Abstract
Solid electrolyte membranes based on alkali-doped polyvinyl alcohol (PVA) and PVA/carbon nanotubes (PVA/CNTs) are used in direct borohydride fuel cells (DBFCs). As 0.05 wt % of CNT is incorporated into the PVA matrix, the polymer crystallinity is decreased from 42.4% to 38.0% and the fractional free volume increases from 2.48% to 3.53%. The KOH-doped PVA/CNT exhibits the highest ionic conductivity of 0.0805 S cm -1 , because of the increased polymer free volume (which promotes vehicular OH - transport) and the presence of CNT (which serves as the conducting microchannels). Sodium borohydride (NaBH 4 ) in NaOH solution and potassium borohydride (KBH 4 ) in KOH mixture are fed into the cells. The power density of the KBH 4 -based DBFC is almost twice that of the NaBH 4 -based DBFC (184 vs. 92 mW cm -2 ) due to less KBH 4 permeability through the films, higher conductivity of the KOH-doped PVA composites than those in the sodium counterpart, and probably higher electro-catalytic kinetics. © 2013 Wiley Periodicals, Inc.