N,O-codoped microporous carbon derived from hypnum plumaeforme for high-rate supercapacitors

N,O-codoped microporous carbon (HPC) was derived from hypnum plumaeforme via precarbonization and KOH activation and utilized as an electrode for supercapacitors. The HPC750 sample, produced at an activation temperature of 750 °C, demonstrated superior capacitive behavior due to its large specific surface area, microporous architecture, and high number of oxygen and nitrogen heteroatoms. These HPC750 electrodes have a specific capacitance of up to 424 F g⁻¹ at a current density of 1 A g⁻¹ while also providing excellent rate performance, maintaining >85 % capacitance over a range of 1 to 100 A g⁻¹. In a symmetric supercapacitor configuration using 6 M KOH and 1 M Na₂SO₄ as electrolytes, the HPC750 electrodes exhibit high specific capacitances of 96.2 F g⁻¹ and 65.8 F g⁻¹ at a current density of 1 A g⁻¹, respectively. With the Na₂SO₄ electrolyte, the device achieved a peak energy density of 29.9 W h kg⁻¹ and a peak power density of 225 W kg⁻¹. In addition, the electrodes retained approximately 90 % of their initial capacitance after 15,000 cycles at a current density of 5 A g⁻¹.