Electrochemical behaviour of some redox couples at layer-by-layer assembled poly(diallyl dimethylammonium)/reduced graphene oxide electrodes

The electrochemical behaviour of three redox couples, namely ferri/ferrocyanide, dopamine and 1,4-naphtoquinone is investigated at the surface of ITO substrates modified with layer-by-layer assembled poly(diallyl dimethylammonium) hydrochloride (PDAC) and reduced graphene oxide (RGO) films. The study with ITO modified with PDAC/RGO films is performed by cyclic voltammetry and electrochemical impedance spectroscopy. Regardless of the type of electrode (bare ITO and PDAC/RGO-modified), the electrochemical behaviour of all three redox couples is diffusion controlled. Despite that, modification of the ITO substrate with the PDAC/RGO film decreases the electron transfer rate constant and makes more irreversible the ferri/ferrocyanide redox interconversion. In fact, it evidences that ferri/ferrocyanide is not a classical outer-sphere redox probe. On the other hand, the PDAC/RGO film HAS an inverse and positive effect on dopamine and 1,4-naphtoquinone redox reactions. Further, impedance spectroscopy data reveal that the PDAC/RGO film reduces by about 9 orders of magnitude the charge transfer resistance with these organic redox couples. As a main conclusion of the study, it is found that the right matching between RGO energy levels and the reduction potential of the redox species is not enough to provide electrocatalytic activity. The surface chemistry of RGO-based electrode plays an equivalent role for the electrodes' response.