Estimando a área ativa eletroquímica: Revisitando um conceito básico em eletroquímica

The well-known electrochemical probe Fe(CN)63-/Fe(CN)64- is widely used for estimating the electrochemical active area of electrodes modified with carbon nanotubes, conductive polymers, enzymes, etc. In this study, we used the platinum electrode, smooth or platinized with different roughness factors, to demonstrate that such redox couple fail to respond to a surface roughness variation. We determined the roughness factors of the Pt surfaces by AFM images, which yielded values between 2.72 and 29.5, and by the hydrogen monolayer desorption in steady-state cyclicvoltammetry experiments performed in acid medium (nearly the same values). They were then compared with those provided by peak current in voltammetry or chronoamperometry with Fe(CN)63-/Fe(CN)64- which all yielded values nearly to one. Such comparison demonstrates that the electrochemical behavior of the redox probe is an outer sphere reaction with a quite small interaction with the electrode surface, thus not being suitable to be related with active areas.