Platinum -solution interface

Ruch and Bartell [84], studying the aqueous decylamine-platinum system, combined direct estimates of the adsorption at the platinum-solution interface with contact angle data and the Young equation to determine a solid-vapor interfacial energy change of up to 40 ergs/cm due to decylamine adsorption. Healy (85) discusses an adsorption model for the contact angle in surfactant solutions and these aspects are discussed further in Ref. 86. 

Schuldiner, determination of the capacitance of platinum-solution interfaces, 129... 

Studies In our laboratories (43-51) have concentrated on the effects of quaternary salts on electrochemical oxidations on platinum electrodes In emulsion and micelle systems. In addition studies have been made of the effect of these surfactants on a noncatalytlc process occurring at the platinum solution Interface. The quaternary salt used for most of the experiments was Hyamlne 2389 (predominantly methyldodecylbenzyl trlmethylammonlum chloride) and the aqueous solution was strongly basic. Under these conditions It was concluded (49) that the anode was covered... 

Other experimental method at a eomparable level of detail, although in some eases the conclusions reached support previous work by XANES using synchrotron radiation. Our results clearly demonstrate that due to a quantum mechanical electron density spillover from platinum, the interface is metallized, as evidenced by Korringa relaxation and Knight shift behavior. Thus, the adsorbate on a platinum electrode belongs to the metal part of the platinum-solution interface, and most likely other d-metal interfaces, and should be considered as such in any realistic models of the structure of the electrical double layer of interest to electrocatalysis. 

In situ optical techniques should be considered as a very im-poitant tool, because of their natural compitability with the usual configuration of electrochemical cells. The limiting factor is always a model of optical signal, and a lot of important experimental results for platinum/solution interface still wait for physically grounded interpretation. 

Second harmonic generation (SHG) of platinum/solution interface was pioneered by Com and coworkers,who managed to get the resportse of hydrogen adatoms and coadsorbed anions despite platintrm signal is rather low as compared with SHG of Cu, Ag and An. Frrrther steps " resulted in a nttmber of particular... 

Platinum/solution interface is also studied by some techniques with less comprehensible background, like contact electric resistance. " Probably the progress of other techniques can later result in some clarification of the meaning of these data. The same is related to immersion techniques applied to determine the potentials of zero charge. "" Who knows, probably what looks mistaken now can be helpful later, when the nature of disagreement of various techniques shall be interpreted. 

The platinum microelectrode appears to act as a potentiostat and maintains the potential of the Pb-solution interface at a crack at a value that favours the re-formation of PbOj, rather than the continuous formation of PbClj which would otherwise result in excessive corrosion. 

CO adsorption on electrochemically facetted (Clavilier), 135 Hamm etal, 134 surfaces (Hamm etal), 134 Platinum group metals in aqueous solutions, 132 and Frumkin s work on the potential of zero charge thereon, 129 Iwasita and Xia, 133 and non-aqueous solutions, 137 potentials of zero charge, 132, 137 preparation of platinum single crystals (Iwasita and Xia), 133 Platinum-DMSO interfaces, double layer structure, 141 Polarization time, 328 Polarons, 310... 

An interesting correlation exists between the work function of a metal and its pzc in a particular solvent. Consider a metal M at the pzc in contact with a solution of an inert, nonadsorbing electrolyte containing a standard platinum/hydrogen reference electrode. We connect a platinum wire (label I) to the metal, and label the platinum reference electrode with II. This setup is very similar to that considered in Section 2.4, but this time the metal-solution interface is not in electronic equilibrium. The derivation is simplified if we assume that the two platinum wires have the same work function, so that their surface potentials are equal. The electrode potential is then ... 

Hydrogen Electrode. The hydrogen electrode is made of a platinum wire in contact with hydrogen gas and solution containing hydrogen ions (Fig. 5.5). Since hydrogen gas and hydrogen ions are present at the electrode-solution interface, this electrode can be represented as Pt H2, and the electrode reaction is... 

The rotating disc electrode is constructed from a solid material, usually glassy carbon, platinum or gold. It is rotated at constant speed to maintain the hydrodynamic characteristics of the electrode-solution interface. The counter electrode and reference electrode are both stationary. A slow linear potential sweep is applied and the current response registered. Both oxidation and reduction processes can be examined. The curve of current response versus electrode potential is equivalent to a polarographic wave. The plateau current is proportional to substrate concentration and also depends on the rotation speed, which governs the substrate mass transport coefficient. The current-voltage response for a reversible process follows Equation 1.17. For an irreversible process this follows Equation 1.18 where the mass transfer coefficient is proportional to the square root of the disc rotation speed. 

Some understanding of liquid flow along a solid-solution interface is useful in understanding these techniques. Consider a stationary platinum electrode immersed in a stirred solution. Three regions of solution flow can be identified. 

The mercury-pool electrode is especially attractive because of its renewable surface and because it allows the use of a stirring bar to vigorously stir the electrode-solution interface. Its major limitation relative to a platinum electrode is its high mass and the awkwardness of rinsing and of weighing a liquid electrode relative to a solid electrode. 

Fig. 13.54. Morphology of a thick oxide layer, showing crystallites, grain boundaries, and pores. The oxide/solution interface area is very large when the layer is impregnated with electrolyte solution. (Reprinted from S. Trasatti and K. Weil, Electrochemical Supercapacitors as Versatile Energy Stores, Platinum Metals Rev., 38 (2) 53, Fig. 8,1994, with permission from Johnson, Matthey Co.)...

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