Browsing by Author "Stankulov T."

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    APPLICATION OF ELECTROCHEMICALLY PREPARED Sn-Co ALLOY POWDERS AS ANODE MATERIAL FOR LITHIUM-ION BATTERIES
    (2024-01-01) Ignatova K.; Stankulov T.
    The electrochemical behavior of active electrode (anode) materials (AEMs) for lithium-ion battery (LIB), prepared with Sn-Co powders electrodeposited in three different current modes, was investigated. It is shown that AEM with Sn-Co powder, obtained in constant-potential mode, has the highest tin content (82.1 wt. %) and the best performance and stability in operation. The anode material, made with this Sn-Co powder, shows a first-cycle charge capacity of 450 mAh g-1, which decreases to 295 mAh g-1 for 10 battery cycles at a current load of 0.8 mA (0.1C). The data also showed that the AEM with Sn-Co powder, deposited in pulse-potential mode, which has the lowest tin content (24.5 wt. % Sn) but the highest dispersity compared to the other powders tested, shows better performance than that of a powder with a tin content of 68.6 wt. %, obtained in constant-current mode. It can be concluded that for the high electrochemical activity of the anode materials, prepared with Sn-Co powders, both the high tin content and the high dispersity and morphological uniformity of the powders are of great importance.
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    MICROWAVE-ASSISTED SYNTHESIS OF SILVER NANOPARTICLES AS CATALYST FOR AIR GAS-DIFFUSION ELECTRODES
    (2022-01-01) Mladenova B.; Stankulov T.; Stankov S.; Boukoureshtlieva R.; Momchilov A.; Karsheva M.; Hinkov I.
    In this work, silver nanoparticles were synthesized from silver nitrate aqueous solution by using microwave irradiation. The morphology of the synthesized nanoparticles was studied by UV-Vis spectroscopy and by transmission electron microscopy showing spherical shapes with diameters of about 10 nm. The X-ray diffraction analysis exhibits their crystalline nature with face-centered cubic structure. Afterward, silver nanoparticles were integrated into activated carbon Norit NK to obtain catalytic composites. These composites were incorporated in the active layer of air gas-diffusion electrodes in order to study the catalytic activity for oxygen reduction reaction. For this purpose, a non-aggressive electrolyte solution of NaCl was used as an electrolyte. The obtained electrochemical results show a stable operation of all electrodes. Higher performance was found for composites containing 2 % wt. silver nanoparticles.
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    SONOCHEMICAL SYNTHESIS OF SILVER NANOPARTICLES FOR GAS-DIFFUSION ELECTRODES APPLICATION
    (2024-01-01) Mladenova B.; Stankulov T.; Stankov S.; Karsheva M.; Hinkov I.; Momchilov A.; Boukoureshtlieva R.
    The aim of the current study is to explore the application of silver nanoparticles (AgNPs) as a catalyst in air gas-diffusion electrodes (AGDE). AgNPs have been successfully synthesized through an original sonochemical method. The effects of reagent concentrations, temperature and reaction time were studied as well. Composites of AgNPs and activated carbon (Norit NK) were prepared by using two adsorption methods to demonstrate the catalytic activity. Method 1 involves homogenizing preliminary prepared AgNPs colloid solution and Norit NK followed by evaporation of the suspension. One-step route was used for Method 2, i.e. all components were mixed altogether and sonicated, resulting in the AgNPs formation directly on the surface and inside the pores of Norit NK. Additionally, some of the samples were thermally treated at 300°C for 1h under air and argon. The composites were characterized by X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-Ray analysis (SEM/EDX) and transmission electron microscopy (TEM). The catalytic activity of the obtained composites regarding oxygen reduction reaction (ORR) was investigated in AGDE using an aqueous 4M NaCl electrolyte. The thermally treated composite obtained via Method 2 appears to show improved electrochemical catalytic activity regarding ORR in comparison to the Method 1 samples.
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    Synthesis and study of carbon-based nanocomposites with Co-Sn nanoparticles for electrode materials
    (2015-01-01) Milanova V.; Markova I.; Piskin M.; Stankulov T.; Petrov T.; Denev I.
    Intermetallic Co-Sn nanoparticles have been synthesized through a template borohydride reduction with NaBH4, using a carbon-containing support in a mixture of aqueous solutions of the corresponding chloride salts (CoCl2.6H2O and SnCl2.2H2O) at mass ratio Co:Sn = 35:65. The ratio is chosen in accordance with the Co-Sn binary system phase diagram. The ``template`` technique involves reductive precipitation of intermetallic nanoparticles on a support. Fluorinated graphite (CF) and graphite/β-cyclodextrin (Dx) hydrate have been used as supports. Subsequently, carbon polymer-based nanocomposites with Co-Sn nanoparticles have been obtained. The content of the polymer in the obtained nanocomposites varies between the samples. The reductive precipitation was carried out at room temperature and atmospheric pressure. Samples were studied by physic-chemical and electrochemical analyses. The morphology, structure, phase composition and surface element content of the prepared nanocomposites have been investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis. The nanocomposite morphology is typical for the alloy materials. CoSn2 and CoSn phases are formed according to the Co-Sn binary system phase diagram. The surface element composition has proven the existence of Co and Sn. Electrochemical study of these nanocomposite materials has been carried out by a cycling voltammetry. The samples are assembled in argon filled glove box and are electrochemically tested as electrode materials (anodes) in a Li-ion battery. The charge-discharge tests have shown that these nanocomposite materials, containing a CoSn2 phase, are characterized by a stable specific capacity after the 20 cycles, better cyclicibility and higher efficiency, as compared to the Co-Sn alloy. Their measured capacity is a reason to be an alternative replacement of the graphite electrodes in Li-ion batteries.