Usability of unstable metal organic framework enabled by carbonization within flow battery membrane under harsh environment

Metal organic frameworks (MOF) with regular pore structure and adjustable pore size show great potential to boost membranes with controllable ion sieving and high proton conductivity for energy storages. However, the instability of framework under harsh conditions such as strong acid and oxidation is still a great challenge for its practical application. Herein, acid-stable carbonized ZIF-8 (CZIF-8) was obtained by carbonization and further introduced into the sulfonated poly (ether ether ketone) (SPEEK) matrix to fabricate SPEEK/CZIF-8 hybrid membranes. The well-retained porous structure of CZIF-8 efficiently blocked the vanadium ions and at the same time provided additional proton pathways. Consequently, the optimized hybrid membranes exhibited significantly improved coulombic efficiency (CE, 98.1–99.1%) and energy efficiency (EE, 82.7–94.4%) compared to that of pure SPEEK (CE: 97.3–99.1% and EE: 76.5–92.7%) and Nafion 212 membrane (CE: 90.8–96.9% and EE: 77.0–86.1%) at 20–100 mA cm⁻². This work affirms that carbonized-strategy is a feasible approach for exploiting the porous properties of unstable MOF materials in developing high-performance proton conductive membrane under harsh environment.