Linear sweep voltammetry slopes

The rate laws and hence the mechanisms of chemical reactions coupled to charge transfer can be deduced from LSV measurements. The measurements are most applicable under conditions where the charge transfer can be considered to be Nernstian and the homogeneous reactions are sufficiently rapid that dEv/d log v is a linear function, i.e. the process falls into the KP or purely kinetic zone. In the 1960s and 1970s, extensive 

It was later shown by Parker, on the basis of an analysis of the extensive theoreticel calculations which had been published, that the LSV slopes could be related directly to reaction orders and hence rate laws without consideration of any particular mechanism [66]. For the general rate law 

Once the mechanism of a reaction is established, for example by the application of (49)—(51), the rate constants can be evaluated from expressions obtained in the numerical calculations. For example, the equations for simple first-order reaction of B (eC mechanism) [25] and second-order dimerization of B [eC(dim) mechanism] [36] are eqns. (52) and (53), respectively, at 298.1 K. 

Linear sweep voltammetry slopes calculated from reaction orders  

---

Figure 1 Potential-time pulses in (a) linear sweep voltammetry (b) cyclic voltammetry. The slope of each line measures the potential scan rate...

The term voltammetry refers to measurements of the current as a function of the potential. In linear sweep and cyclic voltammetry, the potential steps used in CA and DPSCA are replaced by linear potential sweeps between the potential values. A triangular potentialtime waveform with equal positive and negative slopes is most often used (Fig. 6.8). If only the first half-cycle of the potential-time program is used, the method is referred to as linear sweep voltammetry (LSV) when both half-cycles are used, it is cyclic voltammetry (CV). The rate by which the potential varies with time is called the voltage sweep (or scan) rate, v, and the potential at which the direction of the voltage sweep is reversed is usually referred to... 

Linear sweep voltammetry (LSV) in combination with a rotating disk electrode (RDE) is a widely used technique to study electrode kinetics. Different methods exist to extract the values of the process parameters from polarization curves. The Koutecky-Levich graphical method is frequently used to determine the mass transfer parameters (Diard et al., 1996) the slope of a plot of the inverse of the limiting current versus the inverse of the square root of the rotation speed of the rotating disk electrode is proportional to the diffusion coefficient. If more than one diffusing species is present, this method provides the mean diffusion coefficient of all species. The charge transfer current density is determined from the inverse of the intercept. In practical situations, however, the experimental observation of a limiting current... 

Zn + in molten AlCla-LiCl-KCl (59.2-21.1-19.7 mole %). The processes were found to be reversible and the plots of E versus log[(/ — /)//] were straight lines with slopes corresponding to = 2. The diffusion currents for the reduction of Cd + and Zn + were found to be proportional to their concentrations. Francini et employed linear sweep voltammetry to... 

Normalized potential sweep voltammetry (NPSV) involves a three-dimensional analysis of the LSV wave where the normalized current (I/Ip) is taken as the Z axis, theoretical electrode potential data as the X axis, and experimental electrode potential data as the Y axis, with the potential axes defined relative to Ep/2. The method is illustrated by the voltammogram in Fig. 15. The projection of the wave on to the X—Y plane results in a straight line of unit slope and zero intercept if the theoretical and experimental data describe the same process. In practice, NPSV analysis simply involves the linear correlation of experimental vs. theoretical electrode potentials at particular values of the normalized current. 

Figure 48 shows the usefulness of solid electrolyte cyclic voltammetry (SECV) for extracting transfer coefficients. The peak potentials are plotted against the logarithm of the sweep rates. The value can be obtained from the slope of the linear regression curve. It is calculated to be 0.63, which is close to the value, 0.59, obtained from the steady-state potentiostatic study. Similarly, based on the equation for anodic peaks. 

Therefore the electrochemical response with porous electrodes prepared from powdered active carbons is much increased over that obtained when solid electrodes are used. Cyclic voltammetry used with PACE is a sensitive tool for investigating surface chemistry and solid-electrolyte solution interface phenomena. The large electrochemically active surface area enhances double layer charging currents, which tend to obscure faradic current features. For small sweep rates the CV results confirmed the presence of electroactive oxygen functional groups on the active carbon surface. With peak potentials linearly dependent on the pH of aqueous electrolyte solutions and the Nernst slope close to the theoretical value, it seems that equal numbers of electrons and protons are transferred. 

In another important category of electrochemical experiments, there is a command signal with a linear variation with time that is imposed. Included in this category is voltamperometry, frequently abbreviated to voltammetry, in which a linear potential sweep is imposed. The slope of the U[t) or E[t) curve is called the scan rate (in V s ). The response given by the system is usually represented by a curve I=f(U) or 1= f(E), in which Uor E, and consequently / vary with time. The direction of the potential sweep can be reversed when a given value of the potential is reached. In this case, the experiment is then called cyclic voltammetry. 

---