Yolk-shell bimetallic metal-organic frameworks derived multilayer core-shells NiCo2O4/NiO structure spheres for high-performance supercapacitor

The yolk-shell structured Ni/Co-based MOFs were first synthesized via one-step hydrothermal method without any template, followed by the pyrolysis treatment to prepare the multilayer core-shells NiCo2O4/NiO structure spheres. The growth mechanism of the Co/Ni-MOF and multilayer core-shells NiCo2O4/NiO microsphere can be explained by the Ostwald ripening and heterogeneous contraction effect, respectively. The obtained multilayer NiCo2O4/NiO microspheres displayed unique three-layer structure with an average diameter of 1–2 μm by TEM. Due to the compositional and structural benefits, the obtained multilayer NiCo2O4/NiO structure spheres exhibited high specific capacitance of 726 F·g−1 at the current density of 1 A·g−1 and a good cycling stability of 91.4% retention over 5000 cycles. In addition, an asymmetric supercapacitor (ASC) based on multilayer NiCo2O4/NiO microspheres and active carbon was fabricated and shown a high energy density of 22.1 Wh·kg−1 at a power density of 4518.6 W·kg−1. These superior electrochemical properties indicated that the multilayer NiCo2O4/NiO microsphere was a promising electroactive candidate for high-performance supercapacitors.