Solid-electrolyte composites

The equivalent circuit of a section of this SEI is presented in Fig. 13(b). It was recently found [123, 124] that at temperatures lower than 90 °C, the grain-boundary resistance of composite polymer electrolytes and composite solid electrolytes based on Lil-A Ojis many times larger than their ionic resistance. At 30 °C / GB is several orders of magnitude larger than (the ionic resistance) and for 100 pm-thick CPE foils or Lil-A Oj pellets it reaches [125] 105-106Qcm2 (depending on CPE composition). 

Xiong, W. and Kale, G.M. (2006) Microstructure, conductivity, and NO2 sensing characteristics of a-AhOj-doped (8 mol% Sc2O3)ZrO2 composite solid electrolyte. Int. J. Appl. Ceram. Technol.,... 

Caproni, E., Carvalho. F.M.S. and Muccillo, R. (2008) Development of zirconia-magnesia/zirconia—yttria composite solid electrolytes. Solid State Ionics, 179, 1652-4. 

The CTacks on the composite solid electrolyte-alumina interface usually appear when the composite solid electrolyte is rapidly quenching after the fusing temperature, which is normally over 1850°C, down to the temperature around 70Q-1000°C. Consequently, to avoid cracking, more gradual cooling should be provided around the whole interface area by various techniques. As a result, the... 

Dai Y, Wang Y, Greenbaum S, Bajue S, Golodnitsky D, Ardel G, Strauss E, Peled E (1998) Electrical, thermal and NMR investigation of composite solid electrolytes based on PEO, LU and high surface area inorganic oxides. Electrochim Acta 43(10-11) 1557-1561... 

Singh K, Ambekar P, Bhoga SS (2002) Eerroelectric dispersed composite solid electrolyte for CO gas sensor. In Chowdari BVR, Prabaharan SRS, Yahaya M, Talib lA (eds) SoUd state ionics trends in the new millennium. World Scientific Publishing, Singapore, pp 469-476... 

Uvarov N, lusupov V, Sharama V, Shukla K (1992) Effect of morphology and particle size on the ionic conductivities of composite solid electrolytes. Solid State Ionics 51 41-52 Uvarov NF, Ponomareva VG, Lavrova GV (2010) Composite solid electrolytes. Russ J Electrochem 46(7) 722-733 Vaidehi N, Akila R, Shukla A, Jacob KT (1986) Enhanced ionic conduction in dispersed sohd electrolyte systems CaFj-AljO, and CaF -CeO. Mater Res Bull 21 909-916... 

Figure 16.15 [6] schematically represents the li/PE interphase. Solid PEs have a rough surface, so when they are in contact with lithium, some spikes, like 2 in Figure 16.15, penetrate the oxide layer and the lithium metal, and a fresh SEI is formed at the Li/PE interface. In other parts of the interface, softer contacts between the PE and lithium are formed ( 1 and 3 in Figure 16.15). Here the fresh SEI forms on the native oxide layer or, as a result of the retreat of lithium during its corrosion, the native oxide layer breaks and the gap is filled by a fresh SEI ( 1 in Figure 16.15). The net result is that only a fraction 9) of the lithium surface is in intimate contact with the PE. The situation in composite solid electrolytes (CPEs) is more severe because of their greater stiHhess. This complex morphology of the Li/PE and li/CPE interfaces causes difficulties in measuring SEI and PE...

The electrical conductivity also increases with increasing metal oxide content, due to the high mobility of the metal ions. For example several glass compositions have been used as solid electrolytes in galvanic cells in which other metal ions apart from the alkaline and alkaline earth ions have been incorporated. The electrochemical cell... 

The galvanic cell studied (shown in Fig. 5.24) utilizes a highly porous solid electrolyte that is a eutectic composition of LiCl and KCl. This eutectic has a melt temperature of 352 °C and has been carefully studied in prior electrochemical studies. Such solid electrolytes are typical of thermal battery technology in which galvanic cells are inert until the electrolyte is melted. In the present case, shock compression activates the electrolyte by enhanced solid state reactivity and melting. The temperature resulting from the shock compression is controlled by experiments at various electrolyte densities, which were varied from 65% to 12.5% of solid density. The lower densities were achieved by use of microballoons which add little mass to the system but greatly decrease the density. 

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. 

There is a wide variety of solid electrolytes and, depending on their composition, these anionic, cationic or mixed conducting materials exhibit substantial ionic conductivity at temperatures between 25 and 1000°C. Within this very broad temperature range, which covers practically all heterogeneous catalytic reactions, solid electrolytes can be used to induce the NEMCA effect and thus activate heterogeneous catalytic reactions. As will become apparent throughout this book they behave, under the influence of the applied potential, as active catalyst supports by becoming reversible in situ promoter donors or poison acceptors for the catalytically active metal surface. 

It will also be shown that the absolute electrode potential is not a property of the electrode but is a property of the electrolyte, aqueous or solid, and of the gaseous composition. It expresses the energy of solvation of an electron at the Fermi level of the electrolyte. As such it is a very important property of the electrolyte or mixed conductor. Since several solid electrolytes or mixed conductors based on ZrC>2, CeC>2 or TiC>2 are used as conventional catalyst supports in commercial dispersed catalysts, it follows that the concept of absolute potential is a very important one not only for further enhancing and quantifying our understanding of electrochemical promotion (NEMCA) but also for understanding the effect of metal-support interaction on commercial supported catalysts. 

It is thus clear from the previous discussion that the absolute electrode potential is not a property of the electrode material (as it does not depend on electrode material) but is a property of the solid electrolyte and of the gas composition. To the extent that equilibrium is established at the metal-solid electrolyte interface the Fermi levels in the two materials are equal (Fig. 7.10) and thus eU 2 (abs) also expresses the energy of transfering an electron from the Fermi level of the YSZ solid electrolyte, in equilibrium with po2=l atm, to a point outside the electrolyte surface. It thus also expresses the energy of solvation of an electron from vacuum to the Fermi level of the solid electrolyte. 

Equation (7.32) underlines the pinning of the Fermi levels of metal electrodes with the solid electrolyte and reminds the fact that the absolute electrode potential is a property of the solid electrolyte and of the gaseous composition but not of the electrode material.21... 

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