The Mechanism of ~(13)CO_(ad)/~(12)CO Isotope Exchange at Pt Electrode,a Combined Study by Electrochemical in-situ Infrared Spectroscopy and Dipole-dipole Coupling Analysis
- 2010年第16卷 
本文依据偶极耦合理论和相干势近似方法,合理选择粗糙电极上吸附分子的频率分布函数、一氧化碳(CO)吸附层的结构参数以及偶极耦合作用常数,对13CO/12CO同位素取代过程记录的红外光谱进行了拟合.研究发现,只有在拟合过程中引入低频CO分子优先取代,就可成功地模拟整个同位素取代过程的红外光谱随表面吸附的13CO/12CO组分的变化,并由此提出了吸附驱动的脱附机理,COad的脱附不是热激发脱附,而是吸附到表面的CO分子为其邻近位置COad的脱附提供能量.伸缩振动频率较低的COad处于台阶或缺陷位等较开阔的位置(尽管其吸附能较高),周围有较大的空间,利于来自溶液的CO分子的吸附,因此在台阶或缺陷位优先发生同位素的取代.In this contribution,we have analyzed the IR spectra of saturated CO adlayer at rough Pt film electrode as a function of fractional surface coverage of 13COad/12COad recorded during 13COad /12CO isotope exchange process according to dipole-dipole coupling theory and coherent potential approximation. By properly choosing the parameters of adlayer structure and dipole-dipole coupling interaction under coherent potential approximation, we demonstrated that we can successfully simulate the IR spectra as a function of the surface coverage of CO adlayer at rough Pt film electrodes by assuming that COad molecules with low C—O stretching frequencies are dis- placed preferentially during the 13COad/12CO isotope exchange. From this,we proposed that 13COad/12CO isotope exchange proceeds via adsorption assisted desorption mechanism,i. e. ,the adsorption energy released from the incoming COad(to be adsorbed) provides the activation energy for its neighboring COad molecules to be desorbed. The fact that those COad adsorbs at defects or steps (with low C—O stretching frequencies,although with slightly higher adsorption energy than those at terrace sites) are preferentially displaced,comparing to those COad species sitting at terraces,is due to the fact that the defects sites are more open and have much larger free space for the incoming molecules to be adsorbed.