Platinum electrodes effects

Souza-Garcia J, Heirtuo E, Feliu JM (2010) Breaking the C-C bond in the ethanol oxidation reaction on platinum electrodes effect of steps and ruthenium adatoms. ChemPhysChem 11 1391-1394... 

Oxidation-reduction potential Because of the interest in bacterial corrosion under anaerobic conditions, the oxidation-reduction situation in the soil was suggested as an indication of expected corrosion rates. The work of Starkey and Wight , McVey , and others led to the development and testing of the so-called redox probe. The probe with platinum electrodes and copper sulphate reference cells has been described as difficult to clean. Hence, results are difficult to reproduce. At the present time this procedure does not seem adapted to use in field tests. Of more importance is the fact that the data obtained by the redox method simply indicate anaerobic situations in the soil. Such data would be effective in predicting anaerobic corrosion by sulphate-reducing bacteria, but would fail to give any information regarding other types of corrosion. 

Platinum has also had its share of attention in recent years. The effect of phosphoric acid concentration on the oxygen evolution reaction kinetics at a platinum electrode using 0-7 m-17-5 m phosphoric acid at 25°C has been studied with a rotating disc electrode . The characteristics of the ORR are very dependent on phosphoric acid concentration and H2O2 is formed as an intermediate reaction. Also, platinum dissolution in concentrated phosphoric acid at 176 and 196°C at potentials up to 0-9 (SHE) has been reported . 

Fig. 19.16 Schematic E — I diagrams of local cell action on stainless steel in CUSO4 + H2SO4 solution showing the effect of metallic copper on corrosion rate. C and A are the open-circuit potentials of the local cathodic and anodic areas and / is the corrosion current. The electrode potentials of a platinised-platinum electrode and metallic copper immersed in the same solution as the stainless steel are indicated by arrows, (a) represents the corrosion of stainless steel in CUSO4 -I- H2 SO4, (b) the rate when copper is introduced into the acid, but is not in contact with the steel, and (c) the rate when copper is in contact with the stainless steel...

The nature and the physical state of the metal employed for the electrodes. The fact that reactions involving gas evolution usually require less overpotential at platinised than at polished platinum electrodes is due to the much larger effective area of the platinised electrode and thus the smaller current density at a given electrolysis current. 

Therefore, the following method was suggested and realized (the scheme is shown in Fig. 17). A 1.5 M solution of KCl or NaCl (the effect of preventing BR solubility of these salts is practically the same) was used as a subphase. A platinum electrode was placed in the subphase. A flat metal electrode, with an area of about 70% of the open barriered area, was placed about 1.5-2 mm above the subphase surface. A positive potential of +50 -60 V was applied to this electrode with respect to the platinum one. Then BR solution was injected with a syringe into the water subphase in dark conditions. The system was left in the same conditions for electric field-induced self-assembly of the membrane fragments for 1 hour. After this, the monolayer was compressed to 25 mN/m surface pressure and transferred onto the substrate (porous membrane). The residual salt was washed with water. The water was removed with a nitrogen jet. 

A prepassivated platinum electrode and an electrode of the metal of interest have been used to follow the development of a biofilm to determine its effects on the corrosion behavior of structural materials. The time dependence of the open circuit potential of several stainless steels... 

On the surface of metal electrodes, one also hnds almost always some kind or other of adsorbed oxygen or phase oxide layer produced by interaction with the surrounding air (air-oxidized electrodes). The adsorption of foreign matter on an electrode surface as a rule leads to a lower catalytic activity. In some cases this effect may be very pronounced. For instance, the adsorption of mercury ions, arsenic compounds, or carbon monoxide on platinum electrodes leads to a strong decrease (and sometimes total suppression) of their catalytic activity toward many reactions. These substances then are spoken of as catalyst poisons. The reasons for retardation of a reaction by such poisons most often reside in an adsorptive displacement of the reaction components from the electrode surface by adsorption of the foreign species. 

We have also discussed two applications of the extended ab initio atomistic thermodynamics approach. The first example is the potential-induced lifting of Au(lOO) surface reconstmction, where we have focused on the electronic effects arising from the potential-dependent surface excess charge. We have found that these are already sufficient to cause lifting of the Au(lOO) surface reconstruction, but contributions from specific electrolyte ion adsorption might also play a role. With the second example, the electro-oxidation of a platinum electrode, we have discussed a system where specific adsorption on the surface changes the surface structure and composition as the electrode potential is varied. 

Kardash D, Korzeniewski C. 2000. Temperature effects on methanol dissociative chemisorption and water activation at polycrystalhne platinum electrodes. Langmuir 16 ... 

Wang H, Baltruschat H. 2007. DEMS study on methanol oxidation at poly- and monocrystalline platinum electrodes The effect of anion, temperature, surface structure, Ru adatom, and potential. J Phys Chem C 111 7038-7048. 

Beden B, Juanto S, Leger JM, Lamy C. 1987. Infrared spectroscopy of the methanol adsorbates at a platinum electrode Part III. Structural effects and behaviour of the polycrystalline surface. J Electroanal Chem 238 323-331. 

Love B, Lipkowski J. 1988. Effect of surface crystallography on electrocatalytic oxidation of carbon-monoxide on platinum-electrodes. ACS Symp Ser 378 484-496. 

Fig. 10. Half wave potentials (at a rotating platinum electrode) vs. d-electron configuration for Et2dtc complexes. The E1/2 values depend upon solvent and reference electrode used (see text), but this is a minor effect as compared with the influence of the d-electron configuration.

Electrode processes can be retarded (i.e. their overpotential is increased) by the adsorption of the components of the electrolysed solution, of the products of the actual electrode reaction and of other substances formed at the electrode. Figure 5.43 depicts the effect of the adsorption of methanol on the adsorption of hydrogen at a platinum electrode (see page 353). 

More than a decade ago, Hamond and Winograd used XPS for the study of UPD Ag and Cu on polycrystalline platinum electrodes [11,12]. This study revealed a clear correlation between the amount of UPD metal on the electrode surface after emersion and in the electrolyte under controlled potential before emersion. Thereby, it was demonstrated that ex situ measurements on electrode surfaces provide relevant information about the electrochemical interface, (see Section 2.7). In view of the importance of UPD for electrocatalysis and metal deposition [132,133], knowledge of the oxidation state of the adatom in terms of chemical shifts, of the influence of the adatom on local work functions and knowledge of the distribution of electronic states in the valence band is highly desirable. The results of XPS and UPS studies on UPD metal layers will be discussed in the following chapter. Finally the poisoning effect of UPD on the H2 evolution reaction will be briefly mentioned. 

Another advantage of the on-line MS method is the possibility to observe separately the catalyst effects on parallel reactions. This is illustrated in Fig. 4.1 for methanol electroxidation on Pt with 60% of tin. Current and mass signals for C02 and for HCOOCH3 (methylformate) during the oxidation of 1 M CH3OH on a porous platinum electrode were recorded. 

Effect of Surface Crystallography on Electrocatalytic Oxidation of Carbon Monoxide on Platinum Electrodes... 

The conductance of a solution is the inverse of its resistance, and conductance has units of ohms 1 or mohs. The higher the conductance of a solution, the lower is its electrical resistance. A conductivity meter and conductivity cell are used to determine the effective resistance of a solution. The conductivity cell consists of a pair of platinized platinum electrodes with an area of approximately 1.0 cm2 with spacers designed to hold the electrodes rigidly parallel and at a fixed distance from each other. The cell can be standardized with solutions of known conductivity to obtain the cell constant, k so that the instrument response R... 

Turler and coworkers81 (Germany) examined the effectiveness of ECT, in colorectal metastases established in BDIX rats by injection of colon cancer cells under the liver capsule. The tumors thus induced in the liver were subjected to low current level ECT applied via five platinum electrodes (Figure 10). Four different applications were used ... 

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