Directional Growth of Conductive Metal-Organic Framework Nanoarrays along [001] on Metal Hydroxides for Aqueous Asymmetric Supercapacitors.

Abstract

Metal-organic frameworks (MOFs) are promising electrochemical materials that possess large specific surface areas, high porosities, good adjustability, and high activities. However, many conventional MOFs exhibit poor conductivity, which hinders their application in electrochemistry. In recent years, conductive MOFs (cMOFs) have attracted a considerable attention. As an important transition metal hydroxide, Ni(OH)2 nanosheets exhibit a high theoretical specific capacitance and a high energy density but a poor electrical conductivity. In this study, we combined a typical cMOF(Ni-HHTP, HHTP = 2,3,6,7,10,11-hexahydroxybenzene) with Ni(OH)2 nanosheets and synthesized a series of Ni-HHTP@Ni(OH)2 nanoarrays. The composite materials exhibit a high electrical conductivity and ionic transfer efficiency and a good stability. Most importantly, our study reveals the chemical interaction between cMOFs and metal hydroxide composites and the relationship between facet exposure and the growth orientation of cMOFs. When Ni-HHTP@Ni(OH)2-2 was assembled as a positive electrode material in an aqueous asymmetric supercapacitor, 98% of the initial capacitance was maintained after 5000 cycles at a high current density of 3 A g-1. The findings of this study will provide meaningful insights into the design of cMOF composites combining other metal hydroxides.