Enhanced Intrinsic Catalytic Activity of λ-MnO2 by Electrochemical Tuning and Oxygen Vacancy Generation
Enhanced Intrinsic Catalytic Activity of λ-MnO2 by Electrochemical Tuning and Oxygen Vacancy Generation
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DOI：
10.1002/anie.201602851
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发表时间：
2016-07-18
影响因子：
16.6
通讯作者：
Cui, Yi
中科院分区：
文献类型：
--
作者：
Lee, Sanghan;Nam, Gyutae;Cui, Yi
化学制备的α-MnO 2作为金属-空气电池、燃料电池或超级电容器的材料尚未被深入研究，因为与α-和δ-MnO 2相比，它们的电化学性能相对较差。在此，通过从LiMn 2 O 4中电化学去除锂，制备了高度结晶的LiMn 2 O2，作为用于氧还原反应（ORR）的有效电催化剂。材料的ORR活性通过引入氧空位（OVs）而进一步改善，所述氧空位（OVs）可以通过在LiMn 2 O 4合成期间提高煅烧温度来实现; LiMn 2 O 4中的氧空位浓度可以通过其作为锂金属半电池中的阴极的电压曲线来表征。在一系列的MnO 2-z电催化剂中，以最高OV制备的MnO 2-z表现出最高的扩散限制ORR电流（5.5 mAcm（-2））。此外，ORR中涉及的转移电子数（n）> 3.8，表明主要的准4电子途径。有趣的是，样品的催化性能不是其表面积的函数，而是取决于OV的浓度，这表明通过生成OV增强了MnO 2的固有催化活性。这项研究表明，在电化学行为的差异取决于制备方法，并提供了一个独特的催化行为的立方MnO 2的机制。
Chemically prepared lambda-MnO2 has not been intensively studied as a material for metal-air batteries, fuel cells, or supercapacitors because of their relatively poor electrochemical properties compared to alpha- and delta-MnO2. Herein, through the electrochemical removal of lithium from LiMn2O4, highly crystalline lambda-MnO2 was prepared as an efficient electrocatalyst for the oxygen reduction reaction (ORR). The ORR activity of the material was further improved by introducing oxygen vacancies (OVs) that could be achieved by increasing the calcination temperature during LiMn2O4 synthesis; a concentration of oxygen vacancies in LiMn2O4 could be characterized by its voltage profile as the cathode in a lithiun-metal half-cell. lambda-MnO2-z prepared with the highest OV exhibited the highest diffusion-limited ORR current (5.5 mAcm(-2)) among a series of lambda-MnO2-z electrocatalysts. Furthermore, the number of transferred electrons (n) involved in the ORR was > 3.8, indicating a dominant quasi-4-electron pathway. Interestingly, the catalytic performances of the samples were not a function of their surface areas, and instead depended on the concentration of OVs, indicating enhancement in the intrinsic catalytic activity of lambda-MnO2 by the generation of OVs. This study demonstrates that differences in the electrochemical behavior of lambda-MnO2 depend on the preparation method and provides a mechanism for a unique catalytic behavior of cubic lambda-MnO2.