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

Solid-state supercapacitors hold great promise in future portable electronics. However, designing ideal electrode materials from eco-friendly strategies to further improve the energy density and operational potential window is crucial for commercialization of the devices. Herein, a clean and economic strategy to fabricate a 3D self-doped honeycomb-like carbonaceous material from biowaste is reported. The optimal carbon sample (HSC-0.50) features high surface area and relatively high packing density, resulting in outstanding performance. A thorough electrochemical investigation is also involved in this work, which shows that the gravimetric and volumetric capacitances of the prepared HSC-0.50 sample are obtained as high as 281.4 F g^–1 and 247.6 F cm^–3 at 0.5 A g^–1 coupled with a superior rate capability (83.2% retention at 100 A g^–1). In addition, the HSC-0.50 sample can deliver high volumetric and areal 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 of 20 mg cm^–2. Remarkably, a 1.8 V symmetric quasi-solid-state supercapacitor is successfully constructed by using the HSC-0.50 electrode in a seldom used gel electrolyte (carboxymethylcellulose sodium/sodium sulfate, CMC-Na/Na₂SO₄). A superhigh energy output of 23.4 Wh kg^–1 over that of an alkaline device (7.6 Wh kg^–1) with excellent cyclability over 10 000 cycles can be achieved in the as-designed cell. This research highlights that the utilization of high-voltage CMC-Na/Na₂SO₄ gel as a low-cost and eco-environmental electrolyte, coupled with sustainable and high-capacitance biowaste-derived carbon, may open up a new avenue for the establishment of promising energy storage systems.