[中文]1.介绍
由于SOFC的工作温度(800-1000℃)很高,而高温会导致复合材料退化的问题,因此,降低电池的工作温度,发展中温固体氧化物燃料电池(IT-SOFCs)成为SOFC发展的必然趋势。但是,对于当前固体氧化物燃料电池材料来说,尤其是阴极材料,温度降低会造成电极的极化损失大幅增加,电解质欧姆电阻增大,造成电池性能下降[1,2]。所以开发高性能的阴极材料,是发展在中温固体氧化物燃料电池中决定性的一步。
在中温的工作温度下,含有钴,铁,锰,镍的混合离子电子导体(MIECs)同样表现出了优良的催化性能[3,4]。一般情况下,多孔的MIEC 阴极中,氧化还原反应强烈依赖于氧分子的表面吸附和氧离子的扩散。这两个性质,在相当大程度上是通过工作温度进行控制的。为了在较低温度下实现更好的电池性能,人们做出了巨大的努力,试图通过离子替换优化各种钙钛矿氧化物的催化活性[5-7]。
最近,几个研究小组报告了一系列特殊的钙钛矿氧化物,即LnBaCo2O5 + δ(Ln = Y, Pr, Sm, Nd, Gd) [8,9]。图1中显示了相应的晶体结构。这类化合物家族在理论上可以用. . . |BaO|CoO2|LnOx|CoO2 . . .堆积序列来描述的。当x<1,有序的A 位阳离子处的氧空位出现在稀土层[10]。这种特性在改善阴极的性能上有很大的潜力。 Taskin等人[11]表明, GdBaB2O5+ ×(B =Mn和Co)由A位被随机占据的简单立方钙钛矿结构转变成了一个有序镧系和碱土层层状晶体结构,降低了氧的结合强度,并为离子迁移提供无序自由通道,氧离子扩散系数增加。金等人 [9]报道了PrBaCo2O5+ X(PBCO)的性能很好,其氧离子扩散系数和表面交换系数分别为10-5和10-3cms−1。邵等人[12]研究PBCO,欲使其为中温固体氧化物燃料电池的阴极材料。层状钙钛矿氧化物的高性能可以使用通用公式 A位为Ba元素的AA’B2O5+δ理解。当Sr取代部分A位后,它可能会提高层状钙钛矿氧化物的导电性,这一假设被欧文等人的最近的研究证实了[13]。其中锶掺杂氧化物PrBa0.5Sr0.5Co2O5 +δ(PBSC)表现出了优良的面积比电阻(ASR)的值(电解质为GDC,氯化钆掺杂氧化铈),可能会成为未来中温固体氧化物燃料的电池阴极材料。在本文中,基于Ce0.9Sm0.1O1.9(SDC)电解质,研究PBSC作为中温固体氧化物燃料电池阴极材料的可行性。
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[外文]1. Introduction
Since high operating temperature (800–1000 ◤C) conditions lead to complex material degradation problems, there is an increasing interest in developing intermediate temperature (500–800 ◤C) solid oxide fuel cells (IT-SOFCs). However, it will cause substantial increases of electrolyte ohmic resistance and electrode polarization losses when operating temperature is reduced for current SOFC materials, particularly for cathode material [1,2]. Therefore high
performance cathode material development is one of the critical steps toward IT-SOFCs.Mixed ionic-electronic conductors (MIECs) containing Co, Fe, Mn, Ni have demonstrated excellent catalytic performance under intermediate operating temperature conditions [3,4]. In general,oxygen reduction reaction is strongly dependent on oxygen surface absorption and oxide ionic diffusivity in porous MIEC cathode. These two properties, to a large extent, are controlled by operating temperatures. In order to achieve better cell performance at
relatively low temperatures, significant effort has been devoted to
optimizing catalytic activity of perovskite oxides through various
ion substitutions [5–7].
Recently, several research groups have reported a class of special perovskite oxides, i.e., LnBaCo2O5+x (Ln = Y, Pr, Sm, Nd, Gd) [8,9].The corresponding crystal structure is shown in Fig. 1. This family of compounds can be theoretically described with the stacking sequence of . . . BaO|CoO2|LnOx|CoO2 . . .. When x < 1, the ordered A-cations localizing oxygen vacancies appear within the rare earth layers [10]. This characteristic has a great potential to improve cathode performance. Taskin et al. [11] showed that the oxygen ion diffusivity in GdBaB2O5+x (B =Mn and Co) increased by orders of magnitude when a simple cubic perovskite with randomly occupied A-sites transfers into a layered crystal structure with ordered lanthanide and alkali-earth layers, which reduces the strength of oxygen binding and provides disorder-free channels for ionic migration. Kim et al. [9] reported high performance of PrBaCo2O5+x (PBCO) with oxygen ion diffusivity and surface
exchange coefficient being 10−5 and 10−3 cms−1 respectively. Shao et al. [12] examined PBCO as a cathode material for IT-SOFCs. The high performance of layered pervoskite oxides can be understood using general formula AAB2O5+Ĭ with the A site being Ba element. When A site is partially substituted by Sr, it could potentially improve the conductivity of layered perovskite oxides, this hypothesis has been confirmed by recent study from Irvine et al. [13],where Sr-doped oxide PrBa0.5Sr0.5Co2O5+Ĭ (PBSC) demonstrated excellent area-specific-resistance (ASR) values based on gadoliniadoped ceria (GDC) electrolyte, and could be potentially employed as cathode material for IT-SOFCs. In this work, the feasibility of PBSC as a cathode material for IT-SOFCs is examined based on Ce0.9Sm0.1O1.9 (SDC) electrolytes.[/外文]
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