Elucidating the Initial Oxidation of Pt(111) Using Large-Scale Atomistic Thermodynamics: A ReaxFF Study

In situ scanning tunneling microscopy experiments on the initial oxidation of Pt(111) found complex intermediary platinum surface oxides, consisting of spoke wheel and stripe structures [Nat. Commun.2017, 8, 429]. While the stripes have been investigated extensively in the following, the spoke wheels are poorly understood because of their size and complexity. Here we employ atomistic thermodynamics based on an established reactive force field to investigate the structure and stability of spoke wheels at the elevated temperature (>530 K) and pressure (1–4 bar) conditions of the in situ experiments. At those conditions, the thermodynamic stability of the structural model for the spoke wheel is similar to that of the stripes, while the degree of surface oxidation is much lower. The spoke wheel is found to be much more stable than partially formed stripes with a similar degree of oxidation. These results are consistent with experimental findings, where the spoke wheel is observed first, at slightly lower oxygen pressures. They thus provide a better understanding of the oxidation pathway for Pt(111)-based catalysts in the context of oxidative catalysis.

针对Pt(111)初始氧化过程的原位扫描隧道显微镜（scanning tunneling microscopy, STM）实验，观测到复杂的铂表面中间氧化物种，其结构包含辐轮状与条纹状两种形貌[Nat. Commun., 2017, 8, 429]。尽管后续研究已对条纹状结构开展了广泛的表征与分析，但辐轮状结构因自身尺寸与结构复杂性，相关研究认知仍较为匮乏。本研究基于已成熟的反应力场，采用原子热力学方法，探究了原位实验对应的高温（>530 K）、高压（1–4 bar）条件下辐轮状结构的形貌与热力学稳定性。在该实验条件下，辐轮状结构模型的热力学稳定性与条纹状结构相近，但其表面氧化程度显著更低。研究发现，在氧化程度相近的前提下，完整的辐轮状结构稳定性远优于部分形成的条纹状结构。上述结果与实验观测结果一致：在略低的氧分压条件下，辐轮状结构会优先形成。该研究因此深化了氧化催化场景下Pt(111)基催化剂的氧化反应路径认知。