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

In‐suit nitrogen‐doped carbon layer coated on CoFe2O4nanomembrane (NC‐CoFe2O4) directly grown on carbon cloth was successfullyfabricated. 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 rate of 642.9 W kg‐1), and also with a good capacity retention rate of 84.9% after 1000 cycles.