Fabrication And Characterization Of Rare Earth Metal Hexacyanoferrate Modified Electrodes

This thesis investigated systematically electrochemical preparation and characteristics of three rare earth metal hexacyanoferrates, samarium hexacyanoferrate (SmHCF), lanthanum hexacyanoferrate (LaHCF) and dysprosium hexacyanoferrate (DyHCF), modified glassy carbon electrode. The differences among the three rare earth metal hexacyanoferrates were compared in terms of the electrochemical formation process and electrochemical characteristics. SmHCF was also prepared chemically and characterized by several spectroscopic techniques. The solid-state electrochemistry of . SmHCF mechanically attached to the surface of graphite electrode were studied in both aqueous and non-aqueous media, the solvent effects on the solid-state electrochemistry of SmHCF were studied by cyclic voltammetry. The main research woks are described as follows:1. SmHCF was prepared by electrochemically deposited on the surface of a glassy carbon electrode with a potential cycling procedure. The cyclic voltammogram of SmHCF exhibits a pair of well-defined redox peaks with the formal potential of 191 mV (vs. SCE) at a scan rate of 100 mV/s in 0.2 mol/L NaCl solution and the redox peak currents increase linearly with the scan rate up to 100 mV/s. The effects of the concentration of supporting electrolyte on the electrochemical characteristics of SmHCF and the transport behavior of K~+, Na~+ and Li~+ counter ions through the ion channel of SmHCF were studied by voltammetry. The different electrochemical behaviors of SmHCF in various cation-containing supporting electrolytes were investigated by cyclic voltammetry and scanning electron microscope (SEM). The SmHCF was also characterized by FTIR technique. The SmHCF/GC electrode showed the electrocatalytic activity towards the electrochemical reaction of DA.2. LaHCF, which was prepared electrochemically by the similar method of formation SmHCF, was characterized by scanning electron microscope (SEM), FTIR and XPS etc. techniques. The cyclic voltatric results indicated that LaHCF exhibited a pair of well-defined redox peaks with the formal potential of 208 mV (vs. SCE) at a scan rate of 100 mV/s in 0.2 mol/L NaCl solution and the redox peak currents increase linearly with the square root of the scan rate up to 1000 mV/s,3. DyHCF was prepared by a procedure of electrochemically deposited on the surface of a glassy carbon electrode with a potential cycling procedure. The differences among SmHCF, LaHCF and DyHCF were compared in terms of formation process and electrochemical characteristics. The cyclic voltammtric results showed that DyHCF exhibits two pair of redox peaks with the formal potential of +210 and +362 mV (vs. SCE), respectively, at a scan rate of 10 mV/s in 0.2 mol/L KC1 solution. The SEM images of DyHCF indicated that there were two kinds of particles with different size and shape formed. The two kinds of particles occurred the electrochemical reaction at different redox potential corresponding to the two couple of the redox reaction in its cyclic voltammograms.4. SmHCF was prepared chemically and characterized using techniques of FTIR, thermogravimetric analysis (TGA), X-ray powder diffraction, UV-Vis spectrometry and X-ray photoelectron spectroscopy (XPS) etc. techniques. The cyclic voltammetric behavior of SmHCF mechanically attached to the surface of graphite electrode was well defined and exhibited a pair of redox peaks with the formal potential of 180.5 mV (vs. SCE) at a scan rate of 100 mV/s in 0.2 mol/L NaCl solution and the redox peak currents increased linearly with the square root of the scan rates up to as high as 1000 mV/s. The effects of the concentration of supporting electrolyte on the electrochemical characteristics of SmHCF and the transport behavior of K+, Na+ and Li+ counter ions through the ion channel of SmHCF were studied by voltammetry.5. The electrochemical characteristics of SmHCF mechanically attached to the surface of graphite electrode was studied in organic solvents, such as tetrahydrofuran, acetone and Af,iV-dimethylformamide etc., using cyclic voltammetry and ac impedance. The cyclic voltammograms of SmHCF in organic solvent were well defined andexhibited a pair of redox peaks, which corresponded to the redox reaction of the couple of Fe(II)/Fe(III) in SmHCF, and the redox reaction is accompanied by insertion of a counter-cation into the SmHCF during the reduction and its exclusion upon oxidation. The redox potentials increased linearly with the increase of the dielectric constant of solvents. The transport behavior of K+, Na+ and Li+ counter-cations through the ion channel of SmHCF were also studied by voltammetry. The results suggested that the electrochemical activity of SmHCF in aqueous medium is much higher than that in non-aqueous medium.