The electrochemical behaviour of soluble polyimides

The electrochemical behaviour of five soluble polyimides was studied in organic solution using cyclic voltammetry. The relationship between the electrochemical behaviour and the molecular structure was discussed, It was found that the colours of polyimides can be changed due to the electrochemical redox reactions.

Effect of urea on synchronous fluorescence spectra and electrochemical behaviour of cytochrome c

The changes of the synchronous fluorescence spectra and the electrochemical behaviour of cytochrome c with the urea concentration are studied. It has been found that with the increase of urea concentration, there occur sequentially the deaggregation of cytochrome c molecules, the increase of exposure extent of the heme group to the solvent, the disruption of Fe-S bond of the heme group and the change in the electrochemical behaviour of cytochrome c. It is suggested that the reason why the electrochemical reaction of cytochrome c is irreversible is that cytochrome c molecules exist in the concentrated solution as oligomers which are electrochemically inactive.

Electrochemical behaviour of spinel LiMn2O4 as positive electrode in rechargeable lithium cells

The spinel, lithium intercalation compound LiMn2O4 is prepared and studied using the techniques of a.c. impedance and cyclic voltammetry. The impedance behaviour of the LiMn2O4 electrode varies as lithium ions are intercalated or de-intercalated. The reversible behaviour of lithium ions in the LiMn2O4 electrode is confirmed by the results of cyclic voltammetry.

Electrochemical behaviour of TCNQ on platinum supported BLMs

The electrochemical behaviour of TCNQ modified S-BLM has been investigated through capacitor measurement and cyclic voltammetry (CV) which shows the surface wave behaviour of the TCNQ redox form. The voltammetry CV has shown different pairs peak at different scan rates and a possible explanation is provided.

Synthesis of N-(n-octyl)-N'-(10-mercaptodecyl)-4,4'-bipyridinium dibromide and electrochemical behaviour of its monolayers on a gold electrode

A new viologen derivative of N-(n-octyl)-N'-(10-mercaptodecyl)-4,4'-bipyridinium dibromide has been prepared and characterized by elemental analysis, IR, H-1 NMR, MS and TG-DTA. X-Ray photoelectron spectroscopy, cyclic voltammetry and chronoamperometry have been used to characterize the monolayers formed by this compound on the bulk gold electrodes by self-assembly.

Electrochemical, spectroscopic and SPM evidence for the controlled formation of self-assembled monolayers and organised multilayers of ferrocenyl alkyl thiols on Au(111)

Organised multilayers were formed from the controlled self-assembly of ferrocene alkyl thiols on Au(111) surfaces. The control was accomplished by increasing the concentration of the thiol solutions used for the assembly. Cyclic voltammetry, ellipsometry, scanning probe microscopy (STM and AFM) and in situ FTIR spectroscopy were used to probe the differences between mono- and multilayers of the same compounds. Electrochemical desorption studies confirmed that the multilayer structure is attached to the surface via one monolayer. The electrochemical behaviour of the multilayers indicated the presence of more than one controlling factor during the oxidation step, whereas the reduction was kinetically controlled which contrasts with the behaviour of monolayers, which exhibit kinetic control for the oxidation and reduction steps. Conventional and imaging ellipsometry confirmed that multilayers with well-defined increments in thickness could be produced. However, STM indicated that at the monolayer stage, the thiols used promote the mobility of Au atoms on the surface. It is very likely that the multilayer structure is held together through hydrogen bonding. To the best of out knowledge, this is the first example of a controlled one-step growth of multilayers of ferrocenyl alkyl thiols using self-assembly techniques.

ELECTROCHEMICAL-BEHAVIOR OF MOLIBDOSILICIC HETEROPOLY COMPLEX WITH DYSPROSIUM AND ITS DOPED POLYPYRROLE FILM-MODIFIED ELECTRODE

In this paper, the electrochemical behaviour of molibdosilicic heteropoly complex with dysprosium K10H3[Dy(SiMo11O39)(2)]. xH(2)O [denoted as Dy(SiMo11)(2)] was studied. Voltammetric behavior of this complex was greatly influenced by pH of solutions. The polypyrrole (PPy) film doped with this complex was prepared by electropolymerization of pyrrole in the presence of Dy(SiMo11)(2) under potential cycling conditions. The microenvironment within the PPy film has an effect on the electrochemical behavior of Dy(SiMo11)(2) entrapped in the film. The film electrode can catalyze the reduction of ClO3- and BrO3-.

