A simple wet chemical technique has
been employed to fabricate
MnO2 nanolayer-coated α-Fe2O3/MnO2 core–shell nanowire heterostructure arrays
to prepare unique pseudocapacitor electrodes. The coating of MnO2 on α-Fe2O3 nanowires is triggered
by the reduction of KMnO4 solutions by the metallic (Au)
film on which the polycrystalline α-Fe2O3 nanowires have been grown electrochemically. This metallic film
also acts as the current collector by making direct contact with the
arrays of the 1D nanoheterostructures. The as-prepared α-Fe2O3/MnO2 nanoheterostructures are found
to exhibit excellent specific capacitance, high energy density, high
power density, and long-term cyclic stability as compared with the
bare α-Fe2O3 nanowire electrodes. The
unique geometry of the 1D nanoheterostructures with high effective
surface area to allow faster redox reaction kinetics, the incorporation
of two highly redox active materials in the same structure, and the
porous surface structures of the heterostructure to allow facile electrolyte
diffusion help in the superior electrochemical performance of the
α-Fe2O3/MnO2 nanoheterostructures.
The maximum specific capacitance of 838 F g–1 (based
on pristine MnO2) has been achieved by cyclic voltammetry
at a scan rate of 2 mV s–1 in 1 M KOH aqueous solution.
The hybrid α-Fe2O3/MnO2 nanocomposite
electrodes also exhibit good rate capability with excellent specific
energy density of 17 Wh kg–1 and specific power
density of 30.6 kW kg–1 at a current density of
50 A g–1 and good long-term cycling stability (only
1.5% loss of its initial specific capacitance after 1000 cycles).
These studies indicate that the α-Fe2O3/MnO2 nanoheterostructure architecture is very promising
for next-generation high-performance pseudocapacitors.
Nanospindle and nanorhombohedron and nanocube structured
α-Fe2O3
was synthesized by the solvothermal method. An intermixing of ethylenediamine (EN)
either with ethanol (EtOH) or water in different volume ratios (either 15:85,
50:50 or 85:15 in particular) was used to generate the structural forms of
α-Fe2O3. The study showed that, during synthesis, EN functioned as a ligand and facilitated the
growth of nanostructured samples. