Boosting the capacity of biomass-based supercapacitors using carbon materials of wood derivatives and redox molecules from plants†
A hybrid system electrode made from a biomass-based material sodium lignosulfonate-derived hierarchical porous graphitic carbon (PGLS) and an organic redox compound (alizarin) is demonstrated. A derivative of alizarin called “alizarin red S” (ARS) improves energy storage capacity while PGLS-1 synthesized from high-molecular-weight sodium lignosulfonate (LS), using K2FeO4 to achieve synchronous carbonization and graphitization, provides a continuous 3D porous framework with a certain graphitic order for the bulk charge transport and ARS self-organization within the composite electrode. The composite ARS/PGLS-1 electrode exhibits outstanding gravimetric specific capacitances (469.5 and 200.2 F g−1 at current densities of 0.5 and 10.0 A g−1, respectively, for the ARS/PGLS-1 = 1 sample), indicating that ARS is compatible with PGLS-1 carbon-based supercapacitor systems that can be produced on a large scale. Furthermore, the assembled symmetric prototype redox-enhanced supercapacitor (SPRS) in an aqueous gel electrolyte (PVA/KOH/ARS) is demonstrated to have considerable specific capacitance, operational stability of over >2000 cycles, and synergetic energy-power output characteristics in practical applications. This new class of supercapacitors based on biomass materials represents a significant step toward green and sustainable energy storage technologies.