Sulfonated Polybenzothiazoles Containing Hexafluoroisopropyl Units for Proton Exchange Membrane Fuel Cells
Gang Wang, Shuai Yang, Na Yoon Kang, Bingyan Hua, Mingxia Lu, Hongliang Wei, Jiaqi Kang, Wenshuai Tang, Young Moo Lee
Abstract
A sulfonated dicarboxylic monomer containing hexafluoroisopropyl, i.e., 3,3′-disulfonate-2,2-bis(4-carboxyphenyl)hexafluoropropane (SCFA), was prepared via sulfonation and oxidation to synthesize novel sulfonated polybenzothiazoles (sPBT-F) through polycondensation of 2,2-bis(4-carboxyphenyl)hexafluoropropane (CFA), SCFA, and 2,5-diamino-1,4-benzenedithiol dihydrochloride (DABDT). These sPBT-F series polymers exhibited excellent solubility due to the incorporation of a flexible hexafluoroisopropyl group. Meanwhile, the sPBT-F series polymers displayed high thermal stability and were used to prepare tough and soft membranes by solution casting. Interestingly, sPBT-F series membranes exhibited excellent water uptake and low swelling ratio, indicating excellent dimensional stability. AFM images displayed a region of obvious separation of light/dark phases, indicating high proton conductivity of sPBT-F series membranes. The sPBT-F82.5 membrane with a high degree of sulfonation demonstrated a conductivity of 0.14 S cm –1 at 80 °C and 100% RH, superior to the results of Nafion 117. Furthermore, the sPBT-F82.5 membrane displayed a maximum power density of 344.33 mW cm –2 and superb durability at a current density of 0.2 A cm –2 for 20 h. In summary, the sPBT-F polymers are potential matrix materials for PEMs.