Origin of High Activity and Durability of Twisty Nanowire Alloy Catalysts under Oxygen Reduction and Fuel Cell Operating Conditions,Journal of the American Chemical Society

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Origin of High Activity and Durability of Twisty Nanowire Alloy Catalysts under Oxygen Reduction and Fuel Cell Operating Conditions
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2019-12-30 , DOI: 10.1021/jacs.9b10239
Zhijie Kong _{1,

2} , Yazan Maswadeh ₃ , Jorge A Vargas ₃ , Shiyao Shan ₂ , Zhi-Peng Wu ₂ , Haval Kareem ₄ , Asher C Leff ₄ , Dat T Tran ₄ , Fangfang Chang ₂ , Shan Yan ₂ , Sanghyun Nam ₂ , Xingfang Zhao ₂ , Jason M Lee ₂ , Jin Luo ₂ , Sarvjit Shastri ₅ , Gang Yu ₁ , Valeri Petkov ₃ , Chuan-Jian Zhong ₂

Affiliation

The ability to control the surface composition and morphology of alloy catalysts is critical for achieving high activity and durability of catalysts for oxygen reduction reaction (ORR) and fuel cells. This report describes an efficient surfactant-free synthesis route for producing a twisty nanowire (TNW) shaped platinum-iron alloy catalyst (PtFe TNWs) with controllable bimetallic composition. PtFe TNWs with an optimal initial composition of ~24% Pt are shown to exhibit the highest mass activity (3.4 A/mgPt, ~20 times higher than that of commercial Pt catalyst) and the highest durability (<2% loss of activity after 40,000 cycles and <30% loss after 120,000 cycles) among all PtFe-based nanocatalysts under ORR or fuel cell operating conditions reported so far. Using ex-situ and in-situ synchrotron X-ray diffraction coupled to atomic pair distribution function analysis and 3D modeling, the PtFe TNWs are shown to exhibit mixed fcc - bcc alloy structure and a significant lattice strain. A striking finding is that the activity strongly depends on the composition of the as-synthesized catalysts and this dependence remains unchanged despite the evolution of the composition of the different catalysts and their lattice constants under ORR or fuel cell operating conditions. Notably, dealloying under fuel cell operating condition starts at phase-segregated domain sites leading to a final fcc alloy structure with subtle differences in surface morphology. Due to a subsequent realloying and the morphology of TNWs, the surface lattice strain observed with the as-synthesized catalysts is largely preserved. This strain and the particular facets exhibited by the TNWs are believed to be responsible for the observed activity and durability enhancements. These findings provide new insights into the correlation between the structure, activity and durability of nanoalloy catalysts, and are expected to energize the ongoing effort to develop highly active and durable low-Pt-content nanowire catalysts by controlling their alloy structure and morphology.

中文翻译：

在氧还原和燃料电池工作条件下扭曲纳米线合金催化剂的高活性和耐久性的起源

控制合金催化剂表面成分和形态的能力对于实现氧还原反应 (ORR) 和燃料电池催化剂的高活性和耐久性至关重要。本报告描述了一种有效的无表面活性剂合成路线，用于生产具有可控双金属成分的扭曲纳米线 (TNW) 形铂铁合金催化剂 (PtFe TNW)。PtFe TNW 的最佳初始成分约为 24% Pt 显示出最高的质量活性（3.4 A/mgPt，比商业 Pt 催化剂高约 20 倍）和最高的耐用性（40,000 次后活性损失 <2%迄今为止报道的所有基于 PtFe 的纳米催化剂在 ORR 或燃料电池操作条件下的循环次数和 120,000 次循环后的损失 <30%。使用异位和原位同步加速器 X 射线衍射结合原子对分布函数分析和 3D 建模，PtFe TNW 显示出混合 fcc - bcc 合金结构和显着的晶格应变。一个惊人的发现是，活性强烈依赖于合成催化剂的组成，尽管在 ORR 或燃料电池操作条件下不同催化剂的组成及其晶格常数发生变化，但这种依赖性保持不变。值得注意的是，燃料电池运行条件下的脱合金从相分离的域位置开始，导致最终的 fcc 合金结构具有表面形态的细微差异。由于随后的再合金化和 TNW 的形态，使用合成催化剂观察到的表面晶格应变在很大程度上得以保留。这种应变和 TNW 表现出的特定方面被认为是导致观察到的活性和耐久性增强的原因。这些发现为纳米合金催化剂的结构、活性和耐久性之间的相关性提供了新的见解，并有望通过控制合金结构和形态来推动开发高活性和耐用的低铂含量纳米线催化剂的持续努力。

更新日期：2019-12-30

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