Voltammetry curves

The current is recorded as a function of time. Since the potential also varies with time, the results are usually reported as the potential dependence of current, or plots of i vs. E (Fig.12.7), hence the name voltammetry. Curve 1 in Fig. 12.7 shows schematically the polarization curve recorded for an electrochemical reaction under steady-state conditions, and curve 2 shows the corresponding kinetic current 4 (the current in the absence of concentration changes). Unless the potential scan rate v is very low, there is no time for attainment of the steady state, and the reactant surface concentration will be higher than it would be in the steady state. For this reason the... 

FIGURE 27.9 (a) Voltammetry curve for the UPD of TI on Au(l 11) in 0.1 M HCIO4 containing ImMTlBr. Sweep rate 20mV/s. The in-plane and surface normal structural models are deduced from the surface X-ray diffraction measurements and X-ray reflectance. The empty circles are Br and the filled circles are Tl. (b) Potential-dependent diffraction intensities at the indicated positions for the three coadsorbed phases. (From Wang et al., 1998, with permission from Elsevier.)... 

By today s standards of surface preparation, Will s procedures for surface preparation were crude, the surface structures were not characterized by use of surface analytical instrumentation (Which was neither widely available nor well developed at that time), and he employed extensive potentiodynamic cycling through the "oxide" formation potential region prior to reporting the quasi-steady state voltammetry curve, i.e., the potentiodynamic I-V curve. The studies employing surface analytical methods made a decade or more later were... 

Figure 1. a) Cyclic voltammetry curve recorded from a UHV prepared, well-annealed Pt(lll) crystal in dilute HF electrolyte. Crystal was immersed under potential control at 0.6 V (RHE) and swept cathodically to the limiting potential b) same experiment performed with the same crystal but not annealed after ion bombardment. 

Figure 4. a) Model for the double-layer structure on Pt(lll) as viewed both normal to (111) plane and parallel to the (111) plane at the potential 0TOin. The potential 0ro n is defined in the voltammetry curve in b). 

The underpotentlal deposition of lead has been examined on LEED-characterized single crystal silver surfaces with 0.1 M HF as the electrolyte using a special ultra-high vacuum-electrolyte transfer system. Each of the low index surfaces has a characteristic voltammetry curve with multiple adsorption and desorption UPD peaks. 

The underpotential deposition (UPD) of metals on foreign metal substrates is of importance in understanding the first phase of metal electrodeposition and also as a means for preparing electrode surfaces with interesting electronic and morphological properties for electrocatalytic studies. The UPD of metals on polycrystalline substrates exhibit quite complex behavior with multiple peaks in the linear sweep voltammetry curves. This behavior is at least partially due to the presence of various low and high index planes on the polycrystalline surface. The formation of various ordered overlayers on particular single crystal surface planes may also contribute to the complex peak structure in the voltammetry curves. 

Each of the low index Ag single crystals displayed mutually unique voltammetry curves with multiple adsorption/desorption peaks (Figure 2). The nominal features of these curves are similar to those obtained by other authors for Ag single crystal surfaces in HF or HCIO4 using both UHV and non-UHV methods (4-7). 

Voltammetry curves obtained by Vitanov et al. (8) on electro-chemically grown Ag(lll) surfaces with an ultra low step density... 

A similar effect was observed in our work and in the work of others (5), where voltammetry curves changed after extended cycling, particularly if the cathodic sweep was reversed before the full Pb deposition coverage. The observed "cathodic memory effect" may be due to the proposed structural transformation phenomenon and subsequent step density growth, initially facilitated by a high step density on a UHV-prepared or chemically polished (6) Ag(lll) substrate. Post electrochemical LEED analysis on Ag(lll)-Pb(UPD) surfaces provided additional evidence of a step density increase during Pb underpotential deposition, which will be discussed later in this text. (See Figure 3.)... 

Voltammetry curves for all three low-index surfaces are given in Fig. 1. Hydrogen adsorption at Pt(lll), the process at -0.25 < E < -0.05 V in Fig. 1, is not affected by the nature of the anion (such as SO 2-, CIO.- or F-) (12). The lack of a well defined peak, in the drawn-out curve of Fig. 1 clearly indicates a strong lateral repulsion between adsorbed hydrogen adatoms. This is probably a consequence of a partially charge on the adsorbed hydrogen adatoms which, in turn, does not allow the... 

The interpretation of voltammetry curve for the Pt(100) surface poses some problems, e.g. the origin of the peak at E=—0.15 V (Fig. 1). Markovifi et al. (12) ascribed this peak to hydrogen adsorption on particular surface imperfections, the (111)-oriented step sites. The height of this peak varies from one set of data to another, indicating a lack of control of the surface structure. Further support of this view will be shown below with the data for stepped surfaces. 

A single sweep into the oxide formation with the Pt(lll) surface causes a considerable change of voltammetry curve for a well-ordered surface, as can be seen in Fig. 4a. Two new small peaks are seen on the curve of the original Pt(lll). These peaks can be seen on the curves for surfaces by believed to be... 

Fig. 12.11 A schematic view for constructingmultilayerfilms on substrate, (b) Photographs of multilayer films of ITO/(PDDA/PSS-GS/PDDA/Mn02)n, n = 0, 5,10, and 15 for A, B, C, and D, respectively, (c) Cyclic voltammetry curves of ITO/(PDDA/PSS-GS/PDDA/MnO2)10 electrode at different scan rates, (d) Charge-discharge behavior of an ITO/(PDDA/PSS-GS/PDDA/MnO2)10 electrode at different current densities.

Figure 14.8 Cyclic voltammetry curves recorded using a Pt working electrode at a 100 mV/s sweep rate (CH3CN/CH2CI2 (4 1), supporting electrolyte NBu4BF4, 0.1 M, Ag wire pseudoreference). (a) Compound 4(4) + (b) chemically prepared 4(5)2 +. Curve (ii) refers to a second potential sweep following immediatly the first one (i).

Cyclic-voltammetry curve for a reversible system in an E-l plot. Data are in fact identical to those shown in Fig. 2.2. 

Current versus time was recorded and an exponential decrease in the intensity of the current was observed. When the current was close to 0, a new cyclic voltammetry curve of the solution was recorded, resulting in a voltammogram similar to the one represented in Figure 16 b). This confirmed that the electrogenerated tetracoordinated Cu(n) rotaxane had undergone a rearrangement to form the pentacoordinated Cu(n) rotaxane 16 2+. 

Figure 39 First two cyclic voltammetry curves for clean Ag in LiC104(PE0) recorded at a temperature of 323 K (upper panel) and 333 K (lower panel) initiated at the measured open circuit potential v = 5 mV/s.

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