In situ transformation of ZIF-67 into hollow Co2V2O7 nanocages on graphene as a high-performance cathode for aqueous asymmetric supercapacitors

Abstract

In this work, well-designed Co₂V₂O₇/graphene composites with hollow Co₂V₂O₇ nanocages uniformly distributed on the graphene sheets were synthesized through a combined approach of a precipitation reaction to assemble zeolitic imidazolate frameworks-67 (ZIF-67) on graphene and a subsequent in situ ion exchange reaction to transform ZIF-67 into hollow Co₂V₂O₇ nanocages. Morphological and compositional characterization confirmed that ZIF-67 had been successfully transformed into the nanoparticle-assembled hollow Co₂V₂O₇ nanocages, which are densely distributed on graphene. Benefiting from the well-designed structure and compositions, the electrochemical tests indicate that the as-prepared Co₂V₂O₇/graphene electrode exhibits a high specific capacity of 276.5 C g⁻¹ at 1 A g⁻¹, good rate capability, and remarkable long cycling stability (93% capacity retention after 10 000 cycles). The asymmetric supercapacitor devices assembled with Co₂V₂O₇/graphene and reduced graphene oxides deliver a high energy density of 25.7 W h kg⁻¹ at a power density of 663.5 W kg⁻¹ and excellent long cycling stability. The excellent electrochemical performance and the facile synthetic process make Co₂V₂O₇/graphene a promising cathode material for supercapacitors.