Showing papers on "Cyclic voltammetry published in 1998"

Electrochemical determination of the ionization potential and electron affinity of poly(9,9-dioctylfluorene)

Abstract: We report cyclic voltammetry measurements for the blue electroluminescent conjugated polymer poly(9,9-dioctylfluorene). Both oxidation and reduction potentials are determined and thus estimates of both the ionization potential Ip and electron affinity Ea of the polymer are obtained for the same sample under the same experimental conditions. We estimate Ip=5.80 eV and Ea=2.12 eV. These results disagree with the common assumption that Ea is, to good approximation, given by the difference between Ip and the optical gap. Measurements on indium tin oxide/polyfluorene/calcium light emitting diode structures are consistent with the deductions from the electrochemical data.

Common Electroanalytical Behavior of Li Intercalation Processes into Graphite and Transition Metal Oxides

Abstract: This paper compares the electroanalytical behavior of lithiated graphite, , , and spinel electrodes. Slow scan rate cyclic voltammetry (SSCV), potentiostatic intermittent titration (PITT), and electrochemical impedance spectroscopy (EIS) were applied in order to study the potentiodynamic behavior, the variation of the solid‐state diffusion coefficient, and the impedance of these electrodes. In addition, X‐ray diffractometry and Fourier transform infrared (FTIR) spectroscopy were used in order to follow structural and surface chemical changes of these electrodes upon cycling. It was found that all four types of electrodes behave very similarly. Their SSCV are characterized by narrow peaks which may reflect phase transition between intercalation stages, and the potential‐dependent Li chemical diffusion coefficient is a function with sharp minima in the vicinity of the CV peak potentials, in which the differential electrode capacity is maximal. The impedance spectra of these electrodes reflect an overall process of various steps in series. These include ion migration through surface films, charge transfer which depends strongly on the potential, solid‐state diffusion and, finally, accumulation of the intercalants in their sites in the bulk of the active mass, which appears as a strongly potential‐dependent, low‐frequency capacitive element. It is demonstrated that the above electro‐analytical response, which can be considered as the electrochemical fingerprint of these electrodes, may serve as a good in situ tool for the study of capacity fading mechanisms.

Air Stability of Alkanethiol Self-Assembled Monolayers on Silver and Gold Surfaces

Abstract: Surface Raman spectroscopy, electrochemistry, and X-ray photoelectron spectroscopy have been used to study the effects of air exposure on the stability of self-assembled monolayers (SAMs) formed from alkanethiols on mechanically polished, smooth Ag and Au surfaces. Raman spectra exhibit oxidized sulfur modes after only hours of air exposure. X-ray photoelectron spectroscopy of the S 2p region provides additional evidence for sulfur oxidation. Cyclic voltammetry of Ru(NH3)63+ indicates that oxidized alkanethiol SAMs retain blocking characteristics toward electron transfer, even after exposure of the oxidized SAM-surface to a solubilizing solvent. Control experiments suggest ozone as the primary oxidant in ambient laboratory air which causes rapid oxidation of the thiolate moiety. These results have important ramifications for the general use of SAMs in many proposed applications.

Asymmetric Triaryldiamines as Thermally Stable Hole Transporting Layers for Organic Light-Emitting Devices

Abstract: The synthesis of a series of asymmetric triaryldiamines has provided a number of materials with a wide range of thermal, electrochemical, and spectroscopic properties. The asymmetric materials described herein have two different diarylamine groups bound to a 1,4-phenylene or 4,4‘-biphenylene core, i.e., Ar1Ar2N−C6H4−NAr1‘Ar3 or Ar1Ar2N-biphenyl-NAr1‘Ar3, respectively. The diarylamines studied include diphenylamine, phenyl-m-tolylamine, naphthylphenylamine, iminostilbene, iminodibenzyl, and carbazole. These materials were prepared by copper- and palladium-catalyzed coupling of aryl halides and diarylamines. The asymmetry inherent in these compounds prevents these low molecular mass compounds from crystallizing, thus yielding higher thermal stability over that of the symmetric derivatives. In all cases, the asymmetric diamines form stable glasses, with glass transition temperatures up to 125 °C. HOMO levels for these materials, estimated by cyclic voltammetry, show a broad range of values, with oxidation po...

