Second-order collection efficiencies at the RRDE

M represents the diffusion-limited current of X that would be observed if it were electroactive. Thus, the ring current begins to increase from zero 

Analysis of the experimental curves allows the determination of the concentration of the non-electroactive species from the value of M. 

It is interesting that mathematical solution proceeds in a very similar fashion to that for N0 any double electrode system where the convective-diffusion equation can be reduced to the form 

We have assumed above that the rate constant of the homogeneous reaction, fe2, is infinitely large so that the boundary between the A2 and X-dominated zones is clearly defined. When k2 is smaller, this boundary will be less clear. The modified convective-diffusion equations are difficult to solve and numerical solution is necessary. This has been performed at the RRDE making the assumptions that [221, 222] 

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