First-Principles Modeling of Ni4M (M = Co, Fe, and Mn) Alloys as Solid Oxide Fuel Cell Anode Catalyst for Methane Reforming
First-Principles Modeling of Ni4M (M = Co, Fe, and Mn) Alloys as Solid Oxide Fuel Cell Anode Catalyst for Methane Reforming
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DOI：
10.1021/acs.jpcc.5b06847
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发表时间：
2016-01
影响因子：
3.7
通讯作者：
Ho-Cheng Tsai;S. Morozov;T. Yu;B. Merinov;W. Goddard
中科院分区：
文献类型：
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作者：
Ho-Cheng Tsai;S. Morozov;T. Yu;B. Merinov;W. Goddard
在本研究中，我们利用量子力学（QM）研究了甲烷在ni合金催化剂表面的蒸汽重整，并研究了阳极材料修饰对固体氧化物燃料电池（SOFC）催化过程的影响。由于烃类燃料分解、高温下镍颗粒结块以及燃料中含有杂质等原因，传统镍阳极存在焦化、粗化和硫中毒等问题。镍电极表面改性，如将镍与其他金属（如铁和铜）合金化，可能是开发耐焦化和硫中毒SOFC阳极的最实用和最有前途的方法。实验结果表明，Ni_4Fe作为SOFC阳极催化剂具有良好的催化性能和长期稳定性。我们对五层Ni_4M板（M = Co， Fe和Mn）的各种表面结构进行了偏析能的QM计算，发现Ni原子在表面层表现出偏析倾向，最有利的Ni_4M表面结构在第2层有两个M原子，第3层和第4层有一个M原子（从底层开始编号）。我们利用这种结构对CH_x、C和h的结合能进行了进一步的量子力学计算。我们发现，Ni_4M（111）表面对CH_x的结合能比纯Ni弱（1-10 kcal/mol），而Ni_4M合金的C的结合能总是比纯Ni低~ 10 kcal/mol。这与实验中获得的纯镍相比，某些镍基合金的催化性能有所改善是一致的。计算了Ni_4M（111）催化剂表面甲烷分解的反应能垒。在此基础上，确定了甲烷分解的速率决定步骤为CH→C + H反应。结果表明，Ni_4Fe和Ni_4Mn具有较好的活性和抗结焦性能，可作为SOFC阳极催化剂的候选材料，适用于CH_4燃料重整。
In this study, we used quantum mechanics (QM) to investigate steam reforming of methane on Ni-alloy catalyst surfaces and to examine the effect of anode material modifications on the catalytic processes in a solid oxide fuel cell (SOFC). The conventional Ni anode suffers from coking, coarsening, and sulfur poisoning because of the decomposition of hydrocarbon fuels, Ni particle agglomeration at high operating temperature, and impurities contained in fuels. Ni-electrode surface modification, such as alloying Ni with other metals (e.g., Fe and Cu), is probably the most practical and promising way of developing SOFC anodes tolerant to coking and sulfur poisoning. According to experimental data, Ni_4Fe shows a good catalytic performance and excellent long-term stability as an SOFC anode catalyst. We have performed QM calculations of segregation energy for various surface structures of five-layer Ni_4M slabs (M = Co, Fe, and Mn) and found that Ni atoms show segregation preference for the surface layer and the most favorable Ni_4M surface structure has two M atoms in the 2nd layer and one M atom in the 3rd and in the 4th layer (the numbering starts from the bottom layer). This structure was used for our further QM calculations of binding energies for CH_x, C, and H. We find that the Ni_4M(111) surfaces bind CH_x species weaker (by 1–10 kcal/mol) than pure Ni, and the binding energy of C is always ∼10 kcal/mol lower for the Ni_4M alloys compared to pure Ni. This is consistent with improved catalytic characteristics of certain Ni-based alloys compared to pure Ni obtained in experiment. Reaction energy barriers for methane decomposition on the Ni_4M(111) catalyst surfaces were calculated as well. On the basis of these results, the rate-determining step for the methane decomposition was found to be the CH → C + H reaction. Our results predict that Ni_4Fe and Ni_4Mn have both better activity and better coking resistance and can be considered as candidates for an SOFC anode catalyst suitable for the CH_4 fuel reforming.