Anodic Electrodeposition Mechanism of Manganese-Cobalt Oxides for Electrochemical Capacitors

• Main Authors: Po-Yao Chuang, 莊博堯
• Other Authors: Chi-Chang Hu
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/22322287975974954263

碩士 === 國立中正大學 === 化學工程研究所 === 92 === In this research, the phenomena of electrodeposition and electrochemical properties of anodic deposited (Mn+Co)OxnH2O were investigated. The characteristics of oxides were examined by the scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron paramagnetic resonance (EPR), UV/Vis spectroscopy and Fourier transform infrared spectroscopy (FTIR). In the first part, a relatively higher amount of Co ion in the solution was used in order to enhance the content of Co in the (Mn+Co)OxnH2O deposits. There was no obvious difference for the electrochemical characteristics of various oxides when the pH value of plating solution was changed from 2.5 to 7.0. However, the morphology and Co content were slightly affected by the pH value of plating solutions. In addition, the (Mn+Co)OxnH2O deposits were not very stable in 0.1 M Na2SO4 when electrode potentials were negative than ca. 0 V while its stability was enhanced by the introduction of Co oxide. The second part is to investigate the effect of the introduction of acetate ions on the electrodeposition of (Mn+Co)OxnH2O, and to discuss the reason of this effect. According to the experimental results, the overpotential of anodic deposition would be lowered and the growth rate would be increased when acetate ions were introduced. Besides, the Co content in the (Mn+Co)OxnH2O deposit was increased with the amount of acetate ions, which showed that the acetate ions promote the deposition rate of Co oxide in comparison with that of Mn oxide. It was found in the inorganic coordination chemistry that the overpotential of anodic deposition was lowered by the formation of metal-acetate complex. The stability of trivalent complex ions is much higher than that of divalent ones, and thus it is easily oxidized. The third part continues the investigation on the growth rate and mechanism of electroplating manganese oxide under different conditions of Mn and acetate ions. According to the electrochemical kinetics and material analysis results, [MnII(OAc)n(H2O)6-n]2-n could be formed after ligands are substituted for acetate ions. In the next step, the complex ion [MnII(OAc)n(H2O)6-n]2-n is oxidized as [MnIII(OAc)n(H2O)6-n]3-n by outer-sphere reaction. Finally, the trivalent complex ion adsorbs onto the substrate to form [MnIII(OAc)2(H2O)2]+3ads , which is oxidized further to form Mn2O3 or MnO2 as a result of the application of oxidation potentials.