Ultrafine microporous and mesoporous activated carbon fibers from alkali lignin

A facile and sustainable approach has been successfully devised to fabricate ultrafine (100–500 nm) highly porous activated carbon fibers (ACFs) by electrospinning of aqueous solutions of predominantly alkali lignin (low sulfonate content) followed by simultaneous carbonization and activation at 850 °C under N2. Incorporating a polyethylene oxide (PEO) carrier with only up to one ninth of lignin not only enabled efficient electrospinning into fibers but also retained fibrous structures during heating, alleviating the need for a separate thermal stabilization step. In situ impregnation of alkali hydroxide activating chemicals with only up to 50% of the lignin carbon precursor, i.e., merely one tenth to one quarter of the quantities used in manufacturing activated carbon particulates, allowed simultaneous carbonization and activation in a single heating step. A range of micropore-dominant to mesopore-dominant ACFs were successfully fabricated to achieve superior specific surface (>1400 m2 g−1) and porosity (>0.7 cm3 g−1) tuned by varying the type and contents of alkali hydroxides. This streamlined approach was robust and demonstrated the feasibility and versatility in processing and converting a readily available renewable carbon precursor, lignin, into highly porous activated carbon fibers.