铂电极过钝化区域中硫化钠电催化氧化的时空自组织

发布时间：2018-04-06 23:06

本文选题：过钝化　切入点：电催化氧化　出处：《中国矿业大学》2017年硕士论文

【摘要】：本文运用循环伏安法和恒电位法对铂电极过钝化区域中硫化钠电催化氧化动力学进行研究,并对反应过程中的串联外阻效应、硫化钠浓度效应和氯离子效应进行探讨;用CCD摄像机实时监测电极表面,观察到丰富的时空斑图;利用高效液相色谱法检测反应过程中产生的物种,提出振荡机理;利用KarhunenLoeve分解分析时空斑图。首先讨论了串联外阻和硫化钠浓度对电化学振荡的影响。双电层电势作为自催化变量促进铂氧化物的生成,产生负微分阻抗,串联外阻促进双电层电势增大加强体系的正反馈,硫离子作为消耗铂氧化物的物种是体系的负反馈。当体系中正负反馈作用有滞后环,即硫化钠浓度为1.50 mol/L,串联外阻为300?时,在过钝化区域观察到大幅振荡与小幅振荡共存的HN-NDR振荡,大幅振荡对应硫沉积与溶解的协同化。氯离子的引入对体系的不稳定性特征有显著影响。一方面,氯离子作为金属电极化学吸附物种引入一个新的正反馈;另一方面,高浓度氯离子对铂氧化物的溶解带来体系的负反馈。当氯离子浓度较低时,氯离子引起的吸附正反馈效应较小,对过钝化区域的振荡影响不大;随着氯离子浓度的增大,氯离子的化学吸附增强,与硫离子消耗铂氧化物的负反馈相互作用,加强过钝化区域的振荡;当氯离子浓度过大时,氯离子溶解铂氧化物的负反馈为主,正反馈逐渐消失,使得振荡衰减,直至消失。除协同化现象外,在过钝化区域的小幅振荡区域还能观察到螺旋波、闪烁波、前沿波和条纹移动斑图。用恒电位法研究体系过钝化区域的振荡演化过程,振荡电势区域变宽且负移,在小幅振荡区域观察到呼吸波结构,在小幅与大幅振荡共存时观察到呼吸波与协同化的交替。用Karhunen-Loeve(KL)分解时空斑图得到呼吸波有多种模式,能量的百分比较低,而呼吸波与协同化的交替波可以通过一种主要的模式表示。
[Abstract]:In this paper, the kinetics of electrocatalytic oxidation of sodium sulfide in the region of platinum electrode overpassivation was studied by cyclic voltammetry and potentiostatic method. The series resistance effect, concentration effect of sodium sulfide and chloride ion effect in the reaction process were discussed.The CCD camera was used to monitor the electrode surface in real time, and abundant spatiotemporal patterns were observed. The species produced in the reaction were detected by high performance liquid chromatography (HPLC), and the oscillation mechanism was proposed. The KarhunenLoeve decomposition was used to analyze the spatio-temporal pattern.The effects of series resistance and sodium sulfide concentration on electrochemical oscillation were discussed.The double layer potential is used as the autocatalytic variable to promote the formation of platinum oxide, resulting in negative differential impedance. The series resistance promotes the increase of the potential of the double layer to increase the positive feedback of the enhanced system. The sulfur ion as the species consuming platinum oxide is the negative feedback of the system.When the positive and negative feedback in the system has hysteresis ring, that is, the concentration of sodium sulfide is 1.50 mol / L, the series resistance is 300?HN-NDR oscillations coexisting with large oscillations and small oscillations were observed in the over-passivation region, and the large oscillations corresponded to the synergism of sulfur deposition and dissolution.The introduction of chloride ions has a significant effect on the instability characteristics of the system.On the one hand, chloride ion as a chemisorbed species of metal electrode introduces a new positive feedback; on the other hand, the solution of platinum oxide with high concentration of chloride ion brings negative feedback to the system.When the concentration of chloride ion is low, the positive feedback effect of adsorption induced by chlorine ion is small, and the oscillation of the over-passivating region is not affected, and the chemisorption of chloride ion increases with the increase of chloride ion concentration.When the concentration of chlorine ion is too high, the negative feedback of dissolved platinum oxide is dominant, and the positive feedback gradually disappears, which makes the oscillation attenuate until it disappears.In addition to synergetic phenomena, spiral waves, scintillation waves, front waves and fringe movementpatterns can also be observed in the small oscillation region of the passivation region.The oscillatory evolution of the over-passivation region of the system is studied by means of the potentiostatic method. The oscillatory potential region becomes wider and negative. The structure of the respiratory wave is observed in the small oscillation region, and the alternations between the respiration wave and the synergism are observed at the coexistence of the small and large oscillations.Using Karhunen-Loevegne KL) to decompose the spatiotemporal pattern, it is found that there are many modes of respiratory wave, and the percentage of energy is low, and the alternate wave of respiration wave and synergetic wave can be expressed by one main mode.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O646.54

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