The Nernst equation is one of the two central equations in electrochemistry. It describes the dependency of an electrode’s potential E and the activities a or simplified concentrations c of the redox reaction’s species.
The remaining parameters in the equation are the universal gas constant R, the temperature T, the Faraday constant F, the standard potential of the reaction Ox to Red E0 and the number of transferred electrons per molecule z.
It is more common to use the simplified version:
As a new parameter the formal potential E0′ is introduced, which includes the influence of the activity coefficients.
Important for an electrochemist to understand that this equation works in two ways. If the electrodes potential is changed, the solution in contact with the electrode needs to have the concentration ratio of active species indicated by the Nernst equation. To achieve this an electrochemical reaction needs to take place at the electrode.
More information is available in this article.
In this section the reasons for the three electrode setup of most potentiostats is explained, what the task of each electrode is and what to take into consideration when choosing your counter electrode.