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박정화,임하니,Lee Kang Taek 한국세라믹학회 2021 한국세라믹학회지 Vol.58 No.5
Solid oxide fuel cells (SOFCs) are promising energy conversion devices because of their high electrical effi ciency, even for small power systems. However, when the anode is exposed to reduction and oxidation (redox) cycles, the Ni phase causes a large microstructural change as a result of its chemical expansion and contraction. This negatively aff ects the electrochemical performance. However, most studies have focused on the redox cycling behaviors of SOFCs at high operation temperatures (≥ 800 °C). Therefore, in this study, we investigate the degradation behavior of the SOFC anode during redox cycles at 500 °C. To identify the individual steps of the electrochemical processes of the anode, in-situ monitored impedance spectra were analyzed using the distribution of relaxation time method at various oxygen and hydrogen partial pressures. Conse- quently, the electrode polarization process was deconvoluted into fi ve sub-processes. During the redox cycles, three major peaks were altered: gas phase diff usion in the anode substrate (10 –1 –10 1 Hz), gas diff usion coupled with charge transfer reaction and ionic transport (10 2 –10 3 Hz) and charged species across the Ni–yttria stabilized zirconia interface at the anode (10 3 –10 4 Hz). The major degradation of the electrode performance at 500 °C was attributed to the increase in gas phase diff usion resistance due to Ni phase aggregation and the decrease in porosity in the anode during the redox cycles. This was confi rmed by microstructural analysis. By contrast, the other two processes (10 2 –10 3 and 10 3 –10 4 Hz) compensated each other, thus having negligible eff ect on performance degradation.
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Cerium Pyrophosphate-based Proton-conducting Ceramic Electrolytes for Low Temperature Fuel Cells
Bhupendra Singh,김지혜,임하니,송선주 한국세라믹학회 2014 한국세라믹학회지 Vol.51 No.4
Acceptor-doped cerium pyrophosphates have shown significant proton conductivity of >10-2 S cm-1 in the range of 100 - 300oCand are considered promising candidates for use as electrolytes in proton-conducting, ceramic electrolyte fuel cells (PCFCs). But,cerium pyrophosphates themselves do not have structural protons, and protons incorporate into their material bulk only as impuritieson exposure to a hydrogen-containing atmosphere. However, proton incorporation and proton conduction in these materialsare expected to be affected by factors such as the nature (ionic size and charge) and concentration of the aliovalent dopant, processinghistory (synthesis route and microstructure), and the presence of residual phosphorous phosphate (PmOn) phases. An exactunderstanding of these aspects has not yet been achieved, leading to large differences in the magnitude of proton conductivity ofcerium pyrophosphates reported in various studies. Herein, we systematically address some of these aspects, and present anoverview of factors affecting proton conductivity inacceptor-doped CeP2O7.
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Imdadullah Thaheem,조동우,Taimin Noh,임하니,이강택 한국공업화학회 2021 Journal of Industrial and Engineering Chemistry Vol.96 No.-
The application of ceramic coatings has been presented as an effective method to suppress the oxidationscale growth and Cr evaporation of ferritic stainless steels used in solid oxide fuel cell (SOFC)interconnects. In this work, Mn1.45-0.5xCo1.45-0.5xCuxY0.1O4 materials with various Cu contents (x = 0.1, 0.3,and 0.5) were synthesized through a facile glycine nitrate process as a protective coating on a metallicinterconnect (SUS 441). It was observed that the lattice parameter decreased from 8.31 Å (x = 0.1) to8.22 Å (x = 0.5) with increasing Cu content (x). The effects of Cu content (x) on the phase stability as wellas sintering, electrical, and thermal expansion were investigated. The results confirmed that theMn1.3Co1.3Cu0.3Y0.1O4 spinel had the highest electrical conductivity of 115 S cm 1 at 800 C and an averagethermal expansion value of 11.98 10 6 K 1 in the temperature range of 20–1000 C. The ASR ofMn1.3Co1.3Cu0.3Y0.1O4 coated SUS441 (7.7 10 5V-cm2 at 800 C) was 3 orders of magnitude lower thanthat of the uncoated sample. Moreover, the Mn1.3Co1.3Cu0.3Y0.1O4 coated interconnect exhibited excellentlong-term stability up to 1000 h at 800 C without any observable degradation, while the ASR of theuncoated sample increased by >850% for 1000 h (from 0.001 V-cm2 to 0.06 V-cm2) under the sameconditions. The oxidation kinetics obeying the parabolic law with a rate constant of Mn1.3Co1.3Cu0.3Y0.1O4(1.64 10 9mg2cm 4 s 1) was 4 orders of magnitude lower than that of bare SUS 411(7.4 10 5mg2cm 4 s 1) at 750 C for 2000 h. These results demonstrate that the Mn1.3Co1.3Cu0.3Y0.1O4is a promising coating material with high electrical conductivity and excellent durability for metallicinterconnects of intermediate-temperature SOFCs.
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