Novel polyvinyl alcohol nanocomposites containing carbon nano-tubes with Fe3O4 pendants for alkaline fuel cell applications

In this work, multi-walled carbon nano-tubes (CNTs) were modified with pendant Fe3O4 nanoparticles and polyvinyl alcohol (PVA) polymer chains. These functionalized CNTs (FeCNT) were incorporated into a PVA solution and used to prepare a cast film. The use of the pendant Fe3O4 nanoparticles resulted in a loose crystal structure with low crystallinity for the PVA matrix. With an increased fractional free volume, the water solubilities and diffusivities were enhanced in the FeCNT-containing composite membranes. The methanol permeability was reduced in the PVA–FeCNT sample. The PVA and PVA–FeCNT films were doped with a potassium hydroxide (KOH) solution to prepare hydroxide-conducting solid electrolytes. The ionic conductivity of the KOH-doped PVA–FeCNT composite membrane was improved by the FeCNT addition. This improvement was ascribed to the increased polymeric amorphous region with the ionic conducting micro-channels provided by the FeCNT. These electrolytes were used in direct methanol alkaline fuel cells. An open-circuit potential and a peak power density of 0.87 V and 87.8 mW cm−2, respectively, were obtained using a 2 M methanol fuel in 6 M KOH at 60 °C with the PVA-based electrolyte containing 0.15% FeCNT. This peak power density was more than double the value observed without the FeCNT incorporation.