Quasi-Solid, Bio-Renewable Supercapacitors Based on Cassava Peel and Cassava Starch and the Use of Carbon Dots as Performance Enhancers

Abstract

Despite receiving high regard as potential energy storage devices, high-performance supercapacitors that can be produced from bio-renewable sources at low cost are still in need. In this work, a novel fabrication process for cassava-based supercapacitors was described in which carbon dots (CDs) and activated carbon (AC) were prepared from cassava peel and a quasi-solid polymer electrolyte was prepared for the first time from cassava starch (CS). A specific capacitance (Csp) of 138.2 F g–1 was obtained from the AC electrode in the CS/H2SO4 electrolyte, which was much greater than 95.9 F g–1 of the AC electrode in a PVA/H2SO4 solution. The CDs were employed as additives in the electrode and electrolyte. The addition of 10 wt % CDs to the AC electrode in the pristine CS/H2SO4 electrolyte increased the Csp to 239.5 F g–1. When 0.02 wt % CDs were added to the CS/H2SO4 electrolyte, a high specific capacitance of 374.6 F g–1 was obtained. Moreover, the fabricated supercapacitor exhibited an impressive cycling stability of 93.3% after 10,000 cycles and showed good performance in a wide temperature range from −40 to 50 °C. Based on intensive electrochemical analysis using several models, the CDs were demonstrated to improve the Csp and cycling stability by enhancing the surface capacitance and surface-controlled processes. In this work, a novel, simple strategy was demonstrated for fabricating practical, high-performance supercapacitors from cassava at a low cost.