Co3O4/ZnO nanoheterostructure derived from core–shell ZIF-8@ZIF-67 for supercapacitors

Abstract

In this work, we developed a novel and facile method to fabricate a Co₃O₄/ZnO nanoheterostructure via a solid–solid conversion process using core–shell MOFs@MOFs as a template and source of cobalt and zinc. Herein, we set out to prepare core–shell structured ZIF-8@ZIF-67, which consists of ZIF-8 ([Zn(MeIm)₂]_n) (MeIm = 2-methylimidazole) as the core and ZIF-67 ([Co(MeIm)₂]_n) as the shell, through a seed-mediated growth method. Co₃O₄/ZnO nanoheterostructure was prepared through the thermal conversion of core–shell ZIF-8@ZIF-67. This hierarchical Co₃O₄/ZnO exhibits a high specific capacitance of 415 F g⁻¹ at 0.5 A g⁻¹ and an improved rate capability (93.2% retention at 10 A g⁻¹). Asymmetric supercapacitors were fabricated using the Co₃O₄/ZnO heterostructure as the positive electrode and active carbon as negative electrode. The operation voltage is expanded to 1.4 V in aqueous electrolyte, revealing an energy density of 43.2 W h kg⁻¹ at a power density of 1401 W kg⁻¹. This MOF-driven strategy can be expanded to the preparation of other metal oxide nanoheterostructures by varying the type of MOFs, and may find potential application in high-performance supercapacitors.