Platinum voltammetric curves

The situation is quite different in the case of an acetic acid-water system. The energy of acetic acid adsorption on platinum is low and therefore the voltammetric curves taken in the absence and in the presence of acetic acid in the supporting electrolyte are nearly the same. However, radiometric data show that C-labeled acetic acid is adsorbed on the electrode surface. Most likely the acetic acid molecules are adsorbed on the top of the water molecules populating the electrode surface. Simultaneously recorded voltammetric and counting rate data are shown in Fig. 8. 

The similarity of the shape of the voltammetric curves of platinized system to those reported for electrodes treated by the fast repetitive potential perturbation technique or obtained by annealing electrodeposited platinum and the appearance of signs characteristic for stepped surfaces allows us to assume that these phenomena should be ascribed to the similarities in the surface structure. 

Finally, the pFI dependency of the current signals was investigated. Voltammetric curves were recorded obtained at a platinum rotating-disc electrode for different pFI values in the 11.65-12.95 range at constant electrode-rotation rate. These experiments were repeated at other sodium dithionite concentrations. It was found that the measured current in all three regions of the voltammetric waves did not vary with pH. 

Section 2 (Fig. 1, curves A and B), usually performed at the rotating platinum electrode (anode reactions) or the dropping mercury electrode (cathode reactions), should ideally suffice to define the electroactive species and determine its half-wave potential. It may be that systems in which acid-base equilibria exist are somewhat more laborious to study due to the necessity of recording voltammetric curves over a wide pH range, but in most cases the task can be accomplished with some effort. Once the voltammetric characteristics are known, it remains to carry out preparative constant potential electrolysis (cpe) at a suitable potential in order to make sure that the electroactive species is connected with the reaction of interest. 

An investigation of the anodic oxidation of mesitylene in nitrate-ion based electrolytes but with aprotic solvents revealed little more to illuminate the mechanistic picture (Nyberg, 1971d). Again, a very pronounced shift of the voltammetric curve was observed upon addition of the substrate when platinum was the anode material, whereas on graphite a small shift toward less positive potentials was noted. Product distributions are shown below eqn (67). The forma-... 

Chemisorption of hydrogen on platinum metals is a reversible process as demonstrated by the symmetry of the cyclic voltammetric curves (- voltammetry). The voltammetric behavior of these systems depends on the... 

Platinum, gold and carbon are the most frequently employed materials for solid electrodes. Platinum has a high background current, but it also exhibits the highest degree of reproducibility of the obtained voltammet-ric curves. Carbon must not be porous and for this reason the pores must be filled, e.g., with paraffin. The so-called Glassy carbon [9] with a very low porosity is recommended. The electrode surface must in all cases be respected, this makes a mechanical or an electrochemical pretreatment necessary before each recording of a voltammetric curve. 

A mechanically polished tin disk immersed in 0.5 M citric acid was prepared following the procedure described in the literature [59]. Because high-scan-rate voltammetric curves were recorded, a calomel reference electrode is not recommended because of its slow response [60], The reversible hydrogen electrode (RHE) was used as the reference electrode at 25°C. The required materials and reagents are a three-compartment electrochemical cell with a platinized platinum auxiliary electrode and a 0.5 M (pH = 1.8) citric acid solution prepared with triple-distilled water. 

Fig. 4.7 Voltammetric curves for Si(lV) discharge in a KCl-KF-K2SiF6 melt rai platinum and gold cathodes [17]...

Consecutive cyclic voltammetric curves obtained for diphenylamine microciys-tals attached to a platinum electrode in the presence of aqueous solution containing 1 moldm H2SO4 are shown in Fig. 4.11 [134]. 

Fig. 4.11a-d Consecutive cyclic voltammetric curves obtained for diphenylamine microcrystals attached to a platinum electrode (A = cm ) in the presence of aqueous solution containing 1 moldm H2SO4. (Reproduced from [134] with the permission of Elsevier Ltd.) Scan rate 100 mVs . Cycles a 1-5, b 11-30 (started after a 3 min delay at — 0.2 V)... 

Figure 13.7. Polarization curves for O2 reduction reaction on Au/Pt/C (A) and Pt/C (C) catalysts on a rotating disk electrode, before and after 30,000 potential cycles. Sweep rate 10 mV/s rotation rate 1600 rpm. Voltammetric curves for Au/Pt/C (B) and Pt/C (D) catalysts before and after 30,000 cycles sweep rates 50 and 20 mV/s, respectively. The potential cycles were from 0.6 to 1.1 V in an 02-saturated 0.1 M HCIO4 solution at room temperature. For aU electrodes, the Pt loading was 1.95 mg (or 10 nmol) on a 0.164 cm glassy carbon rotating disk electrode. The shaded area in (D) indicates the lost Pt surface area [31]. (From Zhang J, Sasaki K, Sutter E, Adzic RR. Stabilization of platinum oxygen-reduction electrocatalysts using gold clusters. Science 2007 315 220-2. Reprinted with permission from AAAS.)...

The cyclic voltammetric curves were measured at a potential sweep rate varied from 5-10 to 2.0 V-s in the temperature range 973-1123 K. Cyclic voltammograms were recorded on molybdenum and glassy carbon working electrodes 0.5-2.0mm in diameter with respect to a platinum wire, which was used as a quasi-reference electrode, and a reference electrode Ag/NaCl-KCl-AgCl (2 wt%). The glassy carbon crucible served as an auxiliary electrode. 

Voltammetry is a term used to include all the methods that measure current-potential curves (voltammograms) at small indicator electrodes other than the DME [6], There are various types of voltammetric indicator electrodes, but disk electrodes, as in Fig. 5.17, are popular. The materials used for disk electrodes are platinum, gold, graphite, glassy carbon (GC), boron-doped diamond8, carbon paste, etc. and they can be modified in various ways. For electrode materials other than mercury, the potential windows are much wider on the positive side than for mercury. However, electrodes of stationary mercury-drop, mercury-film, and mercury-pool are also... 

In a first set of experiments, the voltammetric behaviour of sodium dithionite was investigated in alkaline solution (pH around 12.5), by variation of the rotation rate of the platinum-disc electrode for different concentrations of sodium dithionite. In Fig. 6.1, current-potential curves are shown, obtained at different rotation rates of the electrode in a solution with constant sodium dithionite concentration. Two anodic waves are observed. In principle, sodium dithionite is the only electroactive species in solution, therefore it is supposed that both well-separated waves can be attributed to the oxidation of sodium dithionite with formation of a relatively stable intermediate product in the first wave. 

Figure 8.4 illustrates the voltammograms with activated platinum electrodes for dissolved H2 in five solvents. The peak potential shifts with the basicity of the solvent and the separation between the potentials for the anodic and cathodic peaks reflects the unbuffered solvent matrix and the system s conformity to Eq. (8.2). The voltammogram for dissolved H2 in MeCN indicates severe adsorption effects, which precludes this solvent system for quantitative determinations via peak-current measurements. The other solvents yield anodic peak currents that are proportional to the concentration of dissolved H2 and its diffusion coefficient (DH2). The H2 concentration, in turn, is dependent on the partial pressure of dissolved H2 (PH2) and its solubility in a particular solvent. Figure 8.5 summarizes the voltammetric peak currents (tp a) as a function of PH2 in H20, Me2SO, DMF, and py. The slopes of the linear curves are proportional... 

The cause of this effect of nickel ions was investigated voltammetrically with a gold-plated rotating platinum disk electrode [158]. The current-potential curves shown in Fig. 33 demonstrate that the anodic oxidation of the reducing agent... 

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