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A Study on TiO2-based Hydrogen Gas Sensors

  • 김인호 (아주대학교 일반대학원)

초록/요약

A semiconductor-type gas sensor made of metal oxides was studied. Semiconductor-based gas sensors can detect various gases up to low concentrations. First, we reviewed the overall technical and industrial aspects of metal oxide gas sensors. Next, we investigated and analyzed catalytic chemistry and electrophysical sensing mechanisms for metal oxide semiconductors such as oxide surface adsorption of gases, energy band controlling and sensitization of catalysts to detect gases. Meanwhile, literature reviews were performed on noble metal doped TiO2 based gas sensors, and MWCNT (multi-wall carbon nano tube)-TiO2 gas sensors, respectively, which are the subject of the detailed research. A total of 4 researchers were studied on each of these subtopics in the form of experiments, analysis, and results/discussions. The results of the study on them are as follows. A low-power micro gas sensor platform was designed, manufactured through a MEMS manufacturing process, and the study was conducted on the design, manufacture, and evaluation of micro hydrogen gas sensors by applying TiO2 thin films and Pd catalyzed metal films as hydrogen gas detection materials. The Pd-TiO2 thin film gas detection material was placed on the MEMS (Micro-Electrical Mechanical System) device by a sputtering process, and stable polycrystalline phase was formed and PdO catalytic activity was confirmed through 550℃ heat treatment. The 3.1nm thick PdO-TiO2 thin film showed excellent hydrogen detection characteristics, showed excellent sensitivity and good selectivity to target gases at an optimal operating temperature of about 270℃ (3.5 mW), and showed the fastest response characteristics of about 3 seconds at about 225℃ (3.0 mW). Regardless of the manufacturing method, the MWCNT (Multi-Wall Carbon Nano Tube)-TiO2 sensing material showed lower operating temperature and wider sensing range characteristics compared to pure TiO2. Fabrication of the MWCNT-TiO2 sensing film used two methods of deposition and paste application. In the case of MWCNT-TiO2 deposit film, since a thin film of TiO2 is deposited on the surface of MWCNT as if it were a coating, the gas element is manufactured while maintaining the wide specific surface area characteristics of MWCNT, which seems to show hydrogen reactivity in a wide concentration range. In the case of MWCNT-TiO2 paste film, MWCNTs are dispersed among TiO2 nano-powders, and MWCNTs diffuse hydrogen deeper inside the sensing material, making it possible to measure hydrogen concentrations more widely. However, in terms of operating temperature characteristics, the MWCNT-TiO2 paste sensor showed optimized sensitivity at lower temperatures, so lower power consumption can be expected. In addition, since the detection characteristics of a wide range (0.01-100%) of hydrogen concentrations have been maintained even below 175 ℃, it is expected that the operating temperature of 150 ℃ or less specified in the stationary hydrogen sensor requirements can be met. As a result of selective hydrogen reaction characterization with a MWCNT-TiO2 paste-based sensor, it showed high hydrogen selectivity compared to pure TiO2 thin films. In the case of carbon monoxide gas, there was no significant difference from TiO2 thin films, but in the case of methane gas, the sensitivity differed by about 5 times. This appears to be due to the exposure of the MWCNT to the surface, and it is believed to be due to the p-type semiconductor properties of the MWCNT. Although the MWCNT-TiO2 deposit film sensor operates at relatively high temperatures, the detection limit for low-concentration hydrogen is lower than that of the MWCNT-TiO2 paste thick film type. In addition, a more linear hydrogen sensitivity result was obtained when measuring a wide range of hydrogen concentrations. However, in terms of reaction speed and recovery speed, it showed unfavorable characteristics. In particular, in the case of recovery speed, it took about 3 minutes based on T10, and it took about 5 ~ 10 minutes to fully recover the hydrogen reaction. The sensing mechanism was analyzed as improving the absorption/desorption characteristics of MWCNT, the smooth channel role of electronic conduction, and p-n junction effects contributed to excellent sensitivity and fast response in MWCNT-TiO2 paste-based sensors. Keywords: gas sensor, metal oxide, catalyst, toxic gas, MWCNT

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목차

Chapter 1. Introduction 1
1.1 Background for Research 1
1.2 Principle of Metal Oxide-based Hydrogen Gas Sensors 25
Chapter 2. Literature Review 38
2.1 Noble Metal Doped TiO2-based Gas Sensors 38
2.2 MWCNT-TiO2 Gas Sensors 49
Chapter 3. Micro-hydrogen Gas Sensor using Pd-TiO2 thin film 57
3.1 Experimental 57
3.2 Characterization of sensing films 66
3.3 Results and discussions 71
3.4 Summary 83
Chapter 4. Hydrogen Gas Sensor of MWCNT -TiO2 with Wide Range Detection 86
4.1 Experimental 86
4.2 Analysis of sensing films 93
4.3 Results and discussions 97
4.4 Summary 116
Chapter 5. Conclusion 120
5.1 Summary of research 120
5.2 Future research directions 121
References 123
국문초록 138

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