Reduction in Aqueous Electrolytes General Aspects

Dioxygen Reduction in Aqueous Electrolytes General Aspects 

a two-electron pathway that produces solution phase peroxide (see dark grey arrow in the same scheme), a species that can be further reduced to water or undergo disproportionation regenerating 02. 

The standard reduction potentials of the most relevant half-reactions involved in the four- and two-electron reduction of dioxygen in acid and alkaline aqueous media are listed in Table 3.1. It follows from these values, that, under full thermodynamic control, the equilibrium concentration of peroxide at the reversible potential for the four-electron reduction of oxygen in acid media, that is, 1.23 V, is of the order of 10 18 M. Hence, a stepwise reduction of dioxygen to yield currents of about 1A cm 2 will require values for the standard heterogeneous rate constants for 

As indicated in the right panel in this figure, rotation about the main axis of the cylinder forces the solution toward the flat end that contains the inlaid disk and ring electrodes. As the surface is closely approached, the solution spreads outward, forming a uniformly accessible diffusion layer along the surface of the disk. The RRDE has proven exceedingly useful in studies of 02 reduction, as solution phase 

Shown in the lower panel are ring currents, lring, as a function of Edisk recorded with the Au ring polarized at Ering = 0.1 V vs. SCE while the potential of the disk was being scanned [17]. 

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