Low Power Consumption CO2 Gas Sensor Using Ionic Liquid

Recently, various gas sensors are investigated. Specially, CO₂ gas sensor is worthy of the notice, because monitoring of CO₂ gas concentration is important for energy-saving. For example CO₂ gas concentration is required for 1000 ppm or less in space, such as office buildings, a building management method, a production plant, and an IT-related server room. An exhaust gas periodically compulsory in order to make the present condition and CO₂ gas concentration below into a steady value. By minimizing the displacement volume of the air which is carrying out air-conditioning management using CO₂ sensor, an air-conditioning system carries out efficient operation, and it aims at development of CO₂ sensor corresponding to the low consumption power high integration interlocked with a sensor network system efficiently. However the conventional CO₂ gas sensors have the following problems, 1) large power consumption, 2) large size and 3) long detection time. These problems are mainly caused by usage of a light source and heater. We are interested in the ionic liquids because the ionic liquids are 1) the conductivity is high at room temperature, 2) thermal and chemical property is high stable, 3) volatility is high and 4) adsorb polarity molecule gases as like CO₂, NH₃, SO₂, and NO₂. Therefore we develop CO₂ sensor which converted CO₂ concentration into ionic liquid which adsorbed CO₂ specifically by impedance. Our sensor feature is that it isn't used light source and heater, it is used ionic response. It compares with conventional CO₂ sensor, 1) low consumption power, 2) miniaturization, 3) high-speed response and 4) low consumption CO₂ gas sensor using ionic liquids. We use ionic liquids of imidazolium salts, EMIMBF₄, EMIMTFSI and DEMEBF₄. The impedance of ionic liquids decreases along with increase of CO₂ gas concentration. By measuring the impedance of ionic liquids, we can estimate CO₂ gas concentration of the atmosphere. From the experiment, measurement resolution of CO₂ gas concentration was 100 ppm. The power consumption of our proposed CO₂ gas sensor is several tens of microwatts, and this value is 1/1000 smaller compared with conventional CO₂ gas sensors (NDIR and Solid state electrolyte cell).