Two-Way Electron Transfer Across an Interface

An easy way to illustrate this is in terms of the two ions of a redox couple, for example Fe and Fe . When in contact with an electrode, the ion with the higher positive charge upon it (and therefore, compared with the atom, having lost a greater number of electrons), the ferric ion, tends to receive electrons from the electronic conductor and become a ferrous ion. 

Such electron transport at the interface, where the electron leaves the electron conductor and goes to the solution, causes a cathodic electron 

FIGURE 5. Two-way traffic of electron from the ion to the electrode and also from the electrode to the ion. 

In some presentations in electrochemical books, the cathodic current is represented by the symbol i, on top of which is an arrow going to the right, and the anodic current by the symbol i with an arrow going to the left. Thus, what one measures on the ammeter, outside the actual electrochemical system in which this two-way track is occurring, is a net current, the difference of the rate of electron transfer in one direction and the opposite direction. 

that which is measured in the outer circuit by the ammeter can be itself net cathodic or net anodic current. In the first case what is meant is that the rate of electrons leaving the electrode for the solution is greater than the rate of electrons leaving the solution for the electrode but in the case of a net anodic current, the electrons leaving the solution for the electrode are greater in rate than the electrons leaving the electrode for the solution. 

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