Effects of one-step and two-step KOH activation method on the properties and supercapacitor performance of highly porous activated carbons prepared from Lycopodium clavatum spores

The fabrication of electrodes from biomass through a simple chemical activation route provides a green and sustainable process for manufacturing high-performance supercapacitors. In this study activated carbons were prepared from Lycopodium clavatum spores (LCSs) by one-step and two-step KOH activation processes. The one-step method was performed via pyrolysis of KOH-impregnated LCSs in a fixed bed reactor at 800 °C. In the two-step procedure, LCSs were pre-carbonized at 300 °C in air an environment, and the resulting biochar was impregnated with KOH and pyrolyzed at 800 °C. The activated carbons were characterized using analytical techniques such as BET, FESEM, EDS, FTIR, Raman spectroscopy, XRD and TGA. The Raman spectra and XRD diffractograms of the activated carbons exhibited the characteristic bands (G and D) and amorphous structure, respectively. According to the obtained results, combining pre-carbonization and KOH activation was more effective than one-step pyrolysis in providing a high specific surface area. The specific surface area and total pore volume were 2048 m2 g−1 and 1.32 cm3 g−1 for the K82 sample (activated carbon prepared via the two-step method) and 1186 m2 g−1 and 0.71 cm3 g−1 for the K81 sample (activated carbon prepared via the one-step method), respectively. The activated carbons were further used as electrode materials, and the electrochemical performance was investigated with the determination of cyclic voltammograms, galvanostatic charge-discharge, electrochemical impedance spectrum and cyclic stability. The results indicated that the K81 had a specific capacitance (Csp) of 182.9 F g−1 at 0.1 A g−1 in a 6.0 mol L−1 KOH electrolyte, which was higher than that of K82 (160.9 F g−1). However, the K82 exhibited low charge transfer resistance (0.23 Ω) and excellent long-cycle stability with approximately 87 % specific capacitance retained at 1 A g−1 after 10,000 cycles. In conclusion, the results indicated that the activated carbons prepared from LCSs exhibited high surface area, good thermal stability, high specific capacitance, remarkable cycling stability and notable rate performance, which makes them promising electrode materials for advanced supercapacitors.