In-situ construction of hierarchical NPO@CNTs derived from Ni-MOF as ultra-high energy storage electrode for battery-type supercapacitor

Owing to the poor electric conductivity and inferior cyclic stability of transition metal phosphates, it is an important challenge to develop MOF-derived transition metal phosphate electrode with open frame structures and high redox-active sites for superior conductivity, favorable chemical stability and enhanced charge storage capacity. Metal organic frameworks (MOFs) are the promising precursors/templates for the construction of porous micro- and nano-structured metal phosphates due to their adjustable structure and composition, abundant stratified pore structure and high specific surface area. However, the low conductivity of phosphates and even MOF-derived electrode often requires to be improved with a conductive network to enhance the overall energy density and cycle stability. Herein, three-dimensional interconnected hierarchical phosphorylated Ni-MOF (Ni2P2O7, NPO)@CNTs nanostructure were synthesized by using Ni-MOF@CNTs as the sacrificing precursor in which CNTs not only acted as a conductive network but also provided rich nucleation sites for the anchoring of redox-active centers. The prepared NPO@CNTs electrode achieved excellent electrochemical performance with an ultrahigh specific capacitance of 3237.6 F g−1 at 1 A g−1 and a specific capacitance retention of 67.1 % at 10 A g−1 and the assembled hybrid supercapacitor (HSC) device showed a maximum specific energy density of 41.9 Wh kg−1 at 750 W kg−1 and long cyclic lifespan with a capacitane retention of 91.0 % at 1 A g−1 after 5000 cycles.