Oxide formation gold electrodes

They form a monolayer that is rich in defects, but no second monolayer is observed. The interpretation of these results is not straightforward from a chemical point of view both the electrodeposition of low-valent Ge Iy species and the formation of Au-Ge or even Au Ge h compounds are possible. A similar result is obtained if the electrodeposition is performed from GeGl4. There, 250 20 pm high islands are also observed on the electrode surface. They can be oxidized reversibly and disappear completely from the surface. With Gel4 the oxidation is more complicated, because the electrode potential for the gold step oxidation is too close to that of the island electrodissolution, so that the two processes can hardly be distinguished. The gold step oxidation already occurs at -i-lO mV vs. the former open circuit potential, at h-485 mV the oxidation of iodide to iodine starts. 

The formation of Au-OHad or surface oxides on gold in alkaline electrolyte was in fact proposed to explain some of the electrocatalytic properties observed for a gold electrode (e.g., incipient hydrous oxide/adatom mediator model ). Our previous measurement of the interfacial mass change also indicated the formation of Au oxides (AU2O3, AuOHorAu(OH)3) on gold nanoparticle surfaces. A detailed delineation of the catalytic mechanism is part of our on-going work. 

According to the presented model of oxides formation on Au, the outer surface of the thick oxide film exposed to the solution is either AU2O3 or Au(OH)3. The type of oxide determines the surface electronic structure and electrocatalytic properties. Electrocatalytic properties of gold oxide-covered electrodes have been discussed by Burke and Nugent [366, 368]. 

The formation of the active surface states of gold was also found in an alkaline solution [376]. Both cathodic and thermal pretreatments were used. As a result, up to five distinct premonolayer oxidation responses in the range O-l.OV(SHE) were observed. In a separate paper, a study of gold electrodes in the metastable states in acid and base solutions was made. The active electrodes were prepared by... 

Numerous bisthiols have been observed to form spontaneously multilayers on gold and silver on the basis of the oxidative formation of disulfides.15-27 Nonetheless, most of these compounds lack electroactive character, with few notable exceptions.23,27 In principle, the introduction of redox centers at the core of these molecules and their subsequent assembly into multilayers can be exploited to generate electroactive films. The concentration of redox centers within the resulting electrode coatings, as well as their thickness, can be significantly larger than those possible with electroactive thiols such as 1-4 (Fig. 7.1).11 14 In addition, the transition from electroactive monolayers to electroactive multilayers can translate into a significant enhancement in stability and a much more effective protection of the electrode surface. 

This reorganisation also explains the decrease of the current of reduction peak IVC and the formation of the third oxidation peak (IVa). However, both peaks and also peak IIIC are too large to be explained by reduction or oxidation of adsorbed Co(II)TSPc only. It is assumed that this is the result of an electrocatalytic reaction, such as reaction with Co(II)TSPc in solution. This is confirmed by the fact that these peaks disappear when the Co(II)TSPc-modilied gold electrode is scanned in a pH 12 buffer in the absence of Co(II)TSPc in solution. In addition, the peak currents of peak IIIC in the first scan and peaks IIIC and IVC at the scan of maximum coverage vary linearly with Co(II)TSPc concentration (Fig. 7.5). Note that small peaks are observed at the same potentials where peaks IIIC and IVC occurred with solutions containing Co(II)TSPc. Electrochemical measurements of TSPc without Co show also a reduction wave at these potentials, explaining the ring reduction of CoTSPc in solution. This confirms the fact that Co(II)TSPc is adsorbed at the surface of the electrode and electro-catalyses the oxidation/reduction of Co(II)TSPc transported from solution towards the electrode surface. 

Figure 5.20 Cyclic voltammograms for platinum, palladium, rhodium, and gold electrodes in 1 M H2S04 f , cathodic current due to oxide reduction ( , anodic current due to oxide formation g , cathodic current due to H2 formation Q, anodic current due to H2 oxidation.

Pitner and Hussey studied the electrochemistry of tin in acidic and basic AICI3/I-ethyl-3-methyl-imidazolium chloride-based ionic liquids by using voltammetry and chronoamperometry at 40 °C [15]. They reported that the Sn(II) reduction process is uncomplicated at a platinum substrate, where in the atidic ionic liquid the reduction wave was observed at +0.46 V on the Pt electrode and the oxidation at +0.56 V. When they used a gold electrode instead of platinum, they observed an underpotential deposition of a tin monolayer and an additional underpotential deposition process that was attributed to the formation of tin-gold alloy at the surface. The deposition of tin on glassy carbon was controlled by nudeation. 

Fig. 5 Immobilized nucleic acid assays utilizing redox-active moieties, a Amplified detection of viral DNA by generation of a redox-active replica and the bioelectrocatalyzed oxidation of glucose (Reprinted with permission from [200]. Copyright(2002) American Chemical Society), b Alternative formats for the capture on a gold electrode SAM of solution-extended primers or direct surface extension of primer with electrotides (adapted from [185]). c Ferrocene-labelled hairpin for electrochemical DNA hybridization detection. A Fc-hairpin-SH macromolecule is immobilized on a gold electrode. When a complementary DNA target strand binds to the hairpin, it opens and the ferrocene redox probe is separated from the electrode, producing a decrease in the observed current (Reprinted with permission from [203], Copyright(2004) American Chemical Society)...

K 29 is the calibration constant for m/z = 29 determined from ethanol oxidation on a gold electrode, which present a current efficiency close to 90% for the formation of acetaldehyde. " " The authors also monitored the mass spectrometric signal for m/z = 15 and m/z = 30 corresponding to fragment of methane (CHs ) and ethane (C2He ), respectively. 

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