K. S. V. Santhanam

Carbon nanotube electrode for oxidation of dopamine

Abstract Carbon nanotube electrodes were constructed using bromoform as binder, and the oxidative behaviour of dopamine was examined at these electrodes. The two-electron oxidation of dopamine to dopaminequinone showed ideal reversibility in cyclic voltammetry, and was significantly superior to that observed at other carbon electrodes. The electrode treated with goats brain tissue homogenate showed the same features as the untreated electrode. The results illustrate the potential of nanotube electrodes for in vitro and in vivo neurotransmitter investigations involving dopamine.

Improved Charge Transfer at Carbon Nanotube Electrodes

The closed topology and tubular structure of carbon nanotubes make them unique among different carbon forms and provide pathways for chemical studies. A number of investigations have been carried out to find applications of nanotubes in catalysis, hydrogen storage, intercalation, etc. Since carbon-electrode-based fuel cells have been experimented with for decades, it is of importance to learn the electrodic performance of these new carbon structures. We report here results of the electrocatalytic reduction of dissolved oxygen (important H2±O2 fuel cell reaction), using microelectrodes constructed from multiwalled nanotubes. In parallel, ab initio calculations were performed for oxygen deposited on the lattice and defect sites of nanotube surfaces to determine the charge transfer during oxygen reduction and compared with similar reactions on planar graphite. The microelectrodes were constructed in the following way (see Fig. 1). Multiwalled nanotubes (10 mg) prepared by the electric arc discharge process and liquid paraffin (4 mL) were intimately mixed, placed in the narrow cylindrical slot of a Perspex holder and then packed by smooth vibration. The assembly was cured at 50 C for 30 min. From the inner side of the Perspex, contact to a copper lead was made through conducting paint. Carbon paste electrodes (based on commercially available graphite powder) were prepared similarly. Carbon nanotube electrodes were prepared earlier by similar techniques to probe bioelectrochemical reactions. The need for oxygen reduction at catalytic surfaces has been recognized in fuel cells, batteries, and many other electrodic applications. Hence, oxygen reduction at nanotube surfaces is of great interest. Electrochemical reduction of dissolved oxygen is carried out in aqueous acidic (H2SO4) and neutral media (1 M KNO3). The solution is first degassed by bubbling nitrogen gas for about 15± 30 min in order to record the background current±voltage curves. Under these conditions, no cyclic voltammetric peak in the potential range 0 to ±0.8 V were observed. The same solutions were then saturated with oxygen by bubbling oxygen gas for 15 min. The cyclic voltammetric curve showed a well-defined peak at Epc = ±0.31 V vs. SCE (saturated calomel electrode) in H2SO4 solution (pH 2) at the carbon nanotube electrodes. At the carbon paste electrodes only an ill-defined peak is seen at Epc = ±0.48 V. In the KNO3 medium (pH 6.2), the reduction of dissolved oxygen is observed at Epc = ±0.51 V at the carbon nanotube electrode. This peak is shifted at the carbon paste electrode by about 30 mV. The shift of the peaks, corresponding to the reaction on the nanotube electrodes, is a strong indication of the electrocatalysis on this electrode (see discussion below). The shift may be considered as an overpotential, which indicates a more facile reaction occurring at the nanotubes compared to other carbons. The electrochemical reduction of oxygen is a function of pH of the medium as proton participation occurs as described by Equation 1.

Chemical bath deposition of cubic copper (I) selenide and its room temperature transformation to the orthorhombic phase

The chemical bath deposition of cubic copper (I) selenide (Cu2-xSe), thin films has been achieved on an inert Pt substrate from a selenosulfite-containing bath at 75 °C. The electrochemical polarisation of this film at −0.78 V vs. SCE leads to the transformation of the compound into the orthorhombic phase. The lattice parameter of the face-centered cubic copper (I) selenide increases from 5.742 A to 5.761 A due to the decrease of the concentration of Cu vacancies upon electrochemical polarisation. The transformation of the cubic to an orthorhombic phase starts to occur when copper vacancies reach a critical value of x < 0.15. This transformation seems to be induced by a Cu3Se2 impurity in the cubic Cu2-xSe phase.

