Defect-rich honeycomb-like nickel cobalt sulfides on graphene through rapid microwave-induced synthesis for ultrahigh rate supercapacitors

Nickel cobalt sulfides (NCS) are regarded as potential energy storage materials due to the versatile valent states and rich electrochemical activity, but their sluggish synthesis process and inferior rate performance hinder them from large-scale application. Herein, microwave-induced strategy has been employed for efficient synthesis of honeycomb-like NCS/graphene composites, which are explored as ultrahigh rate battery-type electrodes for supercapacitors. Due to the internal heat mechanism, the synthesis time of NCS by microwave could be shortened from hours to minutes. Density functional theory was simulated to uncover the interfacial effect between NCS and graphene, and the resulted Schottky barrier is in favor of enhancing redox activity and capacity. Ultimately, the obtained defect-rich nickel cobalt sulfides/graphene with thermal treatment (NCS/G-H) could exhibit a high specific capacitance of 1186 F g(-1) at 1 Ag-1 and sustain 89.8% capacity even after the increase of current density over 20 times, which is much superior to bare NCS and NCS/graphene. Furthermore, the assembled NCS/G-H hybrid supercapacitor delivers supreme energy density of 46.4 Wh kg(-1), and retains outstanding long- term stability of 89.2% after 10 k cycles. These results indicate that the synthesized NCS/G-H by time- saving microwave-induced liquid process could be served as high rate materials for supercapacitors. (C) 2020 Elsevier Inc. All rights reserved.