Influence of Ni Particle Size of SDC-Supported Anode on SOFC Performance
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Influence of Ni Particle Size of SDC-Supported Anode on SOFC Performance Hidenori Yahiro*, Kazunari Sugihara, Tomohisa Takemasa, Makiko Asamoto, Yoshiteru Itagaki, Syuhei Yamaguchi, and Yoshihiko Sadaoka Department of Materials Science and Biotechnology, Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577, Japan. ABSTRACT Both Ni and alkaline earth metal oxide (MO: CaO, SrO, and BaO)-impregnated SDC powders were prepared as an SOFC anode material. The averaged Ni particle size on SDC was affected by the kind of alkaline earth metal oxide added. The addition of SrO and BaO to Ni/SDC anode enhanced power densities of both H2-SOFC and CH4-SOFC and the addition of CaO lowered them. The maximum power density increased with decreasing the averaged Ni particle size of Ni-MO/SDC anode. INTRODUCTION Solid oxide fuel cells (SOFCs) are one of the attractive power generation systems because of their high electric efficiency. Another attractive feature of SOFCs is to utilize the hydrocarbon fuel instead of hydrogen [1-6]. Many efforts have been devoted to developing functional anodes to obtain high electrochemical performance. Ni-YSZ (yttria stabilized zirconia) is a widely used anode material. Samaria-doped ceria ((CeO2)0.8(SmO1.5)0.2, denoted as SDC) which is a mixed conducting oxide was employed as the anode material in combination with highly dispersed metal electrocatalysts. For example, Ni/ [6-8], Ru/, Rh/, Ir/, and Pt/SDC [9, 10], have been reported as an anode. In our previous study [11], we confirmed that 20wt% of Ni content in Ni-impregnation onto SDC particles was optimal composition for the anodic performance. Uchida et al.[12] reported that nanometer-sized Ni supported on SDC surface enhanced the anodic reaction rate because of an increase in effective reaction zone. Furthermore, they demonstrated that both the IR-free polarization performance and the ohmic resistance were not changed during the long-term operation (1100 h) because Ni particles were stabilized by changing the morphology on SDC due to a strong interaction [13]. Recently, we reported that the maximum power density increased with decreasing the averaged size of metallic Ni supported on SDC [14]. It is well-known that coke formation on anode is a serious problem for SOFCs using dry CH4 fuel. Gorte and co-workers [2, 15] investigated rare-earth doped ceria impregnated with CuO as the anode material for direct utilization of hydrocarbon fuels. We reported that the addition of CaO is effective for the tolerance of Ni/SDC anode to carbon deposition [16]. In the present study, the influence of the particle size distribution of Ni in Ni-alkaline earth metal oxide (CaO, SrO, and BaO)/SDC anodes on the electrochemical performance of SOFC using H2 and CH4 fuels was investigated.
EXPERIMENTAL Preparation of Ni-MO/SDC powders
SDC powder was prepared by the ammonia co-precipitation method with Ce(NO3)3·6H2O (Wako, > 99% pure) and Sm(NO3)3·nH2O (Wako, 99.5%) as starting materials [11,16]. The precipitate of hydroxide precursor was cal
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