BACKGROUND: Three-dimensional and hierarchical porous materials enriched with 2D nanostructure can boost the electrochemical performance of carbon-based electrodes in the supercapacitor devices. These materials are obtained from novel precursors of palm oil stock biomass. The unique combination of hierarchical and 2D nanostructures was controlled using ZnCl 2 impregnation of 0.3-0.9 mol L −1 with high-temperature pyrolysis.RESULTS: Impregnation with 0.5 mol L −1 ZnCl 2 (POSC5) produced the highest specific surface area with dominant micropores of 89% in a total volume of 0.343 cm 3 g −1 . POSC5 was shown to have an excellent morphological combination of trimodalfoam-sponge-like hierarchical porosity with large messy short 2D nano-rod structures as the optimum carbon preparation. A symmetrical system was designed as a solid electrode without a binder, confirming high capacitive properties of 256 F g −1 in 1 mol L −1 H 2 SO 4 electrolyte with capacitance retention of 76% at 10 mV s −1 . The results showed that the transport and resistance behavior of the charge tends to be stable and satisfactory at an internal resistance of 0.012 Ω, with the energy density increased from 9.14 to 21.19 W h kg −1 at 1 A g −1 in 1 mV s −1 . CONCLUSION: Therefore, this research provides an environmentally benign and novel approach for developing a high-quality, sustainable biomass carbon-based electrode material for electrochemical energy storage applications.

BACKGROUND: Two-and three-dimensional porous activated carbon (C)-based symmetrical supercapacitors show great potential for extraordinary gravimetric performance as sustainable energy storage. However, the applications of portable and microdimensional supercapacitors are limited by their low volumetric performance stemming from reduced density resulting from increased porosity and high fabrication costs. This study aimed to demonstrate the high gravimetric-volumetric performance of symmetrical supercapacitors from biomass-based porous carbon-sources materials through an environmentally benign development method. Unique porous C sourced from TENERA-type palm oil stick waste was prepared using potassium hydroxide (KOH) as an activating agent. The electrode set resembled a solid plate with an encapsulation density of ≈1.40 g cm −3 .RESULT: The study used superior gravimetric-volumetric electrode materials, including an adjusted specific surface area of 934 m 2 g −1 , single-doped optimization, and a hollow paper-stack-like morphological structure with a high C content of 91%. The results showed that the best electrode in the 1 mol L −1 H 2 SO 4 electrolytes exhibited a high gravimetric capacitance of 233 F g −1 and an extraordinary volumetric capacitance of 326 F cm −3 at 1 A g −1 . Furthermore, their coulombic efficiency was ≈99.1% at 10 A g −1 . The symmetrical electrode device performed a high gravimetric-volumetric energy density of 19.03 Wh kg −1 and 26.6 Wh L −1 at a maximum output power density of 1.7 kW kg −1 and 1.9 kW L −1 , respectively. CONCLUSION: These results indicate that the applied method development and the C-biomass-based electrode material design could achieve a high, well-matched gravimetric-volumetric performance balance in symmetric supercapacitor devices.