Porous Ni2P/Co2(P2O7) heterojunction nanosheets as an advanced electrode for high-performance supercapacitors

• The formation of heterojunction is favorable for the redistribution of interfacial charges between Ni 2 P and Co 2 (P 2 O 7 ), generating the internal electric field to speed up electron transport. • The porous nanostructure of the material greatly increases the specific surface area and chemical active site, and promotes electrolyte penetration. • The assembled Ni 2 P/Co 2 (P 2 O 7 )//AC asymmetric supercapacitor (ASC) device has a high energy density of 57.7 Wh kg -1 at 800.0 W kg -1 and an excellent capacity retention rate of 82.8% after 5500 charge-discharge cycles. Transition metal phosphides (TMPs) are expected to be highly competitive supercapacitor electrode materials because of their pretty metalloid property and high theoretical capacity. But in fact, due to their poor structure and electrochemical stability, their practical applications are largely limited. Herein, heterogeneous Ni 2 P/Co 2 (P 2 O 7 ) porous nanosheet arrays have been successfully synthesized by the combined process of solvothermal reaction and low-temperature phosphating. The formation of heterojunction is favorable for the redistribution of interfacial charges between Ni 2 P and Co 2 (P 2 O 7 ), generating the internal electric field to speed up electron transport. Meanwhile, the porous nanostructure of the material greatly increases the specific surface area and chemical active sites, and promotes electrolyte penetration. As a result, the resultant Ni 2 P/Co 2 (P 2 O 7 ) electrode has an extremely specific capacity of 4052 F g -1 at 1 A g -1 , and the capacity retention rate of the material is 72.1% after 3000 cycles, exhibiting good cycle stability. In addition, the assembled Ni 2 P/Co 2 (P 2 O 7 )//AC asymmetric supercapacitor (ASC) device has a high energy density of 57.7 Wh kg -1 at 800.0 W kg -1 and an excellent capacity retention rate of 82.8% after 5500 charge-discharge cycles. Our results provide a new idea for the design of phosphide/phosphate heterojunction with micromorphology optimization.