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

Abstract

Highly porous carbon microflakes (CMFs) with oxygen and nitrogen dual-doping were prepared from willow catkins by pyrolysis at 500 °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 m² g⁻¹ and a large pore volume of 2.1 cm³ 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.