(Invited) Ionic Liquids in Gas Sensors: Recent Progress and Future Prospects

Since the initial report of Hurley and Weir in 1951 [1] room temperature ionic liquids (RTILs) have been researched extensively for over five decades, starting with the binary eutectic mixtures based on haloaluminates [2,3] and proceeding through a wide array of single component salts containing many different organic cations and organic or inorganic anions [4-6].  The driving force behind research into these media was not only the sheer novelty of them as opposed to molecular liquids, but also the promise of new properties and capabilities, for example, in enabling improved separations, more efficient chemical syntheses and higher performance sensors and analytical methods.  These possibilities are all the more interesting because the single component salts are typically air and moisture stable and therefore much easier to work with under practical conditions than the reactive haloaluminates, which need to be kept under dry, inert atmosphere. 

Our particular interest as a commercial gas sensor developer and manufacturer is whether and how RTILs could be leveraged to improve amperometric gas sensor performance, most importantly in ways that add value to the sensor product from the customer’s point of view.  We are using a new, next generation amperometric gas sensing technology for a variety of toxic gases and gases of environmental interest including CO, H₂S, NO₂, SO₂, O₃, NH₃ and others.  This approach adapts the conventional ideas of amperometric gas sensing into a printed package that is very small and ultralow power for modern applications (Figure 1).  Can RTILs be used effectively as electrolytes in amperometric gas sensors?  How do RTILs compare to conventional aqueous acid electrolytes? Can RTILs impart new capabilities and performance improvements (sensitivity, response time, stability, operational life, tolerance of extreme environmental conditions) to amperometric sensors?  How does one go about selecting the right RTIL from the vast array of possibilities?  What are the materials compatibility issues? What about cost?

This presentation will address these issues from the perspective of several programs on gas sensor development for toxic and environmental gases at KWJ Engineering.

References

[1] F. H. Hurley and T. P. Weir, J. Electrochem. Soc., 98, 203 (1951).

[2] H. L. Chum, V. R. Koch, L. L. Miller and R. A. Osteryoung, J. Am. Chem. Soc., 97, 3264 (1975).

[3] J. S Wilkes, J. A. Levisky, R. A. Wilson and C. L. Hussey, Inorg. Chem., 21, 1263 (1982).

[4] J. S. Wilkes and M. J. Zaworotko, Chem. Commun., 965 (1992).

[5] J. G. Huddleston, A. E. Visser, W. M. Reichert, H. D. Willauer, G. A Broker and R. D. Rogers, Green Chemistry, 3, 256 (2001).

[6] P. Wasserscheid and T. Welton (Eds.), “Ionic Liquids in Synthesis,” Wiley-VCH, Weinheim (2003).

Figure 1.  Printed amperometric gas sensor (15 x 15 x 1 mm).