Preparation and performance of β-MnO2 nanorod @ nanoflake (Ni, Co, Mn) oxides with hierarchical mesoporous structure

Abstract

The rational design and facile synthesis of transition metal oxides are necessary to improve their application in supercapacitors. Herein three kinds of hierarchical mesoporous structured transition metal oxides, which are composed of a β-MnO₂ nanorod core and one of three different nanosheet hybrid (Ni, Co, Mn) oxide shells, are facilely synthesized via a novel in situ nucleation and growth of transition metal oxides on the surface of the β-MnO₂ nanorods. The crystallographic analyses demonstrated that the three kinds of hybrid oxide shells consisted of cobalt manganese oxide (CMO), nickel manganese oxide (NMO), and nickel cobalt manganese oxide (NCMO). These transition metal oxides are evaluated as electrodes for high performance supercapacitors (SCs). The results reveal that β-MnO₂@CMO exhibits a good rate capability of 35% capacity retention even at 20 A g⁻¹, while β-MnO₂@NMO displays a high pseudocapacitance of 560 F g⁻¹ at 1 A g⁻¹. However, β-MnO₂@NCMO combined the advantages of both β-MnO₂@CMO and β-MnO₂@NMO, and exhibits a high specific capacitance of 675 F g⁻¹ at 1 A g⁻¹ with excellent rate performance (about 30% capacity retention at 20 A g⁻¹) and cycling stability (83% capacity retention after 3000 cycles). The improved electrochemical performance can be attributed to the unique hierarchical architecture and the synergistic effect of different components.