Transient techniques at hydrodynamic electrodes

All the electrode kinetic methodology described until now has assumed a steady state (or quasi-steady state in the case of the DME). Many techniques at stationary electrodes involve perturbation of the potential or current in combination with forced convection, this offers new possibilities in the evaluation of a wider range of kinetic parameters. Additionally, we have the possibility of modulating the material flux, the technique of hydrodynamic modulation which has been applied at rotating electrodes. Unfortunately, the mathematical solution of the convective-diffusion equation is considerably more complex and usually has to be performed numerically. 

It has been shown that, under conditions of mass-transfer control at the RDE, the various modulation possibilities are linked via an implicit functional relationship [234] 

The electrochemical impedance may be obtained from potentiostatic or galvanostatic experiments. Alternating current voltammetric techniques are well documented at the DME, as are various kinds of pulse techniques. The former has also been developed at rotating and tubular/channel electrodes. 

Hydrodynamic modulation has been performed almost exclusively at the rotating disc electrode. It has found use for analytical purposes at rotating and tubular electrodes owing to the fact that non-convectively dependent electrode processes are unaffected by the modulation [236]. 

We will first briefly consider some of the treatments of potential step and current step techniques at hydrodynamic electrodes. One should bear in mind, however, that this division is somewhat artificial owing to the implicit dependence of one on the other. We then treat a.c. voltammetric techniques, LSV, and finally consider hydrodynamic modulation. 

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