Electrochemical Behavior And Properties Of High Nuclearity Polyoxometalates

Recently, the design and fabrication of chemical modified electrodes based on Polyoxometalates are of great interest owing to not only their fascinating electrochemical behavior and excellent electrochemical properties but also potential applications in catalysis, electronic devices and electrochemical sensors.In this paper, several novel Polyoxometalates such as Keplerates-type, Sandwich-type and Bielefeld-type are synthesized according to the literature methods, and fixed on the electrode by different methods of electrode-modifying. The electrochemical behavior, electrochemical properties,and potential of application were firstly investigated in detail here:1. The electrochemical behavior and properties were systematically studied by cyclic voltammograms of 5μM{Mo132} on the glassy carbon electrode in aqueous and organic solution.The result indicates that the electrode process of 5μM{M0132} in aqueous solution consists of absorption process, electrochemical reaction and protonantion process, which is different from that of the traditional POMs; The different slopes of protonation-65mV/pH,-50.46 mV/pH,-23.85 mV/pH indicate that the types of radical L coordinating and stabilizing the{Mo2} unit inside the capsule actually effects and the capability of combined protons. The different relationship between peak currents and scan rates is attributable to different surface charge density arised from the various acid radical L inside. The electrode process of 5μM{Mo132} in organic solution mostly obeys the rule of homogeneous electrode reaction; the relationship between the reduction peak potentials and acceptor number of organic solvents is nonlinearity, which is opposite to the traditional POMs. The catalytic experiments for substrates demonstrate that the{Mo132} family cluster can catalyze the reduction of IO3-, and the {Mo132}(L=CH3COO-) shows the larger sensitivity 79.16μA/mM and lower limit of detection 0.123mM towards IO3- according to the flow injection analysis. 2.The modified multilayer film based{Mo132} were firstly fabricated on GCE and quartz substrates by Layer-by-Layer methods with chitosan used. The linear relation between the number of layers and absorption value of POMs's characteristic peak was observed by Uv-Vis spectrum measurement. The Cylic Voltammetry indicate that the POMs was well fixed on the surface of electrode and the process of electron-transfer was accelerated comparing to the bare GCE in solution. The positive shift of reduction peak with the increased pH indicates that the pH sensitivity of the chemically modified electrode (CME) is opposite to other POMs based CMEs.3. The{Mo132} saturated in RTIL [BMIM]BF4 was modified on the glass carbon electrode. Cylic voltammetry indicates that the high nuclearity POMs was also well fixed on the surface of electrode by the media of RTIL, and the electron-transfer rate is faster compared to the bulk solution.The result of several cycles experiment was carried by CV shows the good stability of electrode.4. The{Mo154} derived family whose inner surface modified by the organic ligands Glu-was firstly carried out by Cylic voltammetry in order to find the relationship between the modified inner face and CV behavior.The large peak separation and the large ratio of current indicates the inner surface modification by amino acid remarkably changes the electrode process: electron-trasfer becomes slower and reversibility gets less.5. A bulk-modified carbon paste electrode based on the mixed-valence iron molybdophosphate [(C10H8N2)3FeⅡ]3FeⅡ2FeⅢ2Mov24(H2P04)8(HP04)4 (PO4)4O48 (OH)12(H2O)4·12H2O was firstly carried out by electrochemical cylic voltammetry in order to find the law of the electrode process and the electrocatalytic properties. By varying the parameters such as scan rate and pH,we found that the two electron-transfer process obeys different rule. The electrocatalysis toward idote indicates that the modified electrode shows good catalytic properties for idote reduction.