Csaba Visy - Profile on Academia.edu (original) (raw)

Papers by Csaba Visy

Direct in situ conductance evidence for non-faradaic electrical processes in poly(3-methylthiophene)

Electrochimica Acta, Feb 1, 2000

ABSTRACT Registration of the conductance after the end of the electrochemical polymerisation of 3... more ABSTRACT Registration of the conductance after the end of the electrochemical polymerisation of 3-methylthiophene (PMT) indicated a large conductance increase at open circuit. Further in situ conductance measurements with the polymeric film in Bu4NPF6/acetonitrile base solution provided direct evidence for that — after the oxidation of the film — the final achievement, the accomplishment of the state of high conduction is not necessarily coupled with current flow any more. The non-faradaic step which may explain this observation is described as a chemical reorganisation within the film, which involves the transformation of solvated polymer segments to a more conjugated, non-solvated form.

Electrochimica Acta, 2005

Redox transformation of electronically conducting polymers was studied by different in situ combi... more Redox transformation of electronically conducting polymers was studied by different in situ combined electrochemical techniques. Results obtained with polypyrrole/dodecyl sulfate film in aqueous solution and with polythiophene/hexafluorophosphate films in acetonitrile by in situ ac conductance and EQCM support the assumption of the key role of the desolvation in the achievement of the so-called quasi-metallic state of electronically conducting polymers. The desolvation considered as a phase transition is the chemical background of the capacitive behaviour, and it causes the structural changes, which lead to a film in which the interchain interactions may form the large-scale conducting polymer matrix.

Electrochimica Acta, Jul 1, 2000

3-Thiophene-acetic acid and 3-methylthiophene co-polymers have been prepared with the considerati... more 3-Thiophene-acetic acid and 3-methylthiophene co-polymers have been prepared with the consideration that the solvation behaviour of the film could be modified. The modification is coupled with the observed splitting of the oxidation peak on the cyclic voltammograms. The redox transformation of the films was studied by electrochemical quartz crystal microbalance (EQCM) and in situ conductance (ISC) techniques. Mass changes during the electrochemical processes showed that the cation is not involved into the charge balancing of the film. Manifestation of self-doping was excluded by analogous measurements with an aprotic co-polymer of methylthiophene. Results completed with in situ conductance and spectroelectrochemical observations confirmed the assumption of a chemical step taking place after the first oxidation. In this process desolvation of the oxidised intermediate occurs, which is a necessary step for the achievement of the quasi-metallic state.

Journal of Physical Chemistry B, Jan 10, 2003

The relaxation process of pristine polypyrrole/dodecyl sulfate (PPy/DS) films at open circuit, im... more The relaxation process of pristine polypyrrole/dodecyl sulfate (PPy/DS) films at open circuit, immediately after electropolymerization, was studied by in situ spectroelectrochemical, alternating-current conductance, electrochemical quartz crystal microbalance, and pH-metric techniques. A new phenomenon, called irregular reduction, involving apparent redoping and resulting in a polymer with a lower conjugation length is observed, which may occur if the pristine film is reduced without a waiting period. During this waiting period at open circuit, the film is deprotonated and partially desolvated with concurrent stacking of the polymer chains. The length of the waiting period allowed for the newly made polymer is of utmost importance, and ignorance of the relaxation of the film may explain the well-known irreproducibility in the fabrication of conducting polymers.

Electrochimica Acta, Dec 1, 2007

Vitamin B12 (B12)-possessing a redox active cobalt centre-is a candidate to be used as a mediator... more Vitamin B12 (B12)-possessing a redox active cobalt centre-is a candidate to be used as a mediator in bioelectrochemical processes. In order to exploit the possible redox activity of B12, Pt has been modified by a bio-conform conducting layer polypyrrole/piperazine-1,4-bis(2-ethane sulfonate) PPy/PIPES. The electrochemical and spectral behaviour of this film proved to be similar to PPy/dodecyl-sulfate (DS), widely considered and accepted as one of the best combinations of conducting polymer films. The capability of the PPy/PIPES film for acting as adsorbant in the accumulation of B12 has been evidenced by the electrochemical quartz crystal microbalance (EQCM) technique. B12 could also be incorporated into the polymer layer during its electrochemical deposition. The results proving the preserved redox activity of B12 within the film open new perspectives towards redox mediated bioelectrochemical applications based on the immobilization of this biomolecule.

