电子顺磁共振现场研究多孔电极表面自由基的电化学行为

本文建立了一套ESR-EC联合现场测试多孔电极表面顺磁粒子的方法, 并对多孔碳电极上吸附的醌化合物在电极上还原时的自由基中间产物的ESR进行了研究。首次获得了固体电极表面自由基有hfs的高分辨ESR信号。研究结果表明,醌在RB碳电极表面有多种行为各异的吸附态。在测量电位范围内, 观察到了四种吸附醌化合物是通过自由基过程还原的。其中两种通过可旋转单键吸附到碳电极表面, 给出有hfs的ESR谱; 另两种表现为各向异性ESR信号,可能是通过多个位置吸附在碳表面。

SIMULTANEOUS ESR-ELECTROCHEMICAL MEASUREMENT OF SURFACE RADICALS ON POROUS ELECTRODES

A technique was developed for simultaneous ESR-electrochemical measurements of surface radicals on porous electrodes. The ESR-electroehemical cell consists of a Teflon bonded carbon electrode(WE) and a porous Ag electrode(CE)packed parallelly with a separator in between. A grain of Ag/Ag_2O is placed in the separator,serving as the reference electrode. The electrolyte contained in the cell is no more than 4μl, confining the dielectrical loss to an tolerable level. Using the cell we have been able to obtain the ESR signals of surface radicals generated by electroreduction for a quinone-modified RB carbon electrode. To our best knowledge, this is the first report on ESR spectra with hfs for species adsorbed on electrode surfaces. It is deduced from the ESR data that on the electrode surface there are several absorbed radicals with different electrochemical behaviors. In the potantial range studied, there seem to be four types of surface quinoid compounds which can be reduced according to a radical mechanism. Two of them exhibiting hfs are probably surface species linked to the carbon surface by a singl bond, (possibly through a surface group) while the other two which give the anisotropic spectra are assumed to be multi-site absorbed.