抗坏血酸在PPy-HEImTfa/Pt电极上的电催化氧化及其机理

以铂为基底电极,在1-乙基咪唑三氟乙酸盐(HEImTfa)离子液体中电化学合成导电聚吡咯(PPy),制得PPy-HEImTfa/Pt电极;采用循环伏安法研究了PPy-HEImTfa/Pt电极对抗坏血酸的电催化氧化性能.结果表明:PPy-HEImTfa/Pt电极对0.1mo·lL-1抗坏血酸具有较高的电催化氧化活性,与相同条件下硫酸溶液中在铂表面修饰的聚吡咯(PPy-H2SO4/Pt)电极和裸铂电极相比,其氧化峰电位分别降低了0.10和0.19V,氧化峰电流分别增加了3.0和3.6mA.同时采用原位傅里叶变换红外(insitu FTIR)光谱技术对抗坏血酸在PPy-HEImTfa/Pt电极上的电氧化机理进行了研究,结果表明:抗坏血酸在PPy-HEImTfa/Pt电极上首先被氧化为脱氢抗坏血酸,在水溶液中脱氢抗坏血酸迅速发生水合作用形成水合脱氢抗坏血酸,它进一步水解并发生内酯开环反应生成2,3-二酮古洛糖酸;在较高电位下,部分抗坏血酸最终被氧化成CO2.

Electrocatalytic Oxidation of Ascorbic Acid on a PPy-HEImTfa/Pt Electrode and Its Mechanism

A platinum electrode was electrochemically modified with polypyrrole (PPy) in the ionic liquid 1-ethylimidazolium trifluoroacetate (HEImTfa) to produce a modified electrode (PPy-HEImTfa/Pt). Its electrocatalytic performance toward the oxidation of ascorbic acid (0.1 mol·L^-1) was investigated by cyclic voltammetry. Compared with a bare Pt electrode and a PPy-H₂SO₄/Pt electrode, which was prepared in a solution of H₂SO₄, the peak potentials for ascorbic acid oxidation on the PPy-HEImTfa/Pt electrode decreased by 0.19 and 0.10 V, respectively. Additionally, the peak currents increased by 3.6 and 3.0 mA, respectively. Therefore, the electrocatalytic activity of the PPy-HEImTfa/Pt electrode for the oxidation of ascorbic acid was far better than that of the other systems. In situ Fourier transform infrared (In situ FTIR) spectroscopy results showed that the ascorbic acid was firstly oxidized to dehydroascorbic acid on the PPy-HEImTfa/Pt electrode and then underwent a fast hydration reaction to give hydrated dehydroascorbic acid in the aqueous solution. The hydrated dehydroascorbic acid then underwent further hydrolysis to form 2,3-diketogulonic acid by a ring opening reaction. Finally, a part of ascorbic acid was oxidized to CO₂ at high potentials.