Template-free synthesis of hierarchical porous carbon derived from low-cost biomass for high-performance supercapacitors

Three kinds of hierarchical porous carbon were successfully fabricated in the absence of any templates by carbonizing kenaf-nickel ion stems complex and subsequently etching nickel-doped carbon composites with hydrochloric acid. The pore size was easily controllable by changing the concentration of nickel ion solution. The unique porous structure of the products resulted in high specific surface area of 1480 m(2) g(-1). The creation of mesopores and macropores and construction of hierarchical pores not only improve the accessibility of the active centers, but also provide highways for reaction species, which result in an enhanced performance in a supercapacitor. The resulting porous carbon electrode materials showed improved specific capacitance of 327 F g(-1) at a scan rate of 2 mV s(-1) in 1.0 M H2SO4. Furthermore, the electrode showed a super-long cycle life with 95.6% retention of the initial specific capacitance after 5000 cycles at a current of 1 A g(-1). This research demonstrated that the hierarchical porous carbon derived from kenaf stems was a good potential material in energy conversion and storage devices.