Prepration Of Well-oriented Metalloporphyrine Modified Electrodes And Their Electrocatalytic Activities Toword Oxygen Reduction

According to the different coordination abilities between metalloporphyrin in different redox states, an electrochemical enhanced self-assembling process was developed to prepare the metalloporphyrin modified electrode(CoTMPP/4Mpy/Au(E)) in this thesis. And the electrocatalytic activity of the CoTMPP/4Mpy/Au(E) electrode toward oxygen reduction was investigated. The main resuls are outlined as follows.(1) Tetraphenylporphyrin and Cobalt(II) meso-tetraphenylporphyrin were successfully synthesized. The products proved to be the correct products by UV-Vis, IR, H1NMR characterizations.(2) The coordinating ability of metalloporphyrin in different redox states can be qualitatively and quantitatively studied by electrochemical methods. By studying the shifts of the potential waves in a voltammogram of metalloporphyrin in different medias (with or without axial ligands), we knew that the affinity of axial ligands such as DMF and pyridine towards the metalloporphyrin is much higher when the metal center is Co(III) or Fe (II) rather than Co (II) or Fe (III). The speed of the coordinating reaction between pyridine and Co (III) is higher than that between pyridine and Fe (II).(3) By controlling the potential to oxidize the Co-porphyrin from CoTMPP to CoTMPP+, Co-porphyrin could be more easily to self-assemble onto the 4-mercaptopyridine modified gold electrode surface to form a CoTMPP/4Mpy/Au electrode. The electrochemical enhanced self-assembling process was monitored by the electrochemical quartz crystal microbalance (EQCM). The formation of the CoTMPP film was confirmed by Raman spectrum. Results suggested that the present process is a less time consumption process to prepare the well oriented five-ligands coordinated CoTMPP monolayer modified electrode.(4) The formation of the CoTMPP film was also confirmed by the electrocatalytic activity of the CoTMPP/4Mpy/Au(E) electrode toward oxygen reduction. Results in cyclic voltammetry study demonstrated that, due to the effect of the fifth axial pyridine ligand, the CoTMPP/4Mpy/Au(E) electrode showed a higher electrocatalytic activity compared with the other CoTMPP modified electrodes.(5) Electrocatalytic activity of the CoTMPP/4Mpy/Au(E) electrode toward oxygen reduction was further investigated by rotating ring-disk voltammetry (RRDE). Results demonstrated on CoTMPP/4Mpy/Au electrode i) H2O2 was generated, which is consistent with the results in the previous reports about electrocatalytic reduction of O2 at a monomeric cobalt porphyrin; ii) larger rate constant has been determined compared with that reported for the other self-assembling Co-porphyrin monolayer modified electrode.(6) The additional ligands in the oxygen reduction system would compete with oxygen molecule as the sixth-ligand and impact the reduction activity of the CoTMPP/4MPy/Au modified electrode.(7) The CoTMPP/Bridge/Au modified electrodes were constructed with different molecular as bridges. The electrocatalytic activities toward oxygen redution of the different electrodes have been studied. Compared with 2-mercaptopyridine, 1,4-benzenedimethanethiol, ethanethiol, the Co-porphyrin modified electrode with 4-mercaptopyridine ligand showed outstanding electrocatalytic activity.