In situ K₂S activated electrospun carbon nanofibers with hierarchical meso/microporous structures for supercapacitors

Porous electrospun carbon nanofibers (CNFs) can be produced by a more advantageous 'in situ activation' method by electrospinning polyacrylonitrile (PAN) with an activation agent. However, most in situ activated electrospinning processes yield porous CNFs with rather limited surface area and less porosity due to the inappropriately selected activation agents. Here we found K₂S could perfectly meet both compatibility and reactivity requirements of PAN electrospinning to generate hierarchical meso/micropores inside electrospun CNFs. During the whole fabrication process, K₂S experiences a phase evolution loop and the hierarchical pore structures are formed by the reaction between K₂S oxidative derivatives and the as-formed carbon during heat treatment. The hierarchical meso/microporous CNFs not only showed a large surface area (835.0 m² g^-1) but also exhibited a high PAN carbonization yield (84.0 wt%) due to improved cyclization of PAN's nitrile group during the pre-oxidation stage. As an electrode material for supercapacitors, the corresponding electrodes have a capacitance of 210.7 F g^-1 at the current density of 0.2 A g^-1 with excellent cycling durability. The hierarchically porous CNFs produced via in situ activation by K₂S combine the advantages of interconnected meso/micropores and are a promising candidate for electrochemical energy conversion and storage devices.