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

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 30wt% of SPAni and 70wt% of Nafion produced selectivity ratios of 7.91×10⁴Sscm^-3 (at 20°C) and 1.97×10⁵Sscm^-3 (at 60°C), an ion-exchange capacity of 1.2meqg^-1 (at 20°C), methanol permeabilities of 9.12×10^-8cm²s^-1 (at 20°C) and 1.2×10^-7cm²s^-1 (at 60°C), and a current density of 128.7mAcm^-2 at +0.2V and 60°C and a corresponding maximum power density of 25.76mWcm^-2 using 6M methanol feed concentration. The cell performance, thus observed, is far better than that produced by pristine Nafion membrane under the same operating conditions.