In this work, ITO electrodes have been modified by means of the oxidative electrodeposition of two different cobalt porphyrins, CoTSPP and CoTMPyP, and the composition of such deposits have been studied by visible and reflection-FTIR spectroscopies. The data indicate that the porphyrin deposits are formed by a mixture of cobalt hydroxides, beta-Co(OH)(2) and alpha-Co(OH)(2), and the porphyrin ring as radical. Moreover, the porphyrin electrodeposits absorb molecular oxygen as peroxo species (O-2(2-)), which has been detected in the films by IR spectroscopy. and which acts as a bridge between Co atoms (Co-O-O-Co). Also, monolayers containing a viologen derivative have been transferred onto the porphyrin-MIE (MIE, modified ITO electrode) by using the LB technique. and its redox process has been investigated. The results show an excellent mediator character of both cobalt electrodeposits throughout the viologen redox processes. Furthermore, the Co-porphyrin electrodeposits store atmospheric oxygen in a ratio proportional to the deposited porphyrin amount. This oxygen can be totally released from the porphyrin film via the electrocatalytic action of the viologen monolayer on top. (C) 2008 Elsevier Ltd. All rights reserved.