Improved proton conduction of sulfonated poly (ether ether ketone) membrane by sulfonated covalent organic framework nanosheets

Abstract A type of sulfonated covalent organic framework nanosheets (TpPa-SO3H) was synthesized via interfacial polymerization and incorporated into sulfonated poly (ether ether ketone) (SPEEK) matrix to prepare proton exchange membranes (PEMs). The densely and orderly arranged sulfonic acid groups in the rigid skeleton of the TpPa-SO3H nanosheets, together with their high-aspect-ratio and well-defined porous structure provide proton-conducting highways in the membrane. The doping of TpPa-SO3H nanosheets led to an increased ion exchange capacity up to 2.34 mmol g−1 but a 2-folds reduced swelling ratio, remarkably mitigating the trade-off between high IEC and excessive swelling ratio. Based on the high IEC and orderly arranged proton-conducting sites, the SPEEK/TpPa–SO3H–5 membrane exhibited the maximum proton conductivity of 0.346 S cm−1 at 80 °C, 1.91-folds higher than the pristine SPEEK membrane. The mechanical strength of the composite membrane was also improved by 2.05-folds–74.5 MPa. The single H2/O2 fuel cell using the SPEEK/TpPa–SO3H–5 membrane presented favorable performance with an open voltage of 1.01 V and a power density of 86.54 mW cm−2.