Mesoporous layered hexagonal platelets of Co₃O₄ nanoparticles with (111) facets for battery applications: high...

The thermally stable and crystalline 2D layered mesoporous hexagonal platelets of cobalt oxide (Co₃O₄) with (111) facets were prepared by using the template-free wet chemical synthesis approach. The high surface energy (111) facets known for a highly electroactive surface are expected to enhance the electrochemical properties, especially the rate capability. The highly crystalline Co₃O₄ with an average particle size of 25 nm formed a 2D mesoporous layered structure, with an average thickness of ∼40 nm, a pore size of 8-10 nm, and a specific surface area of 45.68 m² g^-1 promoting large surface confined electrochemical reaction. The 2D layered mesoporous Co₃O₄ exhibits a maximum specific capacity of 305 mA h g^-1 at a scan rate of 5 mV s^-1 and 137.6 mA h g^-1 at a current density of 434.8 mA g^-1. The maximum energy and power densities of 32.03 W h kg^-1 and 9.36 kW kg^-1, respectively, are achieved from the 2D hexagonal platelets of mesoporous Co₃O₄ nanoparticles with (111) facets. An excellent ultra-high rate capability of ∼62% capacity retention was observed after increasing the discharge current density from ∼434.8 mA g^-1 to 43 480 mA g^-1. Furthermore, a cycling stability of 81.25% was achieved even after 2020 charge-discharge cycles at a current density of 12 170 mA g^-1. This high performance and ultra-high rate capability could be attributed to the (111) facets 'crystal plane' effect of Co₃O₄. Our results presented here confirm that the 2D mesoporous layered hexagonal platelets of Co₃O₄ exhibit "battery-mimic" behaviour in an aqueous electrolyte of KOH.