High methanol resistance semi-crystalline sulfonated poly(ether ketone) proton exchange membrane for direct methanol fuel cell

Abstract

Three new sulfonated and semi-crystalline poly(ether ketone)-type copolymers (Cr-SPEK) with densely sulfonated microblock of different length are synthesized and evaluated as proton exchange membranes. The relationship between molecular structure of copolymers, microscopic morphology and macroscopic performance of membranes are studied: The increase in the length of the hydrophilic sulfonated microblock facilitates constructing well-connected ionic transport channels, which improves the proton conduction of Cr-SPEK membranes. And expanding the size of hydrophobic poly(ether ketone) (PEK) block promotes higher crystallinity of copolymers, resulting in enhancing dimensional stability, mechanical tensile, oxidation stability and methanol resistance of Cr-SPEK membranes. The tCr-SPEK membrane with longest hydrophilic microblock and maximum crystallinity (15.2%) exhibits best comprehensive performance. The proton conductivity and swelling ratio of the tCr-SPEK membrane measured under fully hydrated state at 80 °C are 146.7 mS cm−1 and 11.9%, respectively. And the methanol permeability of tCr-SPEK membrane is only 1.1 × 10−7 cm2 s−1, which is nearly one-sixteenth of that of Nafion 117 membrane. The single cell performance of tCr-SPEK membrane in direct methanol fuel cells (DMFCs) continuously grows with the higher concentration of methanol solution until 12 M. Therefore, the tCr-SPEK membrane represents great potential for application in DMFCs.