Surface cyclic voltammogram

For Pt catalyst, the surface cyclic voltammogram shows that the electrooxidation starts to occur when the electrode potential is more positive than 0.6 V vs RHE to form Pt oxides such as PtO. In the presence of O2, the electrode potential is more positive than 1.0 V, at which Pt will be definitely electrochemically oxidized to form PtO. In an acidic environment, the formed PtO will be dissolved according to Reaction (3-1) ... 

The gas inlet and gas outlet shown in Figure 5.8 are used for gas (pure oxygen, nitrogen, or argon) purging. For measuring catalyst surface-cyclic voltammograms, pure N2 or Ar gas will be used to de-aerate the electrolyte solution for 30—60 min. For an... 

Underpotential deposition (UPD) of and other metals such as Pd and Cu on polycrystalline materials such as gold and platinum has been used as an example system in developing pseudocapacitance theory and practice [2]. For example, the reaction of H+ on a Pt electrode surface, shown by the surface cyclic voltammogram in Figure 3.3, can be written as... 

Figure C2.10.2. Cyclic voltammogram of Cu(l 11)/10 mM HCl and in situ measured STM micrographs revealing tire bare Cu(l 1 l)surface (-1.05 V, left) and tire (V3 x A/3)R30°-Cladsorbate superstmcture (-0.6 V, right) (from [39]).

The following two pictures (Figure 6.2-8a and b) were acquired at h-500 mV and at -I-450 mV vs. Cu/Cu and show that at h-450 mV vs. Cu/Cu monolayer high Cu clusters nucleate at the steps between different Au terraces. Thus, the pair of shoulders in the cyclic voltammogram is correlated with this surface process. 

If the film is nonconductive, the ion must diffuse to the electrode surface before it can be oxidized or reduced, or electrons must diffuse (hop) through the film by self-exchange, as in regular ionomer-modified electrodes.9 Cyclic voltammograms have the characteristic shape for diffusion control, and peak currents are proportional to the square root of the scan speed, as seen for species in solution. This is illustrated in Fig. 21 (A) for [Fe(CN)6]3 /4 in polypyrrole with a pyridinium substituent at the 1-position.243 This N-substituted polypyrrole does not become conductive until potentials significantly above the formal potential of the [Fe(CN)6]3"/4 couple. In contrast, a similar polymer with a pyridinium substituent at the 3-position is conductive at this potential. The polymer can therefore mediate electron transport to and from the immobilized ions, and their voltammetry becomes characteristic of thin-layer electrochemistry [Fig. 21(B)], with sharp symmetrical peaks that increase linearly with increasing scan speed. 

Both the TPD spectra (Fig. 5.2b) and the cyclic voltammograms (Fig. 5.2c) show clearly the creation of two distrinct oxygen adsorption states on the Pt surface (vs. only one state formed upon gas phase 02 adsorption, Fig. 5.2b, t=0). 

Figure 3. Cyclic voltammograms of ascorbic acid at a freshly polished, active (a) and a deactivated (b) glassy carbon electrode surface. See text for details.

Figure 6. Simulated cyclic voltammogram for the oxidation of ascorbic acid without Inclusion of ec catalysis by the surface qulnone functionalities. Filled circles represent the simulated data and an experimental curve Is shown with a line for comparison. A scan rate of 100 mV s was assumed for experimental and simulated data.

Figure 3.2 Cyclic voltammograms for H adsorption on Pt(lll) and Pt(lOO). Two different methods have been applied. In (a) and (b), the H particles were assumed not to interact in the expression for the configurational entropy. In (c) and (d), the more elaborate model involving Metropolis Monte Carlo was applied. As can be seen, for these homogenous surfaces, the simple method suffices. The figure is adopted from [Karlberg et al., 2007a], where the full details of the calculations can also be found.

Figure 7.5 Cyclic voltammogram of a Pt(775) electrode in 0.5 M H2SO4 solution and a hard sphere model of this surface. Sweep rate 50 mV/s. In the hard sphere model, four atoms forming the (110) step site have been identified in black.

Figure 8.13 In situ electrochemical SXS characterization of PtsNi) 11) and Pt(l 11) surfaces (a)XRV measurements forPtsNitlll) at the (0, 0, 2.7) (filled squares) andPt(lll)at (1, 0, 3.6) (open triangles) (b) surface coverage by underpotentially deposited hydrogen (Hupd) and hydroxyl species (OHad) calculated from the cyclic voltammograms (c) segregation profile ascertained from the SXS measurements. (Reprinted with permission from Stamenkovic et al. [2007a]. Copyright 2007. American Association for the Advancement in Science.)...

Figure 11.11 Linear cyclic voltammograms of carbon-supported nanosized Pt and Pt-Cr alloy catalysts with different atomic ratios (prepared using the carbonyl route [Yang et al., 2004]) recorded in 0.5 M HCIO4 saturated with pure oxygen at a scan rate of 5 mV s and a rotation speed of 2000 rev min Current densities are normalized to the geometric surface...

Figure 14.8 STM images (7 nm x 7 nm) (a-e) and corresponding cyclic voltammograms (f-j) of different PtcRui /Ru(0001) surface alloys. The voltammograms on the right-hand side have an expanded current scale, (a, f) xpt = 0.07 (b, g) 0.12 (c, h) 0.25 (d, i) 0.53 (e, j) 1.05. [Hosier et al., 2008]—Reproduced by permission of the PCCP Owner Societies.

Since model compounds reveal well-defined cyclic voltammograms for the Cr(CNR)g and Ni(CNR)g complexes (21) the origin of the electroinactivity of the polymers is not obvious. A possible explanation (12) is that the ohmic resistance across the interface between the electrode and polymer, due to the absence of ions within the polymer, renders the potentially electroactive groups electrochemically inert, assuming the absence of an electronic conduction path. It is also important to consider that the nature of the electrode surface may influence the type of polymer film obtained. A recent observation which bears on these points is that when one starts with the chromium polymer in the [Cr(CN-[P])6] + state, an electroactive polymer film may be obtained on a glassy carbon electrode. This will constitute the subject of a future paper. 

In an ideal case the electroactive mediator is attached in a monolayer coverage to a flat surface. The immobilized redox couple shows a significantly different electrochemical behaviour in comparison with that transported to the electrode by diffusion from the electrolyte. For instance, the reversible charge transfer reaction of an immobilized mediator is characterized by a symmetrical cyclic voltammogram ( pc - Epa = 0 jpa = —jpc= /p ) depicted in Fig. 5.31. The peak current density, p, is directly proportional to the potential sweep rate, v ... 

Fig. 8. Cyclic voltammograms of polyacetylene films on a platinum surface measured in acetonitrile containing 0.1 M Et4NBF4. Reproduced from [98],...

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