Browsing by Author "Fedorovskaya, Ekaterina O."

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Comparative Study of the Structural Features and Electrochemical Properties of Nitrogen-Containing Multi-Walled Carbon Nanotubes after Ion-Beam Irradiation and Hydrochloric Acid Treatment
(2021-09) Korusenko, Petr M.; Nesov, Sergey N; Iurchenkova, Anna A.; Fedorovskaya, Ekaterina O.; Bolotov, Valery V.; Povoroznyuk, Sergey N.; Smirnov, Dmitry A.; Vinogradov, Alexander S.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Using a set of microscopic, spectroscopic, and electrochemical methods, a detailed study of the interrelation between the structural and electrochemical properties of the as-prepared nitrogen-containing multi-walled carbon nanotubes (N-MWCNTs) and their modified derivatives is carried out. It was found that after treatment of nanotubes with hydrochloric acid, their structure is improved by removing amorphous carbon from the outer layers of N-MWCNTs. On the contrary, ion bombardment leads to the formation of vacancy-type structural defects both on the surface and in the bulk of N-MWCNTs. It is shown that the treated nanotubes have an increased specific capacitance (up to 27 F·g-1) compared to the as-prepared nanotubes (13 F·g-1). This is due to an increase in the redox capacitance. It is associated with the reversible Faraday reactions with the participation of electrochemically active pyridinic and pyrrolic nitrogen inclusions and oxygen-containing functional groups (OCFG). Based on the comparison between cyclic voltammograms of N-MWCNTs treated in HCl and with an ion beam, the peaks on these curves were separated and assigned to specific nitrogen inclusions and OCFGs. It is shown that the rate of redox reactions with the participation of OCFGs is significantly higher than that of reactions with nitrogen inclusions in the pyridinic and pyrrolic forms. Moreover, it was established that treatment of N-MWCNTs in HCl is accompanied by a significant increase in the activity of nitrogen centers, which, in turn, leads to an increase in the rate of redox reactions involving OCFGs. Due to the significant contribution of redox capacitance, the obtained results can be used to develop supercapacitors with increased total specific capacitance.
A complex study of the dependence of the reduced graphite oxide electrochemical behavior on the annealing temperature and the type of electrolyte
(2021-02-20) Iurchenkova, A. A.; Lobiak, Egor V.; Kobets, Anna A.; Kolodin, Alexey N.; Stott, Ash; Silva, Ravi P.; Fedorovskaya, Ekaterina O.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
In this work we investigate the influence of thermal treatment of reduced graphite oxide (RGO) on its functional composition and electrochemical performance. It is found that carboxyl, carbonyl, hydroxyl and epoxy groups are present on the RGO surface, witch when subject to thermal annealing in the temperature range 230-250°C can be controllably modified. In the process of thermal annealing, we show the formation of quinoid groups due to an increase in the number of defects. Decrease of the number of layers in RGO material and the quantity of oxygen-containing functional groups (OCFG) also occurs. With increase in annealing temperature, sequential removal of OCFG occurs as follows: carboxyl (250°C-600°C), hydroxyl (600°C-800°C), carbonyl and quinoid (700°C-1000°C). Electrochemical measurements over a wide range of pH values of the buffer electrolytes is possible to correlate the peaks in the cyclic voltammogram curves with the redox reactions of oxygen-containing functional groups as a function of applied potential. Peaks correlated with specific redox reactions which are identified as two-electron. The dependence of the specific capacities of materials on the electrolyte type has been studied. Highest capacitance was detected in 1M NaOH at a scan rate 2 mVs−1 and is equal to 210 Fg−1.
Electrochemical properties of nitrogen and oxygen doped reduced graphene oxide
(2020-01-01) Hartmann, Sean J.; Iurchenkova, Anna A.; Kallio, Tanja; Fedorovskaya, Ekaterina O.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Carbon nanostructures are promising electrode materials for energy storage devices because of their unique physical and chemical properties. Modification of the surface improves the electrochemical properties of those materials because of the changes in morphology, diffusion properties, and inclusion of additional contributions to redox processes. Oxygen-containing functional groups and nitrogen doped into the carbon matrix significantly contribute to the electrochemical behavior of reduced graphite oxide (RGO). In this work, RGO was synthesized during hydrothermal treatment of graphite oxide with a hydrazine sulfate aqueous solution. Different amounts of hydrazine sulfate were used to synthesize RGO with different nitrogen contents in the structure, and the same synthesis conditions made it possible to obtain a material with a similar composition of oxygen-containing functional groups. The materials with different nitrogen concentrations and similar amounts of oxygen were compared as electrode materials for a supercapacitor and as a negative electrode material for a Li-ion battery. It was shown that the presence of oxygen-containing functional groups has the greatest influence on the behavior and efficiency of supercapacitor electrode materials, while nitrogen atoms embedded in the graphene lattice play the largest role in lithium intercalation.
