Potentiostatic technique modified

Metal nanoparticles can also be electrodeposited onto a CP modified electrode to obtain nanocomposites. The number, size and distribution of metal particles can be controlled by the conditions of electrochemical deposition. The pulse potentiostatic technique results in an efficient dispersion of Pt particles in the polymer matrix. 

Figure 2.17. Polarization routine of the modified pulse potentiostatic technique. The zero of the ordinate denotes the potential of the reference electrode [2.168]. (With permission from Elsevier Science).

The experimental data presented in Figure 2.3 are obtained by means of the standard pulse potentiostatic technique, which does not allow us to distinguish between the already considered three particular cases. The reason is that the slope dN(t)/dt and the intercept to of the experimental N(t) relationships depend on the applied electrode potential E, which affects the two electrochemical overpotentials 7 and 7. However, if the modified pulse potentiostatic technique is employed it appears that different types of N t) relationships can be obtained depending on the values of the rate constants Ka, K and K ... 

Figure 2.18. Schematic representation of N t) relationships obtained using the modified pulse potentiostatic technique when Ka (rj ) + Ka p ) (a) and K,lTf) Ka ri ) + Ko ...

As seen, the modified pulse potentiostatic technique allows us to comprehend the information obtained in a nucleation experiment already from the shape of the experimental N(t) relationships (Figures 2.18 and 2.19). In the following we comment upon the concentration and the... 

The above formula applies to both mechanisms of critical nucleus formation direct attachment of ions from the electrolyte and surface diffusion of adatoms on the electrode surface. Clearly, the number No of active sites remains unchanged when varying the concentration c since E, T and pH are fixed in the modified pulse potentiostatic technique. 

Concluding this Qiapter we present a set of experimental N t) relationships obtained by means of the modified pulse potentiostatic technique in the case of mercury electrodeposition on a platinum single crystal microelectrode (Figure 2.20) [2.179]. The data for Al(t) refer to the whole electrode surface S = 1.4xl0 cm and the nucleation rate J t) = dN(t)/dt m dimensions s instead ofcm s. ... 

Over the years the original Evans diagrams have been modified by various workers who have replaced the linear E-I curves by curves that provide a more fundamental representation of the electrode kinetics of the anodic and cathodic processes constituting a corrosion reaction (see Fig. 1.26). This has been possible partly by the application of electrochemical theory and partly by the development of newer experimental techniques. Thus the cathodic curve is plotted so that it shows whether activation-controlled charge transfer (equation 1.70) or mass transfer (equation 1.74) is rate determining. In addition, the potentiostat (see Section 20.2) has provided... 

In this paper we report the application of bimetallic catalysts which were prepared by consecutive reduction of a submonolayer of bismuth promoter onto the surface of platinum. The technique of modifying metal surfaces at controlled electrode potential with a monolayer or sub-monolayer of foreign metal ("underpotential" deposition) is widely used in electrocatalysis (77,72). Here we apply the theory of underpotential metal deposition without the use of a potentiostat. The catalyst potential during promotion was controlled by proper selection of the reducing agent (hydrogen), pH and metal ion concentration. 

A milder version of the potentiostatic intermittent titration technique (PITT) consists in modifying the initial potential by small steps, may be 1 mV, recording the current after a constant delay, and waiting until it has decreased to almost zero before modifying again the potential (staircase voltammetry). This version gives more information (activity potential and capacity) about the different redox couples present in the electrodes which are successively electroactive, but needs more sensitive equipment. 

As it was mentioned in Section 8.1, an experiment is included in order to illustrate the selection procedure. Each model was developed for specific experimental conditions. Sometimes, a description can be modified, extended, and corrected in order to cover other experimental conditions. Thus, a model initially developed with the purpose of describing a film formed under potentiostatic conditions can be adapted, via mathematical derivations, to potentiodynamic conditions. In the present experiment, the film considered was generated under potentiodynamic conditions by the use of voltammetric techniques. As a consequence, only the models developed for potentiodynamic conditions were considered [56-58]. 

Let us now turn our attention to the electronic requirements of microelectrode experiments where the main difficulty presented is the measurement of the inherently low current levels (often less than 10-10A). Many measurements have been successfully made using conventional three-electrode techniques with a potentiostatic system that has been modified to increase the gain of the current follower. Potentiostats are, however, inherently... 

Yamauchi et al. developed a modified version of liquid crystalline templation where liquid crystallinity appears progressively during ethanol solvent evaporation. This technique was used for the templated potentiostatic electrodeposition at -0.144 V vs. SCE of 50-800 nm PtRu particles wifli internal mesochannels [244]. 

The measuring technique utilizing an animated Excel sheet was an important step in the development of hot-wire electrochemical methods. Later, the system has been substituted by a combination of a home-built heating device with a commercial, freely programmable potentiostat. Till now, it is not determined yet which variant will predominate either a dedicated instrument or a modified commercial device. Meanwhile, microcontroller boards became widespread and are easily available. Modem boards are much better programmable than the example presented here. The well-known Arduino due mentioned further above is an example only. It is equipped with ADC, DAC and UART, and it can be programmed... 

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