Rationally engineering hierarchical porous carbon via oxidation-induced strategy for a high-performance flexible quasi-solid-state supercapacitor

The microporous carbon with abundant porosity contributes the most to the specific capacitance of double-layer capacitors. However, the single microporous structure limits the transport of electrolyte ions, resulting in unsatisfactory specific capacitance and rate performance of the material. In this work, the oxidation-induced pores customization strategy provides more active sites for the diffusion of CuCl2, which facilitates the formation of hierarchical porous structures. The optimal sample exhibits high specific capacitance (322.3 F/g at 0.5 A/g) and long cycle stability (the capacitance retention increased to 108.49% after 50,000 cycles) in 6.0 M KOH electrolyte. The universality of the oxidation-induced strategy can also be proved by different carbon sources (apples and carrots). Moreover, potato starch is cross-linked with polyvinyl alcohol/glycerol/KCl to form a gel electrolyte with good flexibility and conductivity (4.7 S/m). As a result, a symmetric flexible quasi-solid-state supercapacitor is constructed with all key components (electrode, separator, and electrolyte), which are entirely derived from potato. It has delivered the maximum energy density and power density of 28.2 Wh/kg and 20,000 W/kg, respectively, at the voltage of 0–1.6 V. This work offers an effective way for the conversion of single biomass to the construction of flexible energy storage devices.