Olena Kohut - Academia.edu (original) (raw)

Papers by Olena Kohut

Effect of Hofmeister ions on the spectro- and electrochemical performance of PANI

Journal of Materials Chemistry C

PANI nanofibrils were electrochemically synthesized in the presence of Hofmeister ions and their ... more PANI nanofibrils were electrochemically synthesized in the presence of Hofmeister ions and their electrochemical and electrochromic properties were studied in 1 M Al(ClO4)3 aqueous solution. PANI film has coloration efficiency of 102.7 cm2 C−1 at 633 nm.

Macromolecular Chemistry and Physics, 2018

When we describe the morphology of an electroactive material, we discuss the size of its pores an... more When we describe the morphology of an electroactive material, we discuss the size of its pores and its degree of crystallinity. The size of the pores in an electroactive material is directly connected with the ability of the electrolyte to penetrate the material. More importantly, the pore size is proportional to the specific surface area and the ability of the material to store energy. The morphology of PANI, which is related to its pore size, depends on the method of polymer preparation. It was established earlier that potentialinduced phase changes in polymer can cause cracking, leading to dramatic rises in the electrode resistance and a rapid loss in its cycling stability. It was shown earlier that PANI possesses poor mechanical stability and cycling stability possibly due to the high volume changes it undergoes during charging/discharging processes. [3] To overcome the poor mechanical stability of PANI during electrochemical processes, 3D PANI networks (semiconducting polymer gels) have been prepared. [3] Additionally, to improve the mechanical stability and performance of polyaniline, the polymer was deposited as a thin layer on top of a NiCo 2 O 4 /carbon cloth substrate, and it was demonstrated that in such a case, the overall morphology of polyaniline did not change, even after 500 repeated cycles. [4] Polypyrrole, another member of the semiconducting polymer family, combined with cellulose similarly exhibited excellent cycling stability with no changes in the morphology of the electrode material after 4000 galvanostatic cycles. [5] The crystallinity of an electroactive material is a key parameter for understanding its mechanism of energy storage. In detail, the physical mechanism of the insertion/intercalation of ions into a host was described by McKinnon and Haering. [6] It was shown that for Li ion batteries, the intercalation of Li ions into different crystalline lattices (the occupation of van der Waal gaps) slightly changed the crystalline structure. Moreover, it was shown that the under-potential deposition of H on Pt or Pb on Au could lead to small changes in the adlayer host lattice. [2,6] For semiconducting polymers, until now, it was believed that under electrochemical treatment (during which the polymer has not degraded) morphological or/and structural changes do not occur. In this Communication, we prove using scanning electron microscopy (SEM), X-ray diffraction (XRD), and electrochemical measurements that polyaniline chains, as synthesized, Energy Storage It is known that semiconducting polymers undergo structural changes only during overoxidation, which is simultaneously connected with the degradation of these polymers. However, if their electrochemical performance is studied within a potential window in which the polymer is stable, no morphological and/or structural changes are observed. It is demonstrated for the first time that polyaniline is able to undergo phase transitions (morphological/structural changes) between the potential cutoff limits of 0 and 0.7 V, within which no degradation is observed. Scanning electron microscopy measurement provides evidence that the polymer surface changes from porous to smooth film, and differential scanning calorimetry and X-ray diffraction data are used to investigate and confirm structural changes during the electrochemical treatment. Electrochemical performance is studied for polyaniline before and after phase transitions and is higher for polymer, in which morphological/structural changes occur. These results demonstrate that morphological/structural changes predetermine physical-chemical performance. In particular, the rearrangement of the polyaniline chains during electrochemical treatment has a crucial impact on the ability of the polymer to store energy.

ChemElectroChem, 2017

Polyaniline/carbon-cloth electrodes with various mass loadings of polyaniline are prepared for us... more Polyaniline/carbon-cloth electrodes with various mass loadings of polyaniline are prepared for use as high-rate charge/discharge pseudocapacitors. The dependence of the capacitance, energy and power density on the polyaniline mass loading is studied in the current work, to determine the operating power spectrum of the polyaniline/carbon-cloth electrodes. In this work, we demonstrate for the first time that the polyaniline/carbon-cloth electrode simultaneously possesses high values of the specific and areal characteristics. Moreover, we showed that such high values of the specific power and energy were obtained with time constants in the range from 0.8 s to 6.25 s, depending on the amount of active material. It is determined that the maximum areal capacitance is obtained for the highest mass loading of polyaniline with a value of 2450 mF/cm 2 measured at 75 mA/cm 2 corresponding to an areal energy density of 265 µWh/cm 2 and areal power density of 48 mW/cm 2. On the other hand, the maximum specific capacitance is obtained for the lowest mass loading of

The Journal of Physical Chemistry C, 2018

Polyaniline (PANI), is one of the promising candidates for utilization as electrode material in s... more Polyaniline (PANI), is one of the promising candidates for utilization as electrode material in supercapacitors and its electro-and physical-chemical properties have been studied for several decades. However, there are fundamental questions that need to be answered. For example, is it possible to obtain and characterize individual PANI chains or what is the impact of

Vacuum, 2019

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Effect of Hofmeister ions on the spectro- and electrochemical performance of PANI

Journal of Materials Chemistry C

PANI nanofibrils were electrochemically synthesized in the presence of Hofmeister ions and their ... more PANI nanofibrils were electrochemically synthesized in the presence of Hofmeister ions and their electrochemical and electrochromic properties were studied in 1 M Al(ClO4)3 aqueous solution. PANI film has coloration efficiency of 102.7 cm2 C−1 at 633 nm.

