In the present study, valence band (VB) and core level photoelectron spectroscopy was carried out to investigate the electronic structural changes from polycrystalline Co to spinel Co₃O₄, via CoO at near ambient pressures (NAP; ∼0.1 mbar). O₂–Co and H₂–CoO_x gas–solid oxidative and reductive interactions, respectively, have been explored with UV photons (He–I) or low kinetic energy electrons (≤16 eV) under NAP conditions. Typical VB features of Co metal, CoO, Co₃O₄, and a mixed phase between any two adjacent features were observed and well corroborated with core level changes. Very significant and characteristic changes were observed with Co 3d features in the VB for each stage from Co oxidation to Co₃O₄ as well as Co₃O₄ reduction to CoO. Co₃O₄ and CoO can be reversibly obtained by alternating the conditions between 0.1 mbar of H₂ at 650 K and 0.1 mbar of O₂ at 400 K, respectively. A meaningful correlation is observed between the changes in work function with cation oxidation state; small changes in the stoichiometry can strongly influence the shift in Fermi level and changes in work function under NAP conditions. Reversible work function changes are observed between oxidation and reduction conditions. While the O 2p derived feature for CoO_x was observed at a constant BE (∼5 eV) throughout the redox conditions, the Co 3d band and molecular oxygen or hydrogen vibration feature shifts significantly underscoring the physicochemical changes, such as charge transfer energy and hence changes in satellite intensity. The peak close to E_F originated from the 3d⁶L final state of the octahedral Co³⁺ 3d band of Co₃O₄.

中文翻译：

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金属钴到尖晶石Co ₃ O ₄的近环境压力光电子能谱电子结构演化

在本研究中，通过价带（VB）和核心能级光电子能谱研究了在接近环境压力（NAP;〜0.1 mbar）下通过CoO从多晶Co到尖晶石Co ₃ O ₄的电子结构变化。在NAP条件下，分别使用UV光子（He–I）或低动能电子（≤16eV）探索了O ₂ -Co和H ₂ -CoO _x气体-固体的氧化和还原相互作用。Co金属，CoO，Co ₃ O _4的典型VB特性，并且观察到任意两个相邻特征之间的混合相，并与岩心能级变化很好地证实了这一点。从Co氧化到Co ₃ O ₄以及从Co ₃ O ₄还原成CoO的每个阶段，VB中的Co 3d特征都观察到非常显着的特征变化。通过在650 K下的0.1 mbar H ₂和0.1 mbar O ₂之间交替改变条件，可以可逆地获得Co ₃ O ₄和CoO。分别为400 K 在功函数的变化与阳离子氧化态之间观察到有意义的相关性；在NAP条件下，化学计量的微小变化会极大地影响费米能级的变化和功函数的变化。在氧化和还原条件之间观察到可逆的功函数变化。虽然在整个氧化还原条件下，在恒定的BE（〜5 eV）时观察到了CoO _x的O 2p衍生特征，但Co 3d谱带和分子氧或氢振动特征发生了明显变化，从而突出了物理化学变化，例如电荷转移能，因此卫星强度的变化。接近E _F的峰源自八面体Co的3d ⁶ L最终状态Co ₃ O _4的³⁺ 3d带。