Chemical sensors for gaseous species using oxide semiconductors

本研究旨在验证化学传感器高选择性、高灵敏度测定复杂混合气体中化学物种浓度的可能性。提出的传感器用于测量当施加稳态交流热脉冲时，由于目标气体的化学吸附而引起的表面电导率的变化，或由于表面反应的变化而在不对称电池构型之间建立的混合电势。在本研究中，由于NCCO与NOx具有极高的反应活性，本文主要研究了NCCO的表面反应/吸附行为。用直流极化和交流阻抗法研究了Au(PO_2，P_2O/P_2O_2)/Nd_2O_3掺杂CeO_2/NCCO(P‘O_2，P’NO/P‘NO_2)固体电化学电池中NO_2^2=NO_2 2E’(反应A)和O^&lt；2-&gt；=1/O_2 2E‘(反应B)的电荷转移反应，并与…反应进行了比较进一步讨论了电池混合电势增强和电极/电解液界面电荷转移反应速率的机理。此外，还进行了类似的实验，以估算在YSZ电解液与Au、Pt和NiO电极组成的电池上NO2/O2=NO2反应的总速率(反应C)作为比较。结果表明，混合电势在450℃左右出现极大值，在此温度范围内催化效果出现极大值。通过分析直流极化结果的Tafel图，由交换电流密度估算了电荷转移反应的速率。通过讨论反应A和B的反应速率对NO_2和O_2的依赖关系，作者得出结论：速率决定步骤位于NCCO表面上NO_2和O_2的竞争吸附和表面电荷转移反应之间，混合电势是由反应A和反应B之间的反应速率不同引起的。此外，还对可能的传感器部件、工艺和制造技术进行了探讨。金属/氧化物界面的电子电荷转移和电子输运性质及其基于候选材料的电子结构的解释。作为结论，证实了利用气体物种在特定氧化物上的化学吸附速率和活化能的差异来制作化学传感器的可能性。较少

The present research project has been conducted to verify the possibility of a novel approach for chemical sensors to determine the concentration of chemical species in complex gas mixtures with high selectivity and sensitivity. The sensor proposed is to measure either change in the surface conductivity by the chemisorption of a target gas or the mixed potential build up between asymmetric cell configuration due to the change in the surface reactions, when steady-state ac heat pulse is applied. In the present study, Nd_<2-x>Ce_xCuO_4(NCCO)was mainly investigated for the surface reaction/adsorption behavior, due to the extraordinarily high reactivity with NOx. In the present study, the solid-state electrochemical cell written as Au (PO_2, PNO/PNO_2)/Nd_2O_3-doped CeO_2/NCCO(P'O_2, P'NO/P'NO_2)was examined by a dc polarization and ac impedance measurements, in order to characterize the charge transfer reactions of NO+O^2=NO_2+2e' (Reaction A) and O^<2->=1/O_2+2e'(Reaction B), and the dis … More cussion on the the mechanism was made for the build-up of the mixed potential across the cell and the reaction rate of the charge transfer at the electrode/electrolyte interface. In addition, similar experiments were made to estimate the overall rate of the reaction NO+1/O_2=NO_2(Reaction C)on the cells composed of YSZ electrolyte with Au, Pt and NiO electrodes for comparison. The present results indicated that the maximum values of the mixed potential were observed at around 450 C and that the catalytic effects showed maxima at this temperature range. The rate of the charge transfer reaction was estimated from the exchange current density determined by analyzing the Tafel plot on the results of dc polarization. From the discussion on the NO_2 and O_2 dependencies of the rates of reactions A and B, the author concluded that the rate determinant step lies midway between the the competing adsorption of NO_2 and O_2 on the NCCO surface and the the charge transfer reaction at the surface, it is also concluded that the mixed potential is caused by the difference in the reaction rates between reaction A an4 B.Also examined are further survey of the possible candidates for the sensor component, the processing and fabrication technique, the electronic charge transfer across the metal/oxide interface and electronic transport properties and their interpretation based on the electronic structure of the candidate materials.As a conclusion, it has been confirmed the possibility of the chemical sensor utilizing the difference in the chemisorption rate of gas species on a specific oxide and the activation energy. Less