Amperometric glucose biosensor based on sol-gel organic-inorganic hybrid material.

Abstract: A new type of sol-gel organic-inorganic hybrid material was developed and used for the production of biosensors. This material is composed of silica sol and a grafting copolymer of poly(vinyl alcohol) with 4-vinylpyridine. It prevents the cracking of conventional sol-gel-derived glasses and eliminates the swelling of the hydrogel. The optimum composition of the hybrid material was first examined, and then glucose oxidase was immobilized in this matrix to demonstrate its application. The characteristics of the biosensor were studied by cyclic voltammetry and chronoamperometry. The biosensor exhibited a series of good properties: high sensitivity (600 nA mmol-1 L-1), short response time (11 s) and remarkable long-term stability in storage (at least 5 months). In addition, the characteristics of the second-generation biosensor with the use of tetrathiafulvalene as a mediator were discussed.

Anthraquinonedisulfonate Electrochemistry: A Comparison of Glassy Carbon, Hydrogenated Glassy Carbon, Highly Oriented Pyrolytic Graphite, and Diamond Electrodes

Abstract: The electrochemistry of anthraquinone-2,6-disulfonate (2,6-AQDS) at glassy carbon (GC), hydrogenated glassy carbon (HGC), the basal plane of highly oriented pyrolytic graphite (HOPG), and boron-doped diamond was investigated by cyclic voltammetry and chronocoulometry. Quantitative determination of the surface coverage and qualitative assessment of the physisorption strength of 2,6-AQDS adsorption on each of these electrodes were done. The diamond and HGC surfaces are nonpolar and relatively oxygen-free, with the surface carbon atoms terminated by hydrogen. The polar 2,6-AQDS does not adsorb on these surfaces, and the electrolysis proceeds by a diffusion-controlled reaction. Conversely, the GC and HOPG surfaces are polar, with the exposed defect sites terminated by carbon−oxygen functionalities. 2,6-AQDS strongly physisorbs on both of these surfaces at near monolayer or greater coverages, such that the electrolysis proceeds through a surface-confined state. Less than 40% of the initial surface coverage can...

Cobalt Porphyrin Catalyzed Reduction of CO2. Radiation Chemical, Photochemical, and Electrochemical Studies

Abstract: Several cobalt porphyrins (CoP) have been reduced by radiation chemical, photochemical, and electrochemical methods, in aqueous and organic solvents. In aqueous solutions, the CoIP state is stable at high pH but is shorter lived in neutral and acidic solutions. Stable CoIP is also observed in organic solvents and is unreactive toward CO2. One-electron reduction of CoIP leads to formation of a species that is observed as a transient intermediate by pulse radiolysis in aqueous solutions and as a stable product following reduction by Na in tetrahydrofuran solutions. The spectrum of this species is not the characteristic spectrum of a metalloporphyrin π-radical anion and is ascribed to Co0P. This species binds and reduces CO2. Catalytic formation of CO and HCO2- is confirmed by photochemical experiments in acetonitrile solutions containing triethylamine as a reductive quencher. Catalytic reduction of CO2 is also confirmed by cyclic voltammetry in acetonitrile and butyronitrile solutions and is shown to occur ...

Mechanochemical Synthesis and Characterization of the Fullerene Dimer C120

Abstract: The bulk synthesis of the [2 + 2] dimer of fullerene C60 was achieved by the solid-state mechanochemical reaction of C60 with KCN by the use of a high-speed vibration milling (HSVM) technique. This reaction took place also by the use of potassium salts such as K2CO3 and CH3CO2K, metals such as Li, Na, K, Mg, Al, and Zn, and organic bases such as 4-(dimethylamino)- and 4-aminopyridine. Under optimum conditions, the reaction afforded only the dimer C120 and unchanged C60 in a ratio of about 3:7 (by weight) regardless of the reagent used. The dimer C120 was fully characterized by IR, UV−vis, 13C NMR, and TOF MS spectroscopies, cyclic voltammetry, and differential scanning calorimetry. Comparison of the IR and 13C NMR spectral data of C120 with those reported for all-carbon C60 polymers implied that the [2 + 2] dimer C120 represents the essential subunit of these polymers. The dimer C120 underwent facile dissociation into two C60 molecules by heat, HSVM treatment, exposure to room light, or electrochemical re...

