Quasi-solid, bio-renewable supercapacitor with high specific capacitance and energy density based on rice electrolytes and rice straw-derived carbon dots as novel electrolyte additives

In this work, novel quasi-solid electrolytes and carbon dots as additives were developed for the bio-renewable, high energy-density supercapacitor. The activated carbon from rice straw was used to make an electrode while the carbon dots also from rice straw were combined with rice electrolytes. The supercapacitor using H3PO4/rice electrolyte yielded a specific capacitance, potential window, and energy density of 88 F g−1, 2 V, and 12 Wh kg−1, respectively, at a scan rate of 30 mV s−1. For comparison, electrolyte prepared from conventional H3PO4/poly(vinyl alcohol) yielded only 45 F g−1, 1.6 V, and 4 Wh kg−1. The addition of carbon dots to H3PO4/rice electrolytes further increased the specific capacitance, potential window, and energy density to 144 F g−1, 2.4 V, and 29 Wh kg−1, equivalent to 163%, 120%, and 241% enhancement, respectively. The maximum specific capacitance and energy density reached 491 F g−1 and 98 Wh kg−1, respectively, at a scan rate of 2 mV s−1. The carbon dots improved the supercapacitor performance by simultaneously enhancing the adsorption and diffusion of electroactive species and surface capacitance. Interestingly, the electrode was prepared without the addition of highly conductive carbon and still produced excellent supercapacitor performances. This work thus demonstrates a novel and simple strategy for using a bio-renewable resource for the fabrication of high-performance supercapacitors, which have great practical potential in the field of portable and wearable electronic devices.