Enhanced Intrinsic Catalytic Activity of λ-MnO2by Electrochemical Tuning and Oxygen Vacancy Generation

Sanghan Lee, Gyutae Nam, Jie Sun, Jang Soo Lee, Hyun Wook Lee, Wei Chen, Jaephil Cho*, Yi Cui

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

75 Scopus citations

Abstract

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 languageEnglish (US)
Pages (from-to)8599-8604
Number of pages6
JournalAngewandte Chemie - International Edition
Volume55
Issue number30
DOIs
StatePublished - Jan 1 2016

Keywords

  • electrocatalysts
  • manganese
  • oxides
  • oxygen reduction reaction
  • zinc–air battery

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

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