Mixed ionic electronic conductive material

As in the case of the previous family of iron perovskites, this new series of compounds are of interest for their use as mixed ionic electronic conducting materials, mainly from the point of view of cathodes for Solid Oxide Fuel Cells (SOFC), although they could also be used as ceramic membranes for oxygen separation. In the ptresent case, the degree of lanthanide substitution was fixed to x=0.5 given that previous studies have shown that it is precisely at this degree of substitution when electronic and ionic conductivity are maximised (Hansen, 2010 Vidal et al., 2007). 

The total conductivity of an oxide-type material with mixed ionic-electronic conduction, o, can be expressed as ... 

Solid-state electrochemistry is an important and rapidly developing scientific field that integrates many aspects of classical electrochemical science and engineering, materials science, solid-state chemistry and physics, heterogeneous catalysis, and other areas of physical chemistry. This field comprises - but is not limited to - the electrochemistry of solid materials, the thermodynamics and kinetics of electrochemical reactions involving at least one solid phase, and also the transport of ions and electrons in solids and interactions between solid, liquid and/or gaseous phases, whenever these processes are essentially determined by the properties of solids and are relevant to the electrochemical reactions. The range of applications includes many types of batteries and fuel cells, a variety of sensors and analytical appliances, electrochemical pumps and compressors, ceramic membranes with ionic or mixed ionic-electronic conductivity, solid-state electrolyzers and electrocatalytic reactors, the synthesis of new materials with improved properties and corrosion protection, supercapacitors, and electrochromic and memory devices. 

Generally, the activation layer is a functionally graded porous structure made of the same composition as the membrane layer. A second case is when the two porous interfaces, acting as mixed ionic/electronic-conducting electrodes, are made of materials different from the membrane (a purely ion-conducting electrolyte), as shown in Figure 9.10c. In this case, the oxygen flux can be precisely controlled by the... 

Teraoka, Y., Zhang, H. M., Okrunoto, K. Yattrazoe, N. Mixed ionic-electronic conductivity of Lal-xSrxCol-yFey03-8 perovskite-type oxides. Materials Research Bulletin 23, 51-58, doi Doi 10.1016/0025-5408(88)90224-3 (1988). 

On the first step catalytic metals and materials with high ionic (or mixed ionic-electronic) conductivity are studied, for example, thin film of Pd, ultra thin films of Pt, Ir thick layers or bulk of hydrates of antimonic acid, Prussian Blue, beta-alumina, thin films of transition metal oxides etc. 

In Riga we are planning to use materials with mixed ionic-electronic conductivity as gate electrodes, thereby making the available region of selectivity and sensitivity of different elements in an array broader... 

There are several eomprehensive reports [7, 74-79] devoted to mixed ionic-electronic conducting ceramic membranes for gas separation and selective catalytic reactions. The requirements to membrane materials differ fixrm those to SOFC cathodes. For membranes, the most promising concept is based upon supported asymmetric functionally graded design combining a dense permselective l er and l ers with different porosity. Cathode materials may be not dense, they operate in air and m be unstable in a reducing atmosphere. On the other hand, cathode materials should be chemically inert towards other SOFC components and keep their characteristics under the working conditions. 

The anode material in SOF(7s is a cermet (rnetal/cerarnic composite material) of 30 to 40 percent nickel in zirconia, and the cathode is lanthanum rnanganite doped with calcium oxide or strontium oxide. Both of these materials are porous and mixed ionic/electronic conductors. The bipolar separator typically is doped lanthanum chromite, but a metal can be used in cells operating below 1073 K (1472°F). The bipolar plate materials are dense and electronically conductive. 

Solid mixed ionic-electronic conductors (MIECs) exhibit both ionic and electronic (electron-hole) conductivity. Naturally, in any material there are in principle nonzero electronic and ionic conductivities (a i, a,). It is customary to limit the use of the term MIEC to those materials in which a, and 0, 1 do not differ by more than two orders of magnitude. It is also customary to use the term MIEC if a, and Ogi are not too low (o, a i 10 S/cm). Obviously, there are no strict rules. There are processes where the minority carriers play an important role despite the fact that 0,70 1 exceeds those limits and a, aj,i< 10 S/cm. In MIECs, ion transport normally occurs via interstitial sites or by hopping into a vacant site or a more complex combination based on interstitial and vacant sites, and electronic (electron/hole) conductivity occurs via delocalized states in the conduction/valence band or via localized states by a thermally assisted hopping mechanism. With respect to their properties, MIECs have found wide applications in solid oxide fuel cells, batteries, smart windows, selective membranes, sensors, catalysis, and so on. 

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