Self-assembled monolayers of a thiol-derivatized porphyrin on gold electrode: Film formation and electrocatalytic dioxygen reaction

A novel thiol-derivative porphyrin (5-[p-(mercaptopropyloxy)-phenyl]-10,15,20-triphenylporphine shortly as H2MPTPP) and its cobalt(II) complex (MPTPPCo(II) ) have been successfully immobilized on gold surface by self-assembly technique. The surface coverages (Γ) of MPTPPCo(II) was calculated to be 4.86 x 10-11 mol/cm2 by investigating the reductive desorption of S-Au which demonstrated that the monolayer was not packed well and had many interval pinholes. The gold electrodes modified with MPTPPCo(II) and MPTPPCo(II) + thiolglycolic acid show good activity to the two-electron catalytic reduction of O2 to H2O2. Nanoscopic structures gained by atomic force microscopy (AFM) not only provided further evidence for the successful formation and immobilization of such monolayers, but also elucidated the potential reasons for the electrocatalytic activity of such monolayers to dissolved oxygen, which was proved to be very interesting and significant that the mixed monolayer could enhance the electroreduction and proceed more readily for the electroreduction of O2