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.
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