CoSx/C hierarchical hollow nanocages from a metal–organic framework as a positive electrode with enhancing performance for aqueous supercapacitors†
Benefiting from abundant redox chemistry and high electrochemical properties, metal sulfides have been broadly employed as electrode materials in supercapacitor systems. However, the predominant limitation in their performance, which arises from indifferent electron and ion dynamics for transportation and a rapid slash in capacitance, is of particular concern. Herein, we portray the cobalt sulfides/carbon (CoSx/C) hierarchical hollow nanocages using ZIF-67 nanocrystals coated with carbon from resorcinol–formaldehyde (ZIF-67@RF) as a self-sacrificial template. The RF acted as a hard framework to prevent the hollow structure from breaking and was transformed to a carbon layer to enhance the charge transfer process. When used as positive electrodes in supercapacitor systems with aqueous electrolytes, the optimized CoSx/C hierarchic hollow nanocages exhibited a considerable specific capacitance (618 F g−1 at 2 A g−1), superior rate performance (83.6% capacitance retention of the initial capacity when the current density was amplified from 2 A g−1 to 50 A g−1) and an extraordinary cycle stationarity along with an undiminished specific capacitance after 10 000 cycles. In this study, the meticulously designed hierarchical hollow structure that we conceived not only provides an outstanding electrochemical performance but also provides options for other related materials, such as various MOFs.