Studies On The Electron Transfer Mechanism Of Electrochemical Redox Reaction Of Keggin-type Polyoxometalates Anion

Polyoxometalates (POMs) attract increasing attention worldwide due to their unique electrochemical behavior. It is recognized as one of the most promising green redox catalyst. In this study, the nature of electron transfer of the POMs was studied, and a rationalization model of the electron transfer was proposed. Furthermore, we propose a simple method for the fabrication of POMs modified electrodes. These studies could provide an important theoretical basis for the application of POMs in the fields of catalysis, chemical analysis, medicine and materials. The main results and conclusions are summarized as following:1) The polyoxometalate anions usually have large negative charges. In the electrochemical redox reaction, it has been commonly thought that the energetic barriers of the reduction of POMs come from the electrostatic repulsion and the redox potentials linearly depends on the charges of the POMs ions. By carefully studying the electrochemical behavior of Keggin-type Polyoxometalate PMo₁₂O₄₀^3- and SiMo₁₂O₄₀^4- anion in aqueous and ionic liquid solutions, and relatively LBL modified electrode, it has been found that the redox barrier of POMs can be divided into two parts. One part results from the electrostatic interactions, which depend on the permittivity of the solvents; and another one reflect the energetic barrier for the electron introducing into the antibanding of Mo-O_b of Keggin anion, which are independent from the reaction medium such as the solvent. In this study, the energetic barrier of the first one-electron reduction of Keggin-type Polyoxomolybdate is measured about 110mV.2) PMo₁₂O₄₀^3- anion modified electrodes were prepared by simply immersing the glassy carbon electrode in the ionic liquids solution of Polyoxometalates (POMs). The electrochemical properties of the as-prepared POM-modified glassy carbon electrode were investigated by cyclic voltammetry, which not only displayed a reversible redox electrochemical behavior and high stability in aqueous solution, but also exhibited good electrocatalytic activity toward the reduction of nitrite. The proposed strategy for the fabrication of POM modified electrodes shows remarkable advantages, which should be important for practical applications.