Department of Chemical, Biological, and Environmental Engineering , Oregon State University , Corvallis , Oregon 97331 , United States.
Department of Materials Science and Engineering, Faculty of Engineering , National University of Singapore , Singapore 117576 , Singapore.
ACS Appl Mater Interfaces. 2019 Feb 13;11(6):5682-5686. doi: 10.1021/acsami.8b20780. Epub 2019 Feb 1.
The development of commercially friendly and stable catalysts for oxygen reduction reaction (ORR) is critical for many energy conversion systems such as fuel cells and metal-air batteries. Many Co-based perovskite oxides such as LaCoO have been discovered as the stable and active ORR catalysts, which can be good candidates to replace platinum (Pt). Although researchers have tried substituting various transition metals into the Co-based perovskite catalysts to improve the ORR performance, the influence of substitution on the ORR mechanism is rarely studied. In this paper, we explore the evolution of ORR mechanism after substituting Fe into LaCoO, using the combination of X-ray photoelectron spectroscopy, high-resolution X-ray microscopy, X-ray diffraction, surface-sensitive soft X-ray absorption spectroscopy characterization, and electrochemical tests. We observed enhanced catalytic activities and increased electron transfer numbers during the ORR in Co-rich perovskite, which are attributed to the optimized e filling numbers and the stronger hybridization of transition metal 3d and oxygen 2p bands. The discoveries in this paper provide deep insights into the ORR catalysis mechanism on metal oxides and new guidelines for the design of Pt-free ORR catalysts.
对于许多能量转换系统，例如燃料电池和金属空气电池，开发商业友好且稳定的氧还原反应（ORR）催化剂至关重要。许多基于钴的钙钛矿氧化物，如 LaCoO，已被发现是稳定且活性的 ORR 催化剂，可作为替代铂（Pt）的良好候选物。尽管研究人员已尝试用各种过渡金属替代基于钴的钙钛矿催化剂以改善 ORR 性能，但很少研究取代对 ORR 机制的影响。在本文中，我们使用 X 射线光电子能谱、高分辨率 X 射线显微镜、X 射线衍射、表面敏感软 X 射线吸收光谱表征和电化学测试相结合，研究了 Fe 取代 LaCoO 后 ORR 机制的演变。我们观察到在富钴钙钛矿中，ORR 过程的催化活性增强，电子转移数增加，这归因于优化的 e 填充数和过渡金属 3d 和氧 2p 带之间更强的杂化。本文的发现深入了解了金属氧化物上的 ORR 催化机制，并为设计无 Pt 的 ORR 催化剂提供了新的指导。
