Rotating double ring electrode

In reactions involving gas evolution, the RRDE can be problematic in that bubbles may become trapped at the centre of the disc electrode. To obviate this, a rotating double ring electrode was suggested [34], The collection efficiency, N0, is given by eqn. (41) if we define... 

Clarenbach S, Grabner EW, Brauer E (1973) Digital simulation of a rotating double-ring electrode. Ber Bunsenges phys Chem 77 908. 

The homogeneous reaction may be of first or second order in the latter case, X is a non-electroactive species. Both these cases have been studied at the rotating ring—disc electrode and the first-order case at a double channel electrode. 

The rotating ring—disc electrode (RRDE) is probably the most well-known and widely used double electrode. It was invented by Frumkin and Nekrasov [26] in 1959. The ring is concentric with the disc with an insulating gap between them. An approximate solution for the steady-state collection efficiency N0 was derived by Ivanov and Levich [27]. An exact analytical solution, making the assumption that radial diffusion can be neglected with respect to radial convection, was obtained by Albery and Bruckenstein [28, 29]. We follow a similar, but simplified, argument below. 

At a double electrode, such as the rotating ring—disc electrode, a potential step at the disc will produce a ring current transient, the form of which is affected only by Faradaic current components at the disc. This fact can be very useful in separating Faradaic and non-Faradaic processes. 

Double- and triple-band electrodes have been constructed in a similar fashion by placing thin insulating films (e.g., Mylar) between the metal foils. These have been used in generator-collector experiments, in which one electrode (the collector) is used to monitor a product formed at the other electrode (the generator). This can be considered the microelectrode equivalent of the rotated ring-... 

For the investigator who wants to study electrode processes at depth, a number of more physically oriented methods are available, such as double layer capacitance measurements19 rotating disc and ring disc techniques 25 and radio-. active tracer methods 40a Spectroscopical methods in conjunction with optically transparent electrodes can be used for the study of intermediates 40b), as can also total reflectance spectroscopy 40c). 

In the non-steady state, changes of stoichiometry in the bulk or at the oxide surface can be detected by comparison of transient total and partial ionic currents [32], Because of the stability of the surface charge at oxide electrodes at a given pH, oxidation of oxide surface cations under applied potential would produce simultaneous injection of protons into the solution or uptake of hydroxide ions by the surface, resulting in ionic transient currents [10]. It has also been observed that, after the applied potential is removed from the oxide electrode, the surface composition equilibrates slowly with the electrolyte, and proton (or hydroxide ion) fluxes across the Helmholtz layer can be detected with the rotating ring disk electrode in the potentiometric-pH mode [47]. This pseudo-capacitive process would also result in a drift of the electrode potential, but its interpretation may be difficult if the relative relaxation of the potential distribution in the oxide space charge and across the Helmholtz double layer is not known [48]. 

The response recorded in many electrochemical experiments is extensively changed by the chemical reactivity of the product of electron transfer. Indeed, the study of chemical reactions of intermediates either adsorbed on the surface or free in the solution close to the electrode surface has become a major application of several techniques, e.g. cyclic voltammetry, rotating ring disc electrodes, spectroelectrochemistry, and double potential step. 

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