Electroactive edge site enriched nickel cobalt sulfide into graphene frameworks for high performance asymmetric supercapacitors
Tailor made edge site enriched inorganics coupled graphene hybrids hold a promising platform material for high performance supercapacitors. Herein, we report a simple strategy for fabricating edge site enriched nickel cobalt sulfide (Ni Co S) nanoparticles decorated on graphene frameworks to form integrated hybrid architectures (Ni Co S/G) via an in situ chemically converted method. The Kirkendall effect involved anion exchange reaction, e.g. the etching like effort of the S2 ions, plays a crucial role for the formation of the edge site enriched nanostructure. Density functional theory (DFT) calculations reveal that the Ni Co S edge sites have a high electrochemical activity and strong affinity for OH in the electrolyte, which are responsible for the enhanced electrochemical performance. Benefiting from the integrated structures of Ni Co S nanoparticles and conductive graphene substrates, the resultant Ni Co S/G hybrid electrodes exhibit a high specific capacitance of 1492 F g 1 at the current density of 1 A g 1, a superior rate capability of 96% when the current density is increased to 50 A g 1, and excellent electrochemical stabilities. An asymmetric supercapacitor fabricated using the edge site enriched Ni Co S/G hybrids as the positive electrode and porous carbon nanosheets (PCNS) as negative electrodes shows a high energy density of 43.3 W h kg 1 at a power density of 0.8 kW kg 1, and an energy density of 28.4 W h kg 1 can be retained even at a high power density of 22.1 kW kg 1.