Solid potentiometric gaseous oxide

Because of the unavailability of the requisite solid electrolytes to form a concentration cell of gaseous oxides, it is impossible to fabricate type I potentiometric sensors for detecting gaseous oxides. 

Although employing inorganic radicals in solid electrolytes opens the possibility to detect gaseous oxides by a potentiometric method, it is a chemical choice rather than a material choice for solid electrolytes. Since salts involving inorgaific radicals are not usually good solid electrolytes due to limited chemical stability. 

Although the basic principles of type III potentiometric sensors are apphcable for gaseous oxide detection, this should not obscure the fact that these sensors still require further development. This is especially true in view of the kinetics of equilibria and charged species transport across the solid electrolyte/electrode interfaces where auxiliary phases exist. Real life situations have shown that, in practice, gas sensors rarely work under ideal equilibrium conditions. The transient response of a sensor, after a change in the measured gas partial pressure, is in essence a non-equilibrium process at the working electrode. Consequently, although this kind of sensor has been studied for almost 20 years, practical problems still exist and prevent its commercialization. These problems include slow response, lack of sensitivity at low concentrations, and lack of long-term stability. " It has been reported " that the auxiliary phases were the main cause for sensor drift, and that preparation techniques for electrodes with auxiliary phases were very important to sensor performance. ... 

Gauthier M, Chamberland A (1977) Solid-state detectors for potentiometric determination of gaseous oxides. JElectrochem Soc 124(10) 1579-1583... 

Alberti G, Carbone A, Palombari R (2001) Solid state potentiometric sensor at medium temperatures (150-300 °C) for detecting oxidable gaseous species in air. Sens Actuators B 75 125-128 Alcock CB (1961) The gaseous oxides of the platinum metals. Platin Met Rev 5(4) 134-139... 

The oxidation of propylene oxide on porous polycrystalline Ag films supported on stabilized zirconia was studied in a CSTR at temperatures between 240 and 400°C and atmospheric total pressure. The technique of solid electrolyte potentiometry (SEP) was used to monitor the chemical potential of oxygen adsorbed on the catalyst surface. The steady state kinetic and potentiometric results are consistent with a Langmuir-Hinshelwood mechanism. However over a wide range of temperature and gaseous composition both the reaction rate and the surface oxygen activity were found to exhibit self-sustained isothermal oscillations. The limit cycles can be understood assuming that adsorbed propylene oxide undergoes both oxidation to CO2 and H2O as well as conversion to an adsorbed polymeric residue. A dynamic model based on the above assumption explains qualitatively the experimental observations. 

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