Highly conductive and robust reinforced poly(fluorene‐alkylene isatin) based anion exchange membrane: Effect of chain length in alkylated isatin

Abstract A series of poly(fluorene‐alkylene isatin) based anion exchange membranes containing various N‐alkylisatins in the main chain were successfully prepared. Butylisatin‐based polymer (IS‐P4‐TMA) showed good membrane formability but weak mechanical properties. Reinforcement of methylisatin (IS‐P1‐TMA‐PE) and ethylisatin (IS‐P2‐TMA‐PE) based polymers with porous polyethylene (PE) substrate was successful. The cross‐sectional SEM images of reinforced membranes showed a homogenous three‐layered structure. TEM images showed a well phase‐separated morphology of both self‐standing and reinforced membranes. IS‐P1‐TMA‐PE exhibited the highest ion conductivity (135 mS cm −1 at 80°C). However, IS‐P2‐TMA‐PE with ethylisatin exhibited the most balanced properties of low water uptake, reasonable conductivity (88 mS cm −1 ), and excellent alkaline stability in 1 M KOH at 80°C for 1000 h (94.13%, 83.5 mS cm −1 ). Furthermore, IS‐P2‐TMA‐PE achieved excellent viscoelasticity, better thermal stability, and elongation properties (13.5 MPa stress and 170% elongation at break). DFT calculations revealed that the excellent alkaline stability of IS‐P2‐TMA‐PE was attributed to the higher free energy and higher charge density distribution. A single fuel cell with IS‐P1‐TMA‐PE membrane achieved a power density of 112 mW cm −2 at a current density of 228 mA cm −2 . Highlights A series of poly(fluorene‐alkylene isatin) was successfully prepared. Reinforcement using polyethylene as a substrate was successful. High conductivity and alkaline stability of reinforced poly(fluorene‐alkylene isatin). Excellent viscoelasticity, thermal stability, and tensile strength were achieved. Reasonable fuel cell performance of 112 mW cm −2 .