Value-added functional carbon for potential electrodes and its validation

Abstract

Carbon-based porous materials suffer from insufficient electric charge storage capacity and limited energy density; however, those can be tailored to enhance electrochemical performance via induced pseudo-capacitance. This study introduces a facile synthesis technique that delivers a novel class of redox-active porous‑carbon materials from human hair—a keratin fiber from municipal waste feedstock—by direct pyrolysis and surface activation. Retention of ~33 atomic% of redox-active species in microporous‑carbon with a pore volume of 1.1 cm3 g−1 drastically enhances the BET surface area ~ 2957 m2 g−1 and electrochemical electrode properties. This carbon-based electrode exhibits ~70 % rate-capability at 20 A g−1. Contrastingly, mesoporous carbon with relatively low heteroatom content 20–25 atomic%, significantly reduced pore volume ~ 0.1 cm3 g−1 delivers high electrode capacitance 877 F g−1 that diminishes rapidly, providing 20 % rate capability at 20 A g−1. When configured as a supercapacitor device, red-ox active carbons exploit contributions from EDLC and pseudo-capacitance. COMSOL Multiphysics has been used to study the carbon arrangement for delivering high capacitance value. The carbon sphere with an 8 nm diameter having a pore length of 7.3 nm shows a similar capacitance achieved experimentally. While the microporous carbon-based device shows a moderate energy density of 7.6 Wh kg−1, the mesoporous carbon shows a higher energy density of 30 Wh kg−1 at a power density of 325 W kg−1. Both devices offer good high-rate capabilities at high current densities. In organic electrolyte 1 M LiPF6 EC/DEC, the symmetric assembled PC-9 deliver excellent specific capacitance 286 F g−1 at 1 A g−1 with maximum energy density of 124 Wh kg−1 at a power density of 1250 W kg−1. Thus, this research demonstrates a new class of sustainable carbon with tunable energy storage potential.