Metal–Organic Framework Derived Spindle-like Carbon Incorporated α-Fe₂O₃ Grown on Carbon Nanotube Fiber as Anodes for High-Performance Wearable Asymmetric Supercapacitors

Iron oxide (Fe₂O₃) 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 Fe₂O₃ 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-Fe₂O₃@C on oxidized carbon nanotube fiber (S-α-Fe₂O₃@C/OCNTF). The S-α-Fe₂O₃@C/OCNTF electrode is demonstrated with a high areal capacitance of 1232.4 mF/cm² at a current density of 2 mA/cm² and considerable rate capability with capacitance retention of 63% at a current density of 20 mA/cm² and is well matched with the cathode of the Na-doped MnO₂ nanosheets on CNTF (Na-MnO₂ NSs/CNTF). The electrochemical test results show that the S-α-Fe₂O₃@C/OCNTF//Na-MnO₂ NSs/CNTF asymmetric supercapacitors possess a high specific capacitance of 201.3 mF/cm² and an exceptional energy density of 135.3 μWh/cm². Thus, MIL-88-Fe MOF derived S-α-Fe₂O₃@C will be a promising anode for applications in next-generation wearable asymmetric supercapacitors.