Preparation of Random Polymers by Copolymerization of Rigid-Twisted Spirobiindane with Poly(aryl isatin) for High-Performance Anion Exchange Membranes

Designing the packing of polymer chains with reasonable fraction free volume (FFV) is regarded as an effective way to improve the conductivity of polymer-based membranes. We synthesize random polymers by copolymerization of bulky rigid-twisted spirobiindane, isatin, and one of the joint groups p-terphenyl, biphenyl, and 1,2-diphenylethane. The polycondensation reaction is catalyzed by trifluoromethanesulfonic acid. The introduced spirobiindane segments enlarge the distance of polymer chains and increase the FFV of the membrane. The formation of the microphase separation structure is evidenced according to the results of transmission electron microscopy and atomic force microscopy. As a result, a hydroxide conductivity of 126.7 mS cm–1 is achieved at 80 °C by the poly(spirobiindane diphenyl isatin)-based membrane (QP(SBP/BP)-20). The retention rates in hydroxide ion conductivity are 89.7 and 84.0% after soaking the membrane in 1 M KOH for 1152 h and in 4 M KOH for 628 h at 80 °C, respectively. The QP(SBP/BP)-20 membrane-based single-fuel cell exhibits an open-circuit voltage of 0.99 V and a peak power density of 744 mW cm–2 at 60 °C by fueling with humidified H2 and O2 with 0.05 MPa back pressure.