Electrochemical detection of electrochemically inactive cations by self-assembled monolayers of crown ethers

Abstract: Self-assembled monolayers (SAMs) of 2-[(6-mercaptohexyl)oxy]methyl-12-crown-4 (1) and 2-[(6-mercaptohexyl)oxy]methyl-15-crown-5 (2) on gold are able to bind cations reversibly from aqueous solutions. This binding of the electrochemically inactive cations is monitored by cyclic voltammetry and impedance spectroscopy using the redox couple Ru(NH3)62+/3+ as "reporter ion". Gold electrodes modified with 1 detect Na+ even in the presence of a 100-fold excess of K+; SAMs of 2 are K+ selective. As a result of the high surface density of crown ethers, sandwich complexes are formed. Reduced surface concentrations of receptors in mixed monolayers of 2 with heptanethiol prevent the sandwich complexation and decreases the K+/Na+ selectivity of the SAM.

Cobalt-Porphyrin Catalyzed Reduction of CO2: Radiation Chemical, Photochemical, and Electrochemical Studies

Abstract: Several cobalt porphyrins (CoP) have been reduced by radiation chemical, photochemical, and electrochemical methods, in aqueous and organic solvents. In aqueous solutions, the CoIP state is stable at high pH but is shorter lived in neutral and acidic solutions. Stable CoIP is also observed in organic solvents and is unreactive toward CO2. One-electron reduction of CoIP leads to formation of a species that is observed as a transient intermediate by pulse radiolysis in aqueous solutions and as a stable product following reduction by Na in tetrahydrofuran solutions. The spectrum of this species is not the characteristic spectrum of a metalloporphyrin π-radical anion and is ascribed to Co0P. This species binds and reduces CO2. Catalytic formation of CO and HCO2- is confirmed by photochemical experiments in acetonitrile solutions containing triethylamine as a reductive quencher. Catalytic reduction of CO2 is also confirmed by cyclic voltammetry in acetonitrile and butyronitrile solutions and is shown to occur ...

Fast-scan cyclic voltammetry of protein films on pyrolytic graphite edge electrodes: characteristics of electron exchange.

Abstract: The rapid electron-exchange characteristics of metalloproteins adsorbed at a pyrolytic graphite “edge” electrode have been studied by analog dc cyclic voltammetry at scan rates up to 3000 V s-1. The voltammetry of four proteins, azurin (a “blue” copper protein) and three 7Fe ferredoxins, reveals oxidation and reduction peaks that display only modest increases in width and peak separation as the scan rate is raised. This is indicative of a substantially homogeneous population of noninteracting centers which undergo rapid electron exchange with the electrode. Both the Butler−Volmer and Marcus models have been tested. The electrochemical kinetics, as reflected by k0 (the rate at zero overpotential), are too fast to allow the determination of reorganization energies by this method. Nonetheless, the rapid and energetically coherent nature of the electron transfer enables the cyclic oxidation and reduction of protein redox centers to be examined on a time scale sufficiently short to recognize coupled processes ...

Heat‐Treated Iron(III) Tetramethoxyphenyl Porphyrin Supported on High‐Area Carbon as an Electrocatalyst for Oxygen Reduction I. Characterization of the Electrocatalyst

Abstract: Iron(III) tetramethoxyphenyl porphyrin chloride adsorbed on the Black Pearls carbon (FeTMPP‐Cl/BP) was heat‐treated at temperatures from 200 to 1000°C in Ar atmosphere and characterized by using cyclic voltammetry, X‐ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) techniques. Cyclic voltammetry experiments were carried out in acidic and alkaline solutions. Redox peaks due to the Fe(III)/Fe(II) reaction were present in an unheat‐treated sample and in the sample heat‐treated at 200°C but were significantly reduced in height for the sample heat‐treated at 400°C. At higher temperatures they disappeared, indicating decomposition of FeTMPP‐Cl. After heat‐treatment at 700°C or higher, an anodic peak in the first cathodic sweep was observed and it was attributed to the dissolution of metallic Fe. XPS measurements did not show unambiguously the valence state of the Fe in the electrocatalyst heat‐treated at high temperatures, but comparison of cyclic voltammograms of electrodeposited Fe and a bulk Fe electrode with cyclic voltammograms of FeTMPP‐Cl/BP indicated that it was metallic Fe. Fe particles were observed on TEM images. Ma.ny more iron particles were present in the sample heat‐treated at 1000°C than in the sample heat‐treated at 800°C. Some of the particles remained in both samples after electrochemical dissolution, and they were completely surrounded by carbon particles or wrapped in the graphite shell. A well‐defined graphite shell surrounding iron particles was observed only in the sample heat‐treated at 1000°C.

