Aleksandar Dekanski

Glassy carbon electrodes. I. Characterization and electrochemical activation

Abstract Electrochemical properties of glassy carbon electrodes of two types were examined, one thermally treated at 1000°C (sample K) and another thermally treated at 2500° (sample G). Mechanically polished or electrochemically polarized electrodes were characterized in NaOH, HClO4 and H2SO4 solutions by cyclic voltammetry (cv) at different sweep rates in the potential range between the hydrogen and oxygen evolution. The activity of the electrodes depended on the properties of the glassy carbon examined, as determined by both the temperature of thermal treatment and the mechanical or electrochemical pretreatment of the sample. It was noticed that both types of electrodes, when polished exhibited an increase in the double layer charge upon increasing the pH value of the solution. The cv charges, for both types of samples, increase upon anodic polarization. The higher the potential of oxidation, the more pronounced is the increase in charge, particularly in acidic solution. The increase in charge amounts from below 1 mC cm−2 for polished glassy carbon up to few hundreds of mC cm−2 for surfaces anodically polarized in acidic solution. Analysis of the dependence of voltammetric charge, as well as morphological changes of the electrode surface, on the time of oxidation suggests the existence of three stages in the electrochemical activation process. The first one occurs only once at the beginning of the activation, while the other two repeat themselves, reflecting a periodical activation and deactivation process. These stages were discussed and ascribed to a surface layer oxidation, graphite oxide layer growth and mechanical destruction of the surface. Independent surface analysis by AES, XPS and STM confirms the results obtained by electrochemical methods.

Surface characterization of oxidized activated carbon cloth

Cellulose based activated carbon cloth has been oxidized by air, nitric acid, hydrogen peroxide and iron nitrate cristallohydrate melt treatments. Thermogravimetric analysis, selective neutralization, X-ray photoelectron spectroscopy and electrical resistance measurements have been applied to characterize the products. The amount and type of oxygen surface groups have been determined for the different oxidation procedures. The amount of surface groups formed decrease with oxidation procedure in the order: iron nitrate, nitric acid, air and hydrogen peroxide.

Boron and phosphorus doped glassy carbon : I. Surface properties

Abstract The effects of boron and phosphorus incorporation in phenolic resin precursor on the surface properties of glassy carbon (GC) have been studied. Characterization of the surface properties using X-ray photoelectron spectroscopy and mass spectrometry analysis of desorption products showed that boron and phosphorus doped GC contained more carbon-oxygen complexes on the surface than undoped GC. The thermal decomposition of the surface oxide species, resulting in desorption of CO and CO2 as major gas products, showed that the presence of heteroatoms affects the nature of the surface oxide species and contributes to their increased stability. The presence of stable surface oxide species promotes the increased oxidation resistance of doped GC samples.

Glassy carbon electrodes: II. Modification by immersion in AgNO3

Abstract The modification of glassy carbon by immersion in AgNO 3 solution was studied by cyclic voltammetry, vacuum techniques (AES and XPS) and STM. The influence of Ag + concentration, time of immersion, the presence of oxygen in AgNO 3 solution and previous thermal treatment of the glassy carbon were examined on ‘as received’ (untreated), polished and electrochemically treated samples. The results show that glassy carbon electrode immersed in AgNO 3 solution is modified by silver, which is deposited in its elemental state on the surface and near surface layers of the material. Cyclic voltammograms of silver-modified glassy carbon electrodes are similar to those of a silver electrode. The quantity of silver deposited on glassy carbon strongly depends on the pretreatment of the material before its immersion. The results obtained suggest that functional groups participate in the reduction of Ag + , and thus in the electrode modification, as active centers. Metal particles are not uniformly deposited on the surface and the deposition is 3-dimensional with deposits of laminar structure. A mechanism for the modification process is proposed.

The roles of the ruthenium concentration profile, the stabilizing component and the substrate on the stability of oxide coatings

Abstract Electrocatalytic oxide coatings with variable concentration profiles of RuO2 as the active component were obtained through a combination of separately applied layers of RuO2, TiO2, IrO2, RuO2 + TiO2 and RuO2 + IrO2 on titanium and glassy carbon substrates. The stability of the samples was examined by accelerated tests performed at high anodic current densities. Electrochemical techniques, cyclic voltammetry for assessing the charge associated with the coating, polarization measurements for assessing the electrocatalytic activity, and Auger electron spectroscopy to register surface composition of the coatings, were applied to follow changes due to the stability experiments. The stability and the charge depended strongly on the sequence of layers in the RuO2−TiO2 coating, with the samples having the RuO2 + TiO2 layer facing the electrolyte exhibiting the highest values for both properties. In contrast to this, the stability of the RuO2−IrO2 coatings, besides being lower than the stability of RuO2−TiO2 coatings, showed no dependence on the sequence of the applied layers. Much lower stability was exhibited by the coatings applied on glassy carbon rather than on titanium. A mechanism of the stability of the coatings based on the interaction of lower than four valency state titanium with higher than four valency ruthenium, proposed for single-crystal surfaces, is corroborated. Finally, during the thermal treatment a diffusion of titanium originating in the titanium substrate through the coating was established.

