Enhanced proton conductivities of chitosan-based membranes by inorganic solid superacid SO42−–TiO2 coated carbon nanotubes

Abstract

To increase proton conductivity of chitosan (CS) based polymer electrolyte membranes, a novel nanofiller-solid superacide SO42--TiO2 (STi) coated carbon nanotubes (STi@CNTs) are introduced into CS matrix to fabricate membranes for polymer electrolyte membrane fuel cells (PEMFCs). Owing to the STi coating, the dispersion ability of CNTs and interfacial bonding are obviously improved, hence, CNTs can more fully play their reinforcing role, which makes the CS/STi@CNTs composite membranes exhibit better mechanical properties than that of pure CS membrane. More importantly, STi possesses excellent proton transport ability and may create facile proton transport channels in the membranes with the help of high aspect ratio of CNTs. Particularly, the CS/STi@CNTs-1 membrane (1 wt% STi@CNTs loading) obtains the highest proton conductivity of 4.2 × 10−2 S cm–1 at 80 °C, enhancing by 80% when compared with that of pure CS membrane. In addition, the STi@CNTs also confer the composite membranes low methanol crossover and outstanding cell performance. The maximum power density of the CS/STi@CNTs-1 membrane is 60.7 mW cm−2 (5 M methanol concentration, 70 °C), while pure CS membrane produces the peak power density of only 39.8 mW cm−2.