Comparison of the electrochemical properties of engineered switchgrass biomass-derived activated carbon-based EDLCs

Activated carbon-based electrodes with high surface area were synthesized by direct and indirect chemical activation of switchgrass biomass and its biochar, and decorated with MnO₂ in order to enhance and compare the capacitive performance of the fabricated supercapacitors. N₂ physisorption, Raman, XPS and SEM techniques were used to examine the differences in the microstructure and surface characteristics of biomass-derived activated carbon samples and MnO₂ loaded samples. All fabricated supercapacitors were highly stable and showed high-rate capacitive performance. Direct KOH and H₃PO₄ activation increased the specific surface area up to 1272 and 1373 m²/g, respectively. As a result, the capacitive performance increased from 50 to 140 F/g for directly KOH activated biomass, and from 49 to 95 F/g for directly H₃PO₄ activated biomass. MnO₂ loading led to an increase in specific capacitance (110 F/g) for the KOH activated biochar, even though no significant effect was observed for the H₃PO₄ activated biochar. The effectiveness of direct chemical activation of the biomass to enhance the electrochemical performance of the fabricated supercapacitors was demonstrated by comparing it with pseudocapacitive material loading (MnO₂) and indirect chemical activation of biochars.