Conductor, multivalent cations

Irrespective of these controversies, research in this intriguing area is crucially important from both fundamental and applied points of view. For instance, solid electrolytes and mixed conductors with mobile AP + cations may find applications in new types of rechargeable battery, and also in the aluminum industry alkaline-earth cation conductors may be used, in particular, for precise humidity control in gaseous media and for CO2 sequestration. This chapter includes a brief introduction to the field, with emphasis placed primarily on the authors own studies. Although many aspects of materials electrochemical behavior require detailed investigation and further validation, the chapter provides an excellent overview of the phases where multivalent cation conduction may occur. 

Imanaka, N., Kamikawa, M. and Adachi, G.-y. (2002) A carbon dioxide gas sensor by combination of multivalent cation and anion conductors with a water-insoluble oxycarbonate-based auxiliary electrode. Anal. Chem., 74 (18), 4800-4. 

Multivalence Cation Conductors, Fig. 1 Electrical conductivity and activation energies for M2(W04)3 with the Sc2(W04)3-type structure at 600 °C in an air atmosphere... 

Multivalence Cation Conductors, Fig. 5 Temperature dependence of the cation conductivity for... 

Based on optimizing both the chemical stability and the long-term stability of the sensor, multivalent cation-conducting solid electrolytes are considered to be preferable as sensor components. However, since reasonably high ion conductivity is required for the solid electrolyte in order to obtain desired performance parameters such as fast responsiveness, it is necessary to develop multivalent cation conductors with high ionic conductivity. 

Figure 17.4 depicts the sensor output EMFs in both dry and humid atmospheres at 550 °C. Even in an atmosphere containing 3.0 vol% water vapor (saturated water vapor at 25 ""C), the EMF values are essentially identical to those obtained in a dry atmosphere, suggesting that there is no interference by water vapor with regard to the sensing performance. Furthermore, the sensor responds only to CO2 without any interference due to the presence of O2 (tested concentration range 5-40 %), NO (100-500 ppm), or NO2 (100-500 ppm). These results also support the contention that multivalent cation conductors are one of the promising candidates for sensor components. 

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