The high‐temperature zirconia electrolyte fuel cell is materials‐limited in both its performance and its range of potential application. The most significant materials limitations and problems occur with the cathode. Cathode materials must satisfy four general criteria: (i) chemical, (ii) electrochemical, (iii) mechanical, and (iv) economical. In this paper, the interaction between cathode materials and cell performance is considered quantitatively for three general classes of cathodes, viz., metals, oxides with embedded current collectors, and electronically conducting oxides.

A thermochemical analysis of impurity deposits in gas turbines has been carried out for liquid fuels containing sodium and vanadium. The predominant species containing these elements are Na2SO4 , normalNaOH , and VOfalse(OH)3 in the gas phase and Na2SO4 , V2O5 , and Na2V2O6 in the condensed phase. The minimum concentrations of sodium and vanadium in the ruel above which deposition can occur have been determined for various operating conditions of the gas turbine. Effects of the air/fuel ratio, sulfur impurity level, temperature, and pressure have been considered. Detailed calculations have also been performed to determine the composition and amount of deposit per gram‐atom of gas for a gas turbine operating at 5 atm at an air/fuel ratio of 60/1 using a fuel containing 1 w/o sulfur with different amounts of sodium (0.1–10 ppm) and vanadium (0.1–30 ppm).

Following the thermodynamic and electrochemical description of high‐temperature electrolytic dissociation of water vapor discussed in Part I , this paper is concerned with materials problems, design, and fabrication of both single‐cell and multicell devices. Oxygen anodes and depolarized anodes are both considered, and it is concluded that the most feasible system is that employing discontinuous electrolyte segments and depolarized anodes.

This paper describes the dissociation of water vapor in high-temperature, solid oxide electrolyte cells. The characteristics of these cells are related to a composition-dependent open-circuit voltage, which can be obtained from thermodynamic considerations, to ohmic resistance, and to mass transport overvoltages. The problem of maintaining a heat balance in a system consisting of such cells is considered in terms of the heat loss through the leads connecting the cells with the surroundings. A conclusion is that the electrical energy requirement for dissociation can be reduced substantially by series connection of individual cells within the high-temperature region of the system, but that ohmic resistance limits the optimized current density through the electrolyte to values well below the maximum values that are feasible. * Electrochemical Society Active Member.

ELECTRICAL PROPERTIES 2119preparation. For "mixed oxide" materials, the ratio of the inhomogeneity resistance to the intrinsic resistance scales approximately linearly with porosity, but the connection appears to be indirect. The existence of regions, perhaps at the grain boundaries, of variable dopant concentration is a possible explanation, with the incidence of such regions correlating with porosity. For the "chemically prepared" materials, a much larger equivalent inhomogeneity capacitance is observed than with "mixed oxide" materials~ The differences cannot be accounted for on the basis of grain boundary geometry, but may reflect again a chemical effect at grain boundaries, such as an increase in the concentration of electronic charge carriers.With polycrystalline specimens of materials of this kind the use of impedance spectroscopy, the analysis of the frequency dependence of the impedance" over a wide frequency range, appears to be essential to a full understanding of the mass and charge transport processes.