Electrolytic domain

Equation (15.5) shows that for very high and very low A>2(/ o2) the transference number of the ions vanishes. From Eqn. (15.4), we read that ( E/dp oJ is zero if / (= 1 - /<.]) vanishes. This means that stabilized zirconia cannot be uied as a solid electrolyte in the ranges of oxygen potential where po>P and Pq2galvanic cells or in fuel cells. For p >Pot>P < the oxide is said to be in its electrolytic domain (Fig. 15-12). 

The electrolytic domain extends over several orders of magnitude of oxygen partial pressure, n-type semi-conduction occurring in highly reducing media. 

Heat production associated with the electrochemical reactions is also assumed to be confined at the electrode-electrolyte surface, thus the resulting thermal energy produces a discontinuity of the heat flux. The heat generated within this surface, in fact, represents a heat source for the electrode and the electrolyte domains. The sum of the inward heat fluxes is equal to the heat generated as a result of the electrochemical reactions. As explained in Section 3.3.2, the heat is generated by the increase in entropy, associated with the electrochemical reaction (reversible heat), and to the activation irreversibilities. Therefore, the boundary conditions for Equation (3.7) are ... 

A) Stabilized ZrOz. The Standard SOFC Electrolyte with a Large Electrolytic Domain... 

Owing to the activation energy, at intermediate temperatures the electrolytic domain increases and at e.g., 500°C the electronic conductivity plays only a minor role. In view of the ionic conductivity being still high enough at these temperatures, ceria appears to be an appropriate electrolyte for intermediate temperature fuel cells. Further information on the properties of ceria and its use in SOFCs can be found in Ref.106,120... 

Bismlitil oxide — Figure. Comparison of the - electrolytic domain boundaries for solid oxide electrolyte materials. See ref. [iv] for details... 

Electrolytic domain — describes the range of external conditions (- activity of components, temperature or pressure), where the ion transport number of a material is equal to or higher than 0.99 and the material is considered as -> solid electrolyte. Usually this term is related to thermodynamic - equilibrium. 

The overall permeation rate of a material is determined by both ambipolar conductivity in the bulk and interfacial exchange kinetics. For -> solid electrolytes where the electron - transference numbers are low (see -> electrolytic domain), the ambipolar diffusion and permeability are often limited by electronic transport. 

See also - chemical potential, -> electrolytic domain, - gas titration coulometric, - Wagner equation. 

Solid electrolyte — is a class of solid materials, where the predominant charge carriers are -> ions. This term is commonly used for -> conducting solids with ion -> transport number equal to or higher than 0.99 (see also -> electrolytic domain). Such a requirement can only be satisfied if the -> concentration and -> mobility of ionic -> charge carriers (usually -> vacancies or interstitials) both are relatively high, whilst the content of -> electronic defects is low. See also -> superionics, -> defects in solids, - diffusion, and -> Nernst-Einstein equation. 

Analysis of mechanisms of the defect formation, thermodynamics, interaction, association and - diffusion in solid materials, validated by deep experimental studies centered on numerous particular cases, including - solid electrolytes such as -> stabilized zirconia (see also - defects in solids, -> vacancies, -> electrolytic domain, -> electronic defects, -> doping). 

First, let us consider the mathematical model of the electrical field in the tank. It is assumed that the surface of electrolyte domain 2 is surrounded by T (= Yd + r + rm), where Ym is the metal surface, and the potential and current density are prescribed on Yd and Tn respectively. The potential

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While past efforts were focused on expanding the electrolytic domain of oxygen ion conducting fluorite-t5q)e ceramics, more recently one has begim to introduce enhanced electronic conduction in fluorite matrices. Extrinsic elec-... 

Figure 13.4 Electrolytic domains for calcia-stabilized zirconia (CSZ), yttria-doped thoria (YDT), and magnesia partially stabilized zirconia (MgPSZ) [47, 48],...

Fig. 4.2. (a) Schematic representation of electrolytic domain, i.e. relative electronic (for instance n and p type for ZrOj Ca) and ionic conductivity as a function of partial pressure pXj of the more volatile element (e.g. Oj or Ij). Dotted zone corresponds to a mixed conduction domain where the ionic transport number (tj) goes from 0 to 1 (with permission). The Agl area is limited by the a-p transition and by melting on the low and high temperature sides, respectively, (b) Schematic defect structure of an oxide M2O3 as a function of the water pressure. The oxide is dominated by anti-Frenkel defects and protons ([H ]) and doped with cations, concentration of which is assumed to be constant ([MI ]). Metal vacancies are shown as examples of minority defects. 

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