Voltammetry multiple-electrode reactions

Oxygen ion conductors are used in amperometric sensors for a variety of gas species. The selectivity is controlled by selecting electrode materials that catalyze particular reactions hence, multiple electrodes are required for some multicomponent gas mixtures. In such cases, the system is designed so that each electrode removes a particular gas from the gas stream. The particular gas removed by a particular electrode can also be controlled by the voltage at the electrode, just as in cyclic voltammetry, which has also been used in solid-electrolyte based sensors [34]. In addition to providing selectivity, control of the applied voltage can be used to improve the magnitude of the response [35]. 

Second, when multiple metals are deposited simultaneously, as is the case in a real stripping voltammetric measurement, not only is their interaction with the diamond surface important, but equally critical is their interaction with each other. There is a possibility of intermetallic compounds or alloys forming, both of which will affect the oxidation or stripping potential for each. When these heterogeneous deposits form, the oxidation of a particular metal can occur from different sites on the diamond surface or from another metal surface. Oxidation from these multiple sites leads to peak broadening due to a spread in reaction kinetics. Ideally, for this application, highly dispersed metal deposits of low volume, without any intermetallic interactions, are desired. Even with these complexities, it is supposed that diamond will become a useful electrode for the determination of trace metal ions via anodic-stripping voltammetry. 

Multiple-sweep cyclic voltammetry is a useful method for the qualitative investigation of complex reaction phenomena at electrodes. In this method, the potential is swept repetitively in the forward and reverse directions at a relatively high rate, typically from one to several volts per second. A high scan rate permits to distinguish phenomena with fast time constants. Furthermore, it improves the... 

In potential sweep methods, the current is recorded while the electrode potential is changed linearly with time between two values chosen as for potential step methods. The initial potential, E, is normally the one where there is no electrochemical activity and the final potential, 2, is the one where the reaction is mass transport controlled. In linear sweep voltammetry, the scan stops at E2, whereas in cyclic voltammetry, the sweep direction is reversed when the potential reaches 2 and the potential remmed to j. This constitutes one cycle of the cyclic voltammogram. Multiple cycles may be recorded, for example, to study film formation. Other waveforms are used to study the formation and kinetics of intermediates when studying coupled chemical reactions (Figure 11.4c). 

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