V(Ⅳ)/V(Ⅴ)电对在石墨毡电极上的反应机理

Reaction mechanism of V(Ⅳ)/ V(Ⅴ) redox couple at graphite felt electrode

采用循环伏安、极化曲线和交流阻抗三种电化学实验方法研究了V(Ⅳ)/V(Ⅴ)电对在石墨毡电极上的反应机理及其可能的速度控制步骤。研究结果表明:V(Ⅳ)/V(Ⅴ)电对在石墨毡电极上的反应属准可逆过程,且氧化过程包含有后置化学转化步骤;理论计算得到了电化学步骤和后置化学转化过程分别为控制步骤时的Tafel斜率值为0.12和0.06,实验得到的Tafel斜率值为0.124,表明电极氧化过程受电化学过程控制;不同极化电位下的交流阻抗图谱拟合结果表明,电化学反应阻抗值远大于其他阻抗值,说明电化学反应可能是电极反应的控制步骤,与实验得到的极化曲线分析结果相一致。

The V（Ⅳ）/V（Ⅴ） reaction mechanism was investigated on a graphite felt electrode by means of cyclic voltammetry, polarization curve and impedance spectroscopies. Cyclic voltammetry analysis indicates that V（Ⅳ）/V（Ⅴ） redox reaction at graphite felt electrode is quasi reversible. A certain chemical reaction step is suspected to follow the electron transfer step of this reaction. The Tafel slope value （0. 124） obtained from the polarization curve agrees well with theoretical value （0. 12） when the electron transfer step is supposed to be the rate determining step. Impedance spectroscopies at various potentials were studied and simulated by equivalent circuits. The impedance value of the electron transfer step modified is greatly higher than the others, which shows that the electron transfer step is the rate determining step. This further confirms the conclusion obtained by polarization curve test.