Active Cathodes for Super-High Power Density Solid Oxide Fuel Cells Through Space Charge Effects. (Report for April 1, 2005-June 30, 2005)

摘要

This report summarizes the work done during the eleventh quarter of the project. Conductivity relaxation experiments were conducted on porous La(sub 0.5)Sr(sub 0.5)CoO(3-delta) (LSC50) samples over a temperature range from 350 to 750 deg C, and over an oxygen partial pressure, pO(sub 2), switch between 0.04 and 0.06 atm in order to determine the surface exchange coefficient, k(sub chem). The normalized conductivity data could be fitted to a first order kinetic equation. The time constant decreased with decreasing temperature between approx 750 and approx 450 deg C, but sharply increased with decreasing temperature between 450 and 350 deg C. The corresponding k(sub chem) was estimated using three models: (a) A porous body model wherein it is assumed that the kinetics of surface exchange is the slowest. (b) Solution to the diffusion equation assuming the particles can be approximated as spheres. (c) Solution to the diffusion equation assuming the particles can be approximated as cylinders. The values of k(sub chem) obtained from the three models were in good agreement. In all cases, it was observed that k(sub chem) increases with decreasing temperature between 750 and 450 deg C, but below 450 deg C, it sharply decreases with further decrease in temperature.