Sodium-ion conductor

This cell reaction necessitates a so-dium-ion-conductive electrolyte. At present, the best and most stable sodium ion conductor is / "-alumina. This electrolyte has sufficient high sodium ion conductivity at temperatures of about 300 °C. The ft"-alumina electrolyte is normally designed as a tube closed at one end with a negative... 

In the Na/S system the sulfur can react with sodium yielding various reaction products, i.e. sodium polysulfides with a composition ranging from Na2S to Na2S5. Because of the violent chemical reaction between sodium and sulfur, the two reactants have to be separated by a solid electrolyte which must be a sodium-ion conductor. / " -Alumina is used at present as the electrolyte material because of its high sodium-ion conductivity. 

Nasicon solid electrolyte electrochemical promotion with, 440 sodium ion conductor, 440 NEMCA, see electrochemical promotion NEMCA coefficient, 152,319... 

Other crystalline sodium ion conductors, the so-called NASICON compounds of general formula Na1+JCSiJtZr2P3 JtO 2 for 1.8 [Pg.251]

The fast-ion ceramic conductors of interest here are cubic stabilized zirconia (CSZ), an oxygen ion conductor, and a sodium aluminate (/f -alumina), a sodium ion conductor. Both are discussed in detail below. The overview by T.A. Ramanarayanan et al. [8] covering CSZ and its applications is recommended. 

Following a period of intense research on NASICON (Na3Zr2Si2POi2) three-dimensional sodium-ion conductors, research interests drifted toward identifying similar LlSlCON-type three-dimensional lithium-ion conductors. A direct analogue compound (Li3Zr2Si2PO,2) was a stable phase, but exhibited poor ionic conductivity." Researchers also analyzed the ionic conductivity of various... 

The Synthesis and Fabrication of Ceramics for Speciai Appiication 209 17.3.7. Preparation of Soiid State Eiectrolytes 17.3.7.2. Alternative Sodium Ion Conductors... 

Table 1. Alternative Sodium Ion Conductors/Sodium Ion Resistivity Maximum Thickness For Area-Specific Resistance < 0.5 Q-cm (300°C)...

Sensors may also use multiple electrolytes (referredto as electrolyte chains), and two examples of these are shown in Figure 13.Id and e. In both examples, a Na2SO4 auxiliary electrode is used with a sodium ion conductor so that the sensing electrode reaction is given by Equation (13.5). The difference between the two cases is that, in Figure 13.Id, the sodium ion conductor is used with another cation (strontium) conductor, whereas in Figure 13.le the sodium ion conductor is used with an anion (oxygen) conductor. In both cases, an equilibrium reaction is required to relate the... 

Lithium carbonate can be used more directly as the auxiliary electrode with a lithium ion conductor, since the in situ formation of another carbonate phase is not required. Lithium ion conductors used with Li2CO3 include LISICON [163] and other Li3PO4-based electrolytes [164—173]. As with sodium ion conductors, Li2CO3-containing carbonates are used with lithium ion conductors [174, 175], The outputs of some examples of these lithium ion-conducting electrolyte-based sensors are shown in Figure 13.11 [163, 172-174]. 

In a similar way, Na2SO4 has been used as an auxiliary electrode with sodium ion conductors (Na P alumina [179] or NASICON [180]). As with carbonates for CO2 sensors, mixed sulfates (e.g., Na2SO4-BaSO4 [181]) can be used for the auxiliary electrode. At low oxygen partial pressures, sulfur maybe present as H2S, rather than as SOx, in which case sulfides can be used as auxiliary electrodes. For example, CaS has been used with a CaF2 electrolyte for measuring H2S gas concentrations [182]. 

Miura, N., Yao, S., Shimizu, Y. and Yamazoe, N. (1992) Carbon dioxide sensor using sodium ion conductor and binary carbonate auxiliary phase. J. Electrochem. Soc., 139 (5), 1384—8. 

Ono, M., Shimanoe, K., Miura, N. and Yamazoe, N. (1999) Solid-state amperometric sensor based on a sodium ion conductor for detection of total NOx in an atmospheric environment. 

Conventional heterogeneous metal catalysts are commonly enhanced by the addition of so-called promoter species that are used to modify intrinsic metal surface chemistry with respect to activity and/or selectivity. Electrochemical promotion (EP) provides an in situ, reversible and efficacious means of catalyst promotion and it allows for a systematic study of the role of promoters in heterogeneous catalysis. EP studies relevant to the three-way catalytic chemistry i.e., control of automotive CO, NO and hydrocarbons emissions, demonstrate that major enhaneements in activity of Pt catalyst supported on a"-Al203 (a sodium ion conductor) are possible when Na is electrochemically pumped to the catalyst surface. In the case of the important reactions involving NO reduction by CO or by hydrocarbons, major enhancements in selectivity towards N2 (from 15 to 70%) have been also achieved. The promotional effect of Na is due to enhanced NO chemisorpion and pronounced NO dissociation on the Pt surface. 

A sodium-ion conductor (Nasicon) is used as the solid electrolyte. Various oxides have been proposed for the auxiliary phase, depending on the target test gas, includ-... 

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