Keggin型铬取代杂多离子PW11O39Cr(Ⅲ)(H2O)4-的电化学性质

 用循环伏安、交流伏安和交流阻抗法详细研究了Keggin型铬取代杂多离子PW₁₁Cr(Ⅲ)O^4-₃₉(PW₁₁Cr) 的电化学性质。循环伏安扫描表明，1.0 mmol·L^-1 PW₁₁Cr的H₃PO₄-HAc-H₃BO₃ 缓冲溶液(pH2.16)在玻碳电极上有三对氧化-还原波，发生在1.30/0.631 V处的准可逆波属于Cr(Ⅲ)/Cr(Ⅴ)电对的双电子氧化-还原响应，而位于-0.553/-0.505 V和-0.782/-0.725 V处的两对可逆波则对应于W-O骨架的双电子还原-氧化响应。PW₁₁Cr三对氧化-还原波的峰电位皆与溶液的pH有关，随着溶液pH的增大，峰电位负移，峰电流降低，阴极和阳极的峰电位差增大，电极过程的可逆性降低。由第一个W O骨架还原波的峰电流与电位扫描速率平方根的关系得到PW₁₁Cr在H₃PO₄-HAc-H₃BO₃ 溶液(pH 2.16)中的扩散系数为4.4×10^-6 cm²·s^-1。交流阻抗谱表明，Cr(Ⅲ)/Cr(Ⅴ)电对的电极过程受异相电荷传递动力学控制，由相角与频率的关系得到其动力学参数k^o 为0.67 cm·s^-1；而W-O骨架的两个电极过程则受扩散控制。PW₁₁Cr的电极过程存在吸附步骤。

The Electrochemical Properties of the Keggin-type Cr(Ⅲ)- Substituted Heteropolyanion PW11O39Cr(Ⅲ)(H2O)4-

Electrochemical properties of the PW₁₁Cr(Ⅲ)O^4-₃₉(PW₁₁Cr) in H₃PO₄-HAc-H₃BO₃ (pH 2.16) buffer were investigated in detail by cyclic voltammetry, AC voltammograms and alternating current impedance analyses. The result of cyclic voltammogram showed that three pairs of redox waves were observed on the glassy carbon (GC) electrode in H₃PO₄-HAc-H₃BO₃ (pH 2.16) buffer solution containing 1.0 mmol・L^-1 PW₁₁Cr. The pair of quasi reversible wave at 1.30/0.631 V belonged to Cr(Ⅴ)/Cr(Ⅲ) two-electron redox, while the two pairs of reversible waved at -0.553/-0.505 V and -0.782/-0.725 V belonged to W-O skeleton two electron redox. When the pH value increased, the peak potential of the three pairs of two electron waves shifted negatively and the peak current decreased, which showed that H⁺ was involved in the electrode process. In addition, the difference of peak potential between anode and cathode for each pair of waves increased, which showed reversibility of electrode process decreased. The diffusion coefficient D_O of PW₁₁Cr calculated from linear relationship of peak current of the first skeleton reduction wave versus square root of potential scan rate was 4.4×10^-6cm²·s^-1 in H₃PO₄-HAc-H₃BO₃ (pH 2.16)buffer. AC impedance of Cr (Ⅲ) was a semicircle without Wahlberg line occurred at high frequency, which showed the anode oxidation process was controlled by heterogeneous charge transfer dynamics. The dynamic parameter k^o of electrode process was calculated from the relationship between phase angle and frequency. AC impedance of PW₁₁Cr keleton reduction revealed the electrode process was controlled by diffusion.