N-Doped Carbon Coated Bimetallic CoFe2O4 Nanomembranes as An Enhanced Negative Electrode for Asymmetric Supercapacitors

In-suit nitrogen-doped carbon layer coated on CoFe₂O₄ nanomembrane (NC−CoFe₂O₄) directly grown on carbon cloth was successfully fabricated. The electrochemical performance was conveniently manipulated by regulating the molar ration of Co²⁺ : Fe³⁺ (molar ration=1 : 2, CoFe₂O₄ nanomembrane, 2.9 F cm⁻²). Nitrogen-doped (N-doped) carbon coating strategy on CoFe₂O₄ nanomembrane (NC−CoFe₂O₄) via annealing of polypyrrole (PPy) was presented and NC−CoFe₂O₄ nanomembranes displayed a prominent capacitance of 12.1 F cm⁻² (2563.8 F g⁻¹) at 5 mA cm⁻². More important, the composite demonstrated more stable microstructure and showed long-term cycling stability (16.0 % decrease after 7000 cycles), which was significantly better than the unmodified CoFe₂O₄ (55.8 % decrease after 1000 cycles). To verify the practicability of the materials, an aqueous asymmetric supercapacitor has been fabricated using NC−CoFe₂O₄ composite anode and MnO₂/CNTs cathode, and the device has a remarkable wide operating voltage range of 1.9 V. In addition, the assembled device has an exceptional specific capacity of 1.3 F cm⁻² at 10 mA cm⁻², high energy density (43.3 Wh kg⁻¹ at a power density of 642.9 W kg⁻¹), and also with a good capacity retention rate of 84.9 % after 1000 cycles.