Ball milling combined with activation preparation of honeycomb-like porous carbon derived from peony seed shell for high-performance supercapacitors

Porous carbon, derived from biomass, has a high specific surface area and is one of the most attractive electrode materials for supercapacitors. Nonetheless, it is difficult to find a simple and efficient method to process inexpensive raw materials, which is also suitable for large-scale manufacture. This paper proposes a facile and scalable ball-milling combined with KOH chemical activation strategy to prepare the honeycomb-like porous carbon framework with high micropores and small dimensional mesopores from the peony seed shells (PS). Ball-milling technology was used to generate the necessary mechanical force to break the bulk biochar coming from the carbonization of PS into small pieces and increase the accessible surface area for the activation process. In addition, more ordered structures are transformed from sp 3 -hybridized carbon to sp 2 -hybridized carbon, which enhances the degree of graphitization for the obtained porous carbon. Furthermore, during the ball-milling and chemical activation process, the incorporation of oxygen atoms into the carbon base of as-prepared materials increases its hydrophilicity which facilitates a better interfacial contact between the hydrated electrolyte ions and the electrode surface in the process of charge and discharge. As a result, an as-fabricated supercapacitor, which is made of this highly porous carbon material, can reach a high specific capacitance (339 F g −1 ) at a current density of 1 A g −1 . The other obtained key parameters for capacitors are also excellent: rate performance (260 F g −1 at 20 A g −1 ), cycling stability (95.2% capacitance retention after 10,000 cycles at a current density of 1 A g −1 ). In addition, a high energy density (29.6 Wh kg −1 at 180 W kg −1 ) can be achieved when the material is used in a 1.6 V Na 2 SO 4 aqueous symmetrical supercapacitor. These results confirm that ball-milling (together with chemical activation) can successfully produce honeycomb-like porous carbon from peony seed shells. The developed electrode material has great potential to be applied in practical high-performance supercapacitors.