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Electrochemical behavior of dense electrodes for impedancemetric NOx sensors

机译：阻抗式NOx传感器的致密电极的电化学行为

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摘要

NOx (NO and NO2) exhaust gas sensors for diesel powered vehicles have traditionally consisted of porous platinum (Pt) electrodes along with a dense ZrO2 based electrolyte. Advancement in diesel engine technology results in lower NOx emissions. Although Pt is chemically and mechanically tolerant to the extreme exhaust gas environment, it is also a strong catalyst for oxygen reduction, which can interfere with the detection of NOx at concentrations below 100 ppm. Countering this behavior can add to the complexity and cost of the conventional NO x sensor design. Recent studies have shown that dense electrodes are less prone to heterogeneous catalytic oxygen reactions, thereby enabling greater NOx sensitivity. Sensors composed of this novel architecture (i.e., dense electrode and porous electrolyte) are still in an inchoate stage of research. There is particular interest in acquiring greater knowledge of the sensing behavior of non-catalytic dense electrodes as they may offer a lower cost alternative to using Pt electrodes.;This work focuses on the potential of the perovskite, strontium-doped lanthanum manganite (LSM), and LSM based composite materials as NOx sensor electrodes. Perovskite based electrodes are attractive because of their chemical, electrical, and thermal properties. To make LSM based composites three materials of different conductivities were chosen, namely, Au, yttria-stabilized zirconia (YSZ) and strontium-doped lanthanum cobalt ferrite (LSCF). Au was selected for its electronic conductivity, YSZ was chosen because of its ionic conductivity and LSCF was selected as a mixed conductor. LSM-Au, LSM-YSZ and LSM-LSCF composite based NOx sensors were fabricated and analyzed using the impedancemetric method for NOx sensing. The goal was to investigate the electrochemical response, gas cross sensitivity, response rate, and rate-limiting mechanisms due to electrode reactions involving NO, NO2, O2, H2O, and CH4 that impact the NOx sensing response.;From the impedancemetric analysis, it was found that LSM-Au based NO x sensors showed much improved NOx sensitivity along with lower water and CH4 cross-sensitivity. Mixing YSZ and LSCF with LSM did not demonstrate any significant improvement in sensing performance.;Dense gold (Au) is also a promising alternative electrode to Pt, since it does not readily promote O2 reduction and is highly stable under exhaust gas conditions. Yet, the low melting temperature of Au (i.e, 1060 °C) limits the manufacturing feasibility as a NOx sensor electrode. Since Pt electrodes are compatible with high temperature sensor manufacturing processes and Au offers desirable electrochemical sensing behavior Au/Pt twine electrodes were studied as a part of this thesis. The preliminary results showed the Pt component of the Au/Pt twine electrodes did not compromise the NOx sensing capability of Au electrode.
机译：传统上，用于柴油动力车辆的NOx（NO和NO2）废气传感器由多孔铂（Pt）电极以及致密的ZrO2基电解质组成。柴油发动机技术的进步导致NOx排放量降低。尽管Pt在化学和机械上对极端的废气环境具有耐受性，但它还是一种强力的氧气还原催化剂，会干扰浓度低于100 ppm的NOx的检测。应对这种行为会增加传统NOx传感器设计的复杂性和成本。最近的研究表明，致密的电极不易发生异质催化氧反应，从而提高了NOx的敏感性。由这种新颖结构构成的传感器（即致密电极和多孔电解质）仍处于早期研究阶段。特别需要获得对非催化致密电极的传感行为的更多了解，因为它们可以提供使用Pt电极的低成本替代品。这项工作着眼于钙钛矿，锶掺杂镧锰矿（LSM）的潜力，以及基于LSM的复合材料作为NOx传感器电极。基于钙钛矿的电极因其化学，电学和热学性质而具有吸引力。为了制备基于LSM的复合材料，选择了三种电导率不同的材料，即Au，氧化钇稳定的氧化锆（YSZ）和锶掺杂的镧钴铁氧体（LSCF）。选择Au的是电子导电性，选择YSZ是因为其离子导电性，并且选择LSCF作为混合导体。制作了基于LSM-Au，LSM-YSZ和LSM-LSCF复合材料的NOx传感器，并使用阻抗法对NOx进行了分析。目的是研究由于涉及NO，NO2，O2，H2O和CH4的电极反应而影响NOx感应响应的电化​​学响应，气体交叉敏感性，响应速率和限速机制。发现基于LSM-Au的NOx传感器显示出大大提高的NOx敏感性，同时具有较低的水和CH4交叉敏感性。将YSZ和LSCF与LSM混合不会显示任何明显的传感性能改善。致密金（Au）也是Pt的有希望替代电极，因为它不易促进O2还原，并且在废气条件下非常稳定。然而，Au的低熔化温度（即1060℃）限制了作为NOx传感器电极的制造可行性。由于Pt电极可与高温传感器的制造工艺兼容，并且Au提供了理想的电化学传感性能，因此本文研究了Au / Pt麻线电极。初步结果表明，Au / Pt麻线电极的Pt组分不影响Au电极对NOx的感应能力。

著录项

  • 作者

    Pal, Nabamita.;

  • 作者单位

    Louisiana Tech University.;

  • 授予单位 Louisiana Tech University.;
  • 学科 Electrical engineering.;Chemical engineering.;Chemistry.
  • 学位 Ph.D.
  • 年度 2017
  • 页码 139 p.
  • 总页数 139
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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