Hierarchical porous carbon microtubes derived from corn silks for supercapacitors electrode materials

In this paper, efforts are made to develop a novel, simple, efficient yet low-cost method to prepare carbon microtubes (CMTs) derived from corn silks through one-step carbonization process. Furthermore, the CMTs are activated by KOH to prepare hierarchical porous carbon microtubes (HPCMTs) as an electrode material for supercapacitor. The HPCMTs not only inherite the hollow tube-like structure from corn silks but also possess micropores, mesopores, macropores. A maximum specific surface area of 1962.4 m(2) g(-1) is achieved by HPCMTs-2, which the weight ratio of KOH/CMTs is 2. The electrochemical performance of the HPCMTs-2 are appraised in 6 M KOH solution as electrolyte via threeelectrode system. The electrode materials present the maximum specific capacitance of 291.2 F g(-1) at 0.1 A g(-1). When the current density increases 200 times to 20 A g(-1), the capacitance retention rate is 69.6%. Beyond that, the practical application properties of HPCMTs-2 electrode materials are evaluated in symmetric devices assembled with 6 M KOH aqueous electrolyte and 1 M MeEt3NBF4/PC organic electrolyte respectively. The symmetric supercapacitor with aqueous electrolyte provides an energy density of 5.4 Wh kg(-1) at a power density of 5000 W kg(-1) and a superb capacitance retention of 97.9% after 10,000 cycles at 4 A g(-1). Besides, the symmetric supercapacitor assembled with organic electrolyte delivers an energy density of 16.4 Wh kg(-1) at a power density of 6750 W kg(-1) and a good cycling life with a capacitance retention of 81.6% over 10,000 cycles at 4 A g(-1).