Hierarchical FeCo S Nanotube Arrays Deposited on 3D Carbon Foam as Binder-free Electrodes for High-performance Asymmetric Pseudocapacitors.

The ever-increasing global demand for green energy resources calls for more research attention on the development of cheap and efficient energy storage systems. Herein, we propose the rational design of a 3D carbon foam electrode deposited with perpendicularly oriented FeCo S nanotubes arrays (FeCo S /CMF) for high-performance asymmetric supercapacitors. In this work, the macroporous CMF served as conducting backbone not only to enhance the electrical conductivity of the composite, but also to promote the uniform growth of FeCo S nanotubes. Deposited hierarchical FeCo S nanotubes arrays with open hollow structures can afford numerous exposed electroactive sites for Faradaic redox reaction and provide short interior channels for fast electrolyte transmission. Due to these unique features, obtained 3D hierarchical FeCo S /CMF composite foam exhibits a high specific capacitance of 2430 F g (specific capacity of 337.5 mAh g ) at 1 A g , and excellent capacitance retention of 91 % after 5000 cycles at a high current density of 9 A g , which is superior to most of those previously reported binary metal sulfide-based electrodes. Moreover, asymmetric supercapacitor device assembled using the FeCo S /CMF as positive electrode also delivers a high energy density of 78.7 W h kg at a power density of 800.3 W kg . Therefore, this work provides a new strategy for the low-cost synthesis of 3D foam electrodes towards high-performance supercapacitor devices.