Flexible supercapacitors based on free-standing polyaniline/single-walled carbon nanotube films
(2022-09-01) Panasenko, Iurii V.; Bulavskiy, Mikhail O.; Iurchenkova, Anna A.; Aguilar-Martinez, Yenanny; Fedorov, Fedor S.; Fedorovskaya, Ekaterina O.; Mikladal, Bjørn; Kallio, Tanja; Nasibulin, Albert G.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Advances in supercapacitor performance are boosted both by material design helping to improve specific capacitance and by tailoring of device architecture, often addressing flexibility to enable rolling-up packaging to reach high nominal values. This keeps attention to flexible lightweight materials, such as single-walled carbon nanotubes (SWCNTs), and conducting polymers, such as polyaniline (PANI). In this work, we design and study unique “dead-weight” free supercapacitors based on PANI electrochemically deposited on free-standing SWCNT films. Depending on the carbon nanotube film characteristics, we adjusted polymer inclusion into the nanotube films and evaluated its structure by TEM, SEM, XPS and Raman spectroscopy. Electrochemical methods were used to investigate the relationship between the morphology of initial SWCNT films, deposited PANI, and the electrochemical properties of the composite materials, including specific gravimetric capacitance and self-discharge processes. We show that thin free-standing films of SWCNTs with deposited PANI are less prone to self-discharge due to higher resistance arising from the lower density of the nanotubes in the film. Yet, such films enable better and more uniform deposition allowing to reach the maximum gravimetric capacitance value of 541 F g−1. This synergistic performance allows the creation of an electrode material for flexible ultra-light and powerful supercapacitors.
Joint effect of ethylene and toluene on carbon nanotube growth
(2022-04-15) Khabushev, Eldar M.; Krasnikov, Dmitry V.; Goldt, Anastasia E.; Fedorovskaya, Ekaterina O.; Tsapenko, Alexey P.; Zhang, Qiang; Kauppinen, Esko I.; Kallio, Tanja; Nasibulin, Albert G.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
This work contributes to the understanding of single-walled carbon nanotube synthesis by an aerosol CVD method using ethylene and toluene as a hybrid carbon source. We evaluated an extensive set of synthesis conditions revealing the role of ferrocene, toluene, and ethylene. We found the fundamental role of ethylene promoting nanotube nucleation and catalyst activation degree at all the concentrations studied, and enhancing nanotube growth at low ethylene content. We observed the interplay effect of toluene and ethylene concentrations on the nanotube growth rate, accompanied by the detrimental effect of toluene on catalyst activation degree. Nevertheless, toluene apparently promotes nanotube crystallinity, increasing the film conductivity while used as an individual carbon source. Adjusting the ethylene and toluene concentrations, we produced carbon nanotube-based transparent and conductive films with an equivalent sheet resistance (at 90% transmittance at 550 nm wavelength) value of 57 Ω/□ at the synthesis yield of 0.24 cm2 L−1, which is at least two times higher than the results reported earlier.
Long-term cycling behavior of Mg-doped LiCoO2 materials investigated with the help of laboratory scale X-ray absorption near-edge spectroscopy
(2022-07) Lahtinen, Katja; Labmayr, Maximilian; Mäkelä, Ville; Jiang, Hua; Lahtinen, Jouko; Yao, Lide; Fedorovskaya, Ekaterina O.; Räsänen, Samuli; Huotari, Simo; Kallio, Tanja
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The use of Li-ion batteries is increasing rapidly. Understanding the processes behind active material aging helps to enhance the materials, and therefore, development of new in situ methods for structural studies is important. In addition, understanding the effect of different synthesis methods on the active material properties is necessary to optimize the material cycle life. In this work, the performance of LiCoO2 doped with Mg during the lithiation step is compared to LiCoO2 prepared using an Mg-doped Co3O4 precursor. In situ laboratory-scale X-ray absorption near-edge spectroscopy is used to analyze the Co valence changes in LiCoO2 to understand the electrochemical behavior of the investigated materials. The maximum reachable Co valence state is found to decrease upon aging, a small decrease indicating a good cycle-life, and this is attributed to the enhanced stacking order, better Mg distribution in the lattice, and fine primary particle size in the material. In the synthesis conditions used in this study, Mg doping during the lithiation step is shown to perform better compared to the precursor doping. Overlithiation is shown to reduce the electrochemical performance of nondoped and precursor-doped LiCoO2 materials but not to affect the cyclability of lithiation-doped LiCoO2.
Stretchable and transparent supercapacitors based on aerosol synthesized single-walled carbon nanotube films
(2016-09-27) Gilshteyn, Evgenia P.; Kallio, Tanja; Kanninen, Petri; Fedorovskaya, Ekaterina O.; Anisimov, Anton S.; Nasibulin, Albert G.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Stretchable all-solid supercapacitors based on aerosol synthesized single-walled carbon nanotubes (SWCNTs) have been successfully fabricated and tested. High quality SWCNT films with excellent optoelectrical and mechanical properties were used as the current collectors and active electrodes of the stretchable supercapacitors. A transmittance of up to 75% was achieved for supercapacitors made from the assembly of two PDMS/SWCNT electrodes and a gel electrolyte in between. The transparent supercapacitor has a specific capacitance of 17.5 F g-1 and can be stretched up to 120% with practically no variation in the electrochemical performance after 1000 stretching cycles and 1000 charging-discharging cycles.