Influence of deposition temperature on the microstructure of thin-film electrolyte for SOFCs with a nanoporous AAO support structure

In this paper we investigate the influence of deposition temperature on the microstructure of yttria stabilized zirconia thin-films based on an anodized aluminum oxide (AAO) support structure. The yttria-stabilized zirconia (YSZ) electrolytes were deposited on a Pt anode/AAO support using DC magnetron reactive sputtering under deposition temperatures of RT and 500 °C. Elevating the deposition temperature led to enhanced surface mobility in the sputtered adatoms, which helped prevent pinhole generation and minimized the thickness of the electrolyte. A thin-film fuel cell with a YSZ electrolyte only 300 nm thick was successfully fabricated by elevating the deposition temperature. This cell exhibited an open circuit voltage (OCV) of 0.97 V, which is significantly higher than the OCV values of 0.3 V for a cell deposited at RT. However, in spite of the thin electrolyte, the performance of the cell deposited at the higher temperature showed limited value due to its relatively high polarization resistance. Through further investigation into the grain morphology, we verify that the increasing deposition temperature can affect not only the film density but also increase the grain size of the electrolyte, which is related to oxygen incorporation for ORR kinetics. Electrochemical impedance spectroscopy (EIS) results indicate that the grain size change caused by the elevated deposition temperature adversely affected the polarization resistance and the cell performance. These results indicate that careful adoption of elevated electrolyte deposition temperatures are required to optimize fuel cell performance.