(Sensor Division Outstanding Achievement Award Address) Development of Gas Sensors for Safety and Health by Employing Various Sensor Technology

Abstract

In our laboratory, numeral efforts have been directed to improving sensing properties of various kinds of gas sensors, which are based on the different sensing principles, capable of using for our safety and health. The following four topics will be delivered in my presentation. Meso- and Marco-Porous Structural Controlled Metal Oxides for Semiconductor Gas Sensors1) To improve the sensing performance of semiconductor metal oxide gas sensors, strict design and control of meso- and macro-porous structure of sensor materials are of primary importance, i.e. controlling of diffusivity of target gases in the sensing layer toward the position of sensor electrodes, which is the most sensitive region of the sensors, in addition to controlling of catalytic activities of sensor materials. We have used various kinds of surfactants and polymethylmethacrylate microspheres with different sizes to control meso- and macro-porous structure of metal oxides, respectively (see Fig. 1). Examples for the improvement of H2 and NO2 sensing properties by porous structural control will be reported. TiO2-Based Diode-Type H2 Gas Sensors Operable both in Air and in N2 2) For future popularization of hydrogen-powered vehicles, household fuel-cell cogeneration systems and etc., development of more sensitive and selective H2 sensors than commercial ones is of primally importance. We have so far demonstrated that diode-type gas sensors using noble-metal (N) sensing electrodes and an anodized titania film show a quite large H2 response even under oxygen-free atmosphere as well as relatively excellent H2 selectivity to other inflammable gases, in comparison with other gas sensors. The mechanism for enhancing the H2-sensing properties by the surface modification of the Pt-sensing electrode with Au (see Fig. 2) will be mainly reported. Solid Electrolyte CO Gas Sensors Operable at Temperatures less than Room Temperature3) Detection of CO is of primary importance from the view point of safety in many industrial processes as well as our daily life. We have found that the sintered disk-type NASICON(Na3Zr2Si2PO12)-based solid electrolyte gas sensors equipped with a metal oxide (MO)-added Pt sensing electrode and a pristine Pt or another metal oxide-added Pt reference electrode on the same side of the disk can detect CO at temperatures less than room temperature (see Fig. 3). The outstanding CO sensing characteristics of this type of CO sensors will be reported. Adsorption/Combustion-Type Micro VOC Sensors4) We have reported that adsorption/combustion-type micro gas sensors, which were fabricated by utilizing the microelectromechanical system (MEMS) technology and an oxide-film fabrication technique by drop coating employing an air-pulse fluid dispenser, are quite promising as gas-sensing devices for detecting a low concentration of various volatile organic compounds (VOCs) in comparison with other types of gas sensors (see Fig. 4). The potential of this type of sensors, in detecting selectively a low concentration of VOCs, which are possible biomakers for diagnosis of specific diseases and health checking, will be reported.References Ueda, I. Boehme, T. Hyodo, Y. Shimizu, U. Weimar, N. Barsan, Enhanced NO2-sensing properties of Au-loaded porous In2O3 gas sensors at low operating temperatures, Chemosensors, 8, 72 (2020).Shimizu, T. Hyodo, Sensing properties of diode-type gas sensors, Advances in Science and Technology, 99, 61-65 (2017).Ueda, H. Takeda, K. Kamada, T. Hyodo, Y. Shimizu, Enhanced CO response of NASICON-based gas sensors using oxide-added Pt sensing electrode at low temperature operation, Electrochemistry, 85(4), 174-178 (2017).Hyodo, Y. Shimizu, Adsorption/combustion-type micro gas sensors: Typical VOC-sensing properties and material-design approach for highly sensitive and selective VOC detection, Analytical Sciences, 36(4), 401-411 (2020). Figure 1