煅烧
催化作用
电化学
空位缺陷
电催化剂
氧气
锂(药物)
阴极
超级电容器
材料科学
金属
析氧
化学
无机化学
化学工程
物理化学
电极
结晶学
有机化学
冶金
生物化学
内分泌学
医学
工程类
作者
Sanghan Lee,Gyutae Nam,Jie Sun,Jang-Soo Lee,Hyun‐Wook Lee,Wei Chen,Jaephil Cho,Yi Cui
标识
DOI:10.1002/ange.201602851
摘要
Abstract Chemically prepared λ‐MnO 2 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 α‐ and δ‐MnO 2 . Herein, through the electrochemical removal of lithium from LiMn 2 O 4 , highly crystalline λ‐MnO 2 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 LiMn 2 O 4 synthesis; a concentration of oxygen vacancies in LiMn 2 O 4 could be characterized by its voltage profile as the cathode in a lithiun–metal half‐cell. λ‐MnO 2− z prepared with the highest OV exhibited the highest diffusion‐limited ORR current (5.5 mA cm −2 ) among a series of λ‐MnO 2− 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 λ‐MnO 2 by the generation of OVs. This study demonstrates that differences in the electrochemical behavior of λ‐MnO 2 depend on the preparation method and provides a mechanism for a unique catalytic behavior of cubic λ‐MnO 2 .
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