Partially Sulfonated Poly(vinylidene fluoride) Induced Enhancements of Properties and DMFC Performance of Nafion Electrolyte Membrane

Partially sulfonated poly(vinylidene fluoride) (SPVdF) has been prepared by incorporation of sulfonic acid groups within poly(vinylidene fluoride), using chlorosulfonic acid as the sulfonating agent. The degree of sulfonation (DS) has been varied by modulating the duration of the sulfonation reaction. Blending of SPVdF (having DS = 36.78%) with Nafion at a constituent wt.% ratio of SPVdF: Nafion = 70: 30 has resulted in the fabrication of polymer electrolyte membrane with superior properties compared to pristine Nafion-117 membrane. This particular blend composition exhibited a proton conductivity value of 3.6 x 10(-2) S cm(-1) (i. e. similar to 12.5% increase over Nafion-117), a methanol permeability value of 6.81 x 10(-7) cm(2) s(-1) at 6M methanol concentration (i. e. similar to 99.31% decrease from Nafion-117) and a corresponding membrane selectivity value of 5.29 x 10(4) Ss cm(-3) (i. e. an increase of approximately two-orders of magnitude over Nafion-117) at 20 degrees C. In addition, this blend composition has also exhibited (a) better heat stability at temperatures as high as 160 degrees C by virtue of it possessing higher glass transition temperature, (b) higher storage modulus, (c) higher stress relaxation at high angular frequency and (d) superior DMFC performance at high methanol feed concentration in presence of humidified, as well as, non-humidified air as the catholyte, compared to Nafion-117 membrane.