Monolayer cyclic voltammetry

Cyclic voltammetry (adsorption, monolayers) Potentiodynamic polarisation (passivation, activation) Cathodic reduction (thickness) Frequency response analysis (electrical properties, heterogeneity) Chronopotentiometry (kinetics)... 

To overcome some of the problems associated with aqueous media, non-aqueous systems with cadmium salt and elemental sulfur dissolved in solvents such as DMSO, DMF, and ethylene glycol have been used, following the method of Baranski and Fawcett [48-50], The study of CdS electrodeposition on Hg and Pt electrodes in DMSO solutions using cyclic voltammetry (at stationary electrodes) and pulse polarography (at dropping Hg electrodes) provided evidence that during deposition sulfur is chemisorbed at these electrodes and that formation of at least a monolayer of metal sulfide is probable. Formation of the initial layer of CdS involved reaction of Cd(II) ions with the chemisorbed sulfur or with a pre-existing layer of metal sulfide. 

Chesniuk et al. studied the transfer of alkali and alkaline-earth cations across phospholipid monolayers at water-1,2-DCE macrointerfaces by cyclic voltammetry. These authors considered the effect of the cation nature, the concentration of the transferring ion, and the applied potential (at the positive end of the polarization window), and noticed either an enhancement of the current or a blocking of the transfer process [13,14]. The enhancement factors observed were very much larger than in other studies, especially at... 

The initial stages, notably the formation of a monolayer on a foreign substrate at underpotentials, were mainly studied by classical electrochemical techniques, such as cyclic voltammetry [8, 9], potential-step experiments or impedance spectroscopy [10], and by optical spectroscopies, e.g., by differential reflectance [11-13] or electroreflectance [14] spectroscopy, in an attempt to evaluate the optical and electronic properties of thin metal overlayers as function of their thickness. Competently written reviews on the classic approach to metal deposition, which laid the basis of our present understanding and which still is indispensable for a thorough investigation of plating processes, are found in the literature [15-17]. 

A Ru(0001) sample, with vacuum deposited Cu, has been characterized by cyclic voltammetry by transferring to an electrochemical cell (16). Figures 4e-4h shows the anodic stripping curves for four different coverages of Cu. A single stripping peak was observed at +110 mV for 0.6 ML Cu and shifted to +145 mV for 5.2 ML Cu. This peak represents the removal of the first monolayer of Cu or Cu in direct contact with the Ru surface. The curve for 5.2 ML Cu shows an additional peak at -20 mV for the stripping of multilayer Cu. 

Deposition of the mixed monolayer. Deposition solutions were prepared by dissolving octadecylmercaptan [ClsSH] and the respective bipyridinium in a mixture of chloroform and methanol. The electrode was cleaned by heating it in a gas-air flame. After cooling, the electrode was immersed in the deposition solution for 15 - 30 minutes, withdrawn, and rinsed in clean methanol or chloroform. Qualitatively the most reproducible surface redox waves and lowest charging currents during cyclic voltammetry were obtained with a freshly-prepared deposition solution containing 50 mM CiaSH and 10 mM of the bipyridinium in a 1 1 volume ratio of chloroform and methanol. 

Although cyclic voltammetry could fruitfully be applied to the kinetic analysis of these catalytic systems, it has mostly been investigated by means of rotating disk electrode voltammetry (Section 1.3.2). The simplest case is that of an irreversible catalytic reaction at a monolayer coating. The next section is devoted to the analysis of these systems by the two techniques. 

Chen and coworkers were the first to describe the electrochemical behavior of PB NPs [41]. They prepared solutions of PB NPs by reaction of Fe(III) with Fe(CN)6 in the presence of H2O2, giving 30-50-nm diameter NPs. These were then immobilized at cysteine-modified Au electrodes with pendant amine groups by prolonged (10 h) exposure of the modified electrode to a solution of the NPs. This produced a monolayer of immobilized NPs that was subsequently examined using cyclic voltammetry. Interestingly, they observed two redox processes near 0.25 V vs. 

Cuest-Induced Changes in Membrane Permeability. Calixarene derivatives are also used for sensing systems other than ISEs or optodes. Recently, a systematic investigation on the control of membrane permeability by use of oriented monolayers composed of calixarene esters was carried out. The hosts used were short alkyl chain esters of calix[6]arene [28 (R = Bu )] and calix[4]arene [26 (R = Bu ), 30 both cone conformers]. The permeabilities through the intermo-lecular voids of these monolayers were evaluated by cyclic voltammetry, as described earlier for oriented membranes of nucleobase derivatives. Cationic, anionic, and neutral electroactive compounds were used as the permeability markers. The voltammetric measurements were carried out either for a monolayer... 

Calculated as the percentage of the voltammogram peak area relative to that measured in the absence of the calix[6]arene monolayer. Guest induced increase ( f) or decrease (-) are shown in the parentheses. Measured by horizontal touch cyclic voltammetry with an HOPG electrode at an applied surface pressure of 10 mN m . The marker was added as [Co(l,l(>-phenanthroline)3](C104)2 (1.00 x 10 M). 

Measured by conventional cyclic voltammetry. A monolayer of 28 (R BuO prepared on water and compressed at 25 mN m, was transferred on a glassy carbon electrode by the Langmuir-Blodgen method. The markers were added as Na4[Fe(CN)J, mcthylviologen dichloride, orp-quinone (1,4-benzoquinone) (1.00 X 10 M concentration in all cases). 

Figure 17. Experimental system for the measurement of surface pressure-molecular area (n-A) isotherms and the horizontal touch cyclic voltammetry/ and schematic representations for the control of permeabilities through oriented monolayers formed at low and high applied surface pressures.

The application of Cyclic Voltammetry to the study of electro-active monolayers is of special interest and deserves to be treated separately. The general treatment of these systems was developed by Laviron [45, 54] and the cases of reversible and non-reversible processes will be presented separately. 

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