Partially sulfonated polyaniline induced high ion-exchange capacity and selectivity of Nafion membrane for application in direct methanol fuel cells

• Synthesis and blending of partially sulfonated polyaniline with Nafion.
• PEM prepared from blend having 30 wt% sulfonated polyaniline produced best results.
• A methanol permeability of 1.2×10−7 cm2 s−1 was obtained at 60 °C.
• An ion-exchange capacity value of 1.2 meq g−1 was obtained at 20 °C.
• A membrane selectivity ratio of 1.97×105 Ss cm−3 was obtained at 60 °C.

Traditionally used Nafion membranes in direct methanol fuel cells (DMFCs) suffer from high methanol permeabilities, as well as, high material costs; therefore, alternative and more efficient polymer electrolyte membrane (PEM) materials need to be synthesized in order to realize better cell performances. We recently synthesized and reported the use of low cost partially sulfonated polyaniline (SPAni) as a co-constituent along with partially sulfonated poly(vinylidene fluoride-co-hexafluoro propylene) as an effective PEM material. This PEM material exhibited extremely low methanol permeability and very high membrane selectivity. Based on these positive attributes, we demonstrate in this work that blend of Nafion and SPAni can serve as an alternative PEM material; since PEM fabricated using 30 wt% of SPAni and 70 wt% of Nafion produced selectivity ratios of 7.91×104 Ss cm−3 (at 20 °C) and 1.97×105 Ss cm−3 (at 60 °C), an ion-exchange capacity of 1.2 meq g−1 (at 20 °C), methanol permeabilities of 9.12×10−8 cm2 s−1 (at 20 °C) and 1.2×10−7 cm2 s−1 (at 60 °C), and a current density of 128.7 mA cm−2 at +0.2 V and 60 °C and a corresponding maximum power density of 25.76 mW cm−2 using 6 M methanol feed concentration. The cell performance, thus observed, is far better than that produced by pristine Nafion membrane under the same operating conditions.

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