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.

We have reported a new reduced graphene oxidebismuth oxide composite that can be used as a supercapacitor electrode. Bi 2 O 3 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 longterm cycle stability retaining 90 % specific capacitance after 3,000 cycles. Except Bi 3+ ions present in Bi 2 O 3 , some amount of higher energy Bi 5+ was confirmed.

Leaching of the dross containing 28.7% Sn, 18.0 Pb, 10.6% Cu, 8.9% Ge, 8.1% Zn, and 2.7% In in sulphuric and oxalic acid solution was investigated. The dross was obtained from thermal oxidation of by-product alloy generated during a New Jersey (NJ) zinc rectification process. The influence of different process conditions (temperature, time, acid concentration, and solid to liquid ratio) on leaching yield of the main components was determined. Additionally, the impact of oxidant (hydrogen peroxide, sodium hypochlorite, manganese (IV) oxide) addition on leachabilities was investigated. Germanium leaching yields exceeding 80% were observed for both sulphuric and oxalic acid solutions. Indium leachability in H 2 C 2 O 4(aq) was found at the level of 20%, while in H 2 SO 4(aq) , it strongly depends on process temperature, and reached 80% at 80 • C.

Graphite oxide reduction is probably one of the best technique used to obtain large quantities of few-layer graphene. We developed a new method to produce reduced graphene oxide by using sodium metal as a reducing agent with subsequent dehydration in concentrated sulfuric acid. The resulting product was characterized using various analytical techniques with respect to the oxygen content and species of the residual oxygen-containing groups. The reduced graphene oxide prepared by this method was electrochemically tested as electrode in supercapacitors using two-electrode symmetric system and aqueous electrolyte. The product exhibits improved capacitance during cyclic voltammetry measurements. In comparison to parent graphite oxide specific capacity increased from 0.88 to 28 F/g after 10 cycles at scan rate 20 mV/s and dropped to 19.44 F/g after 100 cycles while at scan rate 5 mV/s specific capacity 46.41 F/g was recorded after first cycle and 39.90 F/g after 50 cycles.

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