Polyethyleneimine-Mediated Fabrication of Two-Dimensional Cobalt Sulfide/Graphene Hybrid Nanosheets for High-Performance Supercapacitors.

Two-dimensional (2D) hybrid nanosheets made of electrochemically active materials and graphene, featuring fast reaction kinetics and excellent structural stability, are appealing as electrodes for supercapacitors. Herein, we report a general polyethyleneimine (PEI)-mediated fabrication of the 2D cobalt sulfide/graphene hybrid nanosheets via a facile hydrothermal strategy. Detailed analysis reveals that the uniform cobalt sulfide (CoS) nanoparticles are well-anchored on the 2D graphene surface. Thereinto, the nitrogen species originating from the PEI molecules as bridging sites are helpful in enhancing the coupling effect between the graphene and CoS species, which endows the hybrid nanosheets with high electroactivity and excellent structural stability. The as-obtained hybrid nanosheets with typical pseudocapacitive features demonstrate a high specific capacitance (320 F g-1@1 A g-1) and a superior electrochemical stability with the initial capacitance of 86.5% after 20 000 cycles as electrodes for supercapacitors. The assembled asymmetric supercapacitors by combining activated carbon electrodes further show a high charge storage of 28.8 Wh kg-1 with an output power of 130 W kg-1. More importantly, the similar strategy can be easily extended to fabricate other 2D hybrid nanosheets with extraordinary electrochemical performance with the maximum charge storage of 815 F g-1 and energy density of 44. 6 Wh kg-1. The present work, which achieves the general fabrication of 2D hybrid nanosheets with tuned compositions, may provide a new opportunity for the development of supercapacitors.