The Phosphate Activated Redox Reactivity: Amorphous Co/Ni(O)X(Po4)Y Hollow Microspheres for Boosted Hybrid Zn-Based Supercapacitor Performances

Abstract

Although a series of morphology engineering and phase adjusting strategies have been performed on transition metal oxides to decrease the “dead volume” and suppress the reconstruction of crystallized hydroxides phase, their capacity and lifespan are still unsatisfactory for aqueous supercapacitors application. In this work, a unique amorphous hollow microsphere of Co/Ni-based phosphate oxide salt (CNOP) has been successfully constructed by mixed OH- and PO43- MOF etching process and then annealing dehydration reaction. The involved tetrahedral PO43- can not only activate the redox reactivity of TMOs but also suppress the formation of crystallized hydroxides phase for enhanced energy density and lifespan. Therefore, the optimized CNOP electrode presents high capacities of 1550 F g-1 at a current density of 1 A g-1, and an excellent rate capability of retaining 91.2% initial capacitance when the current density increases from 1 to 10 A g-1. The further assembled CNOP//rGO-Zn supercapacitor device presents a remarkable energy density of 386.4 Wh Kg-1 at 0.46 kW Kg-1 and an ultra-long cycle life of retaining 80% capacity after 5200 charge-discharge cycles. The simple CNOP//rGO-Zn device can operate the electronic thermometer for more than 8 hours after several seconds of charging time, revealing its outstanding application prospect.

Keywords: Metal-organic framework, Hollow structure, Amorphous phase, Etching, Hybrid supercapacitors