2.7 Activation Polarization [2/2]

1. Current Density: Activation polarization increases with current density i, in accordance with the equation            h_a = ± b_a Log (i/i_o)

2. Materials: Materials: Activation polarization varies from one metal to another. At any given current density i,    h_Pb ^> h_Fe and h_Cu ^> h_Pb

3. Surface Roughness: Activation polarization is high on a smooth shining surface.

4. Temperature: Increased temperature decrease polarization since i_o increases with increasing temperature.

5. Pressure: Hydrogen over-voltage increases rapidly on decreasing pressure.

6. pH: Hydrogen over-voltage increases first and then decreases with increasing pH.

7. Agitation: It has no effect on activation polarization

8. Adsorption of ions: The hydrogen over-voltage is decreased by adsorption of anions and increased by adsorption of cations.