Source
Chemical sensors, comprehensive sensors technologies, volume 5: electrochemical and optical sensors. Korotcenkov G ed. New York: Momentum Press, 2011 Jul; 5:1-89
Abstract
Sensor technologies are increasingly being used for sophisticated analytical applications in gases and liquids. Chemical sensors can be based on thermoelectric effects, thermal conductivity, catalytic combustion (combustible gas sensors), surface plasmon resonance, and both aqueous and solid-state electrochemistry; heated metal oxide (HMOX) electronic devices, surface acoustic wave or cantilever mechanical devices, optical and fiber optical effects, and magnetic effects have been reported for various applications (Christofides and Mandelis 1990; Brajnikov 1992; Ishihara and Matsubara 1998; Janata et al. 1998; Wilson et al. 2001; Stetter et al. 2003b; Ando 2006; Aroutiounian 2007; Lundstrom et al. 2007). However in this chapter, we will consider the subclass identified as electrochemical gas sensors and discuss the fundamentals of their construction, operation, performance, and application. Electrochemical approaches to sensing different gas molecules can provide one of the lowest-power approaches combined with analytical performance that includes sensitivity, selectivity, and relatively low cost. For many widespread applications such as personal monitoring, a sensor with simplicity and low cost as well as small size and minimal power consumption is highly desired. Electrochemical sensors, in fact, are very versatile, as they are sensitive to a wide range of toxic gases such as CO, NH3 , 502 , NO, N02 , as well as oxygen and are often amenable to miniaturization (Stetter et al. 1988; Madou and Joseph 1991). The possibility to work at room temperatures (RT) is an important advantage of liquid and polymer electrolyte electrochemical gas sensors, since a power-consuming heater is not needed and the gas sample and sensing environment are unperturbed by the measuring device (Limoges et al. 1996; Shi and Anson 1996). RT operation is also an important criterion to achieve intrinsically safe performance in potentially hazardous situations (Stetter 1984). Liquid and polymer electrolyte gas sensors are not yet as thermally robust as those devices that can be made with solid-state materials such as the HMOX sensors or high-temperature zirconia electrolyte sensors. However, ambient amperometric and potentiometric devices typically offer higher selectivity than the chemiresistor semiconductor sensors. In general, electrochemical sensors are reported to last for years; as is typical for all sensors, the actual lifetime will depend on the conditions of use, but 5 years or more is not an unusual sensor lifetime. The overall electrochemical sensing approach, including that of potentiometric, amperometric, and conductimetric sensors, offers an attractive package of combined analytical and logistical characteristics that result in being able to provide relatively high analytical performance at modest cost for many applications (Stetter and Blurton 1976, 1977; Jana ta 1989; Vaihinger et al. 1991; Mari et al. 1992; Chang et al. 1993; Stetter and Li 2008) Therefore, a variety of electrochemical sensors are found in real-world gas-detection processes, both in stationary and in portable applications. Operation at low temperature typically utilizes liquid or polymer electrolytes, while high temperature requires solid-state materials for sensor component parts. Due to the large number of related publications, in the present chapter we will consider selected results that are important for understanding the principles of operation of electrochemical gas sensors; more detailed discussions of general principles of a broad range of electrochemical sensors can be found elsewhere (Stetter and Blurton 1976, 1977; Janata 1989; Vaihinger et al. 1991; Chang et al. 1993; Mari et al. 1992; Cao et al. 1992; Bontempelli et al. 1997; Alber et al. 1997; Bakker et al. 1997; Holzinger et al. 1997; Buhlmann et al. 1998; Yamazoe and Miura 1998; Kulesza and Cox 1998; Hodgson et al. 1999; Opekar and Stulik 1999, 2002; Brett 2001; Reinhardt et al. 2002; Knake et al. 2005; Bobacka et al. 2008; Stetter and Li 2008). We apologize in advance to any of our colleagues whose work may not be adequately represented here and acknowledge their many important contributions.