The present work explores in detail the effect of alkaline-basic electrolytes on the capacitance performance of biomass-derived carbonaceous materials used as electrodes in symmetric supercapacitors. The proof-of-concept is demonstrated by two commercial carbon products (YP-50F and YP-80F, Kuraray Europe GmbH, Vantaa, Finland), obtained from coconuts. The capacitance performance of YP-50F and YP-80F was evaluated in three types of basic electrolytes: 6 M LiOH, 6 M NaOH and 6 M KOH. It was found that the capacitance performance of YP-50F improved in the following order: NaOH < LiOH < KOH; Meanwhile, for YP-80F, the order changes to LiOH < NaOH < KOH. After 1000 cycles, the cycling stability of both YP-50F and YP-80F increased in the order NaOH < LiOH < KOH. This order of performance improvement is determined by both the electrolyte conductivity and the interaction between the functional groups of carbonaceous materials and alkaline electrolytes. The reactivity of the functional groups was assessed by postmortem SEM/EDS and X-ray photoelectron spectroscopy (XPS) analyses of the electrodes after prolonged cycling.

For the development and optimization of solid-state symmetrical supercapacitors, herein, we propose using carbon-based electrodes and sodium- and lithium-form Aquivion electrolyte membranes, which serve as the separator and electrolyte. Carbon xerogels, synthesized using microwave-assisted sol-gel methodology, with designed and controlled properties were obtained as electrode materials. Commercial activated carbon (YP-50F, “Kuraray Europe” GmbH) was used as the active material for comparison. Notably, the developed solid-state symmetrical supercapacitors provide sufficiently high specific capacitances of 105–110 F g⁻¹ at 0.2 A g⁻¹, along with an energy density of 4.5 Wh kg⁻¹ at 300 W kg⁻¹, and a voltage window of 0–1.2 V in aqueous environments, also demonstrating an excellent cycling stability for up to 10,000 charge/discharge cycles. These results can demonstrate the potential applications of carbon xerogel as the active electrode material and cation exchange membrane as the electrolyte in the development of solid-state supercapacitor devices.

The creation of supercapacitors with superior energy density and power capabilities is critical for advanced energy storage solutions. Ionic liquid electrolytes offer a promising alternative in this respect. However, improving their cycle stability and efficiency is a complex task requiring extensive research and significant effort. The high viscosity of ionic liquids (ILs) limits their lifetime, but this can be mitigated by increasing the temperature or adding solvents. In this research, the electrochemical performance of symmetric activated carbon supercapacitors with 1-Ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF₄) and different ratios of acetonitrile (ACN) as electrolytes were investigated. Long-term galvanostatic charge/discharge tests, impedance studies, and cyclic voltammetry were performed at temperatures between 24 to 60 °C. The addition of ACN to the ionic liquid increased electrochemical stability and reduced internal resistance, with the best performance observed at a 1:2 volume ratio of EMIMBF₄ to ACN. This supercapacitor exhibited 87% cyclic stability after 5000 charge/discharge cycles in the voltage range of 0.05–2.8 V and a current rate of 1 Ag⁻¹. It also achieved an energy density of 23 Whkg⁻¹ and a power density of 748 Wkg⁻¹. The supercapacitors were stable at elevated temperatures up to 60 °C, showing no degradation after operation under various thermal conditions.

Flexible energy storage devices, such as solid-state supercapacitors, are becoming increasingly attractive due to their characteristics of high electrochemical performance, reliability, light weight, flexibility, absence of electrolyte leakage, high power density, and long lifetime. For the optimization of the solid-state symmetrical supercapacitor proposed in this work, it was employed in sodium and lithium form Aquivion electrolyte membrane, which serves as the separator and electrolyte. As electrode materials, carbon xerogels, synthesized by microwave-assisted sol-gel methodology, with designed and controlled properties were obtained. Commercial activated carbon (YP-50F, 'Kuraray Europe' GmbH) was used for comparison. Specifically, the developed solid-state symmetrical supercapacitors deliver sufficient high specific capacitances of 105−110 F g−1 at 0.2 A g−1, along with an energy density of 4.5 Wh kg−1 at 300 W kg−1, and in a voltage window of 0-1.2 V in an aqueous environments, also demonstrating excellent cycling stability up to 10,000 charge/discharge cycles. These results can demonstrate the potential applications of carbon xerogel as an active electrode material and cation exchange membrane as the electrolyte in the development of solid-state supercapacitor devices

A polymerization procedure is presented to increase the molecular weight of hydrocarbons in household chimney soot without thermal treatment at high temperatures. Pristine soot was subject to chlorination, with half of it treated with magnesium (Mg-plates) to create random-type Grignard reagents (R-Mg-Cl) in diethyl ether media. Mixing the Grignard reagent and the rest of the halogenated soot material created new C-C bonds, thus increasing the molecular weight of the final product. The obtained stochastically polymerized soot (SPS) was investigated using Raman spectroscopy, FTIR spectroscopy and XPS and was subjected to electrochemical testing as an assembled supercapacitor with a KOH electrolyte. Results show significant carbon structure differences due to the chemical procedures and newly created functional groups in the soot. Such functional groups could increase the capacity of supercapacitors, creating pseudo-capacitance by participating in redox reactions. The results also unveiled removing any random contaminations in the pristine soot and obtaining a more uniform final product containing hydrocarbons with longer chains, thus increasing the molecular weight.

This study investigated physically and chemically activated chimney soot to evaluate the influence of the activation process on the textural properties and porous structure of materials intended for use in supercapacitors. The materials were characterized by Raman spectroscopy to analyze molecular structure and composition, as well as BET analysis to determine porosity and structural properties based on N₂ adsorption-desorption isotherms. Their electrochemical characteristics were evaluated using a two-electrode configuration with cyclic voltammetry, galvanostatic charge–discharge measurements, and long-term cycling tests of up to 10,000 cycles within a voltage window of 0.05–1.0 V in a 1 M KOH electrolyte. Soot-based symmetric supercapacitors activated with KOH at a ratio of 3:1 exhibit a specific capacitance of 74–78 F g⁻¹ at 0.2 A g⁻¹ and achieve an energy density of 2.3 Wh kg⁻¹ at a power density of 32 W kg⁻¹. The results demonstrate that, by carefully controlling the type and quantity of the activating agent, chemical activation is an effective method for increasing the specific surface area and improving the electrochemical characteristics of the resulting materials. Chemical activation significantly expands the microporous framework, optimizing ion transport at the electrode–electrolyte interface. The results demonstrate the successful valorization of chimney soot as functional carbon electrodes for next-generation energy storage applications.