Electrochemical current transients

As mentioned in potentiostatic current transient method, when the fractal dimension is determined by using diffusion-limited electrochemical technique, the diffusion layer length acts as a yardstick length.122 In the case of cyclic voltammetry, it was... 

Tamura et al. [456] have studied the kinetics of UPD of Bi monolayer on Au(l 11) applying simultaneously, electrochemical methods, current transients, and SXS. 

The most convenient means of making time-resolved SH measurements on metallic surfaces is to use a cw laser as a continuous monitor of the surface during a transient event. Unfortunately, in the absence of optical enhancements, the signal levels are so low for most electrochemical systems that this route is unattractive. A more viable alternative is to use a cw mode-locked laser which offers the necessary high peak powers and the high repetition rate. The experimental time resolution is typically 12 nsec, which is the time between pulses. A Q-switched Nd YAG provides 30 to 100 msec resolution unless the repetition rate is externally controlled. The electrochemical experiments done to date have involved the application of a fast potential step with the surface response to this perturbation followed by SHG [54, 55,116, 117]. Since the optical technique is instantaneous in nature, one has the potential to obtain a clearer picture than that obtained by the current transient. The experiments have also been applied to multistep processes which are difficult to understand by simple current analysis [54, 117]. 

For high values of k°r, very sharp decays of the current-time transients are observed, indicating the almost immediate electrochemical conversion of oxidized species (see solid lines corresponding to k°r = 100). Indeed, for k°t > 100, the faradaic conversion is so fast that the oxidized species disappears at the very first instants of the experiment and under these conditions 0p = 0. When k°r decreases, the observed currents also decrease, since the rate constant modulates the whole faradaic current. For k°t < 1, the current transients appear as quasi-linear, with current-time profile being shifted toward more negative potentials. Under these conditions, general equation (6.130) becomes identical to Eq. (6.134), corresponding to irreversible processes. 

In this respect, this review provides a comprehensive survey of synthetic methods and physicochemical properties of the porous carbon materials. Furthermore, as electrochemical applications of the porous carbons to electrode materials for supercapacitor, the effects of geometric heterogeneity and surface inhomogeneity on ion penetration into the pores during double-layer charging/ discharging are discussed in detail by using ac-impedance spectroscopy, current transient technique, and cyclic voltammetry. 

V. ELECTROCHEMICAL CHARACTERISTICS OF CARBON-BASED POROUS ELECTRODES FOR SUPERCAPACITOR THE USES OF AC-IMPEDANCE SPECTROSCOPY, CURRENT TRANSIENT AND CYCLIC VOLTAMMETRY... 

Figure 11. (a) The cathodic current transients on a logarithmic scale and (b) the derivatives of the logarithmic cathodic current transients theoretically calculated from Eq. (40) based upon the TLM as a function of standard deviation a of PLD. Open circles in Figure 11 represent the cathodic current transient experimentally measured on the ACFCE. Reprinted with permission from G. -J. Lee, S. -I. Pyun, and C. -H. Kim,./. Solid State Electrochem., 8 (2004) 110. Copyright 2003, with kind permission of Springer Science and Business Media. 

Figure 16. The cathodic current transients experimentally obtained from the as-activated carbon (o) and as-reactivated carbon (A) electrode specimens in a 30 wt.% H2SO4 solution by dropping the applied potential from 0.1 to 0.08 V (vs. SCE). Solid lines represent the simulated cathodic current transients. Reprinted with permission from C.-H. Kim, S.-I. Pyun, and H.-C. Shin, J. Electrochem. Soc. 149 (2002) A93. Copyright 2001, with permission from The Electrochemical Society.

Fig. 29. Electrodeposition of Ag from 0.017 M AgCN + 0.92 M KCN + 0.11 M K2CO3 solution dimensionless analysis of experimental potentiostatic current transients (/, and tm are the current and time corresponding to the maximum on the current transient curve, respectively). Upper curve calculated for the instantaneous nucleation mechanism lower curve, for the progressive nucleation mechanism. Different symbols/experimental points relating to different potentials [136], Reproduced by permission of The Electrochemical Society, Inc.

Bewick and Thomas [3.110-3.114, 3.270] measured electrochemically and by optical means different Me UPD systems Ag(A 0/Pb, H, ClOd", acetate and citrate, CnQikt)/ h H C104, acetate, and AgQikt)m SOd with Qikt) = (111), (100), and (110). Potentiostatic pulse measurements showed non-monotonous current transients for Ag(lll) substrates which are attributed to a first order phase transition. As an example, a current transient in the system Pig hkt)/Vf, H, SOd is shown in Fig. 3.46. In the case of Ag(lOO) and Ag(llO) substrates, higher order phase transitions were supposed. Clear evidence of a participation of 2D nucleation and growth steps in the 2D Meads phase formation process was found in the system Cu(lll)/Pb H", ClOd", acetate [3.270]. Non-monotonous current transients and a discontinuity in the q(lsE,fi) isotherm were observed (Fig. 3.13). 

Thin films of Cu, Co and Ni on Si were prepared from different aqueous electrolytes containing sulfates of the respective metals as well as some supporting electrolyte/additive. Voltammetry and current transients were used to analyze the electrochemical aspects of the deposition. The electrodeposited layers were investigated by scanning electron microscopy (SEM), Rutherford backscattering (RBS), magnetooptical Kerr effect (MOKE), X-ray diffractometry (XRD) as well as by electrical measurements. 

Although a major advantage of rotating disk electrode techniques, compared to stationary electrode methods, is the ability to make measurements at steady state without the need to consider the time of electrolysis, the observation of current transients at the disk or ring following a potential step can sometimes be of use in understanding an electrochemical system. For example the adsorption of a component. 

Figure 9.5.2 Simulated ring-current transients. Curve a Potential step at the disk. Curve b Current step at the disk. [From K. B. Prater and A. J. Bard, J. Electrochem. Soc., 117, 207 (1970), with permission of the publisher, The Electrochemical Society, Inc.]...

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