N‐doped Carbon Coated Bimetallic CoFe2O4 Nanomembranes as An Enhanced Negative Electrode for Asymmetric Supercapacitors

In‐suit nitrogen‐doped carbon layer coated on CoFe 2 O 4 nanomembrane (NC−CoFe 2 O 4 ) directly grown on carbon cloth was successfully fabricated. The electrochemical performance was conveniently manipulated by regulating the molar ration of Co 2+ : Fe 3+ (molar ration=1 : 2, CoFe 2 O 4 nanomembrane, 2.9 F cm −2 ). Nitrogen‐doped (N‐doped) carbon coating strategy on CoFe 2 O 4 nanomembrane (NC−CoFe 2 O 4 ) via annealing of polypyrrole (PPy) was presented and NC−CoFe 2 O 4 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 CoFe 2 O 4 (55.8 % decrease after 1000 cycles). To verify the practicability of the materials, an aqueous asymmetric supercapacitor has been fabricated using NC−CoFe 2 O 4 composite anode and MnO 2 /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.