成果報告書詳細
管理番号20110000000941
タイトル*平成22年度中間年報 固体酸化物形燃料電池システム要素技術開発 基礎的・共通的課題のための研究開発 三相界面についての劣化現象と微細構造変化の相関付け
公開日2011/9/28
報告書年度2010 - 2010
委託先名国立大学法人京都大学
プロジェクト番号P08004
部署名新エネルギー部
和文要約和文要約等以下本編抜粋:1. 研究開発の内容及び成果等
本研究開発の内容
電気化学反応の舞台となる三相界面の劣化について、電極反応に影響を及ぼす因子を電極反応の解析(劣化に至る条件の範囲や劣化速度等)、三相界面近傍の化学分析・状態分析、電極微構造との関連から明確にする。これらの知見をシミュレーション手法と組み合わせて、セルの劣化速度を予測、劣化を抑制できる電極材料、電極作製法、電極構造、運転条件等の提言をおこなう。
本年度は以下の項目について実施した。
1)各種運転条件での劣化挙動観察
Ni–YSZ(50:50vol%)を燃料極とするセルを用いて行った、定電流通電下における端子電圧の経時変化を図1 に示す。昨年度は40%加湿水素を燃料として供給した場合、図1(a)に示すようなセルの突然死が観察されることを報告した。そこで、高加湿下におけるこのような劣化挙動が反応場近傍の酸素分圧、或いは水蒸気分圧のどちらに強く影響されるかを明らかにすることを目的として、種々の混合ガスを燃料として通電試験を行った。なお燃料ガス中の酸素分圧は、P(O2) = 1.2×10-15 atm となるように制御した。結果を図1 (b)~(d)に示す。CO-H2O 混合ガス供給時においても40%加湿水素供給時と同様の突然死が観察された。一方で、水蒸気を含まない系では比較的高い酸素分圧下での通電にもかかわらず、電池性能の低下は認められなかった。したがって、高加湿条件下での通電による燃料極の劣化は、酸素分圧ではなく水蒸気分圧の影響を強く受けることが明らかとなった。
英文要約Title: Development of System and Elemental Technology on Solid Oxide Fuel Cells
/ Basic research for improving durability and reliability
/ Degradation behavior related to microstructural change at the triple phase boundary (FY2008-FY2011)
FY2011 Annual Report (Kyoto University)
The triple phase boundary (TPB), gas/electrode/electrolyte, is the active site for the electrochemical reaction and
significantly affects the performance of fuel cells. Thus, the changes in TPB, such as length and surface composition,
during long-term operation lead to the performance deterioration. In this research project, we aim to clarify the
deterioration factors at the TPB and to simulate degradation behavior through the analysis of electrode reaction
(rate of deterioration and boundary operating conditions, etc.), chemical state in the vicinity of TPB, and electrode microstructure. The experimental results obtained in this fiscal year are as follows:
1) The performance stability of electrolyte-supported cell (Ni-YSZ | YSZ | LSM) was examined at 1000ºC by
feeding various fuels with a fixed partial pressure of oxygen, P(O2) = 1.2×10-15 atm. It was clarified that partial pressure of steam was the crucial factor for the sudden degradation of cell rather than partial pressure of oxygen.
2) The characteristic changes in power generation and ac impedance were precisely investigated for the Ni–YSZ
anode during the redox cycles by alternating the supply of hydrogen and oxygen to the anode. The changes in
parameters of anode microstructure were calculated by the 3D-reconstructed images of the Ni–YSZ anode
obtained by FIB–SEM observation. The polarization resistance of the anode increased after the first redox cycle.
The surface area of the nickel phase increased after redox cycles, which indicated that the nickel particles became finer and more complicated in shape. Despite this nickel deformation, the length of TPB decreased from initial 2.49 to 2.39 and 2.11 μmμm3 after the first and fourth redox cycles, respectively. The ohmic loss of the anode increased only
after the thermal cycle most likely because of the large crack formation. The decrease in the length of TPB was clearly correlated with the increase in the polarization resistance of the anode during the early stage of the redox cycles.
Microstructures and compositional variations in the vicinity of triple phase boundary (TPB) in various cells were
investigated using a field-emission transmission electron microscope (FE-TEM) in order to clarify the detailed
mechanisms of deterioration occurred both on the cathode and anode sides of the cells. In the cell with degraded
cathode, the surface of YSZ adjacent to the TPB on the cathode side was confirmed to be covered by nano-scale
surface layer containing La and Mn, which is partly responsible for the degradation of the cathode by reducing the active TPB length.
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