Insight into the Effect of Oxygen Vacancy Concentration on the Catalytic Performance of MnO2

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• 作者：Li Li ; Xianghong Feng ; Yao Nie ; Siguo Chen ; Feng Shi ; Kun Xiong ; Wei Ding ; Xueqiang Qi ; Jinsong Hu ; Zidong Wei ; Li-Jun Wan ; Meirong Xia
• 刊名：ACS Catalysis
• 出版年：2015
• 出版时间：August 7, 2015
• 年：2015
• 卷：5
• 期：8
• 页码：4825-4832
• 全文大小：676K
• ISSN：2155-5435

文摘

Oxygen vacancies (OVs) are important for changing the geometric and electronic structures as well as the chemical properties of MnO₂. In this study, we performed a DFT+U calculation on the electronic structure and catalytic performance of a 尾-MnO₂ catalyst for the oxygen reduction reaction (ORR) with different numbers and extents of OVs. Comparing those results with the experimental XRD analysis, we determined that OVs produce a new crystalline phase of 尾-MnO₂. Changes in the electronic structure (Bader charges, band structure, partial density of states, local density of states, and frontier molecular orbital), proton insertion, and oxygen adsorption in 尾-MnO₂ (110) were investigated as a function of the bulk OVs. The results show that a moderate concentration of bulk OVs reduced the band gap, increased the Fermi and HOMO levels of the MnO₂ (or MnOOH), and elongated the O鈥揙 bond of the adsorbed O₂ and coadsorbed O₂ with H. These changes substantially increase the conductivity of MnO₂ for the catalysis of ORR. However, an excessively high concentration of OVs in 尾-MnO₂ (110) will work against the catalytic enhancement of MnO₂ for ORR. The DFT+U calculation reveals that a moderate concentration of OVs induced a large overlap of the surface Mn d_z2 orbitals, thus introducing an extra donor level at the bottom of the conductive band, which increased the conductivity of 尾-MnO₂ (110). Such a curvilinear change of the catalytic activity and electronic structure as a function of the oxygen vacancy concentration suggests that the 尾-MnO₂ with moderate concentration OVs exhibits the highest conductivity and catalytic activity for ORR.