Proton-Conducting Ceramics

Solid Oxide Fuel Cells (SOFCs) are particularly attractive because of their high efficiencies (especially when integrated with thermal energy conversion devices that utilize the high quality waste heat available from SOFCs), their fuel flexibility, and their operability in the absence of precious metal catalysts. A key hurdle to the commercialization of SOFCs is their high cost, which, in part, is due to their high operating temperatures (800 - 1000C) and associated restrictions on materials choices. Recognition of this challenge has led the fuel cell research community to search for alternatives to the standard SOFC electrolyte, yttria stabilized zirconia (YSZ), that will enable reduced temperature operation (500 - 700C).

One of the most promising such alternatives is the family of proton conducting perovskites (Fig. 1). These materials have particularly high conductivity, but the most promising compositions in terms of electrical properties, Y-doped BaCeO3, readily react with CO2 and suffer from other long-term stability problems. Another promising candidate for Proton Ceramic Solid Oxide Fuel Cell (PC SOFC) applications is Y-doped BaZrO3 (BYZ). It has desirable properties such as high protonic conductivity and excellent chemical and mechanical stability. The current limitation for application of BYZ in PC SOFCs is the extremely high grain boundary resistance, which leads to the relatively poor total conductivity. The key to obtaining high conductivity in BYZ is to enhance grain growth and/or increase conductivity across grain boundaries. While these challenges are not directly amenable to theoretical approaches, computational studies of proton transport through bulk perovskites might help to solve the above-mentioned problem and/or to develop alternative materials that may not suffer from the same microstructural drawbacks.

Figure 1: Perovskite structure.

Personnel: Dr. Boris Merinov, Dr. Sang Soo Han and Dr. Adri van Duin.