Electrochemical Capacitors Using Hydrous Ruthenium Oxide and Hydrogen Inserted Ruthenium Oxide

Abstract: Electrochemical capacitors made with hydrous ruthenium oxide and hydrogen inserted hydrous ruthenium oxide electrode materials were investigated. The electrochemical behavior of in the potential range of −0.2 to 1.3 V vs. saturated calomel electrode (SCE) was characterized using a cyclic voltammetry technique. It was found that, electrochemically, amorphous electrodes behave quite differently from crystalline . The potentials of both the positive and the negative electrodes of the capacitors were monitored relative to SCE. For capacitors made with electrode material, gas evolution and an increase of cell resistance were observed in the first few charge/discharge cycles. This was due to the fact that the potentials of the starting materials were close to the oxidation limit of the potential window. Hydrogen inserted hydrous ruthenium oxide with potentials near the center of the potential window were prepared using both electrochemical and chemical methods. It was demonstrated that capacitors made of hydrogen inserted ruthenium oxide electrodes exhibited high efficiency, high energy, and high power through a cycle life over 60,000 times.

Template Recognition in Inorganic−Organic Hybrid Films Prepared by the Sol−Gel Process

Abstract: Inorganic−organic hybrid sol−gel processing has been utilized to fabricate thin, porous, chemically selective silicate films. These materials have been fabricated using a template-based approach that involves the formation of a cross-linked matrix around a specific reagent followed by removal of that reagent. The silica sol consisted of a hybrid mixture of functionalized organosilicon precursors (phenyltrimethoxysilane and methyltrimethoxysilane), a network former (tetramethoxysilane), and the template molecule, dopamine (DA). Silicate thin films were prepared by spin casting an aliquot of the composite sol on the surface of a glassy carbon electrode. Dopamine was extracted from the dried film via soaking in phosphate buffer, and the affinity and selectivity of the DA-templated films were characterized using cyclic voltammetry. The results show that the DA-templated films have an increased affinity for dopamine over that of structurally related molecules including serotonin, epinephrine, and dihydroxynaph...

Assembly of Covalently-Coupled Disulfide Multilayers on Gold

Abstract: We report on the spontaneous organization of up to eight covalently attached layers formed on gold from solution phase (α,ω)-dithiols 1,6-hexanedithiol (C6), 1,8-octanedithiol (C8), and 1,9-nonanedithiol (C9). The linking chemistry between layers is the oxidative formation of a sulfur−sulfur bond that competes successfully with intralayer S−S bond formation. We have used optical null ellipsometry, FTIR, X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) to characterize the multilayers. Once formed, the multilayers are stable when washed with 1 M KCl, water, ethanol, CHCl3 and n-hexane solutions, before and after prolonged exposure to ambient laboratory conditions. In addition to the formation of multilayers, our data point to the efficient oxidation of the interlayer disulfide bond to an oxidized sulfur moiety where the S−S bond remains intact. Extensive oxidation produces a sulfonate-terminated surface that reacts with Zr4+ and alkanebisphosphonates to form a hybrid multilayer assembly.

Characterization and Electrochromic Properties of Ultrathin Films Self-Assembled from Poly(diallyldimethylammonium) Chloride and Sodium Decatungstate

Abstract: Poly(diallyldimethylammonium) chloride (P) and sodium decatungstate (W) were layer-by-layer self-assembled onto quartz, mica, and ITO-electrode substrates (S). The self-assembled films, S-(P/W)n, were characterized by absorption spectrophotometry, reflectivity, cyclic voltammetry and scanning force microscopy (AFM). The electrochemical properties of the S-(P/W)n films were found to differ from those in which the polyelectrolyte remained at the outermost layer, i.e., S-(P/W)n/P. Photoelectrochemical measurements provided evidence for the electrochromic and photoelectrochromic behavior of these films.

