Highly porous carbon microflakes derived from catkins for high-performance supercapacitors

Highly porous carbon microflakes (CMFs) with oxygen and nitrogen dualdoping were prepared from willow catkins by pyrolysis at 500 degrees C in nitrogen, followed by KOH activation and were used as a high-performance supercapacitor electrode material. The as-prepared CMFs with a thickness of 350 nm possess an incredibly high specific surface area of 3510 m(2) g(-1) and a large pore volume of 2.1 cm(3) g(-1). The CMFs exhibit a high specific capacitance (for a three-electrode system) of 372, 344 F g(-1) at 1 A g(-1) in 2 M H2SO4 and 6 M KOH, respectively. The specific capacitance is 278 F g(-1) at 1 A g(-1) in a two-electrode system (2 M H2SO4 electrolyte). The CMFs electrode demonstrates good rate capability with retention of 79.6% (from 1 A g(-1) to 20 A g(-1)) and excellent cycling stability with 95% capacity retention after 5000 cycles. The CMFs symmetric device shows a high energy density of 9.5 W h kg(-1) at a power density of 500 W kg(-1) in H2SO4.