Template-engaged synthesis of uniform mesoporous hollow NiCo2O4 sub-microspheres towards high-performance electrochemical capacitors

Abstract

An efficient template-engaged synthetic strategy, where silica spheres were applied as hard templates, was developed to synthesize hierarchical mesoporous hollow NiCo₂O₄ sub-microspheres assembled entirely from ultrathin nanosheets with a thickness of a few nanometers. The as-prepared mesoporous hollow NiCo₂O₄ sub-microspheres are very uniform in size, mesoporous in textual property, and structurally robust benefiting from the in situ template removal. The morphologies of the hollow sub-microspherical architecture can be tuned easily by varying the concentrations of Ni²⁺, Co²⁺, and the precipitant. When evaluated as an appealing electroactive material for electrochemical capacitors (ECs), the as-fabricated hierarchical hollow NiCo₂O₄ sub-microspheres delivered a specific capacitance (SC) of 678 F g⁻¹ at a current density of 1 A g⁻¹, and even kept it as high as 540 F g⁻¹ at 10 A g⁻¹. Additionally, a desirable cycling stability of 13% SC degradation over 3500 continuous cycles at a current density of 10 A g⁻¹ is observed, suggesting their promising application in advanced ECs.