Chemically prepared λ-MnO2has 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-MnO2. Herein, through the electrochemical removal of lithium from LiMn2O4, highly crystalline λ-MnO2was 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 LiMn2O4synthesis; a concentration of oxygen vacancies in LiMn2O4could be characterized by its voltage profile as the cathode in a lithiun–metal half-cell. λ-MnO2−zprepared with the highest OV exhibited the highest diffusion-limited ORR current (5.5 mA cm−2) among a series of λ-MnO2−zelectrocatalysts. 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-MnO2by the generation of OVs. This study demonstrates that differences in the electrochemical behavior of λ-MnO2depend on the preparation method and provides a mechanism for a unique catalytic behavior of cubic λ-MnO2.
|Original language||English (US)|
|Number of pages||6|
|Journal||Angewandte Chemie - International Edition|
|State||Published - Jan 1 2016|
- oxygen reduction reaction
- zinc–air battery
ASJC Scopus subject areas