Macromolecular Chemistry and Physics, 2018

When we describe the morphology of an electroactive material, we discuss the size of its pores an... more When we describe the morphology of an electroactive material, we discuss the size of its pores and its degree of crystallinity. The size of the pores in an electroactive material is directly connected with the ability of the electrolyte to penetrate the material. More importantly, the pore size is proportional to the specific surface area and the ability of the material to store energy. The morphology of PANI, which is related to its pore size, depends on the method of polymer preparation. It was established earlier that potentialinduced phase changes in polymer can cause cracking, leading to dramatic rises in the electrode resistance and a rapid loss in its cycling stability. It was shown earlier that PANI possesses poor mechanical stability and cycling stability possibly due to the high volume changes it undergoes during charging/discharging processes. [3] To overcome the poor mechanical stability of PANI during electrochemical processes, 3D PANI networks (semiconducting polymer gels) have been prepared. [3] Additionally, to improve the mechanical stability and performance of polyaniline, the polymer was deposited as a thin layer on top of a NiCo 2 O 4 /carbon cloth substrate, and it was demonstrated that in such a case, the overall morphology of polyaniline did not change, even after 500 repeated cycles. [4] Polypyrrole, another member of the semiconducting polymer family, combined with cellulose similarly exhibited excellent cycling stability with no changes in the morphology of the electrode material after 4000 galvanostatic cycles. [5] The crystallinity of an electroactive material is a key parameter for understanding its mechanism of energy storage. In detail, the physical mechanism of the insertion/intercalation of ions into a host was described by McKinnon and Haering. [6] It was shown that for Li ion batteries, the intercalation of Li ions into different crystalline lattices (the occupation of van der Waal gaps) slightly changed the crystalline structure. Moreover, it was shown that the under-potential deposition of H on Pt or Pb on Au could lead to small changes in the adlayer host lattice. [2,6] For semiconducting polymers, until now, it was believed that under electrochemical treatment (during which the polymer has not degraded) morphological or/and structural changes do not occur. In this Communication, we prove using scanning electron microscopy (SEM), X-ray diffraction (XRD), and electrochemical measurements that polyaniline chains, as synthesized, Energy Storage It is known that semiconducting polymers undergo structural changes only during overoxidation, which is simultaneously connected with the degradation of these polymers. However, if their electrochemical performance is studied within a potential window in which the polymer is stable, no morphological and/or structural changes are observed. It is demonstrated for the first time that polyaniline is able to undergo phase transitions (morphological/structural changes) between the potential cutoff limits of 0 and 0.7 V, within which no degradation is observed. Scanning electron microscopy measurement provides evidence that the polymer surface changes from porous to smooth film, and differential scanning calorimetry and X-ray diffraction data are used to investigate and confirm structural changes during the electrochemical treatment. Electrochemical performance is studied for polyaniline before and after phase transitions and is higher for polymer, in which morphological/structural changes occur. These results demonstrate that morphological/structural changes predetermine physical-chemical performance. In particular, the rearrangement of the polyaniline chains during electrochemical treatment has a crucial impact on the ability of the polymer to store energy.

ChemElectroChem, 2017

Polyaniline/carbon-cloth electrodes with various mass loadings of polyaniline are prepared for us... more Polyaniline/carbon-cloth electrodes with various mass loadings of polyaniline are prepared for use as high-rate charge/discharge pseudocapacitors. The dependence of the capacitance, energy and power density on the polyaniline mass loading is studied in the current work, to determine the operating power spectrum of the polyaniline/carbon-cloth electrodes. In this work, we demonstrate for the first time that the polyaniline/carbon-cloth electrode simultaneously possesses high values of the specific and areal characteristics. Moreover, we showed that such high values of the specific power and energy were obtained with time constants in the range from 0.8 s to 6.25 s, depending on the amount of active material. It is determined that the maximum areal capacitance is obtained for the highest mass loading of polyaniline with a value of 2450 mF/cm 2 measured at 75 mA/cm 2 corresponding to an areal energy density of 265 µWh/cm 2 and areal power density of 48 mW/cm 2. On the other hand, the maximum specific capacitance is obtained for the lowest mass loading of

The Journal of Physical Chemistry C, 2018

Polyaniline (PANI), is one of the promising candidates for utilization as electrode material in s... more Polyaniline (PANI), is one of the promising candidates for utilization as electrode material in supercapacitors and its electro-and physical-chemical properties have been studied for several decades. However, there are fundamental questions that need to be answered. For example, is it possible to obtain and characterize individual PANI chains or what is the impact of

Vacuum, 2019

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.