The Study Of Saturated And Trisubstituted Keggin Polyoxometalates: Electrochemical And Electrocatalytic Properties

Keggin-type polyoxometalates can undergo reversible and stepwise,multielectron-transfer reactions. Their very rich redox chemistry makes them suitable forelectrode modification and electrocatalysis.In this paper，we chose a saturated Keggin polyoxometalate [CoMo₁₂O₄₀]₆and atrisubstituted Keggin-type polyoxometalate [α-SiW₉Fe₃（H₂O）₃O₃₇]^7-, investigating theirelectrochemical and electrocatalytic properties.1. A chemically modified electrode based on the immobilization of molybdocobaltate （Ⅱ）polyoxometalate [CoMo₁₂O₄₀]₆(abbr. CoMo₁₂) in carbon nanotubes-chitosan（CNTs-chitosan） composite film was fabricated by one step self-assembly technique. TheCNTs-chitosan composite film provides a high active area and good conduction pathway, andenhances the adsorptive capability of CoMo₁₂molecules on the GCE. The electrochemicalbehavior of the CoMo₁₂/CNTs–chitosan/GCE including scan rate and pH dependence wasstudied in detail. The apparent surface area （A）, the surface coverage （Γ_C） and the electrontransfer rate constant （k_s） were evaluated. Furthermore, cyclic voltammetry demonstrate thatthe CoMo₁₂/CNTs-chitosan/GCE has good electrocatalytic activities for the reduction of NO₂^-and IO₃^-anions in acidic aqueous solution.2. The electrochemical behavior of tri-iron-substituted Keggin-type polyoxometalate,[α-SiW₉Fe₃（H₂O）₃O₃₇]^7-, has been studied in acid buffer solutions. Electrochemistryinvestigations revealed that the complex is stable from pH1to pH7in solution andrepresentative electrochemical behavior is described at pH5. The reduction wave of the FeIIIcenters is well separated from the redox one of WVIcenters. The dependence of the formalpotentials of the anion on pH and ionic strength is interpreted as the competition betweenprotonation and ion-pairing of the reduced forms of the couples. Notable efficiencyelectrocatalytic of this polyoxometalate is exemplified by the reduction of H₂O₂and S₂O₈^2-.3. The electrocatalytic behavior of Keggin-type polyoxometalate,[CoW₁₂O₄₀]^6-, has beenstudied in acid solutions. The cyclic voltammetry demonstrate that the [CoW₁₂O₄₀]^6-hasfeeble electrocatalytic activities for the oxidation of Tyrosine in acidic aqueous solution.