Galvanic solid-electrolyte gas

Figure 25-3 . Flame probe for the demonstration of the possibility of measurements of the oxygen concentration in oxidizing and reducing hot gases with galvanic solid-electrolyte gas cells [79, 86].

At room temperature -> Nernstian slope (59 mV/decade of concentration change) is usually observed. Partial pressure can be derived by applying Henrys law. A catheter configuration suitable for measurements inside blood vessels has been described [ii]. Using other electrolyte constituents and membranes semipermeable for other types of gas sensors for other analytes were developed (including N02, S02, H2S, HF [iii]). Various CO2 sensors with galvanic solid electrolyte cells have been designed [iv]. 

Galvanic solid-electrolyte sensors for the study of turbulences in gases, particularly qualified for flames [89]. The sensor shown at left side is able to record the oxygen concentration at one point and the sensor shown at right is able to record the difference of the oxygen concentration between two points in a hot gas phase. 

Figure 25-33. The water vapor concentration in a stream of hydrogen (7.5 L/h) with an initial HjO Hj ratio of 0.029 after desiccation with the equal mass (4 g) of different substances versus time The water vapor ratio in the dried gas was calculated from the potential differences measured at 550 °C between the inner electrodes of two parallel galvanic solid-electrolyte tube cells, one of which contained a stream of hydrogen saturated with water vapor at 15 °C [90].

Peters H, Mobius H-H Methods for gas analysis at higher temperatures by means of galvanic solid electrolyte elements, published in German Verfahren zur Gasanalyse bei erhohten Temperaturen mit Hilfe galvanischer Festelektrolytelemente. DDR-P. 21673, angem. 

Schenck et al. (1929) had earlier used the same technique but used CO/CO2 gas mixture for equilibration. They had reported moderate positive deviation from ideality, which was also confirmed by Swerdtfeger andMuan (1967). However, Engell (1962) reported a much higher positive deviation using the solid electrolyte galvanic cell technique, about which we would discuss in the next section. 

The galvanic potential differences in the electrodes of galvanic cells with oxoanionic solid electrolytes are determined by gas components which are not in reaction equilibrium with the cations, whose mobility determines the conductivity. Galvanic potential differences result according to the law of mass action for electrode reactions as follows ... 

Activities of FeO at 1100°C in the solid solution in equilibrium with Fe were measured by several authors using gas equilibration [1975Abb, 1970Tim] and galvanic cells with solid electrolytes [1984Bjo]. Activity of FeO in liquid solutions in equilibrium with Fe was reported at 1400°C by [1980Ban]. The CaO and FeO rich solid solutions were treated as one phase with a miscibility gap with = Acao Feo (22773 - 3140 Xcao + 15522 X cao) J mor was calculated by [1993Wu],... 

In addition to the investigations described, other kinetic experiments have been carried out with the help of solid-electrolyte galvanic cells. The investigations include phase-boundary reactions at the solid-gas phase boundary (including measurements of evaportion and condensation rates) and phase-boundary reactions at the solid-solid phase boundary. These investigations will not be discussed here. 

Rabinovich L, Lev O, Tsirlina GA (1999) Electrochemical characterization of Pd modified ceramic vertical bar carbon electrodes partially flooded versus wetted channel hydrophobic gas electrodes. J Llectroanal Chem 466(l) 45-59 Rog G, Kielski A, Kozlowska-Rog A, Bucko M (1998) Composite (CaFj-AljOj) solid electrolytes-preparation, properties and application to the solid oxide galvanic cells. Ceram Int 24 91-98 Roh S-W, Stetter JR (2003) Amperometric sensing of NOx with cyclic voltammetry. J Electrochem Soc 150(11) H266-H272... 

Heyne E, Engleson D (1977) The speed of response of solid electrolyte galvanic cells for Gas sensing. J Electrochem Soc 124 727-735... 

Galvanic cells can be set up with solid electrolytes rather than electrolytic solutions. Such a cell is the basis for a well-known potentiometric gas sensor, the lambda probe. The latter is designed to determine the oxygen content of combustion gases, e.g. in motor vehicles. The lambda probe can operate in two different modes, either potentiometrically or amperometrically. 

Since the 1980 s, a new type of humidity sensor, based on a solid electrolyte, has been under development. The sensor uses a protonic conductor as a base component and makes a galvanic cell of a water vapor gas concentration type. When the characteristics of this new type of sensor are compared with conventional humidity sensors, two representative advantages of this sensor are seen. The sensor output is an EMF change, and is suitable for continuous operation with a fast response. The sensor can operate at higher temperatures, because the solid electrolyte is stable even at elevated temperatures. These features are expected to accelerate the development of this type of sensor. The base material is a perovskite-type strontium cerate SrCeOa. The pure cerate is not a protonic conductor. 

Fig. 9.14 Example of the solid-electrolyte galvanic cell for thermodynamic measurements, where the solid-state RE is pressed onto electrolyte membrane separating two gas compartments...

FIGURE 1.12 Equivalent scheme of the galvanic concentration element. 1 first electrode (tPi) 2 solid oxygen-ionic electrolyte and 3 second electrode (tpj). (From Zhuiykov, S., Electron model of solid oxygen-ionic electrolytes used in gas sensors, Int. J. Applied Ceramic Techn. 3 (2006) 401-411. With permission.)... 

SPE solid polymer electrolyte, GDE gas diffusion electrode Galvanic mode... 

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