During the last three decades, a large number of investigations has been reported pertaining to the science and technology of solid oxide fuel cells (SOFCs) based mainly on the yttria-stabilized zirconia (YSZ) electrolyte. Because of the problems associated with the high temperature of operation (~ 1000°C) of the YSZ-based cells, there has been a substantial effort to develop alternative electrolytes with ionic conductivity comparable to that of YSZ at relatively lower temperatures. This review presents a systematic evolution in the area of the development of new electrolytes based on bismuth sesquioxide for fuel cell applications at moderate temperatures.

Bismuth oxide-based solid electrolytes for fuel cells

A proton exchange membrane fuel cell power system for producing electrical power is described and which includes a plurality of discrete fuel cell modules having at least two membrane electrode diffusion assemblies, each of the membrane electrode diffusion assemblies having opposite anode and cathode sides; a pair of current collectors are individually disposed in juxtaposed ohmic electrical contact with opposite anode and cathode sides of each of the membrane electrode diffusion assemblies; and individual force application assemblies apply a given force to the pair current collectors and the individual membrane electrode diffusion assemblies. The proton exchange membrane fuel cell power system also includes an enclosure mounting a plurality of subracks which receive the discrete fuel cell modules. Additionally, a control system is disclosed which optimizes the performance parameters of the discrete proton exchange membrane fuel cell modules.

Proton exchange membrane fuel cell power system

Pentavalent uranium chemistry: synthetic pursuit of a rare oxidation state.

High-resolution X-ray photoelectron spectroscopy was used to demonstrate that reduction of aqueous U6+ at ferrous mica surfaces at 25 degrees C preserves U5+ as the dominant sorbed species over a broad range of solution compositions. Polymerization of sorbed U5+ with sorbed U6+ and U4+ is identified as a possible mechanism for how mineral surfaces circumvent the rapid disproportionation of aqueous U5+. The general nature of this mechanism suggests that U5+ could play an important, but previously unidentified, role in the low-temperature chemistry of uranium in reducing, heterogeneous aqueous systems.

Mica surfaces stabilize pentavalent uranium.

The formation mechanism, the temperature range for the growth, and the thermal stability of the 2223 phase in Bi(Pb)─Sr─Ca─Cu─O have been investigated using DTA/TG, XRD, SEM/EDAX, TEM, EPMA, four-probe resistance and acsusceptibility measurement. The formation of the 2223 phase was found to follow a dissolution–precipitation process. A 2212 phase first reacts with the liquid phase formed via an incongruent melting of the Ca2PbO4 phase, and a dissolution of CaO and CuO takes place. The 2201 phase, which has the largest negative free energy, is then precipitated from the melt; the nucleation and growth of the 2223 phase are subsequently developed by the reaction between the 2201 phase precipitates and ions of Ca2+ and Cu2+ present in the liquid phase. The 2223 phase is formed at temperatures in the range 827°C T < 856°C. The optimum temperature Tf for the formation of 2223 phase is 845°± 5°C. The 2223 phase is thermodynamically unstable at temperatures above 856°C.

2223 Phase Formation in Bi(Pb)─Sr─C─a─Cu─O: II, The Role of Temperature—Reaction Mechanism

A crystallization study has been carried out for rapidly solidified Bi-Sr-Ca-Cu-O glasses with nominal compositions ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{x}}$, ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{3}$${\mathrm{Cu}}_{4}$${\mathrm{O}}_{\mathrm{x}}$, and ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{4}$${\mathrm{Cu}}_{5}$${\mathrm{O}}_{\mathrm{x}}$. A temperature-time-transformation diagram for the glass with nominal composition ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{x}}$ has been constructed, within which crystalline superconducting and nonsuperconducting phase regions are identified. Eutectic and primary crystallization have been found to occur during the annealing process in these metal oxides. Glass transition temperature ${T}_{g}$ values, superconducting transition temperature values of crystallized products, and microstructural changes are measured and analyzed by differential thermal analysis, electrical resistivity, and magnetization shielding, x-ray diffraction, and scanning electron microscopy experiments. Also discussed are thermodynamics and kinetics of crystallization processes and the formation of the 110-K superconducting phase.

Crystallization of metal-oxide glasses in Bi-Sr-Ca-Cu-O systems

Oxide-ion conductivity of bismuth aluminates

Solid state synthesis of Bi2Sr2CaCu2Ox superconductor

Thermomechanical processing of reactively sintered Ag-clad (Bi, Pb)2Sr2Ca2Cu3Ox tapes

Crystal chemistry of uranium (V) and plutonium (IV) in a titanate ceramic for disposition of surplus fissile material

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