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题名	质子交换膜燃料电池铁基氧还原催化剂的理性设计与控制合成
作者	胡洋
学位类别	博士
答辩日期	2015-05
授予单位	中国科学院研究生院
授予地点	中国科学院长春应用化学研究所
导师	邢巍 ; 李庆峰
关键词	质子交换膜燃料电池 氧还原 非贵金属 铁基催化剂 包覆结构
中文摘要	质子交换膜燃料电池作为一种高效清洁的能量转化技术，必定会在在未来的非化石能源体系中发挥不可替代的作用。如果将燃料电池和电解池技术结合起来，更能满足多种形式的能量储存及再转化的应用需求。廉价的高性能氧还原催化剂无疑是燃料电池技术大规模应用的关键因素。目前应用于质子交换膜燃料电池阴极的催化剂主要为Pt基的催化剂。虽然它具有很高的氧还原活性和化学稳定性，但是贵金属天然的稀缺性、催化剂的高成本和有待提高的电化学稳定性等问题限制了燃料电池技术的商业化应用。针对这个问题，本论文进行了质子交换膜燃料电池Fe基氧还原催化剂的相关工作，研究了热处理Fe/N/C类氧还原催化剂和新型的石墨化碳层包覆结构Fe基氧还原催化剂。研究主要集中在两个方面：一是探索催化剂结构、组分等性质与催化性能之间的关系，从而设计出性能更理想的催化剂；二是探索实验方法和条件合成出所期望得到的催化剂。主要研究内容如下： 1.热处理Fe/N/C类氧还原催化剂 （1）通过使用聚苯胺纳米线作为C和N共同的前驱体合成了一种自支撑的Fe/N/C类氧还原催化剂。我们发现聚苯胺纳米线形貌结构在热处理过程中能够保存下来，使所合成的催化剂具有均一的纳米棒结构。这个方法为合成形貌可控的自支撑型Fe/N/C催化剂提供了一种新的思路。此外，我们发现所合成催化剂氧还原起始电位为0.905 V (vs. RHE)，氧还原过程为四电子过程。随着前驱体中Fe含量的增加（从0到3 wt%），催化剂的性能逐步提高。前驱体中Fe含量会的进一步增加会引起催化剂活性的降低。 （2）通过比较常规Fe/N/C催化剂和P掺杂的Fe/N/C催化剂的形貌结构与性能，我们发现了P掺杂对于热处理Fe/N/C催化剂氧还原性能的促进作用。P的掺杂是通过在催化剂制备过程中加入磷酸酯作为前驱体来实现的，并且对催化剂的形貌结构没有明显影响。相比没有掺入P的催化剂, 掺杂P后的催化剂表现出了相似的氧还原起始电位但是更高的氧还原电流密度。所制得催化剂的活性和稳定性在直接甲醇燃料电池中也得到了验证。 2. 碳层包覆结构Fe基氧还原催化剂 （1）通过高压热处理的合成方法我们制得了一种新型的石墨化碳层包覆结构Fe基催化剂。这种催化剂具有均一的空心碳球结构，碳球中包覆着均一的Fe3C颗粒，催化剂表面只含有极少量的N和Fe。在酸性溶液中，碳层保护着Fe3C颗粒使其不与溶液进行反应，而Fe3C颗粒与碳层间的电子作用使表面碳层具有了一定的氧还原活性。催化剂无论是在酸性还是碱性溶液中都具有优良的氧还原活性和稳定性。这种新型的催化剂以及这对这种催化剂所提出的活性位点机理对于合成高活性高稳定性的非贵金属催化剂提供了一种新的思路。我们还在低温氢氧质子交换膜燃料电池和高温磷酸掺杂的聚苯并咪唑质子交换膜燃料电池中验证了该催化剂的活性和稳定性。 （2）我们探索了碳层包覆结构Fe基催化剂的结构形成过程和氧还原活性位点。在500oC时，前驱体中的氰胺聚合成球状的三聚氰胺，这决定了催化剂最终的球状结构。在600oC-660 oC时三聚氰胺球开始逐步分解，开始出现一定量Fe3C相以及可能的Fe-Nx/C活性位点。此时催化剂的活性很低，较低的电子导电性可能是原因之一。当热处理温度为700-800oC时，催化剂结构为空心碳球中包裹着Fe3C纳米颗粒。这种催化剂的表面含N和Fe的含量很低，而且氧还原反应是2电子和4电子混合过程。这些结果都支持我们对于催化剂活性位点的观点，即Fe3C颗粒与包裹碳层间的电子作用使外部碳层具有了氧还原活性。 （3）我们发现了一种直接简便的制备石墨烯复合材料的方法，即通过高压热处理非石墨前驱体的方法合成多层石墨烯/Fe3C颗粒复合材料。整个合成过程直接、简便，易进行放大合成。当把所得到的石墨烯/Fe3C颗粒复合材料作为氧还原催化剂进行测试，我们发现它在0.1 M KOH中具有很好的氧还原性能和稳定性。相比Pt/C 催化剂，它们具有基本一样的氧还原起始电位和半波电位。
英文摘要	Proton exchange membrane fuel cells (PEMFCs), as a clean and efficient energy conversion device, should play key roles in the further fossil fuel-free energy scenarios. If combined with a electrolyzer, it will give solutions to different energy appliacations. Highly active and durable catalysts for the oxygen reduction reaction (ORR) are undoubtedly essential for the large-scale application of fuel cells. Pt-based materials have been so far the most active ORR catalysts. However, the prohibitive cost, limited availability and insufficient durability of Pt-based materials hinder the rapid and widespread adoption of PEMFCs. Therefore, we focus our interests in the study of iron-based oxygen reducion catalysts, including heat-treated Fe/N/C type oxygen reduction catalysts, the most active non-precious metal ORR catalyst thus far, and a new iron-based oxygen reduction catalyst with the encapsulation structure. The detailed research results are as follows: 1. Heat-treated Fe/N/C type oxygen reduction catalyst (1) We report a new approach to preparation of self-supported and nano-structured NPMCs using pre-prepared polyaniline (PANI) nanofibers as both nitrogen and carbon precursors. The synthesized NPMCs possess nanoworm structures preserved from the PANI precursor and exhibit a high onset potential of 0.905V vs. RHE and selective activity of nearly four-electron ORR pathways. A significant enhancement in the intrinsic activity and onset potential for the ORR is observed when the Fe content in the precursor is increased from 0 to 3.0 wt.%, while further addition to 10.0 wt.% results in a decrease in the catalytic activity. (2) By comparing the ORR activities of standard Fe/N/C catalysts synthesized with or without the doped phosphorus species, the promotional effect of phosphorus doping is discerned. Such phosphorus doping is achieved by using an acidic phosphate ester as a dopant in the synthesis, which introduces no change in catalyst morphologies and structures. The linked structure of phosphate ester cations with the nitrogen precursor, i.e., polyaniline chain, is favored for the evenly P doping of the catalyst, showing to a superior ORR activity to that for the undoped Fe/N/C catalyst. The activity and durability of the catalysts are demonstrated in direct methanol fuel cells. 2. Iron-based oxygen reduction catalyst with an encapsulation structure (1) We presents a novel type of catalysts prepared by high pressure pyrolysis. The catalyst is featured of hollow spherical morphologies consisting of uniform Fe3C nanoparticles encased by graphitic layers, with little surface nitrogen or metallic functionalities. In acidic media the outer graphitic layers stabilize the carbide nanoparticles, which in turn synergistically activate the graphitic layers for the ORR. As a result the catalyst exhibits super activity and stability in both acid and alkaline electrolytes. The finding of the synthetic approach, carbide-based catalyst and its structure, as well as the proposed mechanism opens new avenues for catalyst development in the field. The activity and durability of the catalysts are demonstrated in both Nafion-based low temperature and acid doped polybenzimidazole-based high temperature proton exchange membrane fuel cells. (2) We present a detailed study of a novel Fe3C-based spherical catalyst with respect to synthetic parameters, nanostructure formation, ORR active sites and fuel cell demonstration. The catalyst is synthesized by high-temperature autoclave pyrolysis using decomposing precursors. Below 500oC, melamine-rich microspheres are first developed with uniformly dispersed amorphous Fe species. During the following pyrolysis at temperatures from 600 to 660 oC, a small amount of Fe3C phase with possible Fe-Nx/C active sites are formed, however, with moderate catalytic activity, likely limited by the low conductivity of the catalyst. At high pyrolytic temperatures of 700-800 oC, simultaneous formation of Fe3C nanoparti
语种	中文
公开日期	2016-05-03
内容类型	学位论文
源URL	[http://ir.ciac.jl.cn/handle/322003/64472]
专题	长春应用化学研究所_长春应用化学研究所知识产出_学位论文
推荐引用方式 GB/T 7714	胡洋. 质子交换膜燃料电池铁基氧还原催化剂的理性设计与控制合成[D]. 中国科学院长春应用化学研究所. 中国科学院研究生院. 2015.

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