Ceramic-based electrolytes

The ionic conductivity of polymer electrolytes is typically 100 to 1000 times less than exhibited by a liquid- or ceramic-based electrolyte. Although higher conductivities are preferable, and indeed a great deal of effort has gone into improving the bulk conductivity of polymer electrolytes over the years, 100-fold or 1000-fold increases are not essential, as a thin film electrochemical cell configuration can largely compensate for the lower values. 

J. Xue, and R. Dieckmann. Oxygen partial pressure dependence of the oxygen content of zirconia-based electrolytes in Ionic and Mixed Conducting Ceramics Second International Symposium 94-12, 191-208 (1994) ES Meeting San Francisco, California. 

Amperometric cells, sensors using, 22 271 Amperometric measurements, 14 612 Amphetamine, 3 89-90 Amphibole asbestos, 1 803 3 288 crystal structure, 3 297-298 exposure limits, 3 316 fiber morphology, 3 294-295 silicate backbone, 3 296 Amphibole potassium fluorrichterite, glass- ceramics based on, 12 637 Amphiphile-oil-water-electrolyte phase diagram, 16 427-428 Amphiphile-oil-water phase diagrams,... 

Fast-ion conductors general comments The essential element of ceramics-based fuel cells and batteries is the electrolyte, a solid, fast-ion conductor. 

A new special type of materials are the ceramics based on J and J "-AI2O3 (see p. 29). These have relatively high electrical conductivity and have been successfully employed as solid electrolytes in sodium-sulphide batteries. The best results have been obtained with ceramics of jS"-Al203 stabilized with 0.7—0.8 % Li02 (Youngblood et al., 1977). 

Other oxygen ion conductors that have potential use as solid electrolytes in electrochemical devices are stabilized bismuth and cerium oxides and oxide compounds with the perovskite and pyrochlore crystal structures. The ionic conductivity and related properties of these compounds in comparison with those of the standard yttria-stabilized zirconia (YSZ) electrolyte are briefly described in this section. Many of the powder preparation and ceramic fabrication techniques described above for zirconia-based electrolytes can be adapted to these alternative conductors and are not discussed further. 

The solid-state electrolytes can also be used as separators, and using solid-state electrolytes may simplify the fabrication and packaging processes of ESs. Solid electrolyte-based ESs can also reduce the leakage concern that related to the liquid electrolyte-based ESs. To data, various kinds of solid-state electrolytes have been developed for ESs. Most of them are polymer-based electrolytes, and inorganic solid materials such as ceramic electrolytes have attracted only very limited attention [718-721],... 

High-temperature electrolysis based on ceramic solid electrolytes... 

It may be seen that the related Arrhenius plot does not break around 70 °C, as typically expected for PEO-based electrolyes. It clearly suggests that the added ceramics prevent PEO crystallisation, with a resulting enhancement in conductivity which at room temperature may reach values of the order of 10 S cm compared to the 10 S cm of the standard, ceramic-free electrolytes. 

Fig. 34.3. Performances of hydrogen fuel-cells using perovskite-type oxide ceramic as solid electrolyte and porous platinum electrodes, (a) SrCe03-based electrolyte (b) BaCe03-based electrolyte. 

Dudek M (2008b) Ceramic oxide electrolytes based on CeO -preparation, properties and possibility of application to electrochemical devices. J Eur Ceram Soc 28(5) 965-971... 

The cell is based upon a liquid sodium anode and liquid sulphur cathode, separated by a beta alumina ceramic-type electrolyte which is an electronic insulator, but through which sodium ions diffuse rapidly at 300-400 C. During discharge the reaction 2Na + 5S —> Na S. leads to an open circuit voltage (GCV) of 2.08V. Continued reaction beyond Na S results in the formation of lower polysulphides in the range Na - Na S (OCV 1.78V), after which solid separates out. The polysulphides... 

A US company has been developing a fuel cell based on a ceramic oxide electrolyte to operate at about 1000° C. It is able to consume either hydrogen or hydrogen-carbon monoxide mixtures (reformed natural gas, etc.) as the anode fuel. Unlike all the other systems which are based on stacks of parallel porous electrodes, the design here is centred on a ceramic oxide tube and cylindrical electrodes. A number of 3 kW units with 144 cells are under test to check performance and to ascertain lifetime under practical conditions. A high electrical efficiency of > 50% has been achieved in early tests and very useful waste heat is available from this high-temperature cell. 

Yoon et al. [48] proposed a liquid junction free polymer membrane-based reference electrode system for blood analysis under flowing conditions. They used silicmi wafers as well as ceramic substrate to fabricate ion selective sensors with an integrated reference electrode. The silver chloride layer was coated with a membrane based on aromatic polyurethane (PU 40 membrane) with equimolar amounts of both cathodic and anodic lipophilic additives (TDMACl and KTpCIPB) to reduce the electrical resistance (see Chaps. 12 and 13). The ceramic-based sensors were fabricated by screen-printing methods. Both reference electrodes showed a rather stable potential in various electrolyte solutions with different pH values and different concentrations of clinically relevant ions, providing that the ionic strength of the solution is over 0.01 M. The integrated ISE cartridge based on the ceramic chip could be used continuously for a week. 

SOFC is a higher-temperature fuel cell that operates at a temperature range of 800°C-1000°C with a high operating efficiency of 65%. Electrolyte in an SOFC is a solid ceramic-based material like yttrium-stabilized zirconium (YSZ). It can operate with hydrogen fuel as well as with other fuel types such as natural gas, biogas, and coal gas. The basic components and the overall reaction are similar in an SOFC with the exception of the electrochemical reactions at the anode and cathode electrodes. 

Ceria has been used as the ceramic part (or as an addition) in nickel- or ruthenium-cermet anodes for hydrogen oxidation. " Beneficial effects have been reported and interpreted as most likely being due to the broadening of the three-phase boundary zone. However, one of the major drawbacks of using ceria in cells with YSZ-based electrolytes is its chemical reactivity with the YSZ electrolyte at high temperatures. Sintering of a doped ceria anode on a YSZ electrolyte at high temperatures (>1200°C) results in the formation of a reaction (diffusion) zone with limited oxide ion conductivity. ... 

Figure 18.1 shows the temperature variation of the ionic conductivities of several polymer-electrolyte systems. At room temperature they are typically 100-1000 times less than those exhibited by a Hquid or the best ceramic- or glass-based electrolytes... 

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