Metal insertion into phosphonic acid terminated porphyrins immobilized on TiO2 electrodes

In this study an easy access for modification of properties of porphyrin covered TiO2 electrodes by post-assembling metal insertion was investigated. Therefore a new type of phosphonic acid terminated porphyrin was synthesized and immobilized on mesoporous TiO2 electrodes by self-assembling. Surface concentrations in a range of 1.5-3.3 x 10(-8) mol. cm(-2), based on the geometric area, were obtained by two independent techniques, UV-vis and cyclic voltammetry. Co(II), Zn(II), Pd(II) and Mn(III) ions could be inserted into the immobilized porphyrin by exposing the electrode to a boiling solution of metal chloride in methanol. The electrode surface was characterized by UV-vis spectroscopy and cyclic voltammetry before and after metal insertion. The electrocatalytic activity towards the reduction of molecular oxygen in acidic solution was examined, further confirming metal insertion into immobilized porphyrin monolayer.