Hierarchical FeCo2 S4 @FeNi2 S4 Core/Shell Nanostructures on Ni Foam for High-Performance Supercapacitors.

The design of electrode materials with rational core/shell structures is promising for improving the electrochemical properties of supercapacitors. Hence, hierarchical FeCo2 S4 @FeNi2 S4 core/shell nanostructures on Ni foam were fabricated by a simple hydrothermal method. Owing to their structure and synergistic effect, they deliver an excellent specific capacitance of 2393 F g-1 at 1 A g-1 and long cycle lifespan as positive electrode materials. An asymmetric supercapacitor device with FeCo2 S4 @FeNi2 S4 as positive electrode and graphene as negative electrode exhibited a specific capacitance of 133.2 F g-1 at 1 A g-1 and a high energy density of 47.37 W h kg-1 at a power density of 800 W kg-1 . Moreover, the device showed remarkable cycling stability with 87.0 % specific-capacitance retention after 5000 cycles at 2 A g-1 . These results demonstrate that the hierarchical FeCo2 S4 @FeNi2 S4 core/shell structures have great potential in the field of electrochemical energy storage.