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

In this work, well-designed Co2V2O7/graphene composites with hollow Co(2)V(2)O(7)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 subsequentin situion exchange reaction to transform ZIF-67 into hollow Co(2)V(2)O(7)nanocages. Morphological and compositional characterization confirmed that ZIF-67 had been successfully transformed into the nanoparticle-assembled hollow Co(2)V(2)O(7)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.