Svetlana N. Eliseeva

Composite electrode materials based on conducting polymers loaded with metal nanostructures

The electrochemical and chemical methods for synthesizing conducting polymer-metal nanocomposite materials are considered as well as the main factors affecting the structure and electrochemical properties of these composites. The experimental data on the catalytic activity of conducting polymer–metal electrodes are analyzed in respect to several electrochemical reactions. The approaches to theoretical description of electrochemical processes on heterogeneous conducting polymer–metal electrodes are discussed and examples of experimental testing of applicability of the proposed the theoretical models are shown. The bibliography includes 335 references.

Redox transformations in electroactive polymer films derived from complexes of nickel with SalEn-type ligands: computational, EQCM, and spectroelectrochemical study

Polymer complexes of nickel with SalEn-type ligands (SalEn = N,N′-bis (salicylidene) ethylenediamine) possess a number of unique properties, such as high redox conductivity, electrochromic behavior and selective catalytic activity in heterogeneous reactions. However, the mechanism of their redox transformation is still not clear. To understand this mechanism, we have performed a combined study of electrochemical and spectral properties of polymers derived from nickel complexes with various SalEn-type ligands containing methoxy substituents in phenyl rings, and methyl substituents in imino bridges. Experimental data were correlated with the results of density functional theory (DFT) calculations for model chains consisting of one to four monomer units. We found that, in acetonitrile-based supporting electrolyte, oxidation of such complexes, regardless of ligand substituents, proceeds via two routes, leading to formation of two oxidized forms: for the first one, a good correlation between experimental and computation results was observed. It has been demonstrated that positive charge in this form is delocalized in the phenyl moieties of ligand. The second oxidized form is stable only in coordinating solvents at high electrode polarizations and is likely to have the charge localized on the central metal atom, stabilized by axial coordination of solvent molecules. The complicated electrochemical response of each of the polymers that we have studied can be explained in the scope of this model without any additional assumptions by taking into account conversion of one oxidized form into another. Understanding the solvent effect on the oxidation route of the complexes will enable controlling their catalytic properties and stability.

Effect of addition of a conducting polymer on the properties of the LiFePO4-based cathode material for lithium-ion batteries

Effect of addition of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) conducting polymer on the structure and properties of a cathode material based on lithium iron phosphate was studied. The X-ray diffraction method was used to examine the structure of lithium iron phosphate in a freshly prepared C-LiFePO4/C/PEDOTS:PSS composite material and in that subjected to a prolonged cycling. The chargedischarge characteristics of the cathode material of the conventional composition, which contains carbon black and poly(vinylidene fluoride) binder, and a new composition with addition of PEDOT:PSS were compared. The specific capacity of C-LiFePO4/C/PEDOT:PSS was 165 mA h g−1 (at 0.2C current), which substantially exceeds the specific capacity of the LiFePO4 material in the conventional composition.

Electochemical characteristics of LiMn 2 O 4 /Li 4 Ti 5 O 12 battery with conducting polymeric binder

Lithium-ion battery based on LiMn2O4/Li4Ti5O12 materials was assembled for the first time. The cathode and anode of this battery are prepared with the aqueous combined binder poly-3,4-ethylenedioxythiophene: polystyrene sulfonate/carboxymethylcellulose (without polyvinylidene fluoride). The capacity of the LiMn2O4/Li4Ti5O12 battery was found to be 75 mA h g–1 at 0.1 C and 55 mA h g–1 at 1 C. A 95% capacity was retained after 100 charge-discharge cycles. The batteries demonstrated a high Coulombic efficiency close to 100%. Scanning electron microscopy demonstrated that using the conducting binder poly-3,4-ethylenedioxythiophene: polystyrene sulfonate/carboxymethylcellulose provides formation of dense compact layers of electrode materials with good adhesion to the substrate. The electrode structure remains maintained after 100 charge-discharge cycles.

Influence of addition of lithium salt solution into PEDOT:PSS dispersion on the electrochemical and spectroscopic properties of film electrodes

AbstractThe present work has studied electrochemical and optical properties of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film electrodes drop-casted from commercial PEDOT:PSS aqueous dispersion with preliminary addition and without addition of LiClO4 electrolyte (further denoted as PEDOT:PSS/LiClO4 and PEDOT:PSS). Cyclic voltammetry measurements showed the significant increase in capacitance of PEDOT:PSS/LiClO4 film electrodes in comparison to PEDOT:PSS. Furthermore, the improved charge transport in PEDOT:PSS/LiClO4 films was demonstrated by electrochemical impedance spectra. In situ spectroelectrochemical measurements revealed that preliminary addition of LiClO4 into PEDOT:PSS aqueous dispersion allows to increase amount of free charge carriers (polaron and bipolaron states) in the resulting film during electrochemical oxidation in LiClO4 propylene carbonate solution. This increase was attributed to ion-induced charge screening between positively charged PEDOT and negatively charged PSS in polyelectrolyte structure, which was supported by structural investigations of both types of film electrodes by using FTIR, SEM, and XPS measurements. Charge screening results from a more open structure that allows conformational relaxation of PEDOT molecules during charge transport, which leads to partial separation of oppositely charged PSS and PEDOT molecules and facilitating the increase of electrochemical activity. Graphical abstractᅟ

Electrochemical deposition of molybdenum oxide into films of poly(3,4-ethylenedioxythiophene) conducting polymer on glassy carbon substrates

Electrochemical deposition of molybdenum oxides from molybdate-containing solutions onto glassy carbon electrodes and the same electrodes coated with a film of poly(3,4-ethylenedioxythiophene) conducting polymer was studied. The morphology of the deposited molybdenum oxides was examined by scanning electron microscopy. The method of X-ray photoelectron spectroscopy was used to determine the state of molybdenum in surface molybdenum oxides and a conclusion was made that the oxide MoO2 is mostly present.