电化学原位红外光谱系统的构建及其在甘油电催化氧化过程中的应用研究

发布时间：2018-03-28 14:26

本文选题：原位红外光谱　切入点：电氧化　出处：《闽南师范大学》2017年硕士论文

【摘要】：在IS50红外仪上,成功地构建了电化学原位Fourier变换红外光谱系统,并应用电化学循环伏安(CV)、原位红外反射光谱以及时间分辨红外光谱等技术研究了碱性介质中甘油在Pd电极上的电催化氧化过程,着重跟踪分析了甘油电氧化过程生成的中间体和产物,考察了甘油浓度对其电氧化机理的影响,为直接甘油燃料电池的产业化应用提供理论指导。得到的主要结果如下:1、通过对反射附件和红外光路密封的设计和调整,成功地在IS50型红外仪上构建了电化学原位Fourier变换红外光谱装置,实验效果良好。2、CV的研究结果表明:正向电位扫描过程中,随着甘油浓度的增大,甘油氧化峰电流增大,氧化峰电位发生正移,其电催化氧化的反应级数约为0.1787,且负向电流峰明显小于正向过程的电流峰,这可能是由于随着甘油浓度的增大,低电位下甘油解离产生的吸附物种更强烈地吸附在电极表面而引起的。3、碱性介质中甘油在Pd电极上只产生桥式吸附态的CO,而检测不到线性吸附的CO。由于桥式吸附的CO较线性吸附态的CO更容易氧化脱附,上述结果表明:碱性介质中甘油在Pd上发生了解离吸附,其电氧化经历了直接途径和间接途径等两条途径,但毒化作用相对较小。4、电极电位对甘油电氧化行为及其机理有显著的影响。1.0M甘油溶液中,低电位下,甘油电氧化产物主要以桥式吸附的CO和甘油醛为主;而高电位下,甘油电氧化产物主要以CO_2、碳酸根和羟基丙酮酸等甘油不完全氧化的产物为主。5、甘油浓度对甘油电氧化行为及其机理也有显著的影响。甘油浓度对红外谱峰强度有明显的影响,浓度越高,谱峰强度越大;吸附态的CO和产物CO_2的谱峰只出现在高浓度的甘油溶液中,而在低浓度中未检测到;低浓度溶液中,甘油电氧化产物以碳酸盐和甘油酸为主,而高浓度溶液中,以CO_2和甘油部分氧化的产物为主。6、高电位下,甘油酸作为中间体可进一步氧化生成羟基丙酮酸;羟基丙酮酸的生成是可能是通过Eley Rideal机理,由中间体甘油酸与吸附态的OH反应而生成的。7、高电位下,甘油电氧化容易形成CO_2产物,其原因可能是由于随着电位的增大,电极表面吸附态的OH覆盖度增大,有利于甘油与多个吸附态的OH反应而引起的。8、高电位下不同浓度甘油的FTIR谱图,其共同特征是在1585 cm-1附近出现强的谱峰,指示高电位下,各种不同浓度的甘油电氧化均可生成羧酸类化合物。9、电化学原位时间分辨红外光谱进一步证实了上述的结果。10、在实验条件下,没有检测到丙酮酸、丙二酸和丙酮二酸等的生成。11、根据实验结果,在不考虑碳链断裂下,初步提出了碱性介质中甘油在钯电极上可能的电氧化机理。12、由于甘油电氧化过程生成的产物和中间体繁多,在实验条件下有些物种是否存在,仍无法准确认定,有待今后进一步确认。
[Abstract]:The electrochemical in situ Fourier transform infrared spectroscopy system was successfully constructed on the IS50 infrared spectrometer. Electrochemical cyclic voltammetry (CV), in situ infrared reflectance spectroscopy and time resolved infrared spectroscopy were used to study the electrocatalytic oxidation of glycerol on PD electrode in alkaline medium. The intermediates and products produced during the electrooxidation of glycerol were analyzed, and the effect of glycerol concentration on the electrooxidation mechanism was investigated. To provide theoretical guidance for the industrial application of direct glycerol fuel cells. The main results obtained are as follows: 1. Through the design and adjustment of reflective accessories and infrared light path seals, The electrochemical in situ Fourier transform infrared spectrometer was successfully constructed on the IS50 infrared instrument. The experimental results show that the oxidation peak current of glycerol increases with the increase of glycerol concentration in the process of forward potential scanning. The oxidation peak potential shifted positively, and the reaction order of electrocatalytic oxidation was about 0.1787, and the negative current peak was obviously smaller than the current peak of the forward process, which may be due to the increase of glycerol concentration. The adsorption species produced by glycerol dissociation at low potential are more strongly adsorbed on the electrode surface. In alkaline medium, only bridged CO-adsorbed on PD electrode is produced, but the linear adsorption is not detected. Because of bridge-type adsorption, the adsorptive species of glycerol are adsorbed on the electrode surface more strongly. The oxidation desorption of CO is easier than that of linearly adsorbed CO. The above results show that the dissociation and adsorption of glycerol on PD occur in alkaline medium, and the electrooxidation of glycerol has two pathways, such as direct and indirect pathways, etc. However, the toxic effect is relatively small. 4. The electrode potential has a significant effect on the electrooxidation behavior and mechanism of glycerol. In glycerol solution of 1.0 M, the oxidation products of glycerol are mainly bridge adsorbed CO and glyceraldehyde at low potential, while at high potential, the electrooxidation products are mainly bridged adsorbed CO and glyceraldehyde. The main products of glycerol electrooxidation are CO-2, carbonate and hydroxy pyruvate. The concentration of glycerol also has a significant effect on the electrooxidation behavior and mechanism of glycerol, and the concentration of glycerol has a significant effect on the intensity of infrared spectrum peak. The higher the concentration, the greater the intensity of the peak, the peak of adsorbed CO and product CO_2 only appeared in the high concentration of glycerol solution, but not detected in the low concentration solution, in the low concentration solution, the products of glycerol electrooxidation were mainly carbonate and glyceric acid. In high concentration solution, the product of partial oxidation of CO_2 and glycerol is the main product. At high potential, glyceric acid can be further oxidized to hydroxy pyruvate, and the formation of hydroxy pyruvate may be through the mechanism of Eley / Rideal. At high potential, glycerol is easily oxidized to form CO_2 products, which may be due to the increase of the OH coverage of the adsorbed state on the electrode surface with the increase of potential. In favor of the reaction of glycerol with the OH of several adsorbed states, the FTIR spectra of glycerol with different concentrations at high potential have a strong peak near 1585 cm-1, indicating a strong peak at high potential. Carboxylic acid compounds .9 can be produced by electrooxidation of glycerol at various concentrations. The results are further confirmed by electrochemical in situ time-resolved infrared spectroscopy. No pyruvate was detected under experimental conditions. The formation of malonic acid and pyruvic acid. According to the experimental results, the possible electrooxidation mechanism of glycerol on palladium electrode in alkaline medium was proposed. The existence or not of some species under experimental conditions is still impossible to be identified accurately, and further confirmation is needed in the future.
【学位授予单位】：闽南师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O657;O643.3

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