Sun Xianhu, Wu Dongxiang, Wang Jianyu, Patel Shyam B, Zhu Wenhui, Yang Ji, Yang Timothy T, Ye Shuonan, Chen Xiaobo, Zhu Yaguang, Qiao Linna, Li Meng, House Stephen D, Su Ji, Saidi Wissam A, Boscoboinik Jorge Anibal, Yang Judith C, Sharma Renu, Zhou Guangwen
Department of Mechanical Engineering and Materials Science and Engineering Program, State University of New York, Binghamton, NY 13902.
School of Chemical Sciences, University of Chinese Academy of Sciences, Beijing 101408, China.
Proc Natl Acad Sci U S A. 2025 Jun 17;122(24):e2422711122. doi: 10.1073/pnas.2422711122. Epub 2025 Jun 11.
The breaking of translational symmetry at oxide surfaces gives rise to coordinatively unsaturated cations/anions and surface restructuring-key factors that govern surface reactivity. Using direct in situ environmental transmission electron microscopy (TEM) observations along with atomistic modeling, we report oscillatory redox behavior in CuO under H, where cyclic surface reconstruction and reactivity modulation occur via the Mars-van Krevelen (MvK) mechanism. We observe self-switching between oxygen-rich and oxygen-deficient surface reconstructions, alternately activating and deactivating the surface for HO formation. During periods of chemical inactivity, the oxygen-deficient surface undergoes slow reoxidation via lattice oxygen diffusing from subsurface and bulk reservoirs, restoring the active oxygen-rich surface termination. The inherent disparity in chemical activity among undercoordinated surface ions, along with sluggish subsurface-to-surface oxygen replenishment, drives this oscillatory redox cycle, modulating H-induced loss of lattice oxygen at the surface and its delayed replenishment from the subsurface. This creates spatiotemporally separated redox steps at the oxide surface. The phenomena and atomistic insights presented here have significant implications for manipulating the surface reactivity of oxides by tuning the separation of these redox steps.
氧化物表面平移对称性的打破会产生配位不饱和的阳离子/阴离子以及表面重构，这些都是决定表面反应性的关键因素。通过直接原位环境透射电子显微镜（TEM）观察以及原子模拟，我们报道了在氢气氛围下CuO中的振荡氧化还原行为，其中通过Mars-van Krevelen（MvK）机制发生循环表面重构和反应性调制。我们观察到富氧和缺氧表面重构之间的自我切换，交替激活和失活表面以形成H₂O。在化学不活跃期间，缺氧表面通过从次表面和体相储库扩散的晶格氧进行缓慢再氧化，恢复活性富氧表面终止态。低配位表面离子之间化学活性的固有差异，以及次表面到表面氧补充的迟缓，驱动了这个振荡氧化还原循环，调节了表面上氢气诱导的晶格氧损失及其从次表面的延迟补充。这在氧化物表面产生了时空分离的氧化还原步骤。本文所呈现的现象和原子层面的见解对于通过调整这些氧化还原步骤的分离来操纵氧化物的表面反应性具有重要意义。
