Composition engineering of ZIF-derived cobalt phosphide/cobalt monoxide heterostructures for high-performance asymmetric supercapacitors

The fabrication of interpenetrated heterostructures from desirable energy materials for the development of efficient supercapacitors is promising yet challenging. Herein, a leaf-shaped cobalt phosphide/cobalt oxide heterostructure, (CoPx)(1-y)/CoOy (0.44 > y > 0.06), was synthesized from 2D-zeolitic-imidazolate-fra mework (ZIF-Co-L) molecular precursor via phosphidation of the Co3O4 intermediate. The efficient construction of heterostructure through the variation of surface/bulk composition significantly alters the interfacial properties and electronic structure, yielding enhanced supercapacitor performance. Further, gas-phase phosphidation entails a core-shell formation mechanism via gas diffusion, regulated by the Kirkendall effect. The optimized heterostructure (y = 0.10) exhibits remarkable interfacial properties derived from the CoO/Co-0/CoP interface, thus facilitating a high specific capacitance (467 F g(-1) at 5 A g(-1)) and excellent cycling stability (similar to 91% after 10000 cycles) at 30 A g(-1). A further increase in the cyclability (similar to 107%) was achieved by employing a graphene hybrid. Further, an asymmetric supercapacitor device was fabricated, that delivers reasonably high energy density of 12.7 Wh kg(-1) at a power density of 370 W kg(-1) and cycling stability of similar to 93% after 10000 cycles. This study reports on the modulation of interfacial properties of CoPx/CoO heterostructure to enhance energy storage performance via bulk/surface compositional variation, thereby providing a strategy to develop heterostructure electrodes for high-performance supercapacitor. (C) 2020 Elsevier Inc. All rights reserved.

Automated summary

The synthesis of leaf-shaped cobalt phosphide/cobalt oxide heterostructure from a ZIF-Co-L precursor via gas-phase phosphorization enhances the supercapacitor performance through the variation of surface/bulk composition. The study also demonstrates that using graphene can further improve the cycling stability of the supercapacitor.