Thermally stable polybenzimidazole/carbon nano-tube composites for alkaline direct methanol fuel cell applications

•CNT causes high fractional free volume in a polymer matrix.•Water diffusivities are enhanced in CNT-containing PBI films.•GDEs without PTFE treatment give higher power density compared to commercial GDEs.•DMAFC containing CNT electrolyte achieves a peak power density of 104.7 mW cm−2.

Nanocomposites of thermally stable polybenzimidazole (PBI) containing small amounts (<1%) of functionalized multi-walled carbon nano-tubes (CNT) are prepared using solution casting methods. These PBI and PBI/CNT composites are doped with potassium hydroxide (KOH) solution to prepare hydroxide-conducting electrolytes for alkaline direct methanol fuel cell (ADMFC) applications. The CNT-containing composites exhibit higher fractional free volumes and higher water diffusivities. CNT also promotes ionic conductivity of electrolytes and improves the fuel cell performance. Gas diffusion electrodes (GDEs) without polytetrafluoroethene (PTFE) treatment give superior cell power density compared to commercial E-tek GDEs, which contain hydrophobic PTFE layers. When the fuel cell is fed with 2 M methanol in 6 M KOH (as the anode fuel) and humidified oxygen (as the cathode oxidant), the system achieves a maximum power density of 104.7 mW cm−2 at 90 °C. These KOH-doped PBI/CNT composites have the potential to be used in high temperature alkaline fuel cell applications.