Optimization of Nickel Hydroxide Electrode of the Hybrid Supercapacitor

Nickel hydroxide is an active material for a wide range of chemical power sources: various types of alkaline accumulators and hybrid supercapacitors. In order to obtain maximum electrode capacity and charge efficiency, the optimization of the electrode composition i.e. the content of activating and electroconductive additives and the binder is needed. The amount of these compounds is governed by various factors, the influence of which is different and often non-linear.The factors that can affect the specific capacity and are determined by the binder content have been reviewed. The effect of these factors has been demonstrated experimentally. The influence of the binder content has been studied. The study has been carried out using polytetrafluoroethylene suspension as a binder, and components used in the manufacturing of accumulators: industrial sample of nickel hydroxide “Bochemie”, and electroconductive additive GAK-1.The optimal binder content in active mass has been determined to be 2 %. It has been demonstrated that PTFE content of 1 % in active mass is insufficient for good contact of active mass with the electrode, resulting in a maximum capacity of 11 F/g at 40 mA/cm2. The PTFE concentration of 3 % is excessive and under high current densities leads to screening of active material particles, with a maximum capacity of 67 F/g at 20 мА/cm2. The best result for specific capacity has been achieved with PTFE content of 2 % and current density of 40 mA/cm2 – 67 F/g.After analyzing the acquired data, it has been assumed that optimal binder content may depend on the particular type of hydroxide, namely its structure and morphology

Selective Anodic Treatment of W(WC)-based Superalloy Scrap

Superalloys based on W/WC are widely used as elements of drilling equipment, high-speed steel-cutting tools, penetrators of armor-piercing munitions. The spent or broken superalloy goods are a valuable waste for recycling with extracting of valuable components. The most economically and technologically attractive methods of superalloy scrap recycling is selective treatment with dissolution of metal binder and obtaining of non-oxidized tungsten/tungsten carbide powder. The aim of the present work was to develop a method of selective anodic reprocessing of superalloys. By using voltamperometry method the anodic behavior of VK20KS (20% Со, 80 WC), VN8 (8 % Ni, 92 % WC), VNG (5 % Ni, 5 % Fe, 90 % W) and VNDS (W, Ni, Cu.) superalloys in a proposed solution has been studied. The possibility of selective anodic dissolution of metal binder without oxidation of solid component (tungsten/tungsten carbide) has been demonstrated. The potential and current density values for this process have been determined. Low reactivity of tungsten-based superalloys in comparison to tungsten carbide-based alloy has been demonstrated. Galvanostatic selective anodic treatment of VK20KS superalloy scrap at 15 A/dm2, which is a dissolution peak current density on the anodic curve, has been conducted. A phenomenon of gradual surface passivation due to dissolution of metal binder and increasing the content of passive tungsten carbide has been found. In order to prevent passivation, the use of rotating titanium basket has been proposed. The composition of tungsten-containing products has been determined to be: 23 % WO3 or H2WO4, 73 % WC

Definition of Factors Influencing on Ni(OH)2 Electrochemical Characteristics for Supercapacitors

Nickel hydroxide is widely used as an active material for hybrid supercapacitors. To improve the characteristics of supercapacitors, Ni(OH)2 with the optimal parameters to be determined should be synthesized. For this, Ni(OH)2 samples were prepared by various methods: decomposition, homogeneous precipitation, electrochemical synthesis using slit diaphragm electrolyzer under various current densities, with diaphragm or membrane, carbonate activation, immediate ultrasound post­treatment and an industrial sample, prepared by chemical route. Structural properties of the samples were studied by X­ray phase analysis, specific surface area – BET method by nitrogen adsorption, electrochemical characteristics – galvanostatic charge­discharge cycling in the supercapacitor mode. It has been demonstrated that high specific capacity is the most affected by α (or layered α+β) structure, optimal (average or low) crystallinity, introduction of activating additive and the ability of particle agglomerates to undergo breakdown into smaller particles during charge­discharge. Specific surface area has little influence on specific capacity. The sample prepared in slit diaphragm electrolyzer at 15.7 A/dm2 has a layered type of crystal structure, and the ability of particle agglomerates to undergo breakdown into smaller particles during charge­discharge, and showed the highest specific capacity of 650 F/g

The Determination of Electrolyte Stability and Conditions for Electrochromic WO3 Films Deposition

The present research is devoted to finding the condition and intricacies of WO3 film electrodeposition from peroxotungstic acid-based electrolyte that can be used for real production process. For deposition of electrochromic WO3 films, the galvanostatic regime with following parameters is proposed: cathodic current density -0.2 mA/cm2, deposition time 30 min. The films prepared under such deposition parameters are transparent and had good adhesion to the substrate – the glass coated with fluorine-doped tin oxide. The averaged coloration degree for film deposited from fresh electrolyte is 10%, while for film deposited from regenerated electrolyte – 5 %. During investigation, the potential window in which WO3 film could be colored and bleached, without reduction of SnO2 to metallic tin is established. It is also demonstrated that electrolytes containing peroxotungstic acid are unstable and degrade over time. It is proposed to use hydrogen peroxide for regeneration of electrolyte. It is demonstrated that electrolyte can be partially regenerated with hydrogen peroxide

Influence of Temperature on the Characteristics of Ni(II), Ti(IV) Layered Double Hydroxides Synthesised by Different Methods

The influence of temperature on the characteristics of Ni(II)–Ti(IV) LDH was investigated in the work.Ni(II)–Ti(IV) layered double hydroxides were synthesized from a solution of Ni2+ and Ti4+ with the cationic ratio of Ni2+/Ti4+=5 by using three coprecipitation techniques: titration, coprecipitation at high supersaturation and homogeneous coprecipitation. The prepared samples were characterized by means of X-ray diffraction (XRD), Thermogravimetric analysis (TGA) and Differential scanning calorimetry (DSC).By means of XRD, it was revealed that all samples prepared using titration and coprecipitation at high supersaturation at 65 and 20 oC correspond to Ni-Ti LDH structure. Elevated temperature during sample preparation using titration and coprecipitation at high supersaturation did not have a significant effect on phase composition, but affected the crystallinity. According to XRD results, the sample prepared using homogeneous coprecipitation at 70 oC had a significant content of b-Ni(OH)2. Increasing the synthesis temperature to 80 oC has led to the almost complete disappearance of b-Ni(OH)2 reflections.By means of TGA and DSC, it was found that titration method leads to formation of samples with higher thermal stability than those prepared by high supersaturation. Elevated temperature and hydrothermal treatment leads to higher thermal stability of the samples. Samples prepared by homogeneous coprecipitation show complicated behavior during thermal decomposition, confirming the presence of cyanate ions in the interlayer gallery