Mechanically stable and economically viable polyvinyl alcohol-based membranes with sulfonated carbon nanotubes for proton exchange membrane fuel cells

Abstract

Crosslinked Polyvinyl alcohol (PVA) membranes with sulfonated CNT (SCNT) fillers were synthesized using solution casting method for proton exchange membrane fuel cells (PEMFC). Sulfonated CNTs are reported to be one of the best additives in ionic membranes as they increase the ionic conductivity and mechanical strength of the membrane. CNTs are high aspect ratio carbon allotropes, and small quantities of SCNTs (0.01 wt%, 0.1 wt%, 0.5 wt%, and 1 wt%) are observed to make a significant difference in properties of membranes. These membranes were characterized for water uptake capacity, ion exchange capacity, and mechanical strength. Ionic conductivity, hydrogen pumping, polarization studies, and gas crossover studies were performed in situ under various conditions of humidity. PVA–SSA–0.1 wt% SCNT showed the maximum power density among all compositions tested while short term performance of PVA–SSA–0.5 wt% SCNT exhibited the least sensitivity to changes in reactant humidity. Nafion® 115 produced 0.33 W cm⁻² at 0.4 V while PVA–SSA–0.1 wt% SCNT exhibited 0.21 W cm⁻² at 0.4 V. Overpotential associated with the purity of hydrogen gas was accounted for in the polarization curve and it resulted in a distinctly improved power density of 0.4 W cm⁻². Performance of PVA–SSA–SCNT membranes was compared with Nafion® 115 by various characterization techniques and the results indicate that the membranes developed are a cost-effective alternative to Nafion® with the best performing PVA–SSA–SCNT membrane costing ≈1% of the cost of the Nafion® 115 membrane for similar performance.