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 (E_d, 35.4 W h kg^-1) at 950.6 W kg^-1, and at the highest power density (P_d) 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 E_d of 32.4 W h kg^-1 at a P_d 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.