Supercapacitors

The research covers the synthesis of ionic liquids containing anions fluoroboric acid and quaternary ammonium cations with one ether group. The ionic conductivities of 1M solutions of the synthesized ionic liquids in acetonitrile were measured. They range from 27 to 36 mS/cm, which allows to use solutions as working electrolytes in electrochemical capacitors. It was found that the window of electrochemical stability of the investigated ionic liquids constitutes 3.6-6.1 V and depends on cation structure.

We have studied the capacitance and kinetic properties of nanoporous carbon material which was obtained from wood. The maximum radius pore distribution of the investigated material was 1.37 nm. The data from X-ray scattering and electrochemical impedance spectroscopy was used to investigate the influence of porous structure change and electronic structure of activated carbon material on the mechanism and kinetics of charge-discharge at 7.6m KOH solution. It was proved that depending on the electrode potential and chemical potentials of electrolyte ions there are two different mechanisms of the charge of the porous structure of investigated material. The first mechanism is a process of electrostatic adsorption of hydrated electrolyte ions, and the second is a process electrosorption of H+ or OH. It was shown the cycle of charge-discharge capacity of 95 F/g can be made for two seconds and this is half of the maximum capacity of the material under study.

The efficiency of the electrolyte based on the mixture of acetonitrile – tetramethylammonium bis(oxalate)borate with the concentration of the latter 0.7 mol/kg in double layer supercapacitors has been shown. Electrochemical properties of active carbon materials Norit DLC Supra 30 and Kausorb-212 have been investigated in supercapacitor samples of disk construction in 2016 dimensions using potentiodynamic and galvanostatic methods.

Recent experimental results on the electrical and electrochemical properties of carbon-carbon electrodes of electrochemical capacitors (supercapacitors) are discussed. The dependence of electronic conductivity, specific capacity and the equivalent series resistance on the concentration and nature of the conductive filler is revealed: carbon black PA-76, carbon fibers VGCF grown in vacuum. It is established that the capacity of the electrical double layer formed on the high extended surface area of carbon-carbon electrode material of electrochemical capacitor obtain a maximum value of 115 F/g at a concentration of conductive filler 15%. The equivalent series resistance does not depend on the concentration and nature of the conductive filler and electrical contact is defined on the boundary of the electrode material/current collector.

In this review electrochemical and structural data for the electrodes made of certain of perspective materials for supercapacitors are considered. These electrodes were made on the basis of high-dispersed carbon materials. The following materials were used: singlelayer and multilayer carbon nanotubes; reduced oxide of graphene; the carbide type activated carbon; polyacrilonitrile fibers treated by carbonization and activation; the activated carbon fibrous material; the activated carbon cloth; a composite of polyporphirine on carbon black; polyporhine of magnesium, electrodeposited on carbon paper; and a polyaniline composite with the singlelayer nanotubes, electrodeposited on carbon paper. The short review of techniques of synthesis of these electrode materials is presented. Comparison of capactance characteristics of these electrodes for the purpose of the recommendation of their use in certain types of electrochemical supercapacitors is carried out.

The solar power is one of the most attractive energy sources from all types of renewable energy sources. Nowadays, the conversation of sunlight to electrical power by using of photoelectrochemical cells is the promising functional approach. In the given article we consider the operation principles of these devices. The issues of possible replacement of widely used mediators on the basis of iodide/triiodide redox electrolyte, possessing a number of shortcomings, on new redox mediators on the basis of transitional metals complexes are discussed. It was shown that these complex compounds are promising mediator systems which will do instead of traditional iodide/triiodide redox electrolyte in the near future.

The new composite material on the basis of polytitanates of potassium and the ionic conductor of iodide of silver with extremely high dielectric permeability is synthesized. Impedance and dielectric characteristics of the received material are investigated.

In the current paper electrospun nanofiber mats were derived from polyacrylonitrile (PAN). The temperature influence on the volumetric and surface composition of the resulting pyropolymers was studied by means of elemental analysis and X-ray photoelectron spectroscopy. Rotating disc electrode (RDE) and rotating ring disc electrode (RRDE) methods were used to determine the catalytic properties of PAN pyropolymers, derived at carbonization temperature interval of 600–1200°C, as well as composite PAN/support catalysts, carbonized at 900°C, in the oxygen reduction reaction in H₂SO₄ и KOH solutions. The methods of cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic polarization were utilized to characterize the charge capacitive properties. An equivalent scheme modeling the electrochemical response of PAN pyropolymer in H₂SO₄ solution was proposed. An assumption was made of interrelation between the PAN-T catalytic activity and the occurrence of condensed parquet aromatic structure comprising of nitrogen-carbon bonds. Evidence was given that Fe atoms play the key role in the synthesis of active non-precious catalysts with high selectivity towards the 4-electron O₂ reduction. The possibility of the catalysts synthesis for 2-electron ORR without the use of metal precursors was evidently shown. Prominent correlation of capacitive and catalytic properties for these materials was observed in H₂SO₄ solution. The optimal PAN pyropolymers synthesis temperature was determined to be in the range of 750–950°C. The mats of PAN-T were shown to be feasible as the negative electrodes of supercapacitors.

The possibility of using organic esters of phosphoric acid as a solvents for the electrolyte for lithium-ion systems and supercapacitors was investigated. Supercapacitors based on activated carbon Norit Supra and on the electrolyte being studied showed fine electrochemical performance which is comparable with standard electrolytes based on propylene carbonate. Lithium-ion batteries (Li4Ti5O12-LiNiO2 system) also showed a good performance. The conductivity of electrolytes based on tributyl phosphate was measured, as well as its thermodynamic stability was estimated.

There are the tests results of the symmetrical carbon super-capacitors (on the sulfuric acid electrolyte), whose electrodes are prepared with two methods (spraying and calendering) from two coals: coal of brand XH-00W1 (China) and coal, developed by the authors together with the Latvian state institute of wood chemistry. It is shown that the specific characteristics of super-capacitor substantially depend on the specific mass of electrodes (mg/sm²), and also from the method of their production.