270 mA cm⁻² at 90 °C and 110 °C, respectively. Comparing the power densities of the single cell fitted with the membrane of Nafion-1 17 (28 mW cm⁻²) and blend of sulfonated-PVdF-co-HFP and Nafion (32 mW cm⁻²), the single cell with the composite membrane S-5 showed an optimum power density (57 mW cm⁻²) at +0.2 V at a high temperature of 90–110 °C. These results indicate that the composite membrane could effectively reduce the anhydrous conditions at high operating temperatures.