Pulsed Laser Deposition of SrCo0.8Nb0.1Ta0.1O3-Δ As a Cathode for Thin Film Solid Oxide Fuel Cells

Abstract

Recently, Li et al. reported co-doped perovskite SrCo0.8Nb0.1Ta0.1O3-δ (SCNT), which shows high oxygen reduction reaction (ORR) activity [1]. This research demonstrates thin film deposition of SCNT by pulsed laser deposition technique and successfully applied to thin-film solid oxide fuel cells (SOFCs). For decades, there have been many researches on SOFCs operating at intermediate or low temperature range (400-600 °C). The operating temperature-lowering strategy can be divided into two: material development and nano-thin architecturing. The material development approach is to develop brand-new materials and the aforementioned SCNT is one of such approaches. According to [1], it shows area-specific charge transfer resistance as low as 0.16 ~ 0.68 Ω·cm2, which is one of the state-of-the-art ORR kinetics in literature, and the SCNT was successfully applied to Gd-doped CeO2 electrolyte-based SOFC as a cathode. The SOFC with SCNT exhibited comparable electrochemical performance in spite of the operating temperature range below 500 °C. Another strategy is to make the ceramic electrolyte as thin as possible because most of the performance comes from the ohmic resistance of the electrolyte inside SOFCs. There have been also many reports on such thin film SOFCs operating below 500 °C, but in this case even with the most well-known yttria-stabilized zirconia (YSZ) did the SOFCs exhibit the comparable performance to normal SOFCs operating at high temperature (>700 °C). However, the previous researches mostly employed Pt as a cathode, which is not suitable for industrial applications due to expensive price. Therefore, it is believed that champion thin film SOFCs without novel metals will be feasible if both materials development and thin-film architecturing are combined together. Otherwise, such thin film SCNT can be used as an interfacial (functional) layer between electrolyte and electrode since thin film could have the fine nano-morphology favorable to electrochemical reaction. The SCNT target was prepared by solid state reactive sintering method and described in detail elsewhere [1]. This target was then mounted to pulsed laser depositing machine and deposited onto the Si wafer. Here, two depositing conditions are selected as the morphology-influencing parameters: internal pressure and substrate temperature. By changing these parameters, we seek the conditions with which the deposited thin film SCNT has columnar structure. Such thin film SCNT was subsequently applied to thin film SOFCs. Here, the thin film SOFCs were fabricated on nano-porous substrates. On top of the nano-porous substrate, Thin Ni film was firstly deposited by sputtering. After that, the YSZ was also deposited by sputtering. The as-fabricated thin film SOFCs with SCNT cathodes were operated at 450 and 500 °C. Polarization characteristics and corresponding electrochemical impedance spectroscopy were employed to deep understandings into the electrochemical kinetics of the fuel cells. Reference 1. M. Li, M. Zhao, F. Li, W. Zhou, V. K. Peterson, X. Xu, Z. Shao, I. Gentle, Z. Zhu, Nat. Commun., 8, 13990(2017)