Urchin-like NiCo2O4 hollow microspheres with oxygen vacancies synthesized by self-template for supercapacitor†
Abstract
NiCo2O4 has been proved to be a promising electrochemical material. In this work, a hollow NiCo2O4 material with an urchin-like structure 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 the 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 F g−1 at 1 A g−1 and preserves 80% of capacitance retention after 5000 cycles. Moreover, the assembled asymmetric supercapacitor of H-NiCo2O4-12//AC delivers an energy density of 33.4 W h kg−1 at 747.7 W kg−1 and a high coulombic efficiency of about 95%. The improved supercapacitive performance of H-NiCo2O4-12 is attributed 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.
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