Hierarchically porous bowknot-like sodium doped Ni2P2O7-Co2P2O7 with improved supercapacitor performances

Hierarchically porous bowknot-like sodium doped Ni2P2O7-Co2P2O7 structures have been successfully prepared via a hydrothermal route using sodium tartaric as guiding reagent and subsequent calcination in air. The bowknot-like sodium doped Ni2P2O7-Co2P2O7 possesses porous characteristics building of nanoparticles. These bowknot-like sodium doped Ni2P2O7-Co2P2O7 have surface area of 45.32 m2 g−1. The unique porous bowknot-like structures can promote the contacting area between electrode materials and electrolyte, and provide rich channels for ions and electrons transport. Electrochemical measurements reveal that the bowknot-like sodium doped Ni2P2O7-Co2P2O7 exhibit a specific capacity of 295.2 C g−1 at 2.0 A g−1, and excellent cycling performances with 98.8% initial capacity retention after 2000 continuous cycles. Moreover, an asymmetric supercapacitor device was assembled by utilizing the sodium doped Ni2P2O7-Co2P2O7 and activated carbon as cathode and anode, respectively. The device delivers a high energy density of 54.1 Wh kg−1 at a power density of 1700 W kg−1. Impressively, the energy density can still reach up to 35.7 Wh kg−1 at 6778.5 W kg−1. These remarkable electrochemical performances demonstrate that the bowknot-like sodium doped Ni2P2O7-Co2P2O7 are promising electrode material for supercapacitors.