Mixed oxides electrolytes

PZC/IEP of Unspecified Zr-Y Mixed Oxide Electrolyte T Method Instrument... 

Synthesis Methods and Properties of Mixed Oxides Electrolytes... 

Hydrometallurigcal Processes. In hydrometaHurgical processes, metal values and by-products are recovered from aqueous solution by chemical or electrolytic processes. Values are solubilized by treating waste, ore, or concentrates. Leaching of copper ores in place by rain or natural streams and the subsequent recovery of copper from mnoff mine water as impure cement copper have been practiced since Roman times. Most hydrometaHurgical treatments have been appHed to ores or overburden in which the copper was present as oxide, mixed oxide—sulfide, or native copper. PyrometaHurgical and hydrometaHurgical processes are compared in Reference 34. 

A unique application of the solid oxygen electrolytes is in dre preparation of mixed oxides from metal vapour deposits. For example, the ceramic superconductors described below, have been prepared from mixtures of the metal vapours in the appropriate proporhons which are deposited on the surface of a solid electrolyte. Oxygen is pumped tluough the electrolyte by the application of a polarizing potential across the electrolyte to provide the oxidant for the metallic layer which is formed. 

In the following chapter examples of XPS investigations of practical electrode materials will be presented. Most of these examples originate from research on advanced solid polymer electrolyte cells performed in the author s laboratory concerning the performance of Ru/Ir mixed oxide anode and cathode catalysts for 02 and H2 evolution. In addition the application of XPS investigations in other important fields of electrochemistry like metal underpotential deposition on Pt and oxide formation on noble metals will be discussed. 

For Cl2 or 02 evolution the stability of ruthenium based electrodes is not sufficient on a technical scale. Therefore the possibility of stabilizing the ruthenium oxide without losing too much of its outstanding catalytic performance was investigated by many groups. For the Cl2 process, mixed oxides with valve metals like Ti or Ta were found to exhibit enhanced stability (see Section 3.1), while in the case of the 02 evolution process in solid polymer electrolyte cells for H2 production a mixed Ru/Ir oxide proved to be the best candidate [68, 80]. 

In order to understand the observed shift in oxidation potentials and the stabilization mechanism two possible explanations were forwarded by Kotz and Stucki [83], Either a direct electronic interaction of the two oxide components via formation of a common 4-band, involving possible charge transfer, gives rise to an electrode with new homogeneous properties or an indirect interaction between Ru and Ir sites and the electrolyte phase via surface dipoles creates improved surface properties. These two models will certainly be difficult to distinguish. As is demonstrated in Fig. 25, XPS valence band spectroscopy could give some evidence for the formation of a common 4-band in the mixed oxides prepared by reactive sputtering [83],... 

The MIOX system is a technology that generates mixed oxidant disinfectants using only salt, 12-V direct current, and an electrolytic cell. By using this technology, oxidants and free available chlorine can be generated on-site for water disinfection and aqueons waste treatment. 

The MIOX Corporation prepared cost estimates on the MIOX system based on bench-scale testing. They estimated that the active mixed oxidant solution produced by the process costs about 7 cents/gal to produce, including the costs of power, salt, and electrolytic cell recycling. At an injection ratio of 1 to 500, two gallons of mixed oxidants would be required to treat 1000 gal of water. The amount of mixed oxidants required varies with each individual waste stream, and with the treatment goals, so this estimate is by no means universal (D15848Z, p. 114). 

Hence the partial pressure of oxygen and the temperature determine whether the solid will exhibit n-type, p-type or ionic conduction. Although the concentration of defects is important it is also necessary to consider the mobilities of the individual defects higher ionic mobilities will result in a larger domain for electrolytic conduction. Figure l4 shows the dominant mode of conduction in some mixed oxide materials, exhibiting solid electrolyte behaviour, as a function of temperature and oxygen partial pressure. 

Saturating the electrolyte with iron(lll) hydroxide (e.g., by addition of aqueous solutions of ferric nitrate) and simultaneously adding cobaltous salts leads to in situ formation of a mixed Fe(llI)/Co(ll)/Co(IIl) deposit, which exhibits catalytic activity comparable to that of Fe304 shown by the current voltage curve in Fig. 11. Such mixed oxidic catalyst coatings are composed of very small oxide crystals, which evidently are dissolved upon current interruption due to dissociative oxide dissolution. The transfer of dissolved metal ions to the cathode followed by cathodic deposition of the metal, however, can be completely prohibited, if the potential of the cathode due to optimal electrocatalysis of cathodic hydrogen evolution proceeds with an over-... 

The ZPC of an unaltered mixed oxide, silicate, or phosphate in a system devoid of specific electrolytes other than the PDI is approximately the average of the IEP(s) s of its component oxides weighted on an atomic (cation) basis. Account must be taken of the correct cation coordination, cleavage and morphological habit, hydration state, and structural modification produced by abrasion. Experimental and calculated ZPC s for a group of silicate and phosphate minerals are compared in Figure 13 to show the accuracy to be expected in prediction. 

Fig. 26. Diagram of oxygen reduction in solid oxide electrolyte cell with (a) a pure electronic conductor, (b) a mixed (electronic and ionic) conductor. From ref. [76].

CHEMICAL SYNTHESIS OF MIXED OXIDE POWDERS FOR SOLID OXIDE FUEL CELL (SOFC) ELECTROLYTE AND ELECTRODES... 

The redox properties of ceria-zirconia mixed oxides are interesting, because these materials find applications as electrolytes for solid oxide fuel cells, supports for catalysts for H2 production, and components in three-way automobile exhaust conversion catalysts. The group of Kaspar and Fornasiero (Montini et al., 2004, 2005) used TPR/TPO-Raman spectroscopy to identify the structural features of more easily reducible zirconia-ceria oxides and the best method for their preparation by suitable treatments. TPR/TPO experiments and Raman spectra recorded during redox cycles demonstrated that a pyrochlore-type cation ordering in Ce2Zr2Og facilitates low temperature reduction. 

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