**New Advances in Fundamental Research in Electrochemical Cells**

**1** 

**A Review of Non-Cottrellian Diffusion** 

The past few decades have seen a massive and continued interest in studying electrochemical processes at artificially structured electrodes. As is well known, the rate of redox reactions taking place at an electrode depends on both the mass transport towards the electrode surface and kinetics of electron transfer at the electrode surface. Three modes of mass transport can be considered in electrochemical cells: diffusion, migration and convection. The diffusional mass transport is the movement of molecules along a concentration gradient, from an area of high concentration to an area of low concentration. The migrational mass transport is observed only in the case of ions and occurs in the presence of a potential gradient. Convectional mass transport occurs in flowing solutions at

In 1902 Cottrell derived his landmark equation describing the diffusion current, *I*, flowing to a planar, uniformly accessible and smooth electrode of surface area, *A*, large enough not to be seriously affected by the edge effect, in contact with a semi-infinite layer of electrolyte solution containing a uniform concentration, *cO*, of reagent reacting reversibily and being present as a minor component with an excess supporting electrolyte under unstirred

> *O <sup>D</sup> I nFAc*

where *n* is the number of electrons entering the redox reaction, *F* is the Faraday constant, *D*

It has long been known that the geometry, surface structure and choice of substrate material of an electrode have profound effects on the electrochemical response obtained. It is also understood that the electrochemical response of an electrode is strongly dependent on its size, and that the mass transport in electrochemical cell is affected by the electrode surface roughness which is generally irregular in both the atomic and geometric scales. Moreover, the instant rapid development in nanotechnology stimulates novel approaches in the preparation of artificially structured electrodes. This review seeks to condense information on the reasons giving rise or contributing to the non-Cottrellian diffusion towards micro-

rotating disk electrodes or at the dropping mercury electrode.

conditions, during the potential-step experiment (Cottrell, 1902)

is the diffusion coefficient, and *t* is time.

and nano structured electrodes.

**1. Introduction** 

**Towards Micro- and** 

Katarína Gmucová

*Slovak Republic* 

**Nano-Structured Electrodes** 

*Institute of Physics, Slovak Academy of Sciences* 

*<sup>t</sup>* , (1)
