Preparation and Mechanism Investigation of Walnut Shell-Based Hierarchical Porous Carbon for Supercapacitors

The reasonable regulation of porous structure and crystallinity has been focused on supercapacitor development. Here, hierarchical porous carbons have been prepared by a hybrid of chemical activation and template methods using walnut shells as carbon source, and KMnO4 as activator and template agent. The activation mechanism of KMnO4 at different activation temperatures has been studied based on the XRD and TG analysis. Due to the synergy of rich oxygen-containing functional groups and hierarchical porous structure, the hierarchical porous carbon materials show a high capacitance of 380 F g−1 at 0.5 A g−1, good cycling stability with 93% capacitance retention even after 10000 continuous charge-discharge cycles at 5 A g−1. Additionally, the assembled symmetric supercapacitor has a high energy density of 8.95 Wh kg−1. This study shows that KMnO4 activation is a mild and highly efficient way to prepare high performance carbon electrode materials for supercapacitors.