Linear Diffusion at a Planar Electrode

To discuss these two aspects let us consider the usual electrode process  

According to Fick s first law, the flux of Ox is proportional to the concentration gradient of Ox along the direction of propagation  

The constant of proportionality, D0x, is defined as the diffusion coefficient of the species Ox. The units of the diffusion coefficients are mi 2 s-1. The negative sign is conventional. 

As the reduction process Ox — Red proceeds, the species Ox, flowing through the plane x at the time t, reaches the electrode surface (x = 0) and instantaneously disappears to generate the species Red, which in turn will cross the plane x in the opposite direction. This means that  

Since the amount of species Ox reaching the electrode [or, 7ox(0 0] will generate a current, the intensity of which is proportional to the number of electrons exchanged with time (Section 2.3)  

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Linear Diffusion at a Planar Electrode. Commonly, in order to deduce the mathematical relationships that govern the diffusion of an electroactive species towards the electrode, one considers an electron transfer process taking place at a planar electrode, in an unstirred solution, so to make active only the diffusive motion of the redox-active species in a direction perpendicular to the electrode surface, Figure 18. 

It must be noted that the above relationship is derived from linear diffusion at a planar electrode. In the case of a spherical electrode of radius, r0, the above relationship becomes ... 

Voltammetry Based on Linear Diffusion at a Planar Electrode... 

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