We have reported a new reduced graphene oxide–bismuth oxide composite that can be used as a supercapacitor electrode. Bi₂O₃ was synthesized from bismuth nitrate pentahydrate and oxalic acid as a precipitating agent using a hydrothermal process in an aqueous graphene oxide suspension. Instead of mixing graphene oxide with bismuth oxide, we have developed a bismuth oxalate precipitation between the layers. As prepared, composite of hydrated bismuth oxalate and graphene oxide was converted to bismuth oxide and reduced graphene oxide by thermal decomposition in a muffle stove. The material exhibited the specific capacitance of 94 F/g at current density 0.2 A/g. Using the cyclic voltammetry, the specific capacitance was as high as 55 F/g at scan rate 5 mV/s over the potential range 0–1 V. The material exhibited long-term cycle stability retaining 90 % specific capacitance after 3,000 cycles. Except Bi³⁺ ions present in Bi₂O₃, some amount of higher energy Bi⁵⁺ was confirmed.

Carbon materials are among the most commonly used components of supercapacitor electrodes. Particularly, active carbons are recognized as cheap, available, and easily tailored materials. However, the carbon family, i.e. carbon products and carbon precursors, consists of many members. In this manuscript some of these materials, including laboratory scale-produced carbon gels, carbon nanotubes and carbonized materials, as well as industrial scale-produced graphites, pitches, coke and coal, were compared. Discussion was preceded by a short history of supercapacitors and review of each type of tested material, from early beginning to state-of-the-art. Morphology and structure of the materials were analyzed (specific surface area, pore volume and interlayer spacing determination), to evaluate their applicability in energy storage. Thermal analysis was used to determine the stability and purity. Finally, electrochemical evaluation using cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy was performed. Outcomes of each analytical technique were summarized in different sections.

There is currently a growing demand for more effective thermal insulation materials with the best performance properties. This research paper presents the investigation results on the influence of two types of filler on the structure and properties of rigid polyurethane foam composites. Fly ash as a product of coal combustion in power plants and microspheres of 5, 10, 15, and 20 wt.%, were used as rigid polyurethane foams modifiers. The results of thermal analysis, mechanical properties testing, and cellular structure investigation performed for polyurethane composites show that the addition of fly ash, up to 10 wt.%, significantly improved the majority of the tested parameters. The use of up to 20 wt.% of microspheres improves the mechanical and thermal properties and thermal stability of rigid polyurethane foams.