The Effect of the Electrode Particle Size Reduction to Nanoscale on the Low-Temperature-Operating Solid Oxide Fuel Cells

There have been intensive research activities to lower the operating temperature of solid oxide fuel cells (SOFC) to avoid problems related to the high-temperature (≥ 800 oC) operation, such as reliability and cost issues, and to expand the application fields toward portable and mobile power sources. In this regard, thin-film electrolytes and nanostructure electrodes have been at the center of interests to reduce the ohmic and polarization losses while decreasing the operating temperatures. The effect of thinning down the electrolyte is straightforward, however, that of particle size reduction at the electrode is rather complicated. One of the main reasons is the difficulty of elucidating various electrode reaction mechanisms. Another reason can be the difficulty of fabricating the nanostructure electrodes. If conventional powder processing is used, it is challenging to reduce the electrode particle size due to the original particle size of the starting powder and high-temperature sintering. On the other hand, in common thin-film-based SOFCs, nanostructure noble metal electrodes, such as Pt, are employed, thus it is difficult to interrogate the effect of the particle size reduction of the widely used SOFC electrodes. Owing to the research efforts during the last decade, we have been able to obtain high-performance low-temperature-operating SOFCs (LT-SOFCs) based on the anode-supported platform by implementing thin-film electrolytes and nanostructure electrodes, while using the common SOFC materials. A peak power density as high as 600 mW cm-2 at 500 oC was achieved based on the nanostructure Ni-YSZ anode, ~1 micron-thick YSZ-GDC bilayer electrolyte, and nanostructure LSC or LSC-GDC composite cathode. The active cell components are fabricated by using pulsed laser deposition (PLD) and the particle size of the anode is 100-200 nm, that of the cathode is around 10-several 10s nm. Since the most interested topic regarding the LT-SOFCs has been the cell power output, the study on the effect of nanostructure electrodes at LT is rather not intensively performed. Therefore, in the current presentation, we will exhaustively review and discuss the impact and influence of the particle size reduction to nanoscale at both the cathode and the anode on LT-SOFCs. The distinctive characteristics of the nanoscale electrodes will be presented based on the half-cell and full-cell tests, and the direct comparisons between the cells in which the only difference is the electrode particle size. Acknowledgement The authors are grateful to the Global Frontier R&D Program on Center for Multiscale Energy Systems (Grant No. NRF-2015M3A6A7065442) of the National Research Foundation (NRF) of Korea funded by the Ministry of Science, ICT & Future Planning (MSIP), and to the Institutional Program (2E26081) of Korea Institute of Science and Technology (KIST) for financial support. References J.-H. Park, W.-S. Hong, G. C. Kim, H. J. Chang, J.-H. Lee, K. J. Yoon, and J.-W. Son, J. Electrochem. Soc, 160, F1027 (2013) H.-S. Noh, K. J. Yoon, B.-K. Kim, H.-J. Je, H.-W. Lee, J.-H. Lee, and J.-W. Son, J. Power Sources, 247, 105 (2014) J.-H. Park, W.-S. Hong, K. J. Yoon, J.-H. Lee, H.-W. Lee, and J.-W. Son, J. Electrochem. Soc., 161, F16 (2014) J. H. Park, S. M. Han, K. J. Yoon, H. Kim, J. Hong, B.-K. Kim, J.-H. Lee, and J.-W. Son, J. Power Sources, 315, 324 (2016)

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