Voltammograms effect

Figure 63. Theoretical simulation of voltammograms obtained from -2500 to 300 mV, showing the effect of the temperature on the shape of the curve and the position of the maximum. (Reprinted from T. F. Otero, H.-J. Grande, and J. Rodriguez, J. Phys. Chem. 101, 8525, 1997, Figs. 3-11, 13. Copyright 1997. Reproduced with permission from the American Chemical Society.)...

From Eq. (68), following a procedure similar to that described for chronoamperograms and voltammograms, theoretical coulovoltagrams were obtained as a function of the variables studied. The results189 can be observed in Fig. 67. Some new effects can be deduced from these experimental curves, which will allow us to provide a complete description of the electrochemistry of conducting polymers. 

Figure 5.2. NEMCA and its origin on Pt/YSZ catalyst electrodes. Transient effect of the application of a constant current (a, b) or constant potential UWR (c) on (a) the rate, r, of C2H4 oxidation on Pt/YSZ (also showing the corresponding UWR transient)3 (b) the 02 TPD spectrum on Pt/YSZ4,7 after current (1=15 pA) application for various times t. (c) the cyclic voltammogram of Pt/YSZ4,7 after holding the potential at UWR = 0.8 V for various times t.

In practice, AGq will also depend on the coverage of the adsorbate, 6. Since this effect has direct implications for cyclic voltammetry, it will be discussed in more detail in Section 3.3.1 on theoretical cyclic voltammograms. 

The radii of both orifices can be either on a micrometer or a submicrometer scale. If the device is micrometer-sized, it can be characterized by optical microscopy. The purposes of electrochemical characterization of a dual pipette are to determine the effective radii and to check that each of two barrels can be independently polarized. The radius of each orifice can be evaluated from an IT voltammogram obtained at one pipette while the second one is disconnected. After the outer surface of glass is silanized, the diffusion-limiting current to each water-filled barrel follows Eq. (1). The effective radius values calculated from that equation for both halves of the d-pipette must be close to the values found from optical microscopy. 

Figure 14. Cyclic voltammograms of /<2c-Re(bpy)(CO)3Cl in acetonitrile-0.1 M Bu4NPF6 at a Pt electrode.144 Scan rate 0.2 V/s. The lower voltammograms show the switching potential characteristics A and F, reversible one-electron wave B and D, redox couple due to a dimer of the complex C, the second metal-based wave. The upper curves show the effect of C02 on the voltammogram. See also Figure 15.

As was discussed above, it is essential to determine the effect, if any, that the emersion process has on the double layer. To do this, Wilhelm and colleagues have performed the definitive type of blank experiment. CO was adsorbed onto the Pt working electrode from sulphuric acid electrolyte. After adsorption, the CO-saturated solution was replaced with pure electrolyte. The potential of the electrode was then ramped in order to oxidise off the adsorbate, as C02, and the voltammogram so obtained is shown in Figure 2.118(a). The experiment was then repeated CO was adsorbed as before, but the electrode was emersed and transferred into the UHV chamber, before being re-immersed and the potential ramp applied. The voltammogram so... 

In this context it is noteworthy to refer to the unsaturated analogue l,2-di(9-anthryl)ethene [32] (Weitzel and Mullen, 1990 Weitzel et al., 1990). Like [6] (Becker et al., 1991), compound [32] forms a stable dianion and tetra-anion upon reduction. In the cyclic voltammogram of [32], the first two electrons are transferred at nearly the same potential, pointing to an effective minimization of the Coulombic repulsion between the charged anthryl units (Bohnen et al, 1992). This situation, which again corresponds to that in [6], could imply a torsion about the central olefinic bond (Bock et al., 1989). 

The cyclic voltammograms of these systems display quasi-reversible behavior, with AEv/v being increased because of slow electrochemical kinetics. Standard electrochemical rate constants, ( s,h)obs> were obtained from the cyclic voltammograms by matching them with digital simulations. This approach enabled the effects of IR drop (the spatial dependence of potential due to current flow through a resistive solution) to be included in the digital simulation by use of measured solution resistances. These experiments were performed with a non-isothermal cell, in which the reference electrode is maintained at a constant temperature... 

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