This system used in electrochemical studies when investigating reaction mechanisms related to redox chemistry and other chemical phenomena.
This design makes a variety of experiments possible, for example a complex could be oxidized at the disk and then reduced back to the starting material at the ring.
Such experiments are useful in studying multi-electrons processes, the kinetics of a slow electron transfer, adsorption/desorption steps, and electrochemical reaction mechanisms.
For example, in a proton exchange membrane (PEM) fuel cell, dioxygen reduction at the cathode is often enhanced by an electrocatalyst comprising platinum nanoparticles.
A narrow gap reduces the "transit time" necessary for an intermediate species generated at the disk to successfully reach the ring electrode and be detected.
It is desirable for an RRDE to have a large collection efficiency if only to assure that the current signal measured at the ring electrode is detectable.
On the other hand, it also desirable for an RRDE to have a small transit time so that short-lived (unstable) intermediate products generated at the disk survive long enough to be detected at the ring.
The choice of actual RRDE dimensions is often a trade-off between a large collection efficiency or a short transit time.