ELECTROCHEMICAL STUDY OF ISOPOLY-OXOMETALLATES AND HETEROPOLY-OXOMETALLATES FILM MODIFIED MICROELECTRODES .3. FURTHER STUDY OF ELECTRODE PROCESS OF ISOPOLYMOLYBDIC ANION DOPED IN POLYANILINE FILM

The isopolymolybdic anion-polyaniline film modified carbon fiber (CF) microelectrode with high stability and electroactivity in aqueous acid solution has been successfully prepared by cycling the potential between -0.15 V and +0.85 V vs. sce at 100 mV s-1 or applying constant potential (+0.85 V) for electropolymerization in a 0.5 M H2SO4 solution containing 5.0 x 10(-2) M aniline and 5.0 x 10(-3) M H4Mo8O26. The electrochemical behaviour of the isopolymolybdic anion entrapped in the polyaniline film is strongly influenced by the sweep-potential range besides the acidity of electrolyte solution. In some acidic electrolyte solution (eg 0.5 M H2SO4), the change of the sweep-potential range causes the structure alternation of the isopolymolybdic anion and resulting in a new electrode process. The cyclic voltammogram of Mo8O264- in 0.5 M H2SO4 solution exhibits three two-electron reversible waves between +0.70 and -0.20 V. However, when the potential sweeps to the lower-limit of -0.3 V, where the fourth four-electron cathodic wave appears, the redoxidation process of the reduction product of Mo8O264- becomes relatively complicated. The 10-electron reduction product seems to change into other isopolyanion (this unknown structure isopolyanions are simply called [Mo-O]), which can be reoxidized to Mo8O264- by five successive two-electron oxidation steps from -0.30 to +0.70 V. However, when the lower-limit of the cycling potential is maintained at -0.30 V and the upper-limit reduces to +0.40 V from +0.70 V, the [Mo-O] in the film exhibits four two-electron reversible waves. We have presented a novel explanation about its electrode reaction mechanism on the basis of our experimental results.

ELECTROCHEMICAL-BEHAVIOR OF HEXACYANOFERRATE(II) ON A GOLD ELECTRODE MODIFIED WITH BIS(4-PYRIDYL)DISULFIDE

The electrochemical behaviour of hexacyanoferrate(II) has been studied by using a bis(4-pyridyl)disulfide modified gold electrode. On the protonated electrode surface, hexacyanoferrate(II) can transfer an electron reversibly but no apparent adsorption was detected. On the deprotonated electrode surface, electron transfer by hexacyanoferrate(II) was more difficult. The electrochemical reversibility varied with the pH of the solution. Relationships between the currents or the standard heterogeneous rate constants and pH were derived.

ELECTROCHEMICAL STUDY OF ISOPOLY AND HETEROPOLY OXOMETALLATE FILM MODIFIED MICROELECTRODES .5. PREPARATION AND ELECTROCHEMICAL-BEHAVIOR OF A 2/18-MOLYBDODIPHOSPHATE ANION MONOLAYER MODIFIED ELECTRODE

In this paper a carbon fibre (CF) microelectrode modified with the 2:18-molybdodiphosphate anion by simple adsorption is described and its electrochemical behaviour is reported. The 2:18-molybdodiphosphate anion (alpha-P2Mo18O626-), which is a Dawson structure, undergoes five successive multielectron reductions in acidic solution. The first three redox waves correspond to the two-electron process, and the last two waves are four-electron and six-electron processes respectively. On the basis of the experimental results it is shown that the electrode process of alpha-P2Mo18O626- on the CF electrode in acidic solution is simultaneously controlled by the diffusion and adsorption of alpha-P2Mo18O626- anions. When the concentration of the alpha-P2Mo18O626- in the solution is reduced, the electrode process mainly exhibits non-diffusion-controlled behaviour, and the diffusion-limited process takes over as the concentration of alpha-P2Mo18O626- becomes higher. The CF electrode modified with a thin film of alpha-P2Mo18O626- exhibits very good stability and redox behaviour in aqueous acidic solution. The alpha-P2Mo18O626- is reduced to heteropoly blue, with an accompanying protonation process. The addition of more than six electrons to the alpha-P2Mo18O626- anion in an aqueous solution does not result in its decomposition. The result obtained is not the same as that reported previously.

ELECTROCHEMICAL STUDY OF ISOPOLY-OXOMETALLATE AND HETEROPOLY-OXOMETALLATE FILM MODIFIED MICROELECTRODES .2. ELECTROCHEMICAL-BEHAVIOR OF ISOPOLYMOLYBDIC ACID MONOLAYER MODIFIED CARBON-FIBER MICROELECTRODES

