Charge transfer at electrostatically assembled tetraruthenated porphyrin modified electrodes

Molecular interfaces constituted by electrostatically assembled tetraruthenated cobaltporphyrin (Co(TRP)) and tetrasulphonated zincporphyrin (Zn(TPPS)) multi-bilayer films, have been recently exploited for the development of sensors and electrochemical devices. In this work, their conducting properties were investigated by means of cyclic and rotating disk voltammetry, and by impedance spectroscopy. The films exhibited an unusually high conductivity, which increased further when the potential approached the redox potential of the Ru(III/II) couple. This behavior is reflected in a very low heterogeneous charge transfer resistance, leading to Nyquist diagrams dominated by or exhibiting solely a wide Warburg region. The kinetics of a previously reported analytical application involving heterogeneous charge transfer from nitrite ions to the porphyrin film interface was carefully examined. According to this study, the limiting step for the nitrite oxidation is the heterogeneous charge transfer to the interfacial Ru(III) complexes, with k=2.7×103 dm3 mol−1 s−1.