Combination of redox-active natural indigo dye and bio-derived carbon from ridge gourd fruit for high-performance asymmetric supercapacitors

A low-cost, high surface area, and hierarchically porous activated carbon (ACRG-800) was derived via KOH activation and a one-step carbonization process of dried ridge gourd (RG) fruits. ACRG-800 was microporous in nature with a specific surface area of ∼1370 m2 g−1. When supercapacitor (SC) electrodes were fabricated using ACRG-800, high charge storage capacity with a specific capacitance of 352 F g−1 (at a current density of 2 A g−1) and 280 F g−1 (at a current density of 2 A g−1) was attained in three-electrode and symmetric two-electrode system in aqueous 1 M H2SO4 electrolyte, respectively. Further, the redox-active indigo (IND) dye was mixed with ACRG-800 to obtain ACRG-800-IND. Asymmetric SC device, fabricated using ACRG-800 positive electrode and ACRG-800-IND negative electrode in 1 M H2SO4 electrolyte, exhibited high specific energy of 13.2 Wh kg−1 at specific power of 1 kW kg−1 when operated at 2 A g−1 in the voltage range of 0 to 1 V. Briefly, the high surface area framework of ACRG-800 provides an outstanding electrical double-layer capacitance, while IND adds faradaic pseudocapacitance. Graphical abstract: [Figure not available: see fulltext.]