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Development of alternative cathodes for intermediate temperature solid oxide fuel cells.

机译：开发用于中温固体氧化物燃料电池的替代阴极。

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摘要

Solid oxide fuel cells (SOFCs) offer the advantage of using less expensive oxide catalysts and directly using hydrocarbon fuels without requiring external fuel reforming due to the higher operating temperatures of > 500°C compared to the proton exchange membrane fuel cells. However, the conventional operating temperature of ~ 1000 °C leads to undesired side reactions and thermal expansion mismatch among the cell components. These difficulties have generated considerable interest in intermediate temperature (500 - 800 °C) SOFC, but the lower operating temperature leads to poor oxygen reduction reaction kinetics with the conventional cathode material, La1-xSrx MnO3. In this regard, the cobalt-containing perovskite cathodes such as La1--xSrxCoO3--delta are appealing, but it suffers huge thermal expansion mismatch with the conventional electrolytes. To address this issue, this dissertation focuses on two series of new cathode materials.;First, the influence of the Ln3+ ions on the high temperature properties and performance in SOFC of the layered LnBaCo2O 5+delta (Ln = La, Nd, Sm, Gd, and Y) oxides is investigated systematically. The oxygen content (5+delta), thermal expansion coefficient (TEC), electrical conductivity, catalytic activity for the oxygen reduction reaction in SOFC, and oxygen permeability decrease with decreasing size of the Ln3+ ions from Ln = La to Y. These results suggest that lanthanide ions with an intermediate size may offer a tradeoff between catalytic activity and TEC. With an aim to tune the properties further, cationic substitutions are then pursued. For example, substitution of Sr for Ba is found to improve the chemical stability of GdBaCo2O5+delta with improved catalytic activity. Similarly, the substitution of Ni for Co is found to lower the TEC to 16.9 x 10-6 K-1 while still maintaining high catalytic activity at x = 0.4 in NdBaCo2-xNixO 5+delta.;Second, non-perovskite RBa(Co,M)4O7 (R = Y, Ca, and In and M = Zn, Fe, and Al) oxides having a hexagonal structure and corner-shared (Co,M)O4 tetrahedra are investigated. Among the various compositions investigated, YBaCo4-xZnxO7 (1 ≤ x ≤ 2) shows good long-term stability at high temperatures with an ideal matching of the TEC with those of standard electrolytes. The low TEC is attributed to the absence of spin state transitions with tetrahedral-site Co2+/3+ ions and relatively small amount of oxygen loss at higher temperatures. The YBaCo3ZnO7 + GDC composite cathodes exhibit low polarization resistance and performance in SOFC comparable to that of well-studied cobalt-based perovskite cathodes.
机译：固态氧化物燃料电池（SOFC）具有使用便宜的氧化物催化剂并直接使用烃类燃料的优点，因为与质子交换膜燃料电池相比，其运行温度高于500°C，因此不需要外部燃料重整。但是，传统的〜1000°C的工作温度会导致电池组件之间发生不良的副反应和热膨胀失配。这些困难引起了对中温（500-800°C）SOFC的极大关注，但是较低的工作温度导致常规阴极材料La1-xSrx MnO3的氧还原反应动力学较差。在这方面，含钴的钙钛矿阴极如La1-xSrxCoO3-delta具有吸引力，但与常规电解质相比，存在巨大的热膨胀失配。为了解决这个问题，本论文着重研究了两种新型的阴极材料。首先，Ln3 +离子对层状LnBaCo2O 5+δ的高温特性和SOFC性能的影响（Ln = La，Nd，Sm，系统地研究了Gd和Y）氧化物。随着Ln3 +离子从Ln = La到Y的减小，氧含量（5 + delta），热膨胀系数（TEC），电导率，SOFC中氧还原反应的催化活性和氧渗透性会降低。这些结果表明中等大小的镧系离子可能会在催化活性和TEC之间进行权衡。为了进一步调节性能，然后进行阳离子取代。例如，发现用Sr代替Ba可以改善GdBaCo2O5 +δ的化学稳定性，并具有改善的催化活性。同样，发现用Ni代替Co可以将TEC降低至16.9 x 10-6 K-1，同时在NdBaCo2-xNixO 5+δ中x = 0.4时仍保持高催化活性;第二，非钙钛矿型RBa（Co研究了具有六边形结构和角共享的（Co，M）O4四面体的，M）4O7（R = Y，Ca和In，M = Zn，Fe和Al）氧化物。在研究的各种成分中，YBaCo4-xZnxO7（1≤x≤2）在高温下显示出良好的长期稳定性，并且TEC与标准电解质具有理想的匹配性。较低的TEC归因于不存在具有四面体位点Co2 + / 3 +离子的自旋态跃迁，并且在较高温度下氧损失相对较少。 YBaCo3ZnO7 + GDC复合阴极在SOFC中的极化电阻低，性能与经过研究的钴基钙钛矿阴极相当。

著录项

  • 作者

    Kim, Junghyun.;

  • 作者单位

    The University of Texas at Austin.;

  • 授予单位 The University of Texas at Austin.;
  • 学科 Alternative Energy.;Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 189 p.
  • 总页数 189
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 工程材料学;
  • 关键词

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