Actually, in my opinion, using the redox complex is not a good method to evaluate the electroactive surface area of electrode with nano-structure because the mass transfer of the redox complex as well as the electrostatic interaction between the electrode surface and the redox complex should not be ignored. On the other hand, by measuring  the non-faradic charging current of the electrode, one may calculate the electrochemical surface area roughly.   [G.M. Swain, T. Kuwana Anal. Chem., 63 (1991), pp. 517-519] 

Hope this helps.

Actually, in my opinion, using the redox complex is not a good method to evaluate the electroactive surface area of electrode with nano-structure because the mass transfer of the redox complex as well as the electrostatic interaction between the electrode surface and the redox complex should not be ignored. On the other hand, by measuring  the non-faradic charging current of the electrode, one may calculate the electrochemical surface area roughly.   [G.M. Swain, T. Kuwana Anal. Chem., 63 (1991), pp. 517-519] 

Hope this helps.

As far I know, the method of measuring electrochemical area is not very simple. There is very few literature on this. The earlier paper on this method is I guess carried out for Pt.

I will share one of my colleagues' paper shortly (Just accepted, N doped Carbon). As your material is CNT, that paper might be helpful.

Artur Braun, thanks but- why 20mF/cm2?.