In Situ Raman Studies on Cathodically Deposited Nickel Hydroxide Films and Electroless Ni−P Electrodes in 1 M KOH Solution

Abstract: Three types of working electrodes, as-deposited nickel hydroxide, deactivated nickel hydroxide, and electroless Ni−P electrode, are studied in this work. The surface state of the electrodes varying with potential are investigated using cyclic voltammetry techniques combined with in situ Raman spectroscopy in 1 M KOH solution. As-deposited nickel hydroxide is electrooxidized to the oxides of higher state with Raman characteristic bands, 475 and 55 cm-1, and the corresponding reaction is assigned to be a α-Ni(OH)2/γ-NiOOH redox reaction in the potential range between 350 and 500 mV. When the film is deactivated by voltammetric cycling, the phases, β-Ni(OH)2, and some untransformed α-Ni(OH)2 are present. β-Ni(OH)2 will be electrooxidized to β-NiOOH, which has Raman characteristic bands of 480 and 560 cm-1 in the anodic sweep between 350 and 450 mV. The redox pair on the electroless Ni−P electrode is recognized as β-Ni(OH)2/β-NiOOH because of the identical Raman bands with β-NiOOH, namely, 480 and 560 cm-1, a...

A cyclic voltammetric study of the kinetics and mechanism of electrodeposition of manganese dioxide

Abstract: The kinetics and mechanism of electrooxidation of Mn2+ ions to MnO2 (EMD) has been studied in electrolytes comprising MnSO4 and H2SO4 by cyclic voltammetry at 80°C. The voltammogram of a Pt electrode cycled between 0.6 and 1.6V vs SCE exhibits an anodic current peak at about 1.3V vs SCE resulting in the deposition of MnO2 on the electrode, while a cathodic peak appears at 0.8V vs SCE. It is shown that the pair of peaks do not correspond to a single reversible reaction but represent two separate irreversible electrode processes. The cyclic voltammetric peak current for the deposition of EMD is found to be proportional to the square root of Mn2+ ion concentration in the electrolyte and independent of acid concentration. Based on these results, a mechanism for the formation of EMD involving diffusion of Mn2+ ions to the electrode surface, oxidation of Mn2+surface to Mn3+ads, and H2O to OHads as the primary oxidation steps is invoked. Mn3+ads ions dissociate disproportionately into Mn2+ads and Mn4+ads ions at the electrode surface. The Mn2+ads and Mn4+ads ions, respectively, react with OHads and H2O resulting in the formation of EMD.

Electrochemical Studies of Carbon Films from Pyrolyzed Photoresist

Abstract: Carbon film electrodes were prepared by pyrolysis of photoresists on silicon wafers at temperatures ranging from 600 to 1,100 C. The physical properties of the carbon films were characterized by scanning and transmission electron microscopies, thermal gravimetric analysis, and four-point probe electrical resistivity measurements. The electrochemical properties of the carbon films were investigated by cyclic voltammetry to observe the kinetics of the Fe(CN){sub 6}{sup 4{minus}}/Fe(CN){sub 6}{sup 3{minus}} redox couple. The carbon film electrodes prepared at temperatures {ge} 700 C showed electrochemical behavior similar to that of glassy carbon. Better electrocatalytic behavior was obtained with carbon films prepared at the higher pyrolysis temperatures, which is attributed to different film compositions at different pyrolysis temperatures. The electrochemical properties of the carbon film electrodes are very stable, exhibiting reproducible behavior even after storing at room temperature in air for 3 months.

Electrochemical and Raman spectroscopic study of polyaniline; influence of the potential on the degradation of polyaniline

Abstract: The polymerization of aniline has been studied employing in-situ electrochemical and Raman spectroscopical techniques. Aniline was polymerized by cyclic voltammetry on a Pt surface in sulfuric acid solutions of aniline. The Raman bands were assigned for degradation products of the overoxidized form of polyaniline. A discussion of the degradation mechanism is given.