Planner disk

Figure 5.3 shows a schematic structure of the RDE. The disk electrode s planner surface is made to contact with the electrolyte solution. An electronic isolator made from isolating material such as Teflon is used to cover the remaining part of the disk with only the planner surface exposed. An electrical brush is used to make the electrical connection between the electrode shaft and the wire during the electrode rotating. When the electrode is rotating, the solution will run from the hulk to the surface, and then be flushed out along the direction parallel to the disk surface, as shown in Figure 5.3(B). Using these three coordinates r, x, and 0, shown in Figure 5.3 through a complicated mathematic operation, the solution flow rates near the electrode surface at x and r directions can be expressed as ...

However, if the electron transfer kinetics of oxidant reduction in Reaction (5-1) is much slower than that of diffusion— convection process, the oxidant s surface concentration cannot be exhausted to zero unless a very larger overpotential is controlled. In this case, the obtained Levich plot of 7dc,o vs according to Eqn (5.14a) is not a straight line anymore, and it will gradually fall off with increasing as shown in Figure 5.5(B). In this case, for a planner smooth disk electrode, we can use the equation similar to Eqn (2.69) to take care of the effect of a slow electron-transfer kinetics ... 

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