Hollow Urchin-Like NiCo 2O 4 Microspheres with Oxygen Vacancies Synthesized by Self-Template for Supercapacitors

NiCo2O4 has been proved to have promising electrochemical performance. In this work, a new type of hollow urchin-like NiCo2O4 material is constructed by a self-template of Ni-Co complex compound based on the Ostwald ripening mechanism. During the thermal annealing in air, the residual carbon from the organic ligands of Ni-Co complex compound leads to the generation of oxygen vacancies in urchin-like NiCo2O4. The as-obtained hollow NiCo2O4 (H-NiCo2O4-12) material manifests admirable specific capacitance of 886 Fg-1 at 1Ag-1, and preserves 80% of capacitance retention after 5000 cycles. Meanwhile, the assembled asymmetric supercapacitor of H-NiCo2O4-12//AC delivers an energy density of 33.4 Wh g-1 at 747.7 W kg-1. The improved supercapacitive performance of H-NiCo2O4-12 should attribute to its synergistic effect of hollow structure and oxygen vacancies. The hollow urchin-like structure of NiCo2O4 can buffer the volume expansion, expose abundant reaction active sites and favor the transport of ions; while oxygen vacancies can adjust the electronic structure of NiCo2O4 which can favor the transfer of electrons. This work may throw some light on designing a virtue supercapacitor electrode material with hollow nanoporous morphology.