Porous Biocarbon Derived from Garlic Peel Biowaste for Symmetric Supercapacitor Applications: Electrochemical Performance in Aqueous and Organic Electrolytes

Abstract Biomass is an inexpensive source of carbon, from which added-value energy materials can be produced. On this matter, this research utilizes a hydrothermal process with pyrolysis treatment to produce a Garlic Peel Biocarbon (GPB) using the outer layers of the species as the source of carbon. The as-produced GPB shows a high specific surface area (SSA) of 1240.7 m2 g–1 and a pore diameter of 3.96 nm, indicating its hierarchical mesoporous structure. GPB has been characterized as active material in a symmetrical GPB||GPB supercapacitor, displaying high cycle stability in 6 M KOH, 0.5 M Na2SO4, and 1 M NaClO4–(EC|PC) (ethylene carbonate|propylene carbonate). Even though the specific capacity (Csp) in KOH is the highest at 1 mV s–1 (112.5 F g–1), those with Na2SO4 and the organic electrolyte are not significantly lower (103.2 and 99.2 F g–1, respectively). More importantly, the supercapacitor achieves an operating voltage window of 1.0, 1.8, and 2.5 V in KOH, Na2SO4, and NaClO4, respectively. Hence, there is an enhanced behavior in the organic electrolyte that has promoted the device to attain energy density (ED) and power density (PD) values of 19.9 Wh kg–1 and 183.9 W kg–1, respectively. The results demonstrate that active material-electrolyte conformation strongly influences the balance between Csp, operating voltage window, ED, and PD. Here, the GPB–NaClO4 system enables a wider voltage window, outperforming the other configurations in terms of ED and PD, as shown in the Ragone plot and radar chart. The findings indicate that GPB has excellent performance and significant promise as an active electrode material for supercapacitors.