Facile hydrothermal synthesis of porous MgCo2O4 nanoflakes as an electrode material for high-performance asymmetric supercapacitors

In this work, porous MgCo2O4 nanoflakes (MgCo2O4 NFs) and MgCo2O4 nanocubes (MgCo2O4 NCs) have been successfully synthesized through a simple hydrothermal method combined with a post calcination process of the precursor in air. The morphology of the MgCo2O4 samples can be easily tuned by changing the hydrothermal temperature and reaction time, respectively. The porous MgCo2O4 NFs with an average pore size of 12.5 nm had a BET specific surface area up to 64.9 m(2) g(-1), which was larger than that of MgCo2O4 NCs (19.8 m(2) g(-1)). The MgCo2O4 NFs delivered a specific capacitance of 734.1 F g(-1) at 1 A g(-1) and exhibited a considerable rate performance with 74.0% capacitance retention at 12 A g(-1). About 94.2% of its original capacitance could be retained after 5000 charge-discharge cycles at a constant current density of 5 A g(-1). An asymmetric supercapacitor (ASC) was assembled by using MgCo2O4 NFs as the positive electrode and AC as the negative electrode, and the ASC had a wide operation voltage of 1.7 V and a high energy density of 33.0 W h kg(-1) at a power density of 859.6 W kg(-1). Such outstanding electrochemical performances make the MgCo2O4 NFs a promising candidate for supercapacitor applications. In addition, the simple and scalable synthesis method can be extended to the preparation of other metal oxide-based electrode materials.