Dear Elsadig,

Chlorine evolution has a standard potential of 1.36 V vs. NHE - that would be roughly 1.11 V vs. SCE, assuming that you're using a saturated calomel electrode.

The standard potential of hydrogen evolution is pH dependent, meaning that its value is (0 - 0.059 * pH) V vs. NHE, or (-0.244 - 0.059 * pH) V vs. saturated SCE.

Since one reaction is pH dependent while the other one is not, their equilibrium potentials will shift relative to each other when the pH is changed - this will happen regardless of the reference you're using. You should keep this in mind if both of them play a role in your experiment. As an example, when you're working in a solution of pH 7, using an SCE as reference, chlorine evolution is thermodynamically allowed at potentials > 1.11 V, while hydrogen evolution is allowed below (-0.244- 7 * 0.059) V = -0.657 V.

I'm not sure what you mean with 'cathodic disbondment of coating'. Hope the rest helps though.

Best, Jan