一种高活性Ni掺杂La_(0.6)Sr_(0.4)FeO_(3-δ)作为碳基燃料固体氧化物燃料电池对称电极（英文）
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摘要
固体氧化物燃料电池(SOFCs)是一种在中高温下可以直接将储存在燃料中的化学能转换成电能的全固态电化学反应装置.因其具有能量转换效率高、环境友好、全固态结构以及可以使用碳氢化合物燃料等优点,近年来受到了广泛的关注.在诸多电极材料当中,Ni基金属陶瓷是SOFCs中最常使用的阳极材料,这是由于金属Ni具有优良的电子电导和催化性能.然而当使用碳基化合物燃料时,传统的Ni金属陶瓷阳极材料面临严重的积碳、Ni颗粒长大以及硫中毒等问题.这些问题不仅会影响SOFCs的寿命,而且还会严重地降低SOFC的商业化进程.因此,开发具有高催化活性、抗积碳的阳极材料对碳氢化合物为燃料的固体氧化物燃料电池的发展至关重要.与金属基阳极相比,氧化物阳极的热膨胀系数与电解质材料更匹配,性能的可调控性更强.铁酸锶镧(LSF)是一种分子式为ABO_3的钙钛矿结构的氧化物,在高温下具有较高的电子电导率.据报道LSF作为阴极材料时,表现出了良好的性能.但是LSF作为阳极材料时,却存在着催化性能不足的问题.我们研究了Ni掺杂的La_(0.6)Sr_(0.4)FeO_(3-δ)(LSFN),以提高其作为SOFCs阳极材料的催化性能.同时采用将LSFN在SOFC工作气氛下原位还原的方法,在LSFN颗粒表面原位生长出分布均匀的纳米颗粒.透射电镜分析结果表明该偏析的颗粒为Ni-Fe合金.有报道显示,Ni-Fe合金对碳氢化合物氧化具有良好的催化活性,所以在LSFN颗粒表面生成这种合金颗粒有利于提高阳极材料的催化活性.对于Ni-Fe合金以均匀的纳米颗粒析出的原因,还有待进一步研究.为了研究LSFN作为SOFC电极材料的性能,我们采用浸渍法将LSFN前驱体溶液浸渍到氧化钇稳定氧化锆(YSZ)一体化电池的对称多孔骨架中,经过焙烧,得到了具有对称结构的SOFC单电池.所使用的YSZ一体化骨架为中间层薄而致密,两边厚而多孔的三层结构,这种结构可以显著地降低电解质的厚度,从而达到降低单电池的阻抗的目的.这一新型对称电池结构具有如下优点:阳极表面上可能发生的硫毒化和积碳问题有可能通过将阳极和阴极反用而消除;氧化剂(空气)将冲走吸附在电极上的硫和碳粒子,从而使电极得以再生.此外,氧化还原稳定的阴极预期将提高阴极的寿命.对单电池的电化学测试结果表明,LSFN电极材料的最佳浸渍量为30wt%,这是因为较低的LSFN浸渍量((27)30wt%),不能形成连续的电子传导网络,电极的电子传导能力不足;而LSFN电极材料的浸渍量高于30wt%时则会降低电极反应的三相界面,从而影响电池的性能.在750oC下,LSFN为电极的单电池在以湿润C_3H_8为燃料时其开路电压(OCV)达到了约1.18V,高于以H_2为燃料电池的电压.以CH_4为燃料时,LSFN为电极的单电池的开路电压远高于LSF为电极的单电池.在750oC下,以C_3H_8为燃料时,LSFN和LSF为电极的电池的峰值输出功率密度分别达到400和230mW/cm~2.这些结果表明,通过Ni掺杂和原位焙烧,在LSFN电极颗粒表面制备了均匀分布的Ni-Fe合金纳米颗粒,极大地提高了铁酸锶镧材料对碳基燃料的催化活性.长期放电测试结果表明,LSF为电极的单电池在测试过程中,尾气可以收集到类似焦油状的黑色物质;而LSNF为电极的单电池在测试过程中并没有观察到明显的焦油状物质生成.通过气相色谱-质谱联用分析,发现所产生的焦油状物质主要成分是含苯环、碳碳双建或碳碳三键的烃类.这说明LSF电极只能使C_3H_8部分氧化,LSFN对C_3H_8等碳氢化合物燃料的氧化具有高的催化活性和良好的耐久性.Ni掺杂的La_(0.6)Sr_(0.4)FeO_(3-δ)阳极材料是一种有希望的碳基燃料SOFCs对称电极.
The conventional Ni cermet anode suffers from severe carbon deposition and sulfur poisoning when fossil fuels are used. Alternative anode materials are desired for high performance hydrocarbon fuel solid oxide fuel cells(SOFCs). We report the rational design of a very active Ni doped La_(0.6)Sr_(0.4)FeO_(3-δ)(LSFN) electrode for hydrocarbon fuel SOFCs. Homogeneously dispersed Ni-Fe alloy nanoparticles were in situ extruded onto the surface of the LSFN particles during the operation of the cell. Sym-metric SOFC single cells were prepared by impregnating a LSFN precursor solution onto a YSZ(yt-tria stabilized zirconia) monolithic cell with a subsequent heat treatment. The open circuit voltage of the LSFN symmetric cell reached 1.18 and 1.0 V in humidified C_3H_8 and CH_4 at 750 °C, respective-ly. The peak power densities of the cells were 400 and 230 mW /cm~2 in humidified C_3H_8 and CH_4, respectively. The electrode showed good stability in long term testing, which revealed LSFN has good catalytic activity for hydrocarbon fuel oxidation.
The conventional Ni cermet anode suffers from severe carbon deposition and sulfur poisoning when fossil fuels are used. Alternative anode materials are desired for high performance hydrocarbon fuel solid oxide fuel cells(SOFCs). We report the rational design of a very active Ni doped La_(0.6)Sr_(0.4)FeO_(3-δ)(LSFN) electrode for hydrocarbon fuel SOFCs. Homogeneously dispersed Ni-Fe alloy nanoparticles were in situ extruded onto the surface of the LSFN particles during the operation of the cell. Sym-metric SOFC single cells were prepared by impregnating a LSFN precursor solution onto a YSZ(yt-tria stabilized zirconia) monolithic cell with a subsequent heat treatment. The open circuit voltage of the LSFN symmetric cell reached 1.18 and 1.0 V in humidified C_3H_8 and CH_4 at 750 °C, respective-ly. The peak power densities of the cells were 400 and 230 mW /cm~2 in humidified C_3H_8 and CH_4, respectively. The electrode showed good stability in long term testing, which revealed LSFN has good catalytic activity for hydrocarbon fuel oxidation.
引文
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