Reference electrode cyclic voltammetry

A standard method to determine capacitance is cyclic voltammetry. One electrode, made of the material of interest (with know surface area A) and a counter electrode, are introduced into the electrolyte solution. A reference electrode can be used in addition. Then a triangular potential is applied and the electric current is measured. From the current, the capacitance can be calculated. 

For PPV-imine and PPV-ether the oxidation potential, measured by cyclic voltammetry using Ag/AgCl as a reference are ,M.=0.8 eV and 0.92 eV, respectively. By adopting the values 4.6 eV and 4.8 eV for the work functions of a Ag/AgCl and an 1TO electrode, respectively, one arrives at zero field injection barriers of 0.4 and 0.55 eV. These values represent lower bounds because cyclic voltammetry is carried out in polar solvents in which the stabilization cncigy of radical ions exceeds that in a polymer film, where only electronic polarization takes place. E x values for LPPP and PPPV are not available but in theory they should exceed those of PPV-imine and PPV-ether. 

FIGURE 2-21 EQCM (a) and cyclic voltammetry (b) profiles at an ion exchanger-coated electrode in the presence of 6 x 10 3 M Ru(NH3)6C16. (Reproduced with permission from reference 65.)... 

FIGURE 11. Cyclic voltammetries of 68 at a mercury microelectrode, concentration 2x10 m, electrolyte OMF/Bu NI 0.1m, reference electrode Ag/Agl/I" 0.1m, sweep rate 300mVs ... 

Cyclic voltammetry was performed on precursor polymer thin films cast on platinum electrodes in order to assess the possibility of electrochemical redox elimination and consequently as an alternative means of monitoring the process. All electrochemical experiments were performed in a three-electrode, single-compartment cell using a double junction Ag/Ag+(AgN03) reference electrode in 0.1M... 

Polythiophene films can be electrochemically cycled from the neutral to the conducting state with coulombic efficiencies in excess of 95% [443], with little evidence of decomposition of the material up to + 1.4 V vs. SCE in acetonitrile [37, 54, 56, 396,400] (the 3-methyl derivative being particularly stable [396]), but unlike polypyrrole, polythiophene can be both p- and n-doped, although the n-doped material has a lower maximum conductivity [444], Cyclic voltammetry shows two sets of peaks corresponding to the p- and n-doping reactions, with E° values at approximately + 1.1 V and — 1.4 V respectively (vs. an Ag+/Ag reference electrode)... 

In the literature the term soluble Prussian blue introduced by Keggin and Miles [5] to determine the KFeFe(CN)6 compound is still widely used. However, it is important to note, that the term soluble refers to the ease with which the potassium ion can be peptized rather than to the real solubility of Prussian blue. Indeed, it can be easily shown by means of cyclic voltammetry that the stability of Prussian blue films on electrode supports is nearly independent of their saturation by potassium cations. Moreover, Itaya and coworkers [9] have not found any appreciable amount of potassium ions in Prussian blue, which makes doubtful structures like KFeFe(CN)6. Thus, the above equation fully describes the Prussian blue/Prussian white redox reaction. 

For the investigation of charge tranfer processes, one has the whole arsenal of techniques commonly used at one s disposal. As long as transport limitations do not play a role, cyclic voltammetry or potentiodynamic sweeps can be used. Otherwise, impedance techniques or pulse measurements can be employed. For a mass transport limitation of the reacting species from the electrolyte, the diffusion is usually not uniform and does not follow the common assumptions made in the analysis of current or potential transients. Experimental results referring to charge distribution and charge transfer reactions at the electrode-electrolyte interface will be discussed later. 

Smooth polycrystalline Au, Pt and Ir thin-layer electrodes were utilized (10-11). Electrodes were cleaned between trials by sequential electrochemical oxidation above 1.2 V [Ag/AgCl (1 M Cl-) reference] and reduction below -0.2 V in 1 M H2SO4 surface cleanliness was verified with the aid of cyclic voltammetry in the same molar sulfuric acid solution. Experiments were carried out in 1 M H2SO4, 1 M NaC104 buffered at pH 7 and 10, and in 1 M NaOH solutions were prepared with pyrolytically triply distilled water (12). Surface reagents employed were iodide, hydroquinone (HQ), 2,5-dihydroxythiophenol [DHT (13)1. and 3,6-dihydroxypyridazine (DHPz). 

FIGURE 1.23. Variations of the transfer coefficient with the electrode potential derived from convolutive cyclic voltammetry of the following systems with double layer correction, t-nitrobutane in acetonitrile ( ), r-nitrobutane in DMF ( ), nitrodurene in acetonitrile + 2%H20 (a), nitrodurene in acetonitrile ( ), nitromesitylene in acetonitrile (y). Data from reference 64 and references therein. 

FIGURE 4.3. Redox and chemical homogeneous catalysis of trans-1,2 dibromocyclohexane. a cyclic voltammetry in DMF of the direct electrochemical reduction at a glassy carbon electrode (top), of redox catalysis by fhiorenone (middle), of chemical catalysis by an iron(I) porphyrin, b catalysis rate constant as a function of the standard potential of the catalyst couple aromatic anion radicals, Fe(I), a Fe(0), Co(I), Ni(I) porphyrins. Adapted from Figures 3 and 4 of reference lb, with permission from the American Chemical Society. 

FIGURE 4.8. Cyclic voltammetry of cobinamide 0.5 mM alone (dashed line) and in the presence of 1.5 mM chloroacetonitrile (solid line) in a 70-30 H20-EtOH + 0.1 M NaCl mixture on a glassy carbon electrode at a scan rate of 0.2 V/s. Adapted from Figure 1 of reference 9, with permission from the American Chemical Society. 

The most well-known hydrodynamic technique is the Rotating Disk Electrode (RDE) voltammetry, which, however, needs proper equipment. For information on this technique the reader is referred to specialized treatments.2"4 We prefer here to mention a simpler technique which can be carried out on the same equipment used for cyclic voltammetry. This technique is referred to as voltammetry at an... 

As in the case of cyclic voltammetry, the electrolysis cell can be built with a thermostatic jacket to carry out measurements at low temperatures. In this case, the apparatus is of an isothermic type (i.e. the compartment containing the reference electrode is also cooled). In this case the most suitable reference electrode is the silver/silver chloride electrode filled by the same solution that will be used to dissolve the electroactive substance. One cannot use the saturated calomel electrode or the aqueous Ag/AgCl electrode because the KC1 (or NaCl) solution would freeze. 

Cyclic voltammetry was conducted using a Powerlab ADI Potentiostat interfaced to a computer. A typical three electrode system was used for the analysis Ag/AgCl electrode (2.0 mm) as reference electrode Pt disc (2.0 mm) as working electrode and Pt rod (2.0 mm) as auxiliary electrode. The supporting electrolyte used was a TBAHP/acetonitrile electrolyte-solvent system. The instrument was preset using a Metrohm 693 VA Processor. Potential sweep rate was 200 mV/s using a scan range of-1,800 to 1,800 mV. 

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]. 

Bott, A.W., Practical problems in voltammetry. 3 Reference electrodes for voltammetry . Current Separations, 14, 64-68 (1995) is an excellent first stop for the novice, as is Bott, A. W Characterization of chemical reactions coupled to electron-transfer reactions using cyclic voltammetry . Current Separations, 18, 9-16 (1999), which also introduces simulations. In addition, the article by Hitchman and Hill in Chemistry in Britain (see above) contains a low-level general introduction to cyclic voltammetry for analyses. 

Fig. 9.12 Cyclic voltammetry of the p-doping(anodic)-undoping(cathodic) process of a polypyrrole electrode in LiClO -PC solution. Pt substrate, Li reference electrode, scan rate 50 mV s .

Figure 3.15 (a) Cyclic voltammetry of SWNT-modified electrodes where the tubes were cut for 2 h and either randomly dispersed or vertically aligned. CVs are recorded relative to an Ag/AgCI reference electrode in 1 mM l<3Fe(CN)6 in a background electrolyte of 0.05 M KH2PO4 and 0.05 M KCI at pH 7.0 at lOOmV/s. The y-axis shows the current normalized to the anodic peak... 

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