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.