Porous MgCo2O4 nanoflakes serve as electrode materials for hybrid supercapacitors with excellent performance

In this work, MgCo2O4 microspheres (MgCo2O4 MSs) and MgCo2O4 nanoflakes (MgCo2O4 NFs) were prepared by one-step and two-step synthetic method, respectively, and combined with a post annealing treatment. Both MSs and NFs electrode materials possessed porous structure and large specific surface areas. The electrochemical properties were evaluated using three-electrode as well as two-electrode systems. The MgCo2O4 NFs delivered a specific capacity of 375.5C g-1 at 1 A g-1 together with a high rate performance (74.9%) at 10 A g-1, while the MgCo2O4 MSs exhibited 276.3C g-1 at the current density of 1 A g-1. A hybrid supercapacitor (HSC) device was assembled with a cathode made from MgCo2O4 and an anode made from activated carbon (AC) for evaluation of real applications, and it was able to run over a high voltage window (1.75 V). This MgCo2O4 NFs//AC HSC delivered a high energy density (Ed, 35.4 W h kg-1) at 950.6 W kg-1, and at the highest power density (Pd) of 8905.0 W kg-1, it could still hold 25.8 W h kg-1. On the other hand, the MgCo2O4 MSs//AC HSC device exhibited an Ed of 32.4 W h kg-1 at a Pd of 1048.0 W kg-1. Both HSCs exhibited good long-term cycling stability due to no capacity decay over 6000 cycles at 6 A g-1. The excellent electrochemical performance demonstrates that these MgCo2O4 electrode materials, especially the MgCo2O4 NFs, have great application potential for electrochemical energy storage. This synthesis method is simple and is possibly to be applied in synthesizing other transition metal oxides (TMOs)-based electrode materials with large surface area and outstanding electrochemical performance.