Humidity-Controlled Preparation of Flexible Porous Carbon Fibers from Block Copolymers

Growing demands in flexible electronics have stimulated the rapid development of electrodes with multifaceted attributes. Porous carbon fibers (PCFs) provide a potential means to simultaneously achieve flexibility, durability, and energy density. High energy density often necessitates large surface areas and thus pores, but pores generally diminish the mechanical properties. Here, we electrospin poly(methyl methacrylate)-block-poly(acrylonitrile) (PMMA-b-PAN) and examine the changes in the polymer morphology and resulting PCF porosity and flexibility in response to relative humidity (R.H.). The determining factors of the fiber morphology evolve from block copolymer microphase separation at 40–50% R.H. to vapor-induced phase separation (VIPS) combined with microphase separation at 60–70% R.H. and to vapor-induced precipitation at 80–90% R.H. After pyrolysis, the PCFs show the corresponding porosity, flexibility, and electrochemical properties. Because VIPS enables the polymer fibers to outwardly reorganize PAN and produce continuous graphitic structures, PCFs prepared from polymer fibers electrospun at 70% R.H. develop a mesoporous core and long-range graphitic carbon sheath. Owing to the core–sheath structure, these PCFs exhibit mechanical strength to withstand repeated bending while retaining a 249 ± 20 F g–1 capacitance in flexible capacitor assemblies. This work highlights the potential for controlling block copolymer morphologies by processing conditions and PCF properties, providing a platform for designing flexible PCFs for energy and environmental sciences.