Holey 2D Nanosheets of Low‐Valent Manganese Oxides with an Excellent Oxygen Catalytic Activity and a High Functionality as a Catalyst for Li–O2 Batteries

• Published in: Advanced functional materials Vol. 28; no. 17
• Main Authors: Adpakpang, Kanyaporn, Oh, Seung Mi, Agyeman, Daniel Adjei, Jin, Xiaoyan, Jarulertwathana, Nutpaphat, Kim, In Young, Sarakonsri, Thapanee, Kang, Yong‐Mook, Hwang, Seong‐Ju
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 25-04-2018
• Subjects: Catalysis; Catalytic activity; Crystallites; Electrocatalysts; Heat treatment; High temperature; holey metal oxide nanosheets; Li–O2 batteries; Manganese dioxide; Manganese oxides; Materials science; Morphology; Nanosheets; Oxidation; oxygen evolution reaction; Oxygen evolution reactions; phase transition; Phase transitions; Transition metal oxides
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201707106

Holey 2D nanosheets of low‐valent Mn2O3 can be synthesized by thermally induced phase transition of exfoliated layered MnO2 nanosheets. The heat treatment of layered MnO2 nanosheets at elevated temperatures leads not only to transitions to low‐valent manganese oxides but also to the creation of surface hole in the 2D nanosheet crystallites. Despite distinct phase transitions, highly anisotropic 2D morphology of the precursor MnO2 material remains intact upon the heat treatment whereas the diameter of surface hole becomes larger with increasing heating temperature. The obtained holey 2D Mn2O3 nanosheets show promising electrocatalyst performances for oxygen evolution reaction, which are much superior to that of nonporous Mn2O3 crystal. Among the present materials, the holey Mn2O3 nanosheet calcined at 500 °C displays the best electrocatalyst functionality with markedly decreased overpotential, indicating the importance of heating condition in optimizing the electrocatalytic activity. Of prime importance is that this material shows much better catalytic activity for Li–O2 batteries than does nonporous Mn2O3, underscoring the critical role of porous 2D morphology in this functionality. This study clearly demonstrates the unique advantage of holey 2D nanosheet morphology in exploring economically feasible transition metal oxide‐based electrocatalysts and electrodes for Li–O2 batteries.
An effective synthetic route to novel holey 2D nanosheets of low‐valent manganese oxides is developed by finely controlled heat treatment of exfoliated MnO2 nanosheet. The resulting holey 2D Mn2O3 nanosheets show promising functionalities as oxygen electrocatalysts and cathode catalysts for Li–O2 batteries with excellent cyclability, underscoring the remarkable advantage of holey 2D nanosheet morphology.