Amorphous mesoporous nickel phosphate/reduced graphene oxide with superior performance for electrochemical capacitors

Nickel phosphate (Ni-3(PO4)(2)) is a promising electrode material for electrochemical capacitors, but the low intrinsic electrical conductivity and poor rate capability of Ni-3(PO4)(2) are the main challenges. To tackle these problems, amorphous mesoporous Ni-3(PO4)(2) with a pore diameter of 2-10 nm is grown on reduced graphene oxide (rGO), and a Ni-3(PO4)(2)/rGO composite is obtained via a facile hydrothermal-calcination method in this work. The Ni-3(PO4)(2)/rGO composite calcined at 300 degrees C (Ni-3(PO4)(2)/rGO-300) possesses a uniform particle size and a high specific surface area of 198.72 m(2) g(-1). Benefiting from the structural characteristics, the synergistic effect of components and the high specific surface area, the Ni-3(PO4)(2)/rGO-300 composite exhibits an extremely high specific capacitance of 1726 F g(-1) at 0.5 A g(-1) and an excellent rate capability of 850 F g(-1) at 25 A g(-1). In addition, the assembled Ni-3(PO4)(2)/rGO-300//activated carbon asymmetric electrochemical capacitor delivers a good energy density of 57.42 W h kg(-1) at a power density of 160 W kg(-1). Compared with Ni-3(PO4)(2)/rGO composites calcined at other temperatures and other nickel-phosphorus compounds reported in the literature, the Ni-3(PO4)(2)/rGO-300 composite containing amorphous mesoporous Ni-3(PO4)(2) exhibits superior electrochemical performance, representing a new kind of electrode material for electrochemical capacitors.