Polyelectrolyte Complexes of Chitosan and Poly(acrylic acid) As Proton Exchange Membranes for Fuel Cells

Abstract

Ionically cross-linked polyelectrolyte complex (PEC) membranes of cationic chitosan (CS) and anionic poly(acrylic acid) (PAAc) were synthesized and assessed for applicability in fuel cells. CS and PAAc were blended in different weight ratios and the resulting membranes were posttreated to enable the formation of the polyelectrolyte complex. The ionic cross-linking occurring on blending the polyelectrolytes excludes the need of using other cross-linking agents. These membranes were extensively characterized for morphology, their intermolecular interactions, thermal stability, and physicomechanical properties using SEM, FTIR, DSC, sorption studies, and tensile testing, respectively. Methanol permeability and proton conductivity were estimated and compared with respective values for Nafion 117. PEC membranes exhibited high ion exchange capacity (IEC), high proton conductivity, low methanol permeability, and adequate thermal and mechanical stability. Among the blends synthesized, the membrane blend with 50 wt % of CS and 50 wt % of PAAc, was identified as ideal for direct methanol fuel cell (DMFC) applications as it exhibited low methanol permeability (3.9 × 10 -8 cm 2 /s), excellent physicomechanical properties and comparatively high proton conductivity (0.038 S·cm -1 ). Above all, the cost-effectiveness and simple fabrication technique involved in the synthesis of such PECs makes their applicability in DMFC quite attractive.