P-doped ternary transition metal oxide as electrode material of asymmetric supercapacitor

•P-doped Co0.21Ni0.79MoO4-n on Ni foam for ASCs are successfully prepared.•3D hierarchical nanosheets arrays can accelerate charge transfer.•P-doping can increase electroactive sites and surface reactivity efficiently.•High capacity, superb stability and high energy density are achieved. Transition-metal oxides have been widely investigated in the fields of asymmetric supercapacitor electrode materials on account of the high specific capacitance, low cost, and environmentally benign nature. To overcome inherently slow reaction kinetics and limited electroactive sites of pure transition-metal oxides, we herein put forward a facile strategy for preparing P-doped Co0.21Ni0.79MoO4 on Ni foam, which is used as the self-supporting cathode for asymmetric supercapacitor. Compared with pure Co0.21Ni0.79MoO4, the optimized P-Co0.21Ni0.79MoO4 displays a high specific capacitance of 1127.5 F g−1 at 0.5 A g−1 and even at a ultrahigh current density of 20 A g−1, it also exhibits a specific capacitance of 547.1 F g−1. The optimized P-Co0.21Ni0.79MoO4 exhibits outstanding electrochemical performance because they couple the merits of the high electrical conductivity of Co0.21Ni0.79MoO4, the high specific capacitance of P-Co0.21Ni0.79MoO4, the good mechanical stability of interconnected nanosheets arrays and the 3D hierarchical structure. Moreover, an asymmetric device assembled by the optimized P-Co0.21Ni0.79MoO4 and activated carbon delivers a high energy density of 49.2 Wh kg−1 at 747.7 W kg−1 as well as good cyclic stability.