A comparison of voltammetric techniques

Sections 3-6 described four voltammetric techniques that may be used in order to analyse a variety of electrode reactions. This section aims to compare the merits of these forms of voltammetry with regard to the mechanistic 

A QUANTITATIVE COMPARISON OF THE KINETIC DISCRIMINATION OF COMMON ELECTRODE GEOMETRIES AT STEADY STATE 

The experimental technique and electrode geometry should be selected to match the kinetic time-scale (the time domain over which a chemical process occurs, e.g. Hk, where k is a first-order rate constant) of the reaction being studied. This is achieved by varying the rate of mass transport via convection, electrode size/shape or potential scan rate. 

Electrode Peclet number Characteristic time-scale 

Tor the rotating-disc electrode the Reynolds number is given by Re = the Schmidt number, Se = v/D. 

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A comparison of voltammetric techniques 96 A quantitative comparison of the kinetic discrimination of common electrode geometries at steady state 97 Steady-state vs. transient experiments 102 Current and future directions of voltammetry 104 Instrumentation 104 Electrodes 105 Voltammetric simulations 108... 

Very limited investigations have been conducted with this alloy system. The results obtained to date suggest that A1 co-deposits with Fe from solutions of Fe(II) in both AlCl3-EtMeImCl at 25 °C [46] and AlCl3-NaCl at 160 °C [100]. In both studies, the A1 co-deposition process was found to commence at nearly the same potential as the Fe(II) reduction reaction therefore, it was difficult to observe a well-defined voltammetric limiting current for the latter process, regardless of the technique that was employed. This behavior is nearly identical to that seen in the Ni-Al system [47], However, a comparison of the voltammetric results recorded for some of the other... 

Donat J. R. and Bruland K. W. (1990) A comparison of two voltammetric techniques for determining zinc speciation in northeast Pacific Ocean waters. Mar. Chem. 28, 301-323. 

The properties of anodic layers of HgS formed on mercury in sulfide solutions have been investigated in comparison with anodic sulfide layers of cadmium and bismuth. Also, the electrochemistry of mercury electrodes in aqueous selenite solutions has been studied (see Sect. 3.2.1). The problem with the presence of several cathodic stripping peaks for HgSe in acidic Se(IV) solutions has been addressed using various voltammetric techniques at a hanging-mercury-drop electrode [119]. 

Fig. 65. Comparison of three voltammetric stripping responses under equal accumulation conditions. (A) linear sweep voltammetry, (B) differential pulse voltmametry, (C) square-wave technique. Conditions 5 x 10 M vitamin K3 in 0.3 M HCIO3, static MDE, accumulation potential, Eacc=-0.1V (vs. Ag/AgCl), tacc = 60s, rest time tr=10s. Linear sweep rate v = 0.02Vs , differential pulse scanning 0.01 Vs , SW-scanning 0.20Vs pulse amplitudes dEop = JEsw = 0.02 V, SW frequency 100 Hz. Adapted according to [162].

Chronoamperometry was used to determine the electron-transfer kinetics and it could provide information regarding the dynamic model of an electrochanical process. In chronoamperometry, the current is integrated over relatively long time intervals thus, it gives a better signal to noise ratio in comparison to other voltammetric techniques. The Faradaic current, which is due to electron-transfer events and is... 

The non-reversible behavior is plotted in Fig. 7.46, which corresponds to the corrected (Jcv/v) — E curves (dashed lines) and the (QDSCVC/AE) — E ones (symbols) of the system 4-PhenylazoPhenol. From these curves, it can be seen that although the DSCVC curves are perfectly superimposable, the CV ones clearly show smaller peak heights in both scans. This systematic decrease of the CV signals, which cannot be theoretically predicted, is 5-10 %, and it has been reported when the response of electro-active monolayers in CV has been compared with other voltammetric and chronopotentiometric electrochemical techniques [71, 72], Due to the quasi-reversible nature of the charge transfer reduction of the 4-PhenylazoPhenol, no simple equations for the peak parameters are available. So, a numerical comparison between theoretical and experimental curves for different sets of parameters should be made in order to obtain the kinetic and thermodynamic parameters of the system. 

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