In this paper, the influences of the graphite precursor and the oxidation method on the resulting reduced graphene oxide (especially its composition and morphology) are shown. Three types of graphite were used to prepare samples for analysis, and each of the precursors was oxidized by two different methods (all samples were reduced by the same method of thermal reduction). Each obtained graphite oxide and reduced graphene oxide was analysed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy (RS).

High-pressure assisted hydrothermal treatment is a green and efficient method for the reduction of graphene oxide. The use of high hydrogen pressure favoured a higher deoxygenation degree and a better restoration of the sp² conjugation.

This review presents a summary of the manufacturing of activated carbons (ACs) as electrode materials for electric double layer capacitors. Commonly used techniques of open and closed porosity determination (gas adsorption, immersion calorimetry, X-ray and neutrons scattering) were briefly described. AC production methods (laboratory and industrial) were detailed presented with the stress on advantages and drawbacks of each ones in the field of electrode materials of supercapacitor. We discussed all general parameters of the activation process and their influence on the production efficiency and the porous structure of ACs. We showed that porosity development of ACs is not the only factor influencing capacity properties. The role of pore size distribution, raw material origin, final carbon structure ordering, particles morphology and purity must be also taken into account. The impact of surface chemistry of AC was considered not only in the context of pseudocapacity but also other important factors, such as inter-particle conductivity, maximal operating voltage window and long-term stability.

In our study, we report a facile solvothermal method for the synthesis of Bi₂S₃ nanoparticles with unique morphologies using water and mixed solvent systems, such as ethylene glycol/water (1:1, v/v) and butyldiglycol/water (1:1, v/v). Altering the solution mixtures used in the solvothermal synthesis allowed the shape of the Bi₂S₃ nanoparticles to be controlled. The synthesis of Bi₂S₃ in water at 150 °C for 24 h led to the formation of sphere-like particles 100–300 nm in size. Very uniform spherical nanospheres with diameters from 50 to 90 nm formed when ethylene glycol/water mixture (1:1, v/v) was used as the solvent under the same solvothermal conditions. The butyldiglycol/water mixture promoted the formation of plate-shaped Bi₂S₃ nanoparticles composed of nanorods. The electrochemical properties of the Bi₂S₃ samples were determined in a three-electrode cell in 6 mol L⁻¹ KOH using cyclic voltammetry, galvanostatic charging/discharging and impedance spectroscopy. Among the synthesized materials, the Bi₂S₃ sample obtained in the butyldiglycol/water mixture exhibited a superior capacitive behavior with an outstanding capacitance of 550 F g⁻¹ (at 0.5 A g⁻¹), and great cycle stability, which was reflected by a capacitance retention of 87% after 500 charge/discharge cycles. These results demonstrate the high potential of Bi₂S₃ as an active electrode material for supercapacitors.

Nitrogen-containing activated carbons were prepared from chitosan, a widely available and inexpensive biopolysaccharide, by a simple procedure and tested as electrode material in supercapacitors. The physical activation of chitosan chars with CO₂ led to carbons with a very high nitrogen content (up to 5.4 wt%) and moderate surface areas (1000–1100 m² g⁻¹). Only chitosan-based activated carbons with a similar microporous structure were considered in this study to evaluate the effect of the nitrogen content and distribution on their electrochemical performance. The N-containing activated carbons were tested in two- and three-electrode supercapacitors using an aqueous electrolyte (1 M H₂SO₄), and they exhibited superior surface capacitance (19.5 µF cm⁻²) and pseudocapacitance compared to a commercial activated carbon with a negligible nitrogen content and similar microporosity. The low oxygen content and the presence of stable quaternary nitrogen improved the charge propagation on the chitosan-based carbons, which was confirmed by the high capacity retention of 83 %. The chitosan-based carbons exhibited excellent cyclic stability and maintained 100 % of their capacitance after 5000 charge/discharge cycles at a current density of 1 A g⁻¹. These results demonstrate the suitability of chitosan-based carbons for application in energy storage systems. Graphical Abstract Chitosan-based activated carbons were characterized by excellent rate capabilities and high capacitance values due to their high content of stable nitrogen functionalities