Junction properties of Schottky diode with chemically prepared copolymer having hexylthiophene and cyclohexylthiophene units

A Schottky diode has been constructed from chemically synthesised copolymer of cyclohexyl and hexyl substituted thiophene units, and various metals such as In, Ag, Al, Sn, etc. The polymer film was deposited on SnO2 coated glass substrate using spin casting technique. The electrical properties of the diode have been investigated by current–voltage and capacitance–voltage measurements. These characteristics were compared with those of poly(3-cyclohexylthiophene) (P3cHT) and poly(3-n-hexylthiophene) (P3nHT) based diode. Junction parameters, such as, ideality factor (n) and barrier height (χ) have been calculated by applying thermionic emission theory. The values of n and χ for copolymer/metal junctions were found to be in between the corresponding values for P3cHT/metal and P3nHT/metal junctions. Poor performance of the copolymer/metal diode, compared to P3cHT was attributed to the steric effects produced by hexyl substituents present in the copolymer.

Electroless deposition on copper substrates and characterization of thin films of copper (I) selenide

Abstract Cuprous selenide films are prepared by reacting oxide free copper metal with selenous acid at room temperature (22°C). The formation of Cu(I) oxide is avoided by degassing the bath with argon. From the X-ray diffractograms (XRD) and electron probe microanalysis (EPMA) of such films it can be concluded that copper deficient, orthorhombic Cu(I) selenide is formed.

Magnetic field assisted convection in an electrolyte of nonuniform magnetic susceptibility

A nonhomogeneous magnetic field is generated electrochemically in an electrodeposition cell which is also an interferometer. Magnetic field strength near 0.5T produce a detectable by interferometry convective slow rotation in a diamagnetic electrolyte with electroactive (Cu2+) and indifferent (Mn2+) paramagnetic ions present in an otherwise stagnant solution with the cathode over the anode (C/A). Approximate calculation of forces and flows are attempted.

Nicotinamide-Nad Sequence: Redox Processes and Related Behavior: Behavior and Properties of Intermediate and Final Products

I. INTRODUCTION The senior author and his collaborators have long been concerned with the use of analytical chemical techniques – more specifically, experimental approaches and methodologies primarily based on polarography – to study problems of general chemical interest. Currently, electroanalytical approaches are being used in a systematic investigation of chemical phenomena involving biologically significant compounds, where such approaches seem to offer distinct advantages. Attention has been focused on the behavior of nucleic acid components, pyridine coenzymes, and relevant model compounds in solution as well as the electron-transfer interface. Behavior at the interface involves (a) adsorption of original, intermediate, and product species, (b) association in the adsorbed state, (c) mechanisms and kinetics of electron-transfer (redox) processes, and (d) chemical reactions (kinetics and mechanisms) involving reactant, intermediate (free radical, carbanion), and product species preceding, accompanying...

Electroless deposition of orthorhombic copper(I) selenide and its room temperature phase transformation to cubic structure

Abstract A phase transformation from orthorhombic copper (I) selenide to its cubic (superionic conducting) structure has been carried out at room temperature by controlling the parameters of the electroless deposition. X-ray diffraction analysis of the film suggests that it has Berzelianite structure with a lattice constant 5.719 ± 0.009 A . It is found to be a direct band-gap semiconductor with a band gap of 1.31 eV and having a resistivity of 0.52 × 10−3 Ω cm at 296 K. The transformation of cubic copper (I) selenide to orthorhombic copper (II) selenide and orthorhombic copper (I) selenide were carried out potentiostatically at +0.20 V and −0.78 V vs. saturated calomel electrode respectively. The lattice constants of orthorhombic copper (II) selenide have been evaluated from the X-ray diffraction data: a0 = 3.958 ± 0.11 A, b0 = 6.958 ± 0.017 A and c0 = 17.229 ± 0.025 A.

Laser Interferometry of Pulsed Galvanostatic Deposition of Polycarbazole

Solution de carbazole et de perchlorate de tetra-n-butylammonium dans le DMF entre 0,1 et 500 Hz

Photoelectrochemical solar cells

Publisher Summary This chapter provides an overview of the photoelectrochemical solar cells. In a photoelectrochemical cell a photoactive electrode is effectively integrated into an electrolytic cell. In a photoelectrochemical cell, injected electrons provide a current in an external circuit, returning to the redox electrolyte through a cathode in contact with it. The uncharged ground state of the dye is then restored by electron transfer from the redox system, completing the circuit and providing a regenerative cycle functionally comparable with other photovoltaic devices. The major loss mechanism associated with semiconductors in photovoltaics, the recombination of the photoexcited charge carriers in the crystalline lattice, is strongly inhibited at a dye-sensitized photoelectrode. Conventional photovoltaic junctions are essentially minority carrier devices, holes being generated in the n-type material, electrons in the p-type material and then, transported to the interface. This chapter begins with an introduction to the origins of photoelectrochemistry. The chapter then explains basic concepts of photoelectrolysis, photoelectrochemistry, photography, and sensitization. Molecular engineering of electroactive dyes is also explained in detail.