Keggin型缺位磷钨杂多阴离子的电化学性质及电催化还原过氧化氢

Electrochemical Properties of the Keggin-type Lacunary Heteropolytungstate Anion and Its Electrocatalysis for H_2O_2 Reduction

循环伏安实验显示,缺位磷钨杂多阴离子PW11O37-9的酸性水溶液在玻碳(GC)电极上有两对可逆的还原-氧化波.第一对波的电荷迁移数为1.4,有2个质子参与反应;第二对波的电荷迁移数为1.0,参加电极反应的质子数为1.根据峰电流与电位扫描速率平方根的关系得到PW11O37-9在0.1mol·L-1NaOAc+HOAc溶液中的扩散系数Do为3.54×10-6cm2·s-1.交流伏安和交流阻抗实验表明,PW11O37-9的电极过程包含吸附和脱附步骤,第一对波的电荷迁移阻抗较大,第二对波的较小,对应的交换电流密度i0分别为4.6×10-5和6.7×10-4A·cm-2.PW11O37-9电极过程的可逆性及其缺位特性使它对H2O2的还原有显著的电催化作用,因此有望用于有机物的氧化和降解.同时,还提出了一个相关的电催化机理.

Cyclic voltammograms indicated that two reversible redox waves were observed on the glassy carbon （GC） electrode in acidic aqueous solution containing PW11O39^7-. The first wave involves in 1.4 electron transfer and two protons during electrode reaction, and one electron and one proton are for the second wave. Diffusion coefficient Do of PW11O39^7- calculated from linear relationship of peak current versus square root of potential scan rate is 3.54 × 10^-6 cm^2·s^-1 in a solution of 0.1 mol·L^-1 NaOAc＋HOAc （pH 3.5）. Alternating current （AC） voltammetry and AC impedance revealed that an adsorption of PW11O39^7- on the electrode surface occurred before electron transfer, which caused larger electron transfer impedance in the first wave than in the second wave. The exchange current density i0 corresponding to the first wave and the second wave is 4.6× 10^-5 and 6.7 × 10^-4 A·cm^-2, respectively. A reversible electrochemical property and a lacunary feature of PW11O39^7- make it electrocatalyze efficiently reduction of H2O2 in acidic aqueous solution. The system of PW11O39^7-/H2O2 thus represents a possible application to electrocatalytic oxidation of organic substrates. Also a novel catalytic mechanism was proposed.