Multi-Layered Thin Film Y:BaZrO3 Electrolytes for Anode-Supported Protonic Ceramic Fuel Cells

Acceptor-doped barium zirconate electrolytes, represented as yttrium-doped barium zirconate (Y:BaZrO₃ or BZY), are expected to allow ceramic fuel cells to be operated at intermediate temperatures in the range below 600 °C. This is because BZY conducts protons and exhibits a relatively high ionic conductivity with relatively small activation energy, especially compared to ceramics that conduct oxide ions, including yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (GDC). The bulk conductivity of BZY is greater than that of YSZ by about one order at 600 °C and by two orders at 400 °C and, unlike cerate-based materials, BZY was found to exhibit good phase stability (1). Thus, there have been numerous efforts to develop BZY-based protonic ceramic fuel cells (BZY-PCFCs). Although several studies have reported BZY-PCFCs to perform well, with outputs of 140 mW/cm² and 180 mW/cm² in the intermediate temperature regime at 400 °C (2) and 450 °C (3), respectively, both of these were achieved in the form of freestanding nanoscale membranes. For practical production and use, however, fabrication of the BZY electrolyte in anode-supported stacks would be more desirable. Yet, the performance of anode-supported BZY-PCFCs is not yet as good as that of solid-oxide fuel cells. To our knowledge, 170 W/cm² is the greatest power output achieved with BZY-based fuel cells at 600 °C (4). An attempt to adopt a thin BZY electrolyte (4μm thickness) in anode-supported PCFCs has produced a power output of merely 110 W/cm² at 600 °C (5), attributed to the prevalence of a relatively large ohmic resistance, which implies the presence of structural defects such as poor grain adhesion (5). After performing a series of experiments, we realized that the adoption of multiple anode support layers with multi-step sintering promotes the structural and mechanical stability of thin film BZY electrolytes. As a result, the power output has exceeded 700 mW/cm² at 600 °C with an open circuit voltage over 1 V. At this presentation, we will share our recent experimental results and discuss the cell performance in relation with structural characteristics and composition.

1. K. D. Kreuer, Annu. Rev. Mater. Res., 33, 333 (2003).

2. J. H. Shim, J. S. Park, J. An, S. Kang, T. M. Gür, and F. B. Prinz, Chem. Mater., 21(14), 3290 (2009).

3. Y. B. Kim, T. M. Gür, S. Kang, H-J. Jung, R. Sinclair, and F. B. Prinz, Electrochem. Commun., 13(5), 403 (2011).

4. L. Bi , E. Fabbri , Z. Sun, and E. Traversa, Energy Environ. Sci., 4, 409 (2011).

5. D. Pergolesi, E. Fabbri, and E. Traversa, Electrochem. Commun., 12, 977 (2010).