Journal of Solid State Electrochemistry, Jun 7, 2001

Properties of polypyrrole/dodecyl sulfate ®lms were studied by dierent spectroelectrochemical, ex... more Properties of polypyrrole/dodecyl sulfate ®lms were studied by dierent spectroelectrochemical, ex situ alternating current conductance and IR techniques. It was demonstrated that the open-circuit time after the accomplishment of the electropolymerisation has a key role in the redox behaviour of the ®lm. Layers reduced immediately after the deposition exhibit dierent charge capacity, conductance and reducibility: once the ®lm was reduced in this manner, it could be transformed into either the totally neutral or the quasimetallic state anymore. The pristine ®lm can reach the quasimetallic state only after a certain period of time at open circuit. The reduction of this ®lm can be interpreted by a dissociation-type ®rst step, instead of the classical consecutive two-step mechanism.

Electrochimica Acta, Apr 1, 2011

Electrochemical synthesis of a novel carboxylic acid functionalized polythiophene-poly(3thiophene... more Electrochemical synthesis of a novel carboxylic acid functionalized polythiophene-poly(3thiophene-butyric-acid), PTBA-has been realized. Its morphology, electrochemical, spectral and conducting properties have been compared to those of poly(3-thiophene-acetic-acid), PTAA, which is widely used to immobilise both bioactive molecules and inorganic nanoparticles. According to scanning electron microscopic (SEM) images, the difference in the real and geometric surface area of the modified electrodes is much more expressed in the case of PTBA. Both the symmetry of the cyclic voltammograms and the concurrent, sustained optical changes proved that this polymer possesses an improved and more stable redox activity. According to simultaneously performed in situ ac. impedance and UV-Vis measurements, both films could be uniformly transformed between the insulating and conducting forms, but PTAA exhibited some degradation. The development of the conducting state during the redox switching of both thiophene derivative polymers proved to be primarily connected to the formation of dicationic species. The electrochemical quartz crystal microbalance (EQCM) results evidenced also differences between the two polymers, which difference can be interpreted by assuming the more expressed effect of the deprotonation-connected (self-) doping process in PTAA. The results confirm that the new conducting polymer, PTBA is much more convenient for being considered as the polymer matrix of practically applicable composites.

Electrochimica Acta, Mar 1, 2014

Effective bio-electrocatalysts require stable immobilization of sufficient amounts of the bioacti... more Effective bio-electrocatalysts require stable immobilization of sufficient amounts of the bioactive component. In this study, a novel and efficient method for specific binding of laccase enzyme onto magnetite nanoparticles (NPs) is presented. The interaction between the chemically modified magnetite NPs and the enzyme was evidenced by both infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS). Subsequently, the enzyme-coated magnetite NPs were successfully incorporated into polypyrrole matrix during galvanostatic electropolymerization. The encapsulation of laccase covered NPs was proved by EQCN, TEM, and FT-IR spectroscopy; whereas the electrochemical behaviour of the formed bionanocomposite was characterized by cyclic voltammetry. In oxygen saturated solution a cathodic charge surplus was observed, related to the electrochemical reduction of oxygen. This surplus was two times higher in the case of the laccase containing layer compared to its only magnetite containing counterpart. Kinetic aspects of the oxygen reduction reaction (ORR) on the laccase containing films were investigated by hydrodynamic voltammetry, and the four-electron route was found to be exclusive, which is promising from the fuel cell perspective. Such synergistic combination of inorganic NPs and enzymes may open new avenues in the application of these bionanocomposite materials.

Journal of Physical Chemistry C, Oct 26, 2010

The number of transferred electrons in the ORR (n=3.75) was calculated from the slope of the fitt... more The number of transferred electrons in the ORR (n=3.75) was calculated from the slope of the fitted line on the Koutecky-Levich plot. Our calculation was based on the following, generally used equations 33 : 1/j=1/j k + 1/j d j d =0.62nFD 2/3 c o ν-1/6 ω 1/2 where j k is the kinetic current density, j d is diffusion limited current density; n is the number of transferred electrons; ω is the rotation rate (ω = 2πf/60 where f is the rotation frequency in rpm); F is the Faraday constant (96485 C mol −1), D is the diffusion coefficient of the molecular O 2 in 0.1 M phosphate buffer solution (1.97 10 −5 cm 2 s −1), ν is the kinematic viscosity (9.87 10 −3 cm 2 s −1), c 0 is the concentration of molecular oxygen (1.2 10 −6 mol cm −3) [S1-S2] .

Synthetic Metals, May 1, 2013

Poly(thiophene-acetic-acid)/magnetite nanocomposite electrodes were fabricated from aqueous solut... more Poly(thiophene-acetic-acid)/magnetite nanocomposite electrodes were fabricated from aqueous solutions on PDADMA (polydiallyldimethylammonium chloride) pre-treated ITO covered glass electrodes, employing layer by layer (LBL) technique. This approach was selected on the ground of the interaction between the surface OH-groups of the magnetite and the carboxylic group of the thiophene derivative. The gradual development of the hybrid assembly was followed by UV-vis spectroscopy, and was found to be continuous up to 30 bilayers. Moreover, the absorbance increase at the characteristic wavelengths was linear in the whole examined region. Importantly, the LBL-prepared composites proved to be electroactive, in aqueous phosphate buffer the Fe 3+ /Fe 2+ redox transformation was observed. The electrocatalytic activity of the modified electrodes was demonstrated for electrooxidation of dopamine (DA), and the role of both components as well as their synergistic contribution was elucidated. Preliminary results indicate possible utilization of such hybrid assemblies in the amperometric detection of this analyte.

Synthesis and characterization of polypyrrole–magnetite–vitamin B12 hybrid composite electrodes

Journal of Solid State Electrochemistry, Mar 24, 2009

In this study vitamin B12 covered magnetite nanoparticles have been incorporated into a conductin... more In this study vitamin B12 covered magnetite nanoparticles have been incorporated into a conducting polypyrrole. This polymer was electrochemically synthesized in the presence of the B12-coated magnetite. The adsorption of B12 was demonstrated by the decrease in absorbance of the vitamin in the supernatant liquid after B12 has been in contact with magnetite sol overnight. The composition of the layers

Journal of Solid State Electrochemistry, Jul 27, 2014

A simple, reproducible, one-step electrochemical synthesis of vertically aligned ZnO nanorod elec... more A simple, reproducible, one-step electrochemical synthesis of vertically aligned ZnO nanorod electrode has been worked out. The gradual decrease in t he photoelectrochemical performance of the hexagonal ZnO nanorod electrode indicated rapid photodegradation. In order to prevent the n-type semiconductor from photocorrosion, different conducting polymers were deposited on it. Composition and morphology of the hybrids were controlled by carefully changing the electropolymerization parameter (e.g., deposition charge) for the various N or S containing heterocycles. Electrochemical measurements proved that the redox activity of these covering polymer layers was preserved in the hybrid configuration. Photoelectrochemical activity of the polymer-covered ZnO nanorods was masked by thicker layers. Thin films however, successfully inhibited the photocorrosion of ZnO while preserving their photoactivity. Effective protection was evidenced using poly(3,4ethylenedioxypyrrole) (PEDOP) in comparison with polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT).

Electrochemical synthesis and characterization of poly(3-hexylthiophene)/single-walled carbon nanotube array hybrid materials

Journal of Solid State Electrochemistry, Jun 21, 2016

AbstractIn this study, we demonstrate that by directly employing single-walled carbon nanotube ar... more AbstractIn this study, we demonstrate that by directly employing single-walled carbon nanotube arrays (SWCNT-arrays)—grown on conductive substrates—as working electrodes, selective and uniform electrodeposition of a conducting polymer, namely poly(3-hexylthiophene), can be achieved on the surface of the nanotubes. The overall kinetic pattern of the electrodeposition was studied by separating the deposition charge from the one related to the redox transformation of the polymer film deposited during the precedent cycles. Both the structure and the electrochemical properties of the hybrid materials were studied as a function of the electrodeposition cycles, thus the amount of the formed polymer. The hybrids were characterized by electron microscopic (SEM, TEM) and vibrational spectroscopic (Raman spectroscopy) means. The obtained results were compared and contrasted with those gathered on macroscopic-sized multi-walled carbon nanotube array-based composites in our group recently. Overall, we conclude that electrochemical polymerization is an attractive tool to synthesize conducting polymer/SWCNT hybrid materials with controlled composition and morphology. Graphical abstractHighy organized nanostructures of conduction polymer/SWCNT array hybrids were obtained via electrodeposition

Journal of Solid State Electrochemistry, Oct 16, 2012

In opposite with the usually applied synthesis in organic media, the polymerization of bithiophen... more In opposite with the usually applied synthesis in organic media, the polymerization of bithiophene in aqueous media has been studied. The use of a non-ionic surfactant (polyoxyethylene octyl phenyl ether (Triton X-100)) is useful not only to solubilize the hydrophobic monomer but it is also important to incorporate various-biologically and catalytically active-additives. In this paper, the optimization of the polymerization conditions as well as the characterization of the electrochemical, spectral and mass exchange behavior of these composite films is summarized. The layers have shown imperceptible electroactivity in monomer-free aqueous LiClO 4 solutions, and electrochemical quartz crystal microbalance (EQCM) studies exhibited scarce ion movements, caused assumingly by the fact that the dopant species-moving together with their hydrate shell in the aqueous media-could not penetrate into the hydrophobic film. In contrast, nice reversible redox transformation could be obtained in organic medium such as acetonitrile, where-according to the EQCM results-the charge carrier formation/depletion is accompanied by the incorporation/removal of ClO 4 − anions. In this solution, the spectral changes have proved the transformation into the conducting state, connected to both mono-and dication forms. The incorporation of the surfactant has been demonstrated by the extraordinary surface morphology of the polybithiophene (pBT) films, characterized by scanning electron microscopy. The elementary composition of the curious shell-shaped objects, monitored by energy dispersive X-ray spectroscopy (EDX), evidenced the presence of Triton X-100 by the increased C/S ratio compared to neat polybithiophene, while the Cl/S data reflected the changes connected to the doping level as a consequence of ClO4− anion movements. Moreover, ex situ attenuated total reflectance (ATR) FT-IR measurements clearly showed the existence of CO bonds, also proving the successful functionalization by the surfactant, built permanently into the redox active films.

Electrochemistry Communications, Jul 1, 2010

The redox transformation of poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3octylthiophene) (P... more The redox transformation of poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3octylthiophene) (POT) has been studied and compared by combining simultaneous in situ UV-Vis-NIR spectroelectrochemical and ac impedance techniques. Simultaneous changes of the conductance and the rate of the absorbance increase/decrease of the optically different charge carriers in the selfsame film gave direct and unquestionable evidence for that in PEDOT synthesised in aqueous solution the mono-cationic, while in POT the di-cationic segments are primarily responsible for the development of the namegiving property of conducting polymers. This difference in the role of the charge carriers could be partially observed between PEDOTs prepared in aqueous and acetonitrile (AN) solutions.

Journal of Electroanalytical Chemistry, 1998

Ž. Previous in situ spectroelectrochemical studies on the redox transformation of poly 3-methylth... more Ž. Previous in situ spectroelectrochemical studies on the redox transformation of poly 3-methylthiophene have been completed by further electrochemical, EQCM and in situ conductance measurements. In the case of thicker films, the generally observed single, wide anodic voltammetric wave could be separated into two oxidation steps, which are not consecutive, but complementary processes. The mass vs. potential curve from the EQCM measurements also reflects the double pattern of the electronic process. The virtual stoichiometric factor per electron of the anion during the first oxidation is lower than 0.5, and it is close to 1 in the second oxidation region. The experimentally obtained smaller values are explained by the parallel removal of solvent. The conductance vs. logarithm of charge curves at small sweep rate show no hysteresis. However, during the first oxidation step the film is nonconducting; its transformation to conducting film is coupled with the second oxidation step. On the basis of the experimental observations, a detailed mechanism of the redox transformation is suggested in which the roles of the solvated and nonsolvated parts of the neutral film are distinguished. The achievement of the quasi-metallic state is connected to a capacitive process in which an intermediate of uncompensated charge is involved.

Synthesis and characterization of chemically and electrochemically prepared conducting polymer/iron oxalate composites

Electrochimica Acta, Apr 1, 2008

Poly(3-octyl-thiophene) (POT) and polypyrrole (PPy) iron oxalate composites were synthesized thro... more Poly(3-octyl-thiophene) (POT) and polypyrrole (PPy) iron oxalate composites were synthesized through a post-polymerization oxidative treatment. The composite of the latter has been prepared also by electrochemical polymerization. The samples have been characterized by X-ray diffraction (XRD), impedance spectroscopy, scanning electron microscope (SEM) combined with energy dispersive X-ray (EDX) spectroscopy, Mössbauer spectroscopy, cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). In

Electrosynthesis and Simultaneously Performed In situ Impedance and UV-Vis-NIR Studies on Poly(3-Thiophene-Butyric-Acid)

Meeting abstracts, 2011

not Available.

Electrochemistry Communications, 2012

Simultaneously performed in situ conductance and spectro-electrochemical measurementscompleted by... more Simultaneously performed in situ conductance and spectro-electrochemical measurementscompleted by EQCN-proved that fast redox switching can only be expected in cation exchanger type polymers, where the conductance develops promptly with the formation of monocationic/polaronic charge carriers-due assumingly to the presence of the charge compensating anions in favourable distribution.

Journal of Solid State Electrochemistry, Apr 6, 2005

Solvation/desolvation effects were studied during the redox transformation of poly(3-methylthioph... more Solvation/desolvation effects were studied during the redox transformation of poly(3-methylthiophene) by electrochemical quartz crystal microbalance technique. The effect was demonstrated by studying the phenomenon in different solvents, and comparing the results after a solution change. From the data obtained with the same film transferred between nitrobenzene and acetonitrile in both directions, the solvation effect was directly evidenced, and the virtual molar mass of the moving species in and from the same film was determined to illustrate semi-quantitatively the effect of the solvation.