Preparation of hierarchical porous carbon through one-step KOH activation of coconut shell biomass for high-performance supercapacitor

Here we report an effective and facile method for preparing porous carbons (CSCK-T-x) with highly developed hierarchical porosity for high-performance supercapacitor by one-step KOH activation of coconut shell carbon. The effects of carbonization temperature (T, °C) and KOH/C ratio (x) on the structure and electrochemical properties were studied systematically. As the KOH/C ratio and activation temperature increase, the SBET rapidly increases and then decreases and reaches a maximum (2143.6m2 g−1) at 800 °C with a KOH/C ratio of 2. Furthermore, CSCK-800-2 displayed abundant micropores and two concentrated mesopores at 4 nm and 14 nm. In a three-electrode test system, CSCK-800-2 exhibits a high specific capacitance of 317 F g−1 at a current density of 0.5 A g−1 and considerable rate retention of 68% at 20 A g−1. The symmetrical supercapacitor that was based on CSCK-800-2 showed a maximum energy density of 13.5 Wh kg−1 at 0.5 A g−1 with a superior cycling stability (99.7% of the capacitance retention after 10,000 cycles at 5 A g−1) in 6 M KOH electrolyte. The large specific surface area and unique hierarchical porosity of CSCK-800-2 enable it to have high ion-accessible surface and low-ion transport resistance. This one-step activation method provides an approach to convert biological waste into high-value hierarchical porous carbon material for electric double-layer capacitors.