Pseudocapacitance electrode and asymmetric supercapacitor based on biomass juglone/activated carbon composites

A novel electrode material incorporating renewable biomass-derived juglone biomolecules with commercial activated carbon (AC) granules has been through simple ultrasonic dispersion and dissolution-recrystallization and was found to exhibit good electrochemical performance. The juglone biomolecules are prepared by an ultrasound-assisted extraction method from abandoned walnut peel, which decreases pollution and increases economic efficiency. Through the dissolution-recrystallization process with AC, a hierarchical structure with nanosized juglone particles was obtained, and the AC particles worked as scaffolding to strengthen the slight biomolecules, thus expanding the active sites and effectively reducing the dissolution of the active materials. The pseudocapacitance fading mechanism was investigated by ex situ FTIR measurement and the porous structure ensures that the composite electrode has an enhanced specific capacitance of 248 F g^-1 compared to 172.8 and 62.5 F g^-1 for the respective AC and juglone samples. Besides, the excellent cyclic stability (retained 75% after 3000 charge-discharge cycles) was demonstrated. The highest area-specific capacitance of the composites was 1300 mF cm^-2. An asymmetric supercapacitor based on this composite electrode was assembled with an AC electrode as the counter electrode and exhibited good cyclic performance at a voltage of 1.2 V (retained 77% after 3000 charge-discharge cycles), which provides a high energy density of 12 W h kg^-1 at a power density of 0.18 kW kg^-1 and a high power density of 2 kW kg^-1 at an energy density of 9 W h kg^-1. This work explores the application of biomolecule-based composites in energy storage devices and provides a potential strategy for constructing environmentally friendly electrodes.