Nernstian Conditions—How it All Works

In cyclic voltammetry, both the oxidation and reduction of the metal complex (called the analyte from now on) will take place in one electrochemical cell. This cell houses the analyte solution as well as three electrodes, the working electrode, the auxiliary electrode and the reference electrode. Electron transfer to and from the metal complex takes place at the working electrode surface (Fig. A.2.2) and does so in response to an applied potential, /iapp, at the electrode surface. During the experiment, current develops at the surface as a result of the movement of analyte to and from the electrode as the system strives to maintain the appropriate concentration ratio (0, through electron transfer, as specified by the Nemst equation. 

Note then that E of equation (A.2.1) is a known quantity (i.e., we dial in a specified /iappi). Through the processes of mass transfer and diffusion of the analyte, Q will be properly maintained. The establishment of Q in response to varying wl will be reflected in the current (e-flow to and from the working electrode) response. A cyclic voltammogram is simply the current measured as a function of the applied potential (/iappi)- From the voltammogram we can extract what we are after, E° for the [Fe3+(CN)5F] -/ [Fe2+ (CN)5F](n+1) half reaction. 

Equation (A.2.5) indicates that the establishment of the Nemstian concentrations (0 at the electrode requires that mass transfer of analyte to and from the electrode be controlled and limited by diffusion due to a concentration difference only, called complete concentration polarization. Once the analyte reaches the electrode surface, the rate of electron transfer must be rapid (i.e., mass transfer not electron transfer limits the rate of 

There are a couple of ways to maximize for the condition of complete concentration polarization experimentally  

The solution must not be stirred. Stirring disturbs mass transfer of the analyte by diffusion and also the concentration ratio at the electrode surface. 

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