Cyclic voltammetry experiments

The electrodeposition of tellurium and silver has been investigated in dilute aqueous solutions of tellurous acid and Ag " ions (concentrations in the order of 10 to 10 " M) in 0.1 M HCIO4 [164], In particular, cyclic voltammetry experiments were conducted with rotating glassy carbon disk electrodes in baths with various concentration ratios of Ag(I) and Te(IV) precursors, and their outcome was discussed in terms of the voltammetric features. For a Ag(I)/Te(IV) ratio close to 0.8, formation of quasi pure silver telluride, Ag2Te, was reported. The authors, based on their measurements and on account of thermodynamic predictions, assumed that silver is deposited first on the electrode (Ag" + e Ag), and then Te(IV) is reduced on the previous silver deposit with formation of Ag2Te according to the reaction... 

The obvious next step was oxidation of the tris(pyrazolyl)borate chromium alkyls to the catalytically active -t-III oxidation state. However, cyclic voltammetry experiments did not show a reversible oxidation in any case, and all attempts to prepare complexes of the type [Tp Bu,Meci-R]+X by chemical oxidation failed, yielding [Tp Cr(THF)n] X instekl. TTie reasons for the apparent instability of TpCr alkyls are not clear, and we arc continuing our efforts to isolate related compounds,... 

Figure 16.8 Pt/TiO c-catalyzed oxygen reduction potential, where 0.01 mA cm is reached during the negative scan in a cyclic voltammetry experiment (scan rate 20 mV s ) in oxygen-saturated 0.5 M HCIO4 at 25 °C. (See color insert.)...

The redox potential of Fc obtained from the cyclic voltammetry experiments at the water-DCE interface can be verified by evaluating the thermodynamic cycle given by Eq. (4). It follows that... 

Recently, Astruc et al. [189] reported novel amido-ferrocene dendrimers (e.g., 91) which were shown to act as supramolecular redox sensors for the recognition of small inorganic ions (Fig. 41). It was further observed that as the den-drimer generation number increased the sensitivity to the guest molecules also increased as observed by cyclic voltammetry experiments. 

Figure 3.6 Reflect vity-potential curve (top) and corresponding cu r rent-poten tial c y clic volta m -mograms (bottom) for a platinum electrode in 1.0M H2S04. The reflectivity curve was taken at 546 nm using S-poiarised light at a 701 angle of incidence. The potential limits for both the reflectivity and cyclic voltammetry experiments were + 0.535 V and —0.006 V vs. NHF, and the scan rate was 26.46 Vs-1. From Bewick and Tuxford (1973).

The Cyclic Voltammetry Experiment. Faradaic and Double-Layer Charging Currents. Ohmic Drop... 

Intensive effort has been devoted to the optimization of CCP structures for improved fluorescence output of CCP-based FRET assays. The inherent optoelectronic properties of CCPs make PET one of the most detrimental processes for FRET. Before considering the parameters in the Forster equation, it is of primary concern to reduce the probability of PET. As the competition between FRET and PET is mainly determined by the energy level alignment between donor and acceptor, it can be minimized by careful choice of CCP and C. A series of cationic poly(fluorene-co-phenylene) (PFP) derivatives (IBr, 9, 10 and 11, chemical structures in Scheme 8) was synthesized to fine-tune the donor/acceptor energy levels for improved FRET [70]. FI or Tex Red (TR) labeled ssDNAg (5 -ATC TTG ACT ATG TGG GTG CT-3 ) were chosen as the energy acceptor. The emission spectra of IBr, 9, 10 and 11 are similar in shape with emission maxima at 415, 410, 414 and 410 nm, respectively. The overlap between the emission of these polymers and the absorption of FI or TR is thus similar. Their electrochemical properties were determined by cyclic voltammetry experiments. The calculated HOMO and LUMO... 

Before discussing the voltammogram obtained with the triangular waveform of figure 16.3, which is simply a plot of the observed current intensity versus the applied potential, it is useful to describe some experimental details of a cyclic voltammetry experiment [335-337] and to recall some basic theory of dynamic electrochemistry [180,332], A typical cell (figure 16.4) consists of... 

Figure 16.4 A three-electrode electrochemical cell used in cyclic voltammetry experiments. Adapted from [335],...

Cyclic voltammetry experiments were controlled using a Powerlab 4/20 interface and PAR model 362 scanning potentiostat with EChem software (v 1.5.2, ADlnstruments) and were carried out using a 1 mm diameter vitreous carbon working electrode, platinum counter electrode, and 2 mm silver wire reference electrode. The potential of the reference electrode was determined using the ferrocenium/ ferrocene (Fc+/Fc) couple, and all potentials are quoted relative to the SCE reference electrode. Against this reference, the Fc /Fc couple occrus at 0.38 V in acetonitrile and 0.53 V in THF [30, 31]. 

One of the simplest ways of indicating the time-scale t of the cyclic voltammetry experiment is to calculate the time required for one voltammetry cycle. During a single cycle, the potential traverses the potential E Ex and then Ex E, so ... 

The monotonic increase of immobilized material vith the number of deposition cycles in the LbL technique is vhat allo vs control over film thickness on the nanometric scale. Eilm growth in LbL has been very well characterized by several complementary experimental techniques such as UV-visible spectroscopy [66, 67], quartz crystal microbalance (QCM) [68-70], X-ray [63] and neutron reflectometry [3], Fourier transform infrared spectroscopy (ETIR) [71], ellipsometry [68-70], cyclic voltammetry (CV) [67, 72], electrochemical impedance spectroscopy (EIS) [73], -potential [74] and so on. The complement of these techniques can be appreciated, for example, in the integrated charge in cyclic voltammetry experiments or the redox capacitance in EIS for redox PEMs The charge or redox capacitance is not necessarily that expected for the complete oxidation/reduction of all the redox-active groups that can be estimated by other techniques because of the experimental timescale and charge-transport limitations. 

When the characteristic time for charge diffusion is lower than the experiment timescale, not all the redox sites in the film can be oxidized/reduced. From experiments performed under these conditions, an apparent diffusion coefficient for charge propagation, 13app> can be obtained. In early work choroamperometry and chronocoulometry were used to measure D pp for both electrostatically [131,225] and covalently bound ]132,133] redox couples. Laviron showed that similar information can be obtained from cyclic voltammetry experiments by recording the peak potential and current as a function of the potential scan rate [134, 135]. Electrochemical impedance spectroscopy (EIS) has also been employed to probe charge transport in polymer and polyelectrolyte-modified electrodes [71, 73,131,136-138]. The methods... 

Of the six possible conformers containing chair rings, two tra/j5-fused conformers 18 and 19, with a slight excess of 18, could be identified as major conformers, with one a>-fused conformer as a minor constituent in the C NMR spectrum of l-methylperhydropyrido[l,2-h]pyridazine in acetone-dfi in the temperature range -75 to -89°C (78JA4012). The low intensity of the signal of the c -fused conformer did not allow determination of the exact structure of this component. The results of low-temperature cyclic voltammetry experiments supported the NMR findings. 

An estimate of the pK value for benzaldehyde radical-anion has also been obtained from fast cyclic voltammetry experiments over a range of pH values [14], Interpretation the results obtained in this case requires first deduction of an overall reaction scheme followed by numerical solution of the corresponding set of differential equations allowing simulation of the cyclic voltammogram. Reaction constants are then adjusted to give good simulations over a range of experimental conditions. The pKj can then be extracted from these reaction constants. 

The electrochemical behavior of Np ions in basic aqueous solutions has been studied by several different groups. In a recent study, cyclic voltammetry experiments were performed in alkali ([OH ] = 0.9 — 6.5 M) and mixed hydroxo-carbonate solutions to determine the redox potentials of Np(V, VI, VII) complexes [97]. As shown in Fig. 2, in 3.1 M LiOH at a Pt electrode Np(VI) displays electrode processes associated with the Np(VI)/Np(V) and Np(VII)/Np(VI) couples, in addition to a single cathodic peak corresponding to the reduction of Np(V) to Np(IV). This latter process at Ep —400 mV (versus Hg/HgO/1 M NaOH) is chemically irreversible in this medium. Analysis of the voltammetric data revealed an electrochemically reversibleNp(VI)/Np(V)... 

Olah generated similar dicationic species upon treatment of 4-hydroxy- or 4-methoxy- nitrosobenzenes with 1 1 HSO F-SbFs in SO2 (Scheme 6) These species were stable in the superacid media and were characterized by NMR spectroscopy. No nitrenium ion species were detected. Although Olah was unable to detect simple monoarylnitrenium ions, a few stabilized diarylnitrenium ions were detected during cyclic voltammetry experiments on the corresponding diarylamine in CHsCN, For example, the di-para-anisylnitrenium ion and its conjugate acid (Scheme 7) were both observed. This ion had a lifetime of about 1 s in CH CN. ... 

The relatively low value is attributed to the absorption of the ferrocene fragment at 280 nm. The isoelectrofocusing of Fc-HPR confirmed its homogeneity with the expectedly shifted isoelectric point to a more basic pH (cf. 8.1 and 8.5 for HRP and Fc-HRP, respectively). Cyclic voltammetry experiments indicated the ferrocene moiety in Fc-HRP (Fig. 12). New anodic and cathodic peaks are around 360 and 300 mV, respectively (Fig. 12b). The redox potential of 327 mV for Fc-HRP is shifted anodically compared with that for Fc-Hemin in water (264 mV). This may indicate that the ferrocene unit is shielded by amino acid residues located in the vicinity of the active site. 

The occurrence of the redox-driven reversible assembling-disassembling process involving copper complexes of 16 has been verified through cyclic voltammetry experiments at a platinum electrode in a MeCN solution. Figure 2.17 shows the CV profile obtained with a solution of the double-strand helicate complex [ Cu 21 (16)212 +. 

These two complementary cyclic voltammetry experiments confirm that in this rotaxane, like in previously studied related systems, the tetracoordinate Cu(I) state is more stable than the pentacoordinate one and the pentacoordinate Cu(II) state is more stable than the tetracoordinate one. 

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