草酸在铅电极上电催化还原过程的in situ FTIRS研究

采用电化学原位傅里叶变换红外反射光谱(electrochemical in situ fourier transform infrared reflection spectroscopy,in situ FTIRS)研究了草酸在铅电极上电催化还原过程。 多步电位阶跃FTIRS(MSFTIRS)和时间分辨FTIRS(TRFTIRS)的结果表明：当研究电位为-0.70 V(vs. SCE)时，即可明显检测到乙醛酸生成；研究电位为-0.85 V时,电极表面累积生成乙醛酸的量达到最大值。 随着电位的负移，生成的乙醛酸的量减少。 同时在-0.95 V时即可明显检测到乙醛酸进一步被还原,生成的乙醇酸在1 093 cm-1 附近为—CH₂OH的CO伸缩振动吸收。 当研究电位为-1.50 V时，电极表面的乙醛酸几乎都被还原成乙醇酸。 另外，随着电位的负移，并没有检测到其他新物种的出现，表明乙醇酸在电极表面不会进一步发生还原反应。 研究电位为-0.75 V的原位时间分辨红外反射光谱显示反应产物乙醛酸在1 750 cm-1 左右CO的伸缩振动吸收谱峰的左右积分强度随时间线性增加；而研究电位在-1.60 V原位时间分辨红外反射光谱还观察到乙醇酸在1 093 cm-1附近—CH₂OH的C—O伸缩振动吸收。 电化学原位红外反射光谱技术有利于对反应中各物种官能团振动吸收的检测,为草酸电催化还原反应机理提供直接实验依据。

Investigation of Electrocatalytic Reduction of Oxalic Acid on Pb Electrode through in situ FTIR Reflection Spectroscopy

Electrochemical in situ Fourier transform infrared reflection spectroscopy was used in the investigation of electrocatalytic reduction of oxalic acid on Pb electrode. The multi-step potential FTIRS and time-resolved FTIRS procedures were used in the present study. The results of MSFTIRS demonstrate that glyoxylic acid could be detected below -0.70 V. The quantity of glyoxylic acid cumulated on Pb electrode surface reaches a maximum at -0.85 V, then it decreases as electrode potential is further decreased. Meanwhile the C-O stretching vibration of -CH2OH group at around 1 093 cm(-1) could be detected at -0.95 V. It was revealed that all the produced glyoxylic acid may be reduced further into glycolic acid at potentials below -1.50 V. Furthermore, none of other new substances could be detected at more negative potentials, which indicated that glycolic acid could not be further reduced. The results of time resolved Fourier transform infrared reflection spectroscopy at -0.75 V indicate that the integrated intensity of the IR band at about 1 750 cm(-1) for the stretching vibration of C=O (-CHO) linearly increases with the reaction time. The TRFTIR spectra at -1.60 V show that not only the IR absorption of C=O (HOOC-CHO) stretching is observed, but also that of C-O (-CH2OH) stretching at about 1 093 cm(-1) can be seen. The current study demonstrated that electrochemical in situ Fourier transform infrared reflection spectroscopy is a powerful tool for the study of electrosynthesis processes, and for the detection of each species involved in the reaction at molecular level. The results are of significance to understand the reaction mechanism of electrocatalytic reduction of oxalic acid.