Highly Enhanced Oxygen Reduction Reaction Activity and Electrochemical Stability of Pt/Ir(111) Bimetallic Surfaces
Highly Enhanced Oxygen Reduction Reaction Activity and Electrochemical Stability of Pt/Ir(111) Bimetallic Surfaces
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DOI：
10.1016/j.electacta.2016.11.149
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发表时间：
2016-12
影响因子：
6.6
通讯作者：
Naoto Todoroki;Hirofumi Watanabe;T. Kondo;S. Kaneko;T. Wadayama
中科院分区：
文献类型：
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作者：
Naoto Todoroki;Hirofumi Watanabe;T. Kondo;S. Kaneko;T. Wadayama
采用分子束外延（MBE）技术在超高真空（UHV）条件下制备了Pt/Ir（111）核壳结构催化剂，并对其氧化还原活性和电化学稳定性进行了研究。表面的反射高能电子衍射图案显示Pt在清洁的Ir（111）衬底上外延生长，并且在UHV中收集的相应扫描隧道显微镜图像显示在673 K的衬底温度下具有50-80 nm宽度的原子平坦的台阶。相反，在303 K的衬底温度下制备的相应表面显示岛状的最高表面结构。在303 K和673 K的衬底温度下制备的在Ir（111）（Pt 2 ML/Ir（111））表面上生长的两个单层（ML）厚度的Pt显示出约100 nm的光致抗蚀性。ORR活性分别是纯Pt（111）的6倍和24倍。在673 K下制备的后者表面的异常活性增强可能是由作用在Pt壳上的均匀表面应变引起的，该应变源于Pt和Ir之间2.2%的晶格失配。与制备温度相关的ORR活性表明，Pt壳-Ir（111）双金属系统的最高表面和界面结构可以决定活性。此外，虽然原始表面的初始ORR活性随着Pt壳层厚度的增加而降低，但在0.1M HClO 4溶液中在0.6 - 1.0V之间的室温电位循环期间的稳定性在3 ML厚度以上大大增强;在673 K下制备的Pt 4 ML/Ir（111）表面即使在5000次电势循环后仍保持比Pt（111）高6.5倍的ORR活性。Pt/Ir（111）Pt/M（111）（M = Ir，Pd，Au）体系的ORR活性和电化学稳定性是目前报道的最高的。在这项研究中获得的结果表明，Pt/Ir核壳纳米结构是高活性和持久的ORR催化剂的潜在候选者。
We demonstrate highly enhanced ORR activity and electrochemical stability of Pt/Ir(111) model core-shell catalysts prepared by molecular beam epitaxy (MBE) in ultra-high vacuum (UHV). Reflection high-energy electron diffraction patterns for the surfaces show that Pt grew epitaxially on the clean Ir(111) substrate and the corresponding scanning tunneling microscope images collected in UHV reveal atomically flat terraces with 50–80 nm widths at a substrate temperature of 673 K. In contrast, the corresponding surfaces prepared at a substrate temperature of 303 K show island-like topmost surface structures. The two-monolayer (ML)-thick Pt grown on Ir(111) (Pt2ML/Ir(111)) surfaces, prepared at substrate temperatures of 303 K and 673 K, show ca. 6 and 24 times higher ORR activities than clean Pt(111), respectively. The anomalous activity enhancement for the latter surface prepared at 673 K is probably caused by homogeneous surface strain acting on the Pt shells that is derived from the 2.2% lattice mismatch between the Pt and Ir. The preparation-temperature–dependent ORR activity suggests that the activity can be dominated by the topmost surface and interface structures of the Pt shell–Ir(111) bimetallic system. Furthermore, while the initial ORR activity of pristine surfaces decreases with increasing Pt shell thickness, the stability during room temperature potential cycling between 0.6 and 1.0 V in a 0.1 M HClO4solution was greatly enhanced above three ML thickness; the Pt4ML/Ir(111) surface prepared at 673 K retained 6.5 times higher ORR activity than Pt(111), even after 5000 potential cycles. The ORR activity and electrochemical stabilities for the Pt/Ir(111) bimetallic surfaces are the highest among the MBE-prepared Pt/M(111) (M = Ir, Pd, Au) systems reported to date. The results obtained in this study show that Pt/Ir core–shell nanostructures are potential candidates for highly active and durable ORR catalysts.