Silane cross-linked network and concentrated flexible sulfoalkyl groups for forming a novel C-SPAEK membrane with enhanced methanol resistance and proton conductivity for DMFC applications

Abstract

In the present work, a novel poly(arylene ether ketone) with a unique molecular design that included concentrated flexible sulfoalkyl groups and a silane cross-linked network (C-SPAEK) was prepared and used as a PEM for DMFCs. The chemical structures, sulfonation degree and phase-separated morphology were characterized and identified by 1H NMR, FT-IR and SAXS. The resulting copolymers exhibited excellent thermal stability (T5%>263.8 °C) and mechanical properties (tensile strength>52.88 MPa). Additionally, the high IEC values and obvious hydrophilic/hydrophobic phase-separated structure (d > 2.71 nm) ensured that the C-SPAEK membranes possessed high proton conductivities. The C-SPAEK PEMs also displayed enhanced methanol resistance and dimensional stability, which were much better than those of a recast Nafion membrane under the same conditions. The C-SPAEK-0.4 membrane maintained a low methanol absorption of less than 48.7%, even in 4 M methanol solution. In particular, the C-SPAEK-0.6 membrane exhibited the best comprehensive performance, with a high proton conductivity (0.164 S cm−1), low methanol uptake (52.1%) and permeability (3.63 × 10−7 cm2 s−1), and maximum power density (83.2 mW cm−2), when immersed in 2 M methanol at 80 °C in a DMFC single-cell. These results suggested that the C-SPAEK membranes were sufficiently tough and had the potential to overcome the problems caused by the high methanol permeability of PEMs. The unique molecular design of C-SPAEK guaranteed a rare combination of high proton conductivity and enhanced methanol resistance, which are the key determining factors for DMFC applications.