In this paper the electrochemical properties of isopolymolybdic anion thin film modified carbon fibre (CF) microelectrode prepared by simple dip coating have been described. The modified electrode shows three couples of surface redox waves between + 0.70 and - 0.1 V vs. sce in 2 M H2SO4 solution with good stability and reversibility. The pH of solution has a marked effect on the electrochemical behaviour and stability of the film, the stronger the acidity of electrolyte solution is, the better the stability and reversibility of isopolymolybdic anion film CF microelectrode will be. The scanning potential range strongly influences on the electrochemical behaviour of the film. The isopolymolybdic anion film prepared by the dip coating resulting a monolayer with estimated surface concentration (F) 2.8 x 10(-11) mol cm-2. From the half-peak widths and peak areas of the surface redox waves of the film electrode, the first three surface waves are corresponding to two-electron processes. The electron energy spectra show the products by six electrons reduction are a mixture of Mo(VI) and Mo(V) species. The electrochemical reaction of the isopolymolybdic anion monolayer can be expressed as Mo8O264- + mH+ + 2ne half arrow right over half arrow left [HmMo8-2n(VI)Mo2n(V)O26](4,2n-m)-n = 1, 2, 3; m = 2, 5, 7.

ELECTROLYTE EFFECTS ON THE ELECTROCHEMICAL POLYMERIZATION OF N-BENZYLANILINE

The electrochemical behaviour of N-benzylaniline polymerization is determined by the nature of the electrolyte. The voltammograms for a poly-N-benzylaniline modified Pt electrode prepared in 1 M HCl (abbreviated to PBAn(HCl)), and 1 M H2SO4 (PBAn(H2SO4)) tested in 1 M hydrochloric, sulfuric, and perchloric acid were almost superimposable. The polymer film electrode prepared in 1 M HClO4 (abbreviated to PBAn(HClO4)) is electroinactive, and exhibits only charging behaviour in 1 M HClO4 solution and can be activated in hydrochloric or other acid electrolytes with a smaller anion. These interesting phenomena are explained in terms of the anions catalyzing the loss of benzyl groups.

Synthesis and characterization of two novel [Ru(bpy)(2)(phen)](2+)-based electrochemiluminescent labels

Two novel electrochemiluminescent labels, bis(2,2'-bipyridine)[5-(3-carboxylic acid-propionamido)1,10-phenanthroline]ruthenium(II) hexafluorophosphate dihydrate and bis(2,2'-bipyridine)[5-(4-carboxylic acid-butanamido)-1,10-phenanthroline]ruthenium(II) hexafluorophosphate dihydrate, were synthesized and confirmed by IRelemental analysis, and H-1-NMR spectra were completely assigned using the (HH)-H-1-H-1 COSY technique. Cyclic voltammograms with different scan rates showed quasireversible electrochemical behaviour of the two Ru (II) complex labels in MeCN solution. Electronic absorption, photoluminescence and electrochemiluminescence of Ru(II) complexes were also characterized. Copyright (C) 2000 John Wiley & Sons, Ltd.

Unidirectional current flow of reversible redox couples on a MoO3 film-modified microelectrode

In this paper, we have investigated the reactivity of the molybdenum oxide film toward some standard redox systems (e.g., ferrocene (Fc) and its derivatives) and observed a few interesting phenomena. The results demonstrate that the electrochemical behaviour of Fc and its derivatives at the oxide-modified carbon fiber (CF) microelectrode differs from that at a bare CF microelectrode, The conductivity of the molybdenum oxide film is seriously affected by the range and the direction of the potential scan, which influences the electrochemical behaviour of these redox systems at the film electrode. If the cycling potential is more positive than the reduction potential of the molybdenum oxide film, the reduction and oxidation peak currents of Fc and its derivatives could not be observed. The result indicates that the molybdenum oxide film on a microelectrode surface cannot transfer electrons between the surface of the electrode and Fc or its derivatives due to the existence of a high resistance between the interface in these potential ranges. On the other hand, if the lower limit of the scan potential was extended to a potential more negative than the reduction peak potential of the film, the oxidation peak of Fc or its derivatives appeared at about the potential relative to E-0 of Fc or its derivatives on the bare electrode, and the peak current is proportional to the concentration of these couples in the electrolyte. To our surprise, the peak height on the modified electrode is much larger than that on the bare CF microelectrode under the same conditions in the range of low concentration of these couples, and the oxidation peak potential of these couples is more negative than that on the bare CF microelectrode. On the basis of the experimental observation, we propose that these redox couples may undergo an interaction with the reduction state of the molybdenum oxide film. The new phenomena that we observed have been explained by using this interaction. (C) 1997 Elsevier Science S.A.

PREPARATION AND PROPERTIES OF POLYPYRROLE FILM DOPED WITH A DAWSON-TYPE HETEROPOLYANION

The electropolymerization of pyrrole in the presence of Dawson-type tungstophosphate yields a polypyrrole (PPy) film doped with tungstophosphate anions on the electrode surfaces. The electrochemical behaviour of this film was described, and the stability