Glassy electrolytes kinetics

The combination of anodic oxidation of benzene using the Ag(I)/Ag(II) mediator with cathodic oxidation of benzene using the Cu(I)/Cu(II) mediator in a single electrolytic cell produces p-benzoquinone selectively in both the anodic and the cathodic chambers [242]. Silver-mediator promoted electrooxidation of hydrocarbon has been attempted [243]. The kinetics of indirect oxidation of catechol and L-dopa with IrCl6 has been studied in polymer-coated glassy carbon [244]. 

One final issue remains to be resolved Of the portion of the AEpi that is due to resistance, what part is caused by solution resistance and what part is caused by film resistance To explore this issue we examined the electrochemistry of a reversible redox couple (ferrocene/ferricinium) at a polished glassy carbon electrode in the electrolyte used for the TiS 2 electrochemistry. At a peak current density essentially identical to the peak current density for the thin film electrode in Fig. 27 (0.5 mV see ), this reversible redox couple showed a AEpi of 0.32 V (without application of positive feedback). Since this is a reversible couple (no contribution to the peak separation due to slow kinetics) and since there is no film on the electrode (no contribution to the peak separation due to film resistance), the largest portion of this 0.32 V is due to solution resistance. However, the reversible peak separation for a diffusional one-electron redox process is —0.06 V. This analysis indicates that we can anticipate a contribution of 0.32 V -0.06 V = 0.26 V from solution resistance in the 0.5 mV sec control TiS2 voltammogram in Fig. 27. 

One typical example of this behavior is the voltammogram of the ferro/ferricyanide couple (test reaction) that at carbon electrodes is less reversible than at noble metal electrodes. The kinetics of the test reaction in 1 M aqueous KCl was used as the reference to compare its electrochemical behavior on different carbon electrodes [20]. This electrochemical reaction occurs via an outer sphere mechanism and its rate depends on the electrolyte composition and can be increased by appropriate treatment of carbon electrodes, for instance, by application of a high current potential routine to electrodes of carbon fibers. Similar results have been obtained with glassy carbon surfaces that had been pretreated at 500°C under reduced pressure. An alternative activation method is based on careful electrode surface polishing [6]. 

Table 7.6. ORR Kinetic Current Densities and Overall Electron Transfer Numbers. Obtained Based on tbe Data in Figure 7.19, Collected on a Co-N/C Coated Glassy Carbon Electrode Rotating at Various Rotation Rates. Electrolyte 02-Saturated 0.5 M H2SO4 Solution Co Loading in the Coating Layer ...

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