O2 Gas Sensors

Wang, R., Okajima, T., Kitamura, R, and Ohsaka, T., A novel amperometric O2 gas sensor based on supported room-temperature ionic liquid porous polyethylene membrane-coated electrodes, Electroanalysis, 16, 66-72, 2004. 

Wang, R., Hoyano, S., and Ohsaka, T., O2 gas sensor using supported hydro-phobic room-temperature ionic liquid membrane-coated electrode, Chem. Lett, 33, 6-7, 2004. 

The advantages of using room temperature ionic liquid (RTIL) electrolyte in membrane-coated electrode as an O2 gas sensor compared to solid electrolyte gas sensors and classic Clark-type gas sensors included easy constraction and the ability to operate at ambient temperature. This would be the direction for future ambient temperature oxygen sensor development. 

In addition to responding to the oxidation and reduction of molecular O2, the sensor can be used to determine the concentration of the gas by... 

Both mechanisms explain the decrease of the resistance with the formation of a rooted or an isolated hydroxyl group out of an O2" of the lattice. In both cases it is assumed that the bonding to the Sn does not contribute to the concentration of free charge carriers, which implies that not all the surface tin atoms are in oxidation state +4 because otherwise the formation of the Sn—OH bond would need an electron from the conduction band. This assumption is reasonable because tin has two stable oxidation states, +2 and +4, and the most stable surface of tin dioxide, (110), can easily be conditioned to show atoms with both oxidation states. Furthermore it is known that defects like vacancies are an essential factor for the performance of Sn02 gas sensors and it probably is not realistic to base a mechanism on the situation on a perfect surface. Emiroglu et al. (2001) and Harbeck et al. (2003) proved the formation of rooted and isolated hydroxyl group on the Sn02 surface in the presence of water, so the final result is clear even if the exact mechanism still allows for speculation. 

Amperometric gas sensors are - electrochemical cells that produce a - current signal directly related to the concentration of the - analyte by - Faraday s law and the laws of - mass transport. The schematic structure of an amperometric gas sensor is shown in Fig. 1. The earliest example of this kind of sensor is the - Clark sensor for oxygen. Since that time, many different geometries, membranes, and electrodes have been proposed for the quantification of a broad range of analytes, such as CO, nitrogen oxides, H2S, O2, hydrazine, and other vapors. 

FIGURE 2.12 Numerical and measured response/recovery transients to 400 ppm NOj in 5 vol. % O2 (N2 balance) in the (a) absence and (b) presence of 5 vol. % water vapor at 850°C. (Reprinted from Zhuiykov, S., Mathematical modelling of YSZ-based potentiometric gas sensors with oxide sensing electrodes part II Complete and numerical models for analysis of sensor characteristics, Sensors and Actuators B, Chem. 120, (2007) 645-656, with permission from Elsevier Science.)... 

Finally, planar, thick-film, YSZ-based sensors for O2, and NO, are expected to reinforce their place in the maiket owing to their rapid response and potential for implementation as multicomponent gas sensors in vehicle exhausts. The performance of recently developed nltra-lean-bum engines and NO, storage catalysts depends significantly on the performance of such sensors. Thus, solid-state electrochemical sensors must reach even higher levels of performance and reliability, so continued development of these sensors is required in order to address more stringent requironents. 

Development of ionic conductors based on stabilized zirconia has reached a level of maturity, where most of the research on such materials concentrates mainly on obtaining incremental empirical improvements in conductivity by better processing control and refinement of the microstructure of the solid electrolyte and SE. Further increases in the conductivity are important in terms of enhancing the efficiency of systems such as O2 sensors, zirconia-based mixed-potential gas sensors, electrochemical oxygen pumps, heating elements, and fuel cells [4-7]. The systematic errors, as have been considered before, are errors with a known determined functional connection with the source of their cause, and the conformity of their appearance can be definitely described. 

In addition to multi-gas sensors, which are discussed later (see Section 10), direct-measuring O2 and IR sensors can be used for this kind of measurement. By use of fast O2 sensors, O2 and N2 wash-out curves are measurable whereas N2 is determined as a complement to 100%. Ethanol, acetone and SF5 can be measured by means of modified IR sensors. For the separation of interfering composites such as additional gases in sample blends like anesthetic gases in the case of ethanol measurements, an appropriate expenditure is required. 

In the next section, a variety of solid state environment gases sensors (NO,, CO2, CO, SO2, O2, etc.) are reviewed, and attention is also paid to semiconducting metal oxide type. Also discussed are the extension of the operating temperature to the near-human temperature regimes and better sensing properties derived from the nanostructured semiconducting metal oxide gas sensors. 

The most extensive efforts to develop the OLED-based sensor platform have focused on PE-based gas-phase and dissolved O2 (DO) sensors. Such sensors, which have been studied for many years, are based on the efficient quenching of the PL of dyes such as Ru complexes and Pt or Pd porphyrins by collisions with O2 molecules the sensitivity to O2 is due to the nearly unique triplet nature of the ground state of O2. In an ideal homogeneous matrix, the O2 concentration [O2I is related to the steady-state PL intensity I and the PL decay time x by the Stern-Volmer (SV) equation ... 

---