Biowaste-Derived Porous Carbon with Tuned Microstructure\nfor High-Energy Quasi-Solid-State Supercapacitors

Abstract

Solid-state supercapacitors\nhold great promise in future portable\nelectronics. However, designing ideal electrode materials from eco-friendly\nstrategies to further improve the energy density and operational potential\nwindow is crucial for commercialization of the devices. Herein, a\nclean and economic strategy to fabricate a 3D self-doped honeycomb-like\ncarbonaceous material from biowaste is reported. The optimal carbon\nsample (HSC-0.50) features high surface area and relatively high packing\ndensity, resulting in outstanding performance. A thorough electrochemical\ninvestigation is also involved in this work, which shows that the\ngravimetric and volumetric capacitances of the prepared HSC-0.50 sample\nare obtained as high as 281.4 F g^–1 and 247.6 F\ncm^–3 at 0.5 A g^–1 coupled with\na superior rate capability (83.2% retention at 100 A g^–1). In addition, the HSC-0.50 sample can deliver high volumetric and\nareal capacitances of 204.7 F cm^–3 and 4.7 F cm^–2 using a 6.0 M KOH electrolyte even under a high loading\nof 20 mg cm^–2. Remarkably, a 1.8 V symmetric quasi-solid-state\nsupercapacitor is successfully constructed by using the HSC-0.50 electrode\nin a seldom used gel electrolyte (carboxymethylcellulose sodium/sodium\nsulfate, CMC-Na/Na₂SO₄). A superhigh energy\noutput of 23.4 Wh kg^–1 over that of an alkaline\ndevice (7.6 Wh kg^–1) with excellent cyclability\nover 10 000 cycles can be achieved in the as-designed cell.\nThis research highlights that the utilization of high-voltage CMC-Na/Na₂SO₄ gel as a low-cost and eco-environmental electrolyte,\ncoupled with sustainable and high-capacitance biowaste-derived carbon,\nmay open up a new avenue for the establishment of promising energy\nstorage systems.