Platinum electrodes oxide film

The relative proportions of oxygen and chlorine evolved will be dependent upon the chloride concentration, solution pH, overpotential, degree of agitation and nature of the electrode surface, with only a fraction of the current being used to maintain the passive platinum oxide film. This will result in a very low platinum consumption rate. 

By setting the ratio of the oxidized and reduced forms of a redox couple in an electrode coating film to unity, the potential of this electrode in an inert electrolyte is poised at the half-wave potential of the couple. This has indeed been shown for platinum wires coated with polyvinylferrocene or ferrocene modified polypyrrole But the long term stability of these electrodes during cell connection... 

Another type of supercapacitor has been developed in whieh instead of ideally polarizable electrodes, electrodes consisting of disperse platinum metals are used at which thin oxide films are formed by anodic polarization. Film formation is a faradaic process which in certain cases, such as the further partial oxidation and reduction of these layers, occurs under conditions close to reversibility. 

Dickinson T, Povey AP, Sherwood PMA. 1975. X-ray photoelectron spectroscopic studies of oxide-films on platinum and gold electrodes. J Chem Soc Faraday Trans 171 298-311. 

The second most widely used noble metal for preparation of electrodes is gold. Similar to Pt, the gold electrode, contacted with aqueous electrolyte, is covered in a broad range of anodic potentials with an oxide film. On the other hand, the hydrogen adsorption/desorption peaks are absent on the cyclic voltammogram of a gold electrode in aqueous electrolytes, and the electrocatalytic activity for most charge transfer reactions is considerably lower in comparison with that of platinum. 

Pyridine was found to polymerize on a Pt electrode from a solution of 1 M pyridine in 1 M LiC104/CH3CN at potentials above 0.8 V vs Ag/AgCl. A colorless film was formed, but it could be oxidized and reduced when placed in plain electrolyte solution. The infrared spectrum of the electrochemically formed poly(pyridine) film is shown in Figure 5. It displays a very intense, narrow band at 1500 cm indicative of C=C stretches that are perpendicular to the surface. 3,5 Lutidine also was polymerized on a platinum electrode under the same conditions, and its infrared spectrum is similar to that for the surface catalyzed poly(lutidine). The C=C stretching band for the poly(lutidine)... 

The formed thin and uniform poly(phenyleneoxide) films on electrode are interesting because of their electric and electrochemical properties. Figure 1 shows a typical cyclic voltammogram for the oxidation of 2,6-dimethylphenol at a platinum electrode in... 

Figure 8-40 shows the electron transfer current of two redox reactions (outer-sphere electron transfer) observed at constant potential for platinum electrodes covered with a thin oxide film in acidic solutions as a function of the film thickness. As e3q>ected fium Eqns. 8-84 and 8-85, a linear relationship is observed between the logarithm of the reaction ciirrents and the thicknesses of the film. 

Fig. 8-40. Transfer currents of redox electrons observed on a platinum electrodes covered with a thin platinum oxide film of PtO in acidic solutions as a function of film thickness hydrated redox particles Fe /Fe at 0.98 V he in acidic solution at pH 0 hydrated redox particles Ce /Ce at 1.0 in acidic solution at pH 3. [From Schultze, 1978 Schultze-Vetter, 1973.]...

To prepare metal hexacyanoferrate films, very frequently the following procedure was followed first a film of the respective metal, for example, cadmium [79], copper [80], silver [81], or nickel [82, 83] was elec-trochemically plated on the surface of a platinum electrode, and that was followed by chemical oxidation of the metal film in a solution of K3[Fe(CN)6], leading to the formation of the metal hexacyanoferrates. The same method has been used to produce films of nickel hexacyanoruthen-ate and hexacyanomanganate using the appropriate anions [83]. It is also possible to perform the oxidation of the deposited metals in solutions containing hexacyano-ferrate(II) by cyclic oxidation/reduction of the latter. In a similar way, films of copper heptacyanonitrosylferrate have been deposited [84]. 

