Atomic Layer Deposition Treatment on Infiltrated Cathodes for Solid Oxide Fuel Cells

Abstract

A solid oxide fuel cell (SOFC) is considered one of the most promising power generation technologies for the future because of its high efficiency, low emission and fuel flexibility. To avoid durability and cost issues originated from high-temperature operation, intermediate temperature SOFCs (IT-SOFCs) operating between 600 – 750 °C has been extensively studied. As an approach to maximize the cathodic surface area and surface-sensitive catalytic activity at the reduced temperature, wet impregnation (i.e. infiltration) of various active catalysts has been widely used. Infiltrated cathodic nanoparticles with the size of few nanometers have indeed proved to be highly effective in boosting the electrochemical activity toward oxygen reduction reaction (ORR).1 In this study, we first applied various infiltrates on a porous LaNi0.6Fe0.4O3 (LNF) cathode. The infiltrated materials were chosen based upon their merits in a specific aspect such as surface exchange rate, ionic conductivity and electronic conductivity. The infiltrated materials of choice include LNF, (La1−xSrx)1−yMnO3 (LSM), Pr6O11, Pr-doped ceria and gadolinia-doped ceria (GDC). It was found that an infiltration of LNF (the same material with the backbone cathode material) reduced the electrode polarization by more than an order of magnitude at 700 °C, indicating the significant impact of surface area itself on the cathodic performance. Among all the cathodes, Pr6O11-infiltrated cathode rendered the lowest cathodic polarization. On the other hand, infiltrated nanoparticles are highly susceptible to thermal agglomeration during operation due to their tiny size and resulting high surface energy. The agglomeration process results in a significant loss of catalytically active surface area, leading to a performance degradation over time.2 To address the issue, an ultrathin oxide layer (ceria, Y-dope ceria (YDC), zirconia and Y-doped zirconia (YSZ)) was coated by the atomic layer deposition (ALD) on the infiltrated cathode. While the application of ALD overcoat on porous cathode material itself is not new,3,4 its application to infiltrated cathodes has rarely been reported. To achieve a proper doping for oxygen conduction, Y2O3 sub-cycles for YDC and YSZ were performed once for every 4 ceria and zirconia sub-cycles, respectively. The electrochemical performance between 600 – 750 °C, short-term durability (~100 h) of the resulting structures (performed at 700 °C under a cell polarization of 0.5 V) and relevant discussions will be presented. This work was supported by the NASA MIRO Program (NNX15AQ01A). References 1 D. Ding, X. Li, S. Y. Lai, K. Gerdes and M. Liu, Energy Environ. Sci., 2014, 7, 552. 2 Y. Zhang, R. Knibbe, J. Sunarso, Y. Zhong, W. Zhou, Z. Shao and Z. Zhu, Adv. Mater., 2017, 29, 1700132. 3 A. Karimaghaloo, A. M. Andrade, S. Grewal, J. H. Shim and M. H. Lee, ACS Omega, 2017, 2, 806–813. 4 Y. Gong, D. Palacio, X. Song, R. L. Patel, X. Liang, X. Zhao, J. B. Goodenough and K. Huang, Nano Lett., 2013, 13, 4340–5.