Hydrothermal synthesis of flower-like MgCo2O4 porous microstructures as high-performance electrode material for asymmetric supercapacitors

MgCo2O4 microflowers (MFs) assembled with porous nanosheets were prepared through a facile hydrothermal method with a post calcination treatment of the precursors at 400 degrees C for 3 h in air. No surfactant or template was used during the synthetic process. These MgCo2O4 MFs possessed a BET specific surface area of 39.1 m(2) g(-1) with an average pore size of 37 nm. The electrochemical performance was evaluated in a typical three-electrode system using 2 M of KOH aqueous solution as electrolyte, and the results indicated that such MgCo2O4 MFs exhibited a high specific capacitance of 749.2 F g(-1) at 1 A g(-1) as well as a high rate capability of approximate 73.3% with the current density increasing from 1 to 15 A g(-1). After 5000 charge-discharge cycles at 5 A g(-1), a specific capacitance of 435.3 F g(-1) with 67.8% capacitance retention of its initial value and Coulombic efficiency of about 100% could be reached. In addition, an asymmetric supercapacitor (ASC) was fabricated with MgCo2O4 MFs as the positive electrode and activated carbon (AC) as the negative electrode. The ASC delivered a high energy density of 35.2 Wh kg(-1) at a power density of 859.2 W kg(-1). At a higher power density of 7415.3 W kg(-1), the energy density still reached 29.3 Wh kg(-1). The ASC also showed a good cycling stability with 100.9% specific capacitance retention after 5000 cycles at 5 A g(-1). The unique MgCo2O4 MFs with mesoporous structures are beneficial for the rapid Faradic reactions because sufficient contact between electrolyte/electrode material and short diffusion path for ions/electrons can be ensured. The current synthesis is involved in simple operation and low cost, and can be extended to the preparation of other binary transitional metal oxides as electrode materials for the next-generation advanced supercapacitors. (C) 2020 Elsevier B.V. All rights reserved.