Confinement effect of natural hollow fibers enhances flexible supercapacitor electrode performance

Flexible and wearable supercapacitors (SCs) have received extensive attention due to their promising applications in wearable electronics. Previous efforts have been mainly devoted to fabricate electrode materials with high surface areas, including activated carbon through carbonizing natural fibers at high temperature. This methodology however frequently disintegrates the fibrous structures and fails to take full advantage of the intrinsic and foremost feature of the fibers as fabrics. Herein we proposed one alternative strategy to enhance SC performance through utilizing natural hollow Calotropis gigantea fibers (CGFs) with hydrophobic surfaces to confine conductive polymer of polypyrrole (PPy) both outside and inside of the fiber lumen. The in situ electrodeposited PPy enabled a full contact between the electrode material and electrolyte, enlarged the electrolyte accessible area and spurred the capacitive performance of the SC, which demonstrated a significantly improved specific capacitance of 785.78 mF cm(-2) at a current density of 4 mA cm(-2) compared with the 648.44 mF cm(-2) of SCs without the fibers (a 21.2% increase). The harness of confinement effect could potentially expand to be a general way to rationally design synthetic fibers with customized inner and outer diameter ratios, superficial hydrophobic/hydrophilic properties to realize optimum electrochemical performance for SCs. (c) 2017 Elsevier Ltd. All rights reserved.