To assess the electrochromic response of the bipyridinium dications embedded into multilayers of 7, we envisaged the possibility of assembling these films on optically transparent platinum electrodes.27d f Specifically, we deposited an ultrathin platinum him on an indium-tin oxide substrate and then immersed the resulting assembly into a chloroform/methanol (2 1, v/v) solution of 7. As observed with the gold electrodes (Fig. 7.5), the corresponding cyclic voltammograms show waves for the reversible reduction of the bipyridinium dications with a significant increase in 2p with the immersion time. In fact, is 0.8,1.5, and 3.1 nmol/cm2 after immersion times of 1, 6, and 72 h, respectively. Furthermore, the correlation between ip and v is linear after 1 h and deviates from linearity after 6 and 72 h. Thus, the bisthiol 7 can indeed form multiple electroactive layers also on platinum substrates. 

The dissolution reaction is Pt - Pt2+ + 2e and the value of its reversible thermodynamic potential is 1.2 V on the normal hydrogen scale. The evolution of O2 in acid solution at a current density of, say, 100 mA cm, needs an overpotential on platinum of nearly 1.0 V, i.e., the electrode potential would be >2.0 V. It follows feat at these very anodic potentials platinum would tend to dissolve, although its dissolution would be slowed down by fee fact feat it forms an oxide film at fee potentials concerned. Nevertheless, fee facts stated show feat fee alleged stability of Pt may be more limited than is often thought. This is an important practical conclusion because dissolved Pt from an anode may deposit on fee cathode of fee cell, and instead of having fee surface one started wife as fee cathode, it becomes in fact what is on its surface, platinum. 

Figure 11.6 Fabrication procedure of an IDA microelectrode. An oxidized silicon wafer (A) is coated with platinum (B). Carbon film is pyrolyzed on it (C). The substrate is coated with photoresist, which is exposed and developed (D) unnecessary portions are then removed by reactive ion etching (E). After removing the photoresist, an Si3N4 layer is deposited on the substrate (G). The substrate is coated with photoresist, which is exposed and developed (H) then the desired shape of the carbon electrode is exposed by reactive-ion etching (I). [Adapted from Ref. 36.]...

Using the HMDE covered by calomel, Kemula and coworkers studied the oxidation of several other substances [67]. Kublik studied the oxidation of various ions at the HMDE covered by a film of HgO [68]. These electrodes may be used at even more positive potentials than platinum electrodes in the same solutions. Although the mechanism of oxidation at these electrodes is very interesting, platinum and carbon electrodes are more useful in practical work since their properties and stability are not as dependent on the nature of the sample. When using such electrodes at positive potentials, some current due to oxidation of mercury is inevitable. This limits the application of passivated mercury electrodes to rather concentrated sample solutions. 

Takahashi and co-workers (69,70,71) reported both cathodic and anodic photocurrents in addition to corresponding positive and negative photovoltages at solvent-evaporated films of a Chl-oxidant mixture and a Chl-reductant mixture, respectively, on platinum electrodes. Various redox species were examined, respectively, as a donor or acceptor added in an aqueous electrolyte (69). In a typical experiment (71), NAD and Fe(CN)g, each dissolved in a neutral electrolyte solution, were employed as an acceptor for a photocathode and a donor for a photoanode, respectively, and the photoreduction of NAD at a Chl-naphthoquinone-coated cathode and the photooxidation of Fe(CN)J at a Chl-anthrahydroquinone-coated anode were performed under either short circuit conditions or potentiostatic conditions. The reduction of NAD at the photocathode was demonstrated as a model for the photosynthetic system I. In their studies, the photoactive species was attributed to the composite of Chl-oxidant or -reductant (70). A p-type semiconductor model was proposed as the mechanism for photocurrent generation at the Chi photocathode (71). 

The electrochemical oxidation of tyramine in NaOH/MeOH media gives films of polytyramine (25). The film, on a platinum electrode, can complex copper(II) ions from aqueous media and cobalt(II), iron(II), manganese(II) and zinc(II) from organic media. X-ray photoelectron spectroscopy established that coordination of the metal ions had occurred. For cobalt, evidence of coordination to both ether and amine functions is obtained, but for the other metal ions evidence of ether coordination is less definitive. 

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