Study of orientation mode of cobalt-porphyrin on the surface of gold electrode by electrocatalytic dioxygen reduction

Three orientation modes of self-assembled monolayers (SAMs) of cobalt-porphyrins on the surface of gold electrode have been prepared and tested in the electroreduction of dioxygen, such as cobalt-5-(4-aminophenyl)-10,15,20-triphenylporphyrin binding covalently to 3-mercaptopropionic acid pre-assembled on gold (Co-ATP-MPA); cobalt-tetra-[p-(3-mercaptopropyloxy)-phenyl]-porphyrin (Co-TMPP) and cobalt-tetraphenyl-porphyrin axially attached with 4-mercaptopyridine SAMs pre-assembled on gold (Co-TPP-4MPY). A cyclic voltammetric investigation was carried out in an attempt to elucidate the net reaction to the dioxygen reduction. These modes were all active in electrocatalytic reduction of dioxygen through a two-electron mechanism with hydrogen peroxide produced. By combining imidazole axial with Co-TPP and the above cobalt-porphyrin SAMs and together with by testing the multilayer cobalt-porphyrin films by reduction dioxygen, the study confirmed that the electrocatalytic properties of metalloporphyrin was directly related with the structure or orientation of porphyrin ring on the surface of the electrodes.

In this paper we prepared three cobalt-porphyrin-overlayered SAMs on gold and combined imidazole axial with Co-TPP to investigate the orientation mode of porphyrin ring by catalytic oxygen reduction. Porphyrin molecules of Co-TPP on 4MPY/SAMs was little parallelly tilted oriented to the gold surface. The porphyrin ring of Co-TPP on Co-TMPP/SAMs was oriented parallelly and on Co-ATP-MPA/SAMs was little perpendicularly tilted oriented on the electrode surface, respectively. Figure optionsDownload as PowerPoint slide