Rational design and facile synthesis of two-dimensional hierarchical porous M3V2O8 (M = Co, Ni and Co-Ni) thin sheets assembled by ultrathin nanosheets as positive electrode materials for high-performance hybrid supercapacitors

The development of advanced supercapacitors (SCs) depends largely on the rational design and facile manufacture of high performance electrode materials. The family of cobalt/nickel-based vanadates M3V2O8 (M= Co, Ni and Co-Ni) including Co3V2O8 (CVO), Ni3V2O8 (NVO) and Co1.5Ni1.5V2O8 (CNVO) has emerged as promising electrode materials for SCs, yet still limited by its unsatisfactory electrochemical performance. Herein, novel two-dimensional (2D) hierarchical porous cobalt/nickel-based vanadates thin sheets were synthesized via a succinct-operated hydrothermal method by direct decompostion of the mixed aqueous solution of NiCl2/CoCl2 and NaVO3 without using any substrate or surfactant. This unique porous architecture assembled by nanoflakes facilitates the ion migration and electronic transportation within the materials and endow the CNVO thin sheetbased electrode with a remarkable specific capacity of 848.5 C.g(-1) (specific capacitance of 2617.5 F.g(-1)) at 1 A.g(-1), which is more superior than the value of as-obtained CVO and NVO thin sheets and reported metal vanadates so far. In addition, a hybrid device (CNVO//activated carbon (AC)), fabricated by employing the CNVO thin sheets as positive material and AC as negative one, shows a maximum energy density of 51.66 Wh.kg(-1) at the power density of 850 W.kg(-1) and still remain 38.01 Wh.kg(-1) at 8500 W.kg(-1). The results presented in this work not only exhibit a promising prospect of 2D CNVO thin sheets in SCs but also provide a practicable pathway for the synthesis of other transition metal oxides.