Characterization of the surface and interphase of plasma-treated HM carbon fibres

Abstract The surface chemistry and morphology of HM carbon fibres, treated with pulse-voltage excited air, oxygen, nitrogen and acrylonitrile plasmas, are characterized by high-resolution X-ray photoelectron spectroscopy and transmission electron microscopy. Oxygen- and nitrogen-containing species are generated on the surface under plasma treatment without significant changes in the fibre morphology. Comparable interfacial shear strengths are found for single-fibre model composites prepared with amine-cured epoxy resin, with a highest value of 61.4 MPa for air-plasma-treated fibres. The surface chemistry of the fibres if found to influence the degree of epoxy consumption at the earlier stages of the cure process, as determined by Fourier transform infra-red microscopy and differential scanning calorimetry.

The effect of the addition of colloidal iridium oxide into sol–gel obtained titanium and ruthenium oxide coatings on titanium on their electrochemical properties

Electrochemical properties of sol-gel processed Ti(0.6)Ir(0.4)O(2) and Ti(0.6)Ru(0.3)Ir(0.1)O(2) coatings on titanium substrate were investigated using cyclic voltammetry, polarization measurements and electrochemical impedance spectroscopy and compared to the properties of Ti(0.6)Ru(0.4)O(2) coating. The role of iridium oxide in the improvement of the electrocatalytic, capacitive and stability properties of titanium anodes activated by a RuO(2)-TiO(2) coating is discussed. The oxide sols were prepared by forced hydrolysis of the metal chlorides. The characterization by dynamic light scattering and X-ray diffraction showed that polydisperse oxide sols were obtained with the particles tending to form agglomerates. The presence of IrO(2) causes a suppression of the X-ray diffraction peaks of TiO(2) and RuO(2) in the sol-gel prepared Ti(0.6)Ir(0.4)O(2) and Ti(0.6)Ru(0.3)Ir(0.1)O(2) coatings. The IrO(2)-containing coatings had an enhanced charge storage ability and activity for the oxygen evolution reaction (OER) in comparison to Ti(0.6)Ru(0.4)O(2) coating. The voltammogram of the Ti(0.6)Ir(0.4)O(2)/Ti electrode showed well-resolved peaks related to Ir redox transitions, which are responsible for the enhanced charge storage ability of IrO(2)-containing coatings. Redox transitions of Ir were also registered in the high-frequency domain of the ac impedance spectra of the coatings as a semicircle with characteristics insensitive to the electrolyte composition and to the electrode potential prior to OER. However, the semicircle characteristics were different for the two IrO(2)-containing coatings, as well as at potentials outside the OER in comparison to those at which the OER occurs.

Properties of glassy carbon modified by immersing in metal cation solutions

Abstract Glassy carbon (GC) surfaces: ‘as produced’ in the carbonization process, abrased and oxidized were studied using AES, XPS and cyclic voltammetry. Evidence for the existence of an outer sheath formed during carbonization, having chemical structure and electrochemical properties different from the bulk of the GC samples has been found. Samples with outer sheath and samples where it was removed by abrasion and/or electrochemical oxidation have been modified by immersing into AgNO 3 solution for about 30 days. A deposit of metallic silver has been observed on the surface of all samples.

The Influence of the Aging Time of RuO2 Sol on the Electrochemical Properties of the Activated Titanium Anodes Obtained by Sol-Gel Procedure

The influence of the aging time of RuO 2 sol on the electrochemical properties and behaviour in chlorine evolution reaction of RuO 2 /Ti and (40%RuO 2 + 60%TiO 2 )/Ti anodes obtained by sol-gel procedure was studied. The electrochemically active surface area of the anode coatings was examined by cyclic voltammetry. The electrocatalytic activity and anode stability in chlorine evolution reaction were investigated by polarization measurements and accelerated stability test. The dependence of electrochemical properties of obtained activated titanium anodes on RuO 2 particle size was established.

Day of the week effect in paper submission/acceptance/rejection to/in/by peer review journals

This paper aims at providing an introduction to the behavior of authors submitting a paper to a scientific journal. Dates of electronic submission of papers to the Journal of the Serbian Chemical Society have been recorded from the 1st January 2013 till the 31st December 2014, thus over 2 years. There is no Monday or Friday effect like in financial markets, but rather a Tuesday–Wednesday effect occurs: papers are more often submitted on Wednesday; however, the relative number of going to be accepted papers is larger if these are submitted on Tuesday. On the other hand, weekend days (Saturday and Sunday) are not the best days to finalize and submit manuscripts. An interpretation based on the type of submitted work (“experimental chemistry”) and on the influence of (senior) coauthors is presented. A thermodynamic connection is proposed within an entropy context. A (new) entropic distance is defined in order to measure the “opaqueness” = disorder) of the submission process.