Polyethyleneimine-Mediated\nFabrication of Two-Dimensional\nCobalt Sulfide/Graphene Hybrid Nanosheets for High-Performance Supercapacitors

Abstract

Two-dimensional\n(2D) hybrid nanosheets made of electrochemically\nactive materials and graphene, featuring fast reaction kinetics and\nexcellent structural stability, are appealing as electrodes for supercapacitors.\nHerein, we report a general polyethyleneimine (PEI)-mediated fabrication\nof the 2D cobalt sulfide/graphene hybrid nanosheets via a facile hydrothermal\nstrategy. Detailed analysis reveals that the uniform cobalt sulfide\n(CoS) nanoparticles are well-anchored on the 2D graphene surface.\nThereinto, the nitrogen species originating from the PEI molecules\nas bridging sites are helpful in enhancing the coupling effect between\nthe graphene and CoS species, which endows the hybrid nanosheets with\nhigh electroactivity and excellent structural stability. The as-obtained\nhybrid nanosheets with typical pseudocapacitive features demonstrate\na high specific capacitance (320 F g^–1@1 A g^–1) and a superior electrochemical stability with the\ninitial capacitance of 86.5% after 20 000 cycles as electrodes\nfor supercapacitors. The assembled asymmetric supercapacitors by combining\nactivated carbon electrodes further show a high charge storage of\n28.8 Wh kg^–1 with an output power of 130 W kg^–1. More importantly, the similar strategy can be easily\nextended to fabricate other 2D hybrid nanosheets with extraordinary\nelectrochemical performance with the maximum charge storage of 815\nF g^–1 and energy density of 44. 6 Wh kg^–1. The present work, which achieves the general fabrication of 2D\nhybrid nanosheets with tuned compositions, may provide a new opportunity\nfor the development of supercapacitors.