Strontium electrode

Another application is in the oxidation of vapour mixtures in a chemical vapour transport reaction, the attempt being to coat materials with a thin layer of solid electrolyte. For example, a gas phase mixture consisting of the iodides of zirconium and yttrium is oxidized to form a thin layer of yttria-stabilized zirconia on the surface of an electrode such as one of the lanthanum-strontium doped transition metal perovskites Lai Sr MO --, which can transmit oxygen as ions and electrons from an isolated volume of oxygen gas. 

In addition to the chemical interactions described above, microstructural changes in the electrode can lead to performance degradation after long operation time. For example sintering of the porous structure can degrade electrode performance. In the case of LSM cathodes, the sintering ability is found to be related to the strontium dopant level and stoichiometric composition of (La, Sr)xMn03. In addition, LSM with A-site deficient compositions (x < 1) sinters more readily than their B-site deficient counterparts (x > 1) [198, 199],... 

The interconnect material is in contact with both electrodes at elevated temperatures, so chemical compatibility with other fuel cell components is important. Although, direct reaction of lanthanum chromite based materials with other components is typically not a major problem [2], reaction between calcium-doped lanthanum chromite and YSZ has been observed [20-24], but can be minimized by application of an interlayer to prevent calcium migration [25], Strontium doping, rather than calcium doping, tends to improve the resistance to reaction [26], but reaction can occur with strontium doping, especially if SrCr04 forms on the interconnect [27],... 

To meet the requirements for electronic conductivity in both the SOFC anode and cathode, a metallic electronic conductor, usually nickel, is typically used in the anode, and a conductive perovskite, such as lanthanum strontium manganite (LSM), is typically used in the cathode. Because the electrochemical reactions in fuel cell electrodes can only occur at surfaces where electronic and ionically conductive phases and the gas phase are in contact with each other (Figure 6.1), it is common... 

Fig. 10-26. Energy diagram for a cell of photoelectrolytic decomposition of water consisting of a platinum cathode and an n-type semiconductor anode of strontium titanate of which the Fermi level at the flat band potential is higher than the Fermi level of hydrogen redox reaction (snao > epM+zHj) ) he = electron energy level referred to the normal hydrogen electrode ri = anodic overvoltage (positive) of hole transfer across an n-type anode interface t = cathodic overvoltage (negative) of electron transfer across a metallic cathode interface.

Highly pure lanthanum oxide is used to make optical glass of high refractive index for camera lenses. It also is used to make glass fibers. The oxide also is used to improve thermal and electrical properties of barium and strontium titanates. Other applications are in glass polishes carbon arc electrodes fluorescent type phosphors and as a diluent for nuclear fuels. In such apph-cations, lanthinum oxide is usually combined with other rare earth oxides. 

Elemental composition Sr 41.40%, N 13.24%, 0 45.36%. An aqueous solution of the salt may be analyzed for strontium by AA, ICP, or other methods. The nitrate anion may be measured by ion chromatography or by nitrate ion-specific electrode. 

The Ba(CN)2 used contains metal cation impurities limited to sodium, aluminum, strontium, and 0.05% potassium, plus traces of iron, magnesium and lithium. Each platinum electrode is a 90-100 cm2 heavy sheet with purity > 99%. During the electrolysis, half of each electrode is submerged in the solution. All water used is distilled, and all filters are medium-pore fritted-glass filters. The electrolysis apparatus consists of a variable ac voltage supply with an ac ammeter included in the circuit. 

While we have not yet carried out detailed kinetic measurements on the rate of photocorrosion, our impression is that the process is relatively insensitive to the specific composition of the strontium titanate. Trace element compositions, obtained by spark-source mass spectrometry, are presented in Table I for the four boules of n-SrTi03 from which electrodes have been cut. Photocorrosion has been observed in samples from all four boules. In all cases, the electrodes were cut to a thickness of 1-2 mm using a diamond saw, reduced under H2 at 800-1000 C for up to 16 hours, polished with a diamond paste cloth, and etched with either hot concentrated nitric acid or hot aqua regia. Ohmic contacts were then made with gallium-indium eutectic alloy, and a wire was attached using electrically conductive silver epoxy prior to mounting the electrode on a Pyrex support tube with either epoxy cement or heat-shrinkable Teflon tubing. 

All but one of the reactions in Figure 4 lead to the formation of the soluble TiO + ion this seems consistent with the observed changes in the visible absorption spectrum of the solid electrode. It may also be that other titanium species are formed in solution, such as peroxytitanium complexes like H Ti05 We have no direct evidence as to the identity of the solution species at this time, and have limited the candidate corrosion reactions shown in Figure 4 to those for which thermodynamic data are readily available. Nonetheless, the fact that titanium is observed in the electrolyte only upon extensive photocorrosion (and then in smaller amounts than strontium) suggests that the initial photocorrosion process involves the loss of strontium from the SrTi03, with the formation of Sr(0Ac)2 or SrSO. ... 

The increasing threat of international terrorism was one motivation for development of ISE for the determination of Cs+ in environmental samples [80]. In an event such as a Chernobyl-type disaster or the explosion of a dirty bomb , cesium is one of the most important reaction products and is expected to be the most significant threat to public health [81]. With a detection limit of 10 8M, the developed electrode is sensitive enough for this application and the successful detection of cesium activities in spiked water samples has been demonstrated (see Procedure 2 in CD accompanying this book). In addition, the electrode shows excellent selectivity to cesium in the presence of high levels of strontium, an important interferent originating from nuclear explosions. 

It is noteworthy to mention that under normal conditions, cesium is not considered a major contaminant of natural and ground waters since it preferentially adheres to soils, thereby showing relatively low mobility. Therefore, a cesuim-selective electrode for the successful determination of cesium in natural waters that exhibits negligible interference by strontium was characterised and developed utilising UIC as the ion exchanger. 

The stack electrolytes are scandia-stabilised zirconia, about 140 (im thick. The air-side electrodes (anode in the electrolysis mode) are a strontium-doped manganite. The electrodes are graded, with an inner layer of manganite/zirconia ( 13 pm) immediately adjacent to the electrolyte, a middle layer of pure manganite ( 18 pm), and an outer bond layer of cobaltite. The steam/hydrogen electrodes (cathode in the electrolysis mode) are also graded, with a nickel-zirconia cermet layer ( 13 pm) immediately adjacent to the electrolyte and a pure nickel outer layer ( 10 pm). 

The oxygen electrode of the cells under analyses in our project is a perovskite material Ao.8Sr0.2Mn03 (element A is not disclosed because it is proprietary information). Scandia-stabilised zirconia (SSZ) is used as the electrolyte. The cathode consists of a Ni-SSZ cermet. Also, a lanthanum strontium cobaltite (La0.8Sr0.2CoO3, also known as LSC) is used as the bond layer. 

Dabestani, R. Bard, A. J. Campion, A. Fox, M. A. Mallouk, T. E. Webber, S. E. White, J. M. Sensitization of titanium dioxide and strontium titanate electrodes by ruthenium(II) tris(2,2 -bipyridine-4,4 -dicarboxylic acid) and zinc tetrakis(4-carboxy-phenyl)porphyrin An evaluation of sensitization efficiency for component photo-electrodes in a multipanel device, J. Phys. Chem. 1988, 92, 1872. 

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