Reversible binding of molecular dioxygen to CoTSPP electrodeposited films from aqueous basic media

The oxidative electrodeposition of CoTSPP (tetrakis 4-sulfonatophenyl Co porphyrin) on ITO electrode from NaOH 0.1 M aqueous solution has been studied, and cyclic voltammetry, spectroelectrochemistry, UV–Vis and reflection-FTIR spectroscopies have been used to analyze the composition of such a film. Our experimental data lead us to propose that electrodeposited CoTSPP films are composed by (OH)2Co(III)O2- and the porphyrin ring as radical cation. Futhermore, the Co(OH)2 species is formed from the reduction of the film in oxygen absence. However, the properties of these films do not match with those corresponding to Co(II) hydroxide films, since the electrodeposited CoTSPP is able to absorb atmospheric oxygen to form Co(III)O2- species. Moreover, in oxygen absence, the Co(II) may interact with the porphyrin radical cation to regenerate CoTSPP.