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

In this work, porous MgCoO nanoflakes (MgCoO NFs) and MgCoO nanocubes (MgCoO 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 MgCoO samples can be easily tuned by changing the hydrothermal temperature and reaction time, respectively. The porous MgCoO NFs with an average pore size of 12.5 nm had a BET specific surface area up to 64.9 m g, which was larger than that of MgCoO NCs (19.8 m g). The MgCoO NFs delivered a specific capacitance of 734.1 F g at 1 A g and exhibited a considerable rate performance with 74.0% capacitance retention at 12 A g. About 94.2% of its original capacitance could be retained after 5000 charge-discharge cycles at a constant current density of 5 A g. An asymmetric supercapacitor (ASC) was assembled by using MgCoO 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 at a power density of 859.6 W kg. Such outstanding electrochemical performances make the MgCoO 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.