Sun Xianhu, Wu Dongxiang, Zhu Wenhui, Chen Xiaobo, Sharma Renu, Yang Judith C, Zhou Guangwen
Department of Mechanical Engineering & Materials Science and Engineering Program, State University of New York, Binghamton, New York 13902, United States.
Nanoscale Device Characterization Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States.
J Phys Chem Lett. 2021 Oct 7;12(39):9547-9556. doi: 10.1021/acs.jpclett.1c02369. Epub 2021 Sep 27.
Reducibility is key for the use of bulk metal oxides in chemical transformations involving redox reactions, but probing microscopic processes of oxide reduction is challenging. This is because the insulating nature of bulk oxides restricts ion and electron spectroscopic measurements of oxide surfaces. Herein, using a combination of environmental transmission electron microscopy and atomistic modeling, we report direct in situ atomic-scale observations of the surface and subsurface dynamics and show that the hydrogen-induced CuO reduction occurs through the receding motion of Cu-O/Cu bilayer steps at the surface, the formation of the partially reduced CuO superstructure by the self-ordering of O vacancies in the subsurface, and the collapse of Cu-O layers in the bulk. All these substeps can be traced back to the progressively increased concentration and activity of O vacancies in the surface and subsurface of the oxide, thereby leading to the self-accelerated oxide reduction. These results demonstrate the microscopic details that may have a broader applicability in modulating various redox processes.
可还原性是在涉及氧化还原反应的化学转化中使用块状金属氧化物的关键，但探究氧化物还原的微观过程具有挑战性。这是因为块状氧化物的绝缘性质限制了对氧化物表面的离子和电子光谱测量。在此，我们结合环境透射电子显微镜和原子尺度建模，报告了对表面和亚表面动力学的直接原位原子尺度观察，并表明氢诱导的CuO还原是通过表面Cu-O/Cu双层台阶的后退运动、亚表面O空位的自排序形成部分还原的CuO超结构以及块状Cu-O层的坍塌而发生的。所有这些子步骤都可追溯到氧化物表面和亚表面O空位浓度和活性的逐渐增加，从而导致氧化物的自加速还原。这些结果展示了在调节各种氧化还原过程中可能具有更广泛适用性的微观细节。
