YSZ基氧传感器电极制备及响应原理研究
文献类型：学位论文
| 作者 | 夏朝阳 |
| 学位类别 | 博士 |
| 答辩日期 | 2012-06-05 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 卢旭晨 |
| 关键词 | YSZ基氧传感器 电极 工作温度 响应时间 |
| 其他题名 | Investigation of electrode fabrication and sensing principles for YSZ based oxygen sensor |
| 学位专业 | 化学工程 |
| 中文摘要 | YSZ基氧传感器可以监控各种燃烧反应的进程，因此已经被广泛的应用于环保、材料、化工、能源、宇航等领域。降低YSZ基氧传感器的工作温度和缩短传感器的响应时间是目前该领域的主要发展趋势。本文围绕着降低YSZ基氧传感器工作温度和缩短传感器响应时间这两个基本目标，在对国内外关于YSZ基氧传感器研究现状及发展进行综述的基础上，系统地研究了YSZ基氧传感器的响应原理和电极制备过程。论文主要开展了以下几个方面的研究工作：（1）利用线性极化和交流阻抗等方法研究了电极焙烧温度、电极组成和电极催化剂载量对Pt/YSZ体系中的氧还原反应机理和电极极化性能的影响。结果表明，优化电极焙烧温度、电极组成和电极催化剂载量对Pt/YSZ体系中的氧还原反应机理影响不大，但有利于增加Pt/YSZ体系电极中三相反应界面长度，从而提高电极极化性能。 Pt/YSZ体系中的氧还原反应过程由氧分子的气相扩散、氧分子在Pt电极上的吸附和解离、氧原子在Pt电极表面的扩散、氧原子在三相界面处的还原等步骤组成。当气相扩散的影响可忽略时，在较高温度下（≥700℃），氧原子在Pt电极表面的扩散为电极反应的速控步骤；而在较低温度下（≤600℃），氧分子在Pt电极表面的吸附解离为电极反应的速控步骤；温度为600℃-700℃的区间可以看作是过渡区间，此时电极反应由“氧原子在Pt电极表面的扩散”和“氧分子在Pt电极表面的吸附解离”联合控制。（2）研究了浓差电池型YSZ基氧传感器和极限电流型YSZ基氧传感器在不同条件下的暂态和稳态响应性能。浓差电池型YSZ基氧传感器的工作温度和响应时间与传感器电极的催化活性密切相关；电极对氧还原反应的催化活性越高，则传感器的工作温度越低、响应时间越小。极限电流型YSZ基氧传感器的响应时间随传感器工作温度的增加而减小，与检测气体中的氧浓度大小无关。（3）根据极限电流型YSZ基氧传感器的暂态响应特征，提出了一种暂态响应模型。模型计算得到的结果表明，当扩散层中Knudsen扩散占主导地位时，传感器的暂态输出电流可用下述公式表示： 传感器的响应时间与检测气体中的氧浓度、气体总压强以及传感器扩散障的有效截面积无关，但随扩散层中孔径以及传感器工作温度的增加而减小，随扩散障厚度增加而增加。该模型能较好的解释极限电流型YSZ基氧传感器响应时间随工作条件的变化规律，且能推广应用到扩散层中普通分子扩散占主导地位时的情况。 (4) 提出了一种Pt-YSZ复合电极制备方法，该制备方法由复合物粉末制备和复合电极制备两个步骤组成。Pt-YSZ复合物粉末制备以炭黑、氯铂酸、硝酸锆和硝酸钇为基本原料，制得的复合物中仅含有Pt相以及YSZ相，其中Pt颗粒的粒径约为25-35nm，而YSZ颗粒的粒径约为5-10nm。由Pt-YSZ复合物粉末制得的Pt-YSZ复合电极在不同温度下均表现出优异的极化性能, 如在700℃，Pt-YSZ复合电极的极化电阻仅为1.0Ω·cm2。将Pt-YSZ复合电极引入浓差电池型氧传感器，可将传感器的工作温度降低到约380℃，将传感器在400℃时的响应时间缩短到约5s。（5）研究了电化学活化对浓差电池型氧传感器响应性能的影响。结果表明，电化学活化可大幅提高浓差电池型氧传感器的响应性能，包括降低传感器的工作温度和缩短传感器的响应时间。电化学活化的核心措施为：在传感器的检测电极端和参比电极端分别通O2和H2，使传感器成为“燃料电池，然后在较高温度下，使“燃料电池”放电一段时间。电化学活化对所有以Pt为电极催化剂、以YSZ为电解质材料的浓差电池型氧传感器的响应性能均具有不同程度的激励作用。根据电化学活化前后传感器阻抗的变化情况，分析了电化学活化的内在机理。电极中含氧物质（OCS）浓度的减少、电解质离子电导率的增加以及电解质元件和电极元件的接触面积变大可能是导致传感器响应性能在活化后大幅提升的主要原因。 |
| 英文摘要 | YSZ based oxygen sensors can monitor and control the process of various kinds of combustion reactions, therefore have been widely used in environmental protection, chemical industry, materials, energy, aerospace and other fields. Reducing sensors’ working temperature and response time are now the major development trends for YSZ based oxygen sensors. In this paper, in order to reduce the working temperature and the response time of the YSZ based oxygen sensors, we have systematically investigated the electrode preparation technology and the sensing principles of YSZ based oxygen sensor on the basis of thoroughly collecting domestic and abroad related literatures. The following several aspects of research works have been done in this paper: (1) The influences of sintering temperature, electrode composition and catalyst loading onto the electrode performance and reaction mechanism in Pt/YSZ system have been thoroughly investigated with linear polarization and AC impedance method. The optimization of sintering temperature, electrode composition and catalyst loading is beneficial to the improvement of the length of the three-phase-boundary (TPB) and the polarization performance of the electrode, but has no influences onto the oxygen reduction mechanism in Pt/YSZ system. Oxygen reduction reaction in Pt/YSZ system includes such steps as gas diffusion, adsorption and dissociation of oxygen molecular on Pt electrode, surface diffusion of oxygen atom on Pt electrode, reduction of oxygen atom at the three-phase-boundary and so on. As the influences of gas diffusion can be neglected , in higher temperature region(≥700℃), surface diffusion of oxygen atom on Pt electrode is the rate controlling step; while in lower temperature region(≤600℃), the dissociative adsorption of oxygen molecular is the rate controlling step; when the operating temperature is between 600℃ and 700℃, the reaction rate is controlled by both the step of “surface diffusion of oxygen atom on Pt electrode” and the step of “dissociative adsorption of oxygen molecular”. (2) The stable and transient sensing performances of concentration cell type and limiting current type YSZ based oxygen sensors have been studied. The working temperature and the response time of the concentration cell type oxygen sensors are closely related with electrode’s catalytic activity for oxygen reduction. The higher the catalytic activity of the electrode, the lower the working temperature and the response time of the sensor. The response time of the limiting current oxygen sensor decreases with sensor’s working temperature, but is independent with oxygen concentration in the detected gas. (3) A transient response model has been put forward on the basis of the experimental response characteristics of the limiting current oxygen sensor. The calculation results of the model show that when Knudsen diffusion is dominated in the diffusion barrier, sensor’s output current can be expressed with the following formula: Sensor’s response time is independent on the oxygen concentration in the detected gas, the gas pressure and the effective cross section area of the diffusion barrier, but decreases with sensor’s working temperature and pore radius in the diffusion barrier, and increases with the thickness of the diffusion barrier. The transient response model can be used to explain the variation principles of sensor’s response time with the working conditions, and also can be extended to explain the sensing principles of sensors with ordinary molecular diffusion. (4)A new preparation method for Pt-YSZ composite electrode has been put forward. The method includes the steps of the pareapration of Pt-YSZ composite and the preparation of electrode. Nano-structured Pt-YSZ composite has been prepared with carbon black, H2PtCl6, Zr(NO3)4•6H2O and Y(NO3)3•3 H2O. The prepared composite only comprise Pt phase and YSZ phase, and particle sizes of Pt and YSZ are 25-35nm and 5-10nm, respectively. The Pt-YSZ composite electrode prepared with this composite exhibits excellent polarization performances at different temperatures, e.g. 1.0Ω·cm2 at 700℃. The introduction of the Pt-YSZ composite electrode into the concentration cell type sensor can reduce sensor’s working temperature to be about 380℃, and reduce sensor’s response time to be about 5s at 400℃. (5) The influences of electrochemical activation onto performances of YSZ based oxygen sensors have been studied, the results show that senors’ performances can be greatly improved by electrochemical activation, including reducing sensor’s working temperature and improving sensor’s response rate. During the electrochemical activation, the YSZ based sensor was firstly employed as a “fuel cell” by feeding O2 and H2 into sensor’s sensing electrode and reference electrode, respectively; then the “fuel cell” was discharged for some time. The electrochemical activation is valid for all YSZ based oxygen sensors which employing Pt as electrode catalyst, and YSZ as electrolyte. On the basis of the experimental results and the literature reports, the reasons that have led to “promotion effect” of the electrochemical activation have been analyzed. The decrease of the oxygen containing species (OCS) at the electrode, the enhancement of the ion conductivities in the electrolyte and the increase of the contact area between the electrode component and the electrolyte component may be main reasons that have resulted in the “promotion effects” of the electrochemical activation onto the concentration cell type oxygen sensor |
| 公开日期 | 2013-09-25 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1787]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 夏朝阳. YSZ基氧传感器电极制备及响应原理研究[D]. 北京. 中国科学院研究生院. 2012. |
入库方式： OAI收割
来源：过程工程研究所
浏览0
下载0
收藏0
其他版本
除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。