Enhanced Ceria Solid Electrolyte Fuel Cell Development. Reduction of Electronic Conductivity Permits use of a Solid Ceria Electrolyte in High Efficiency High Power Density Fuel Cells at Temperatures Compatible with Metallic Cell Hardware.

摘要

The primary obstacle to the use of ceria as a high power density solid oxide fuel cell electrolyte has been a low level electronic short. This develops under reducing (anode) conditions as a result of partial reduction of the CeO2 lattice. The result is a decrease in: a) cell voltage, b) useful external current, c) efficiency, d) power density. A dopant concept has been shown to lower the anode PO2 below which the short becomes detrimental (electrolytic domain boundary) by two orders of magnitude. Two dopants, A and B have been shown to be effective. The optimum dopant A level was shown to be 1-3 metal atom percent. This reduction in the electronic short current is the primary achievement of this program. Analysis of the activation energies for electronic and ionic conduction indicate that the dopant is effective in reducing the short by trapping the electronic charge carriers rather than preventing partial reduction of the ceria. Measurement of the grain boundary and bulk conductivities show the overall ionic conductivity is limited by grain boundary resistance. If lower grain boundary resistance can be achieved by processing changes, another two orders of magnitude improvement in electrolytic domain boundary is possible. An attempt to limit the short by establishing an electronically resistive grain boundary barrier layer was abandoned. A separate grain boundary phase was difficult to maintain during the sinter densification step. The dopant approach was selected for further development in Phase II. (jhd)