Amorphous vanadyl phosphate/graphene composites for high performance supercapacitor electrode.

Amorphous vanadyl phosphate/graphene nanohybrids is successfully synthesized by first exfoliating bulk layered vanadyl phosphate (VOPO 4 ·2H 2 O) into nanosheets, and then hydrothermal treatment with graphene oxide (GO). The electrochemical properties of the resulted materials are systematically investigated. It is found that a phase transformation from crystalline to amorphous is occurred to VOPO 4 ·2H 2 O. As supercapacitor electrode material, the amorphous VOPO 4 /graphene composite exhibits a high specific capacitance (508 F g −1 at 0.5 A g −1 ), an excellent rate capability (359 F g −1 at 10 A g −1 ), and a good cycling stability (retention 80% after 5000 cycles at 2 A g −1 ). Particularly, it simultaneously has a greatly enhanced energy density of 70.6 Wh·kg −1 with a power density of 250 W kg −1 . The outstanding energy storage performance mainly originates from the generation of amorphous VOPO 4 phase that facilitates ion transport by shortening ion diffusion paths and provides more reversible and fast faradic reaction sites, the hybridization with graphene that greatly improves the electric conductivity and structure stability, and the unique layer-on-sheet nanohybrid structure that effectively enhances the structure integrity. This work not only provides a facile method for the preparation of amorphous VOPO 4 /graphene composites, but also demonstrates the enhanced energy density and rate capability of amorphous VOPO 4 -based materials for potential application in supercapacitors. [ABSTRACT FROM AUTHOR]