Structure-tunable Mn₃O₄-Fe₃O₄@C hybrids for high-performance supercapacitor

Controlling the morphology and structure of nanomaterials is of great importance for enhancing the electrochemical properties. In the paper, Mn₃O₄-Fe₃O₄@C hybrids with different architectures were synthesized by incubation of electrospun FeOx-containing carbon fiber (Fe-CNF) in KMnO₄ solution followed by annealing. The presence of FeOx on the CNF plays a vital role in determining the morphology and structure of the final hybrids, and the Mn₃O₄-Fe₃O₄@C hybrids with half-tube, tube and oolite-filled fibers are formed conveniently by tuning Fe content in the carbon fiber precursor. The good conductivity of fiber and various redox states of Mn and Fe afford the facile charge transfer and excellent reversible redox properties, thus enhancing the capacitor performance. The oolite-filled Mn₃O₄-Fe₃O₄@C with tubular structure exhibited a high specific capacitance of 178 F g^-1 at a discharge rate of 1 A g^-1. This capacitor electrode has an excellent cyclic stability with 95% capacitance retention after 1000 cycles at 3 A g^-1. This work provides a very simple strategy to tune the unique nanostructures of metal oxide on Fe-CNF for high-performance supercapacitor application in the future.