Enhancement in proton conductivity and methanol resistance of Nafion membrane induced by blending sulfonated poly(arylene ether ketones) for direct methanol fuel cells

Abstract

In the present work, three kinds of sulfonated poly(arylene ether ketones) (SPAEKs) with different structures are introduced into Nafion as blending modifiers to enhance the properties of Nafion, especially methanol resistance. Characterizations such as transmission electron microscope (TEM), proton conductivity, methanol crossover, and single cell performance, are carried out to evaluate these composite membranes (SPAEK@Nafion) as prepared. Besides, recast Nafion membrane is prepared and characterized for comparison via the same method. By investigating the microstructure of SPAEK@Nafion membranes, p-BPAF@Nafion membrane is found to have the most homogeneous distribution and Nafion-like phase separation among these membranes. The pendent sulfobutyl side-chain and fluorinated main chain of p-BPAF make it most similar structure with Nafion among three modifiers, and such Nafion-liked structure provides p-BPAF a good compatibility with Nafion, which can facilitate its enhancement for Nafion. Consequently, p-BPAF@Nafion-7.5 exhibits higher proton conductivity (0.256 S cm−1), lower methanol permeability (1.87 × 10−6 cm2 s−1), and better selectivity (13.69 × 104 S s cm−3) than those of recast Nafion. Therefore, owing to high proton conductivity and good methanol resistance, p-BPAF@Nafion-7.5 possesses a good DMFC performance with an open circuit voltage of 0.836 V and a peak power density of 111.53 mW cm−2, when fed with 2 M methanol at 80 °C.