Considerations of the Effects of Naphthalene Moieties on the Design of Proton-Conductive Poly(arylene ether ketone) Membranes for Direct Methanol Fuel Cells

Novel sulfonated poly(arylene ether ketones) (SDN-PAEK-x), consisting of dual naphthalene and flexible sulfoalkyl groups, were prepared via polycondensation, demethylation, and sulfobutylation grafting reaction. Among them, SDN-PAEK-1.94 membrane with the highest ion exchange capacity (IEC = 2.46 mequiv.g(-1)) exhibited the highest proton conductivity, which was 0.147 S. cm(-1) at 2 degrees C and 0.27.1 S.cm(-1) at 80 degrees C, respectively. The introduction of dual naphthalene moieties is expected to achieve much enhanced properties, compared to those of sulfonated poly(arylene ether ketones) (SNPAEK-x), consisting of single naphthalene and flexible sulfoalkyl groups. Compared with SNPAEK-1.60 with a similar IEC, SDN-PAEK-1.74 membrane showed higher proton conductivity, higher MC normalized conductivity, and higher effective proton mobility, although it had lower analytical acid concentration The SDN-PAEK-x membranes with IECs higher than 1.96 mequiv.g(-1) also exhibited higher proton conductivity, than that of recast Nafion membrane. Furthermore, SDN-PAEK-1.94 displayed a better single cell performance with a maximum power density of 60 mW.cm(-2) at 80 C.-Considering its high proton conductivity, excellent single cell performance, good, mechanical stabilities, low membrane-swetting, and methanol permeability, SDN-PAEK-x membarnes are promising candidates alternative polymer electrolyte membranes to Nafion for direct methanol fuel cell applications.