Tuning MnO₂ to FeOOH replicas with bio-template 3D morphology as electrodes for high performance asymmetric supercapacitors

Abstract

Controlled synthesis of tunable Mn-iron-oxide (Mn-FeOx) hybrids with unique three-dimensional (3D) porous structure based on diatoms for high performance supercapacitors is demonstrated. Successful transition process from MnO₂ to FeOOH on diatomite was performed by two-step hydrothermal method and resultant replicas with 3D diatom morphology were obtained via etching process. The fabricated MnFeOx-0 diatom replica without transition was composed by MnO₂ nanosheets and exhibited a high specific capacitance (228.6 F g⁻¹ at 1 A g⁻¹), good rate capability (74.6% retention after current density were increased to 10 A g⁻¹), high coulombic efficiency (about 93.1% at 10 A g⁻¹), and steady cycling performance (94.3% capacitance retention after 4000 cycles). MnFeOx-110 replica with FeOOH nanorods owned 224.6 F g⁻¹ at 1 A g⁻¹, high coulombic efficiency about 80% at 10 A g⁻¹ and steady cycling performance about 92.5% retention after 4000 cycles. Finally, an asymmetric supercapacitor was assembled based on MnO₂ nanosheets as the positive electrode and FeOOH nanorods as the negative electrode, which delivered a wide potential of 2 V with maximum energy density of 51.5 Wh kg⁻¹ and power density of 9.1 kW kg⁻¹. Considering that the two replicas owned great energy storage property, it opens an opportunity for rational design of the diatom morphology samples applied to high-performance supercapacitors.