It has been demonstrated that Pt foil cannot act as a reference electrode in molten electrolytes, since it is neither stable nor depolarised 4. It can therefore can be used as a pseudo-reference electrode for the study of electrode reaction kinetics, with the advantages of simplicity, convenience and ease of operation 7.
Unlike conventional reference electrodes even when modified for high temperature , the Pt reference electrode is applicable to measurements in complex polluted brines 8. In certain electrolytes, modification of the Pt surface is important for its stability.
Anodised, nonporous Pt has demonstrated its usefulness as a solid-state reference electrode by virtue of its near-Nernstian behaviour, low hysteresis and rapid response Modifications to Pt wire may extend its usefulness to more electrochemical systems. The use of polypyrrole 16 , poly-1,3-phenylendiamine 15 or polyvinyl ferrocene 17 as a surface modifier can successfully suppress significant interference by any coupled redox systems or contaminants. The fact that a Pt electrode can be modified with nitrogen-based polymers or be incorporated as part of a biosensor assembly 18 indicates its resistance to interference from these compounds.
Some of the problems associated with the reference electrode can be solved outside the electrochemical cell. A reference electrode is defined as an ideal non-polarisable electrode; thus its potential does not vary with the current passing. In practice, no electrode follows this ideal behaviour; consequently, the interfacial potential of the counterelectrode in the two-electrode system varies with the flow of current passed through the cell.
In order to overcome this problem, a three-electrode cell can be used. The functions of the counterelectrode in a three-electrode cell are divided between the reference and auxiliary electrodes. The passage of current between the working and auxiliary electrodes ensures that less current passes through the reference electrode. Furthermore, the three-electrode cell allows the potential between the working and reference electrodes to be controlled. Most electrochemical devices include an operational amplifier of high input impedance for the reference electrode input, to eliminate the possibility of any current passing through the reference electrode.
Since no Faradaic process takes place at the reference electrode, its area relative to that of working electrode has no effect on the electrochemical results. The physical form of the Pt reference electrode may contribute to its performance.
Studies 19 indicate that the Pt mesh electrode yields very reproducible results, and that it can be used as a convenient reference electrode. On the other hand, Pt sheet or wire has been used in all-solid-state electrochemical cells at room temperature 20—22 , and in reactions in frozen agar or frozen aqueous electrolytes 23, Most of these studies involved only one-electron redox systems.
In this study, the usefulness of Pt as a reference electrode in electrochemical systems was investigated using CV techniques. Single or multi-electron redox systems involving one- or two-electron redox waves were used in this study. To verify the suitability of Pt as a reference electrode, kinetic parameters were determined for comparison with corresponding measurements on traditional reference electrodes.
A purified agar powder was obtained from Sigma Chemical Co. All other reagents were of at least reagent grade and were used without further purification. Cyclic voltammogram for a smooth Pt electrode in 0. The various regions are discussed in the text. The shape, number and size of the peaks depend on the pretreatment of the electrode, solution impurities and supporting electrolyte. Reprinted with permission from A. Bard and L. Copyright J.
Surface cleanliness is a major issue with all electrodes. Pt is unique in that the surface impurities can be removed by repetitive scanning through a potential region where the impurities can be oxidized or removed into solution as platinum oxide is reduced. In the double-layer region, the high surface activity of Pt, due to its atoms having unfilled d-orbitals, can be used advantageously to detect analytes eluted in liquid chromatography utilizing a technique called "pulse amperometric detection PAD " [ref 5].
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