Metal-Organic Framework Derived Spindle-like Carbon Incorporated α-FeO Grown on Carbon Nanotube Fiber as Anodes for High-Performance Wearable Asymmetric Supercapacitors.

Iron oxide (FeO) has drawn much attention because of its high theoretical capacitance, wide operating potential window, low cost, natural abundance, and environmental friendliness. However, the inferior conductivity and insufficient ionic diffusion rate of a simple FeO electrode leading to the low specific capacitance and poor rate performance of supercapacitors have impeded its applications. In this work, we report a facile and cost-effective method to directly grow MIL-88-Fe metal-organic framework (MOF) derived spindle-like α-FeO@C on oxidized carbon nanotube fiber (S-α-FeO@C/OCNTF). The S-α-FeO@C/OCNTF electrode is demonstrated with a high areal capacitance of 1232.4 mF/cm at a current density of 2 mA/cm and considerable rate capability with capacitance retention of 63% at a current density of 20 mA/cm and is well matched with the cathode of the Na-doped MnO nanosheets on CNTF (Na-MnO NSs/CNTF). The electrochemical test results show that the S-α-FeO@C/OCNTF//Na-MnO NSs/CNTF asymmetric supercapacitors possess a high specific capacitance of 201.3 mF/cm and an exceptional energy density of 135.3 μWh/cm. Thus, MIL-88-Fe MOF derived S-α-FeO@C will be a promising anode for applications in next-generation wearable asymmetric supercapacitors.