Polarization Curve of a Single Electrode

When positive overpotential is applied, the current is considered to be positive, and when negative overpotential is applied, the current is negative. When the dependence of the current vs. overpotential is plotted, it is called the polarization curve. A polarization curve of the Cu +(aq)/Cu+(aq) single redox electrode in high concentrated HCl(aq) is shown in Figme 6.3. 

FIGURE 6.3 Polarization curve of a single Cu +(aq)/Cu (aq) redox electrode taken at ambient temperature and pressure, initial concentration of CuCl2(aq) and CuCl(aq) of 0.1 mol kg , and concentration of HCl(aq) of 8 mol kg .  

As a reminder, the anodic polarization is always related to an oxidation reaction [e.g., Cu+(aq) Cu +(aq) + e ] and cathodic polarization related to the reduction reaction [e.g., Cu +(aq) -t- e Cu +(aq)]. As can be seen from the polarization curve of the Cu +(aq)/Cu (aq) electrode, the current-potential can be highly nonlinear. Our further goal will be to find out where the shape of the polarization curve is coming from. 

When we consider a single electrode, the current density, j (usually in A cm ), can be more useful than just current. 

The difference between the applied potential, and the equilibrium potential, E, is called the overpotential of single electrode, q = E - E, which can be either positive or negative. 

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