Biologically Inspired Small Herbal Biomolecules and Biomass Carbon for High-Performance Supercapacitors

A hybrid system electrode composed of porous lignin-based graphitic carbon (PLGC) and small herbal biomolecules such as Rhein (RH) with abundant redox centers is demonstrated to increase the specific capacitance and cycle stability of biomass electrode materials. RH molecules with abundant anthraquinone content, derived from the rhubarb (Rheum palmatum L.) root extracts, are responsible for increasing energy storage capacity, whereas PLGC with continuous three-dimensional (3D) porous framework provides an effective platform for bulk charge transport corresponding to the RH redox process within the composite electrodes. The RH/PLGC composite electrodes exhibited exceptional specific capacitance values of 250.2 F g–1 at 1.0 A g–1, and meanwhile, the capacity fading was effectively suppressed using an RH-saturated electrolyte, indicating the excellent compatibility of this biomass-based electrode material and the corresponding redox-active biomolecule-saturated electrolyte for large-scale production. Furthermore, through the use of gel electrolyte (PVA/KOH/RH), the assembled symmetric biomass-based supercapacitors demonstrate the significant specific capacitance, operational stability >3000 cycles, and considerable energy density. The utilization of biomolecules with redox centers by elucidating the charge storage mechanism will enrich the efficient and green energy storage technologies.