Integration of microcatalysts on thin membrane for thermoelectric gas sensor devices
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Integration of microcatalysts on thin membrane for thermoelectric gas sensor devices Yeongsoo Choi, Woosuck Shin, Kazuki Tajima, Noriya Izu, Ichiro Matsubara, Norimitsu Murayama National Institute of Advanced Industrial Science and Technology, Nagoya 463-8560, Japan, ABSTRACT Dispenser technique was employed to integrate the Pt loaded on alumina (Pt/alumina) micro-catalysts on thin membrane of micro-thermoelectric hydrogen sensor (µ-THS). The µ-THS with Pt loaded alumina showed higher sensing performance than bulk-type THS with Pt thin film prepared by RF sputtering method. For the µ-THS with Pt/alumina catalyst, its voltage signal was 7.3 mV for hydrogen concentration of 1 % in dry air at catalyst temperature of 100 °C. In the case of the bulk-type THS with Pt thin film catalysts, the voltage signal was 0.33 mV under the same condition. INTRODUCTION Micro-thermoelectric hydrogen sensor (µ-THS) is one of the promising candidates for hydrogen leak alarm system because of its simple structure, its reliable working principle, and its sensing performance for wide-range of hydrogen concentrations. We have reported sensing properties of bulk-type THS, previously [1-4]. The thin films of Pt and SiGe were used as a catalyst and a thermoelectric layer, respectively. In the THS, the integration of the catalyst is very important to make a sensor of high efficiency. In particular, the catalytic properties such as Pt grain size, thickness, and surface structure are closely related to the high sensing performance. Furthermore, the thick-film type ceramic catalysts have several advantages such as high sensitivity and long-term stability. In this present work, micro-THS with single membrane was used to investigate the sensing property because its power consumption was greatly reduced by the micro-heater in the membrane compared to the bulk-type THS or micro-type THS with two membranes [5]. The ceramic thick-film with Pt loaded on alumina (Pt/alumina) was used as a catalyst. As a paste, the Pt/alumina was deposited on the membrane in the micro-THS by a dispenser technique. This technique has the advantages of no mask necessary, precise positioning, and non-contacting. The purpose in this work is to investigate the sensing property of micro-THS with Pt/alumina catalyst for the hydrogen. EXPERIMETAL Pt loaded on alumina (Pt/alumina) catalyst was used in this work. The Pt/alumina catalyst was prepared by impregnation of a commercial alumina support with an aqueous solution of platinum (IV) chloride pentahydrate. The Pt content in the Pt/alumina catalysts was 10 wt%. The slurry was kept under stirring at 100 °C for 30 min and dried at 120 °C for 2 h in air. The dried precursor was calcined to the firing temperature of 300 °C for 2 h. The precursor was mixed with organic vehicle to make ceramic pastes. The organic vehicle was a conventional dispersant, a blend of terpineol and ethyl cellulose. A millimeter size drop of the paste was deposited on the
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membrane of the micro-THS by a dispenser N2 gas system with CAD-Robot o
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