Novel sulfonated poly(oxybenzimidazole) membranes bearing sulfo-napthalimide pendant groups with improved proton conductivity and fuel cell performance

Abstract

The goal of the present work is to introduce a new aromatic bulky six-membered sulfo-napthalimide pendant groups, specifically 2-(2,5-dicarb-oxyphenyl-1,3-dioxo- 2,3-didihydro-1Hbenzo[de]isoquinoline-6-sulfonate (PDDDBIS), into the poly(oxybenzimidazole) (POBI) main chain. As no sulfo-napthalimide-bearing POBI has been reported yet, this could be a potential strategy to improve the solubility, processability, and proton conductivity of sulfonated POBIs in addition to boosting fuel cell performance. Out of six membranes synthesized, one sulfonated POBI membrane with pendant PDDDBIS groups (SPOBI-100) exhibited a fairly high proton conductivity of 0.172 S/cm, which is higher than Nafion-117 (0.161 S/cm) at 90 °C. Notably, an H2/O2 PEM fuel cell fabricated with the SPOBI-100 membrane displayed good performance with the maximum peak power density of 547 mW/cm2 and output current density of 1259 mA/cm2 in 0.99 V at 90 °C with100% RH, which is higher than the Nafion 117 power density (519 mW/cm2) and current density (1215 mA/cm2) under the same testing conditions.