Zhang Zhenhua, Ke Xiaoxing, Zhang Bin, Deng Jiguang, Liu Yuxi, Liu Weiwei, Dai Hongxing, Chen Fu-Rong, Sui Manling
College of Materials and Environmental Engineering, Institute for Advanced Magnetic Materials, Hangzhou Dianzi University, Hangzhou 310018, China.
Beijing Key Laboratory of Microstructure and Properties of Solids, Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing 100124, China.
J Phys Chem Lett. 2020 Nov 19;11(22):9913-9919. doi: 10.1021/acs.jpclett.0c02901. Epub 2020 Nov 10.
CoO is an important catalyst widely used for CO oxidation or electrochemical water oxidation near room temperature and was also recently used as support for single-atom catalysts (SACs). CoO with a spinel structure hosts dual oxidation states of Co and Co in the lattice, leading to the complexity of its surface structure as the exposure of Co and Co has a significant impact on the performance of the catalysts. Although it is acknowledged that different facets exhibit varied catalytic activities and different abilities in hosting single atoms to provide active centers in SACs, the CoO surface structure remains under-investigated. In this study, major facets of {111}, {110}, and {100} were studied down to subangstrom scale using advanced electron microscopy. We noticed that each facet has its own most stable surface configuration. The distribution of Co and Co on each facet was quantified, revealing a facet-dependent distribution of Co and Co. Co was found to be preferentially exposed on {100} and {110} as well as surface steps. Surface reconstruction was revealed, where a subangstrom scale shift of Co was confirmed on facets of {111} and {100} due to polarity compensation and oxygen deficiency on the surface. This work not only improves our fundamental understanding of the CoO surface structure but also may promote the design of CoO-based catalysts with tunable activity and stability.
氧化钴是一种重要的催化剂，广泛应用于室温附近的一氧化碳氧化或电化学水氧化反应，最近还被用作单原子催化剂（SACs）的载体。具有尖晶石结构的氧化钴在晶格中具有Co²⁺和Co³⁺两种氧化态，由于Co²⁺和Co³⁺的暴露对催化剂性能有重大影响，导致其表面结构复杂。尽管人们认识到不同晶面表现出不同的催化活性以及在承载单原子以提供SACs活性中心方面具有不同能力，但氧化钴的表面结构仍未得到充分研究。在本研究中，使用先进的电子显微镜对{111}、{110}和{100}等主要晶面进行了亚埃尺度的研究。我们注意到每个晶面都有其最稳定的表面构型。对每个晶面上Co²⁺和Co³⁺的分布进行了量化，揭示了Co²⁺和Co³⁺的晶面依赖性分布。发现Co²⁺优先暴露在{100}和{110}晶面以及表面台阶上。揭示了表面重构现象，由于表面的极性补偿和氧缺陷，在{111}和{100}晶面上证实了Co原子的亚埃尺度位移。这项工作不仅增进了我们对氧化钴表面结构的基本理解，还可能促进具有可调活性和稳定性且基于氧化钴的催化剂的设计。
