Chronopotentiometry techniques

The system TiCl4-BMMlmBF4 was studied by CV and chronopotentiometry techniques at 65 °C. The experimental details can be found in [9]. 

Indeed the best electrochemical m od to solve this indetermination is the chronopotentiometry techniques. The experimental results are rqwrted in figure 2, they are consistent with Sand s law. 

The method, as so far developed, is limited by the condition that the hydration-dehydration reaction must proceed at a rate that is slow compared with the time needed to obtain a polarogram. In principle, the method is capable of much wider application to covalent-hydration studies if use is made of oscillographic polarographic techniques or of chronopotentiometry. These refinements are currently being investigated. 

The possibility that adsorption reactions play an important role in the reduction of telluryl ions has been discussed in several works (Chap. 3 CdTe). By using various electrochemical techniques in stationary and non-stationary diffusion regimes, such as voltammetry, chronopotentiometry, and pulsed current electrolysis, Montiel-Santillan et al. [52] have shown that the electrochemical reduction of HTeOj in acid sulfate medium (pH 2) on solid tellurium electrodes, generated in situ at 25 °C, must be considered as a four-electron process preceded by a slow adsorption step of the telluryl ions the reduction mechanism was observed to depend on the applied potential, so that at high overpotentials the adsorption step was not significant for the overall process. 

For controlled-current DC polarography, especially its current density mode, see under Chronopotentiometry at a dme (p. 172). For charge-step polarography, i.e., a controlled charge of coulostatic technique, see ref. 9, pp. 424-429, and ref. 3, pp. 270-276. 

A more usual procedure for overcoming the disturbances from contaminants is current reversal chronopotentiometry here the current is reversed at the initial transition time tf of the forward reaction and the next transition time xb of the backward reaction is measured as a rule the reversal wave will not be influenced by the contaminant because it will react either before the forward or after the backward reaction of the analyte (see Fig. 3.60a) the entire procedure can be even repeated as cyclic chronopotentiometry (see Fig. 3.60b), which may provide a further check on the reliability. The reversal technique can be applied to initial reduction followed by re-oxidation and also to initial oxidation followed by re-reduction79. 

Stan Van Den Berg is a Professor of Chemical Oceanography at the University of Liverpool. His research interests focus on the chemical specia-tion of trace elements and organic compounds in natural waters and the redox chemistry of metals and sulfides. His research group has pioneered advances in analytical techniques using electroanalytical methods (cathodic stripping voltammetry and chronopotentiometry). Dr. Van Den Berg is a broad-based analytical chemist. 

Chronopotentiometry is a transient constant-current technique in which the potential of the electrode is followed, as a function of time, in a quiet solution (Figure 6). Double-step applications [30], as well as programmed current experiments [31] have been described. 

Chronopotentiometry, galvanostatic transients, 1411 as analytical technique, 1411 activation overpotential, 1411 Clavilier, and single crystals, 1095 Cluster formation energy of, 1304 and Frumkin isotherm, 1197 Cobalt-nickel plating, 1375 Cold combustion, definition, 1041 Cole-Cole plot, impedance, 1129, 1135 Colloidal particles, 880, 882 and differential capacity, 880 Complex impedance, 1135 Computer simulation, 1160 of adsorption processes, 965 and overall reaction, 1259 and rate determining step, 1260... 

Other Techniques - Other electrochemical techniques that could be employed in sensor technology would include potential-step methods (or chrono-amperometry, as current is recorded with time), current-step methods (or chronopotentiometry, as potential is recorded with time) and AC impedance. None of these techniques appear to have yet been applied to catalyst sensing in a systematic way. 

Chronopotentiometry is the electrochemical technique in which a current step is impressed across an electrochemical cell containing unstirred solution [1-5]. The resulting potential response of the working electrode versus a reference electrode is measured as a function of time (thus, chronopotentiometry), giving a chronopotentiogram as shown in Figure 4.3. 

Controlled-current chronoabsorptometry involves the simultaneous optical monitoring of the product or other redox component in the electrode mechanism during a chronopotentiometry experiment [14]. Although this technique has been demonstrated with Sn02 optically transparent electrodes, it has generally received little use, since the resistance effects in thin-film electrodes can give unequal current densities across the electrode face. This results in distorted potential-time and absorbance-time responses. Consequently, the more prevalent spectro-electrochemical methods utilize potential rather than current as the excitation signal. 

Many of the electroanalytical techniques that are routinely employed in conventional solvents, such as, chronoamperometry, chronocoulometry, chronopotentiometry, coulometry, cyclic (stationary electrode) voltammetry, rotating electrode voltammetry, and pulse voltammetry, have also been applied to molten salts. Some of these techniques are discussed next with special attention to their employment in molten salts. References to noteworthy examples appearing in the literature are included. Background information about these techniques is available elsewhere in this book. 

For other techniques other kinds of data are given Instead. For chronopotentiometry these Include the area of the indicator electrode and the current or current density for stationary-electrode voltammetry they include the area of the indicator electrode and the scan rate for cyclic voltammetry they include the starting and reversal potentials and the area of the indicator electrode, and so on. The list of abbreviations must always be consulted regarding the units of the quantities given In this column. In the space that was available for these purposes it is quite Impossible to give a full description of the experimental conditions, but art attempt has been made to give an accurate Idea of their nature. 

This term denotes a potential whose nature depends on the technique used. Typical characteristic potentials are the half-wave potential in polarography, the quarter-transition-time potential in chronopotentiometry, and the peak or half-peak potential in stationary-electrode voltammetry. Regardless of its nature, the characteristic potential always depends on the identity of the electroactive substance, on the kinetics or thermodynamics of the electron-transfer process, and of course on the experimental conditions for any particular technique and under any completely defined set of experimental conditions the value of any characteristic potential is a reproducible property of the electroactive substance. 

In this section, we will show that the stationary responses obtained at microelectrodes are independent of whether the electrochemical technique employed was under controlled potential conditions or under controlled current conditions, and therefore, they show a universal behavior. In other words, the time independence of the I/E curves yields unique responses independently of whether they were obtained from a voltammetric experiment (by applying any variable on time potential), or from chronopotentiometry (by applying any variable on time current). Hence, the equations presented in this section are applicable to any multipotential step or sweep technique such as Staircase Voltammetry or Cyclic Voltammetry. 

Equation (7.116) indicates that the charge-potential curves for reversible processes are only dependent on the square wave amplitude Sw and are independent of the frequency / = 1 jh and the staircase amplitude AEs. As a consequence, they are superimposable on those obtained at any differential electrochemical technique, such as DSCVC, provided that the differences between the successive potential pulses coincide (AE = 2 sw)- Moreover, when this difference is much less than RT/F (i.e., less than 25 mV at T = 198 K), the responses obtained in Cyclic Voltammetry (CV), Alternating Current Voltammetry, Potentiometric Stripping Analysis (PSA) and also in any Reciprocal Derivative Chronopotentiometry (RDCP) fulfill [5, 74, 75] ... 

Viscosity. In many applications a low viscosity is desirable so that mass transport by diffusion or convection will extend the time range for mass transport by pure diffusional control to periods as long as 40-50 s, which can be advantageous to electroanalytical techniques such as chronopotentiometry.34 At low temperatures the solvent may not appear to crystallize, but may form a rigid glass whose viscosity is so high that mass transport practically ceases the experimentalist must be alert to this possibility. 

Thin-layer cells have been used with linear sweep, in coulometry and in chronopotentiometry. Here we limit the discussion to linear sweep— descriptions of this and other techniques can be found in Refs. 19-21. 

A number of electrochemical techniques were applied for the electrochemical analysis of Li electrodes in a large variety of electrolyte solutions. These include chronopotentiometry [230-233], potentiodynamic measurements (cyclic voltammetry) [88,89], transient methods (micropolarization) [81], fast OCV measurements [90,91] and impedance spectroscopy (EIS) [92-100], It should be noted that electrochemical analysis of Li electrodes is very complicated for the following reasons ... 

Owing to its stability, solubility, and highly reproducible oxidation behavior, ferrocene has long been used as an electrochemical standard in nonaqueous solvents. Not surprisingly, the electron-donor or -acceptor properties of ring substituents in ferrocenes and other metallocenes have been repeatedly evaluated with electrochemical techniques. Measurements have been obtained using polarography,150 cyclic voltammetry (CV),151 chronopotentiometry,152 photoelectron spectroscopy, 53 and Fourier transform ion cyclotron resonance mass spectrometry.154 Extensive compilations of such data are available.155 156 Historically, variations of oxidation potentials have been discussed almost solely in terms of the... 

Chronopotentiometry — is a controlled-current technique (- dynamic technique) in which the - potential variation with time is measured following a current step (also cyclic, or current reversals, or linearly increasing currents are used). For a - nernstian electrode process,... 

Current step— The excitation signal used in controlled current techniques in which the potential is measured at a designated time [i]. See also - chronopotentiometry, -> cyclic chronopotentiometry, - staircase voltammetry. Ref. [i] Heineman WR, Kissinger PT (1984) In Kissinger PT, Heine-man WR (eds) Laboratory techniques in electroanalytical chemistry. Marcel Dekker, New York, pp 129-142... 

Analyses of insertion electrodes include structural analysis by XRD, neutron diffraction, HRTEM with electron diffraction, chemical analysis by EDAX, XPS and dissolution followed by ICP, morphological analysis by electron microscopy, surface area measurements by gas adsorption, and electrochemical analysis by voltammetry chronopotentiometry (primary techniques) and fine electrochemical tools such as EIS, PITT, GITT, and... 

Stability constant — is the - equilibrium constant of formation of a - complex. The reciprocal quantity is called instability constant. Extensive compilations of various kinds of stability constants are available [i—iv]. Stability constants are reported for a given ionic strength (or extrapolated to zero ionic strength), and pH. In many cases, stability constants can be determined with the help of electrochemical techniques, e.g., -> chronopotentiometry, -> potentiometry, -> polarogra-phy, and - voltammetry, provided that the systems exhibit -> electrochemical reversibility, and some other prerequisites are fulfilled [v]. See also -> conditional equilibrium constants. 

Transient technique — A technique whose response is time dependent and whose time dependence is of primary interest, e.g., -> chronoamperometry, -> cyclic voltammetry (where current is the transient), -> chronopotentiometry and -> coulostatic techniques (where voltage is the transient). A transient technique contrasts with steady-state techniques where the response is time independent [i]. Some good examples are cyclic voltammetry [i, ii] (fast scan cyclic voltammetry), the indirect-laser-induced-temperature-jump (ILIT) method [iii], coulostatics [i]. The faster the transient technique, the more susceptible it is to distortion by -> adsorption of the redox moiety. 

Transition time (for chronopotentiometry) — Electrolysis time required before the surface concentration of a redox species drops to zero in - chronopotentiometry. In constant-current chronopotentiometry (see also -> constant-current techniques), the transition time r is given by the - Sand equation ... 

In the development of electrochemical genosensors, carbon screen-printed electrodes have been coupled with modern electro analytical techniques such as square wave voltammetry or chronopotentiometry at constant current, and... 

Platinum, glasslike carbon, and tungsten are often used as inert working electrodes for the fundamental electrochemical studies in the ionic liquids. For such transient electrochemical techniques as cyclic voltammetry, chronoamperometry, and chronopotentiometry, it is safer to use the working electrode with a small active area. This is because most of the ionic liquids will have low conductivity, and this often causes the ohmic drop in the measured potentials by the current flowing between the working and counter electrode. Microelectrodes may be useful for the electrochemical measurements in the case of handling low conductive media. 

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