Cathodic pulses

The most efficient voltage profile for voltammetry, called square wave voltammetry, uses the waveform in Figure 17-18, which consists of a square wave superimposed on a staircase.22 During each cathodic pulse, there is a rush of analyte to be reduced at the electrode... 

The signal in square wave voltammetry is increased relative to a sampled current voltammogram and the wave becomes peak shaped. The signal is increased because reduced product from each cathodic pulse is right at the surface of the electrode waiting to be oxidized... 

An interesting extension of the cpe technique is pulse electrolysis. The electrode is maintained not at one single potential, but at a series of potentials of controlled duration according to a predetermined program. Tills is done by means of a pulse generator (also commercially available). Pulse techniques have hitherto been used mainly for mechanistic studies 91,92-1 but hold great promise for synthetic applications too 90,2 65 As an example, in the anodic oxidation of aliphatic hydrocarbons in non-aqueous medium at a platinum anode, the electrode activity falls rapidly with time if the potential is kept constant, probably because of the formation of an adsorbed film of intermediates or products. However, regular, short cathodic pulses reactivate the anode and the reaction proceeds without difficulties 30 ... 

Various pre-treatment protocols have been developed including pickling and anodic/cathodic pulses to remove the oxide films. It was apparent that different types of steel require different pre-treatments, i.e. cast pieces behave differently to rolled pieces. Significant success was achieved in electropolishing cast pieces and the finish obtained with the ionic liquid was superior to that with phosphoric add, however, the converse was true for rolled pieces because the oxide film is thicker in the latter samples and hence slower to dissolve in the ionic liquid. 

An expanded (ep) 2D Meads phase is polarized by a potentiostatic cathodic pulse (large signal system perturbation) leading to the formation of a condensed (cd) phase ... 

Fig. 4.7 shows Hg droplets formed on a spherical Pt single-crystal electrode [4.37]. The nuclei are formed with a cathodic pulse with a given amplitude and duration, and are then grown at a lower overvoltage until of a visible size. The density of nuclei [nuclei cm ] is determined simply by counting the number of droplets on a given surface area of the electrode. 

Fig. 5.7 shows a current-time record after a cathodic pulse excitation. As seen, the cathodic current rises in the beginning (initially linearly with time as a rule), passes over a maximum, and falls to zero again after a certain period of time. The explanation of this observation is obvious ... 

Consider the formation of one monatomic layer during cathodic pulse application, assuming that nucleation is not possible on top of already formed nuclei. If a nucleus is formed at time r after starting the overvoltage pulse the surface Aj(f) occupied by... 

Electrodeposition using pulsed currents is known as pulse plating. The pulsed currents can be unipolar (on-off) or bipolar (current reversal). Pulses can be used along or be superimposed on a DC feed. By using the bipolar pulse, metal deposition occurs in the cathodic pulse period, with a limited amount of metal being... 

Certain electrode materials are activated by the application of alternate anodic and cathodic pulses. Activation may be due to one or more of the following reasons ... 

During the anodic pulse, a layer of chemisorbed oxygen covers the electrode, and during the cathodic pulse (with pulse time of 10 sec), this layer is removed. The surface is cleaned and inhibiting impurity layers are not allowed to build up, thereby maintaining a... 

First ac electrodeposition of Cu, Ni, Co, and Sn was reported in [2,3]. However there was no any detail analysis of the regimes used for the deposition. In this work we developed a pulsed deposition technique by taking into account transients observed under anodic and cathodic pulses. 

The block diagram of the electronic circuitry is presented in Fig.2 the cathodically pulsed potential (Fig.3a) for the electroluminescence generation was provided by a microprocessor-based pulse generator with a home-made potentiostat (single operational amplifier (741) with a transistor booster) photomultiplier output was amplified, demodulated by a simple gated integrator and finally registered on a recorder. 

Although the process is readily reversible and can be repeated a large number of times by applying anodic and cathodic pulses in alternate sequence, a careful inspection of the voltammetric response reveals some slight differences between the first initial cycle and the following subsequent cycles (Figure 8.2), this suggesting that the development of the electro-chromic effect requires a sort of preliminary activation process. Such a process, which is commonly encountered in insertion compounds [13], may be described as an initial and permanent uptake of ions which some-... 

An ECD works on the basis of the electrochromic processes, for instance of process [8.3]. The process can be promoted to induce coloration (formation of the deep blue M WOs bronze) by applying a cathodic pulse between the WO3 electrode and the counter-electrode. The process can then be reversed to bleaching (restoration of pristine WO3) by an opposite anodic pulse (Figure 8.8) and the coloration-bleaching effect can be repeated many times. 

The surface concentration changes during the cathodic pulse in RC deposition in the second range according to Eq. (4.46). 

Fig. 5.12 Copper deposits obtained by the RC regimes with the anodic current densities of (a, d) a = 40 mA cm (b, e) 4 = 240 mA cm and (c, f) 4 = 640 mA cm . The cathodic current density 440 mA cm . The cathodic pulse 10 ms. The anodic pulse 5 ms. Solution 0.15 M CuSOa in 0.50 M H2SO4 (Reprinted from Ref [23] with kind permission from Springer and Ref [59] with permission from Elsevier)...

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