Permeant transport properties and cell performance of potassium hydroxide doped poly(vinyl alcohol)/fumed silica nanocomposites

Abstract

Polyvinyl alcohol/fumed silica (PVA/FS) nano-composites were prepared through a solution casting method. The water diffusivity increased as FS was incorporated into the PVA matrix. The ionic conductivity of the KOH-doped PVA composites increased with the FS concentration. Meanwhile, the methanol permeability in the resulting composites decreased with FS addition due to suppressed methanol solubility and diffusivity. The PVA/KOH and PVA/FS/KOH electrolytes were employed in direct methanol alkaline fuel cells (DMAFCs). The effects of methanol and KOH concentrations, oxygen humidification, oxygen flow rate and the operating temperature on cell performance were investigated from the standpoints of kinetics and material characteristics. Oxygen humidification was necessary and a higher oxygen flow rate improved the cell performance. The open-circuit voltage and maximum power density of the PVA/(20%)FS/KOH electrolyte increased with increasing FS concentrations and operating temperatures. Among the tested methanol and KOH concentrations, the maximum power density of 15.3 mW cm −2 was achieved for a DMAFC consisting of a PVA/(20%)FS/KOH electrolyte with 2 M methanol and 2 M KOH as the anode feed. This inexpensive electrolyte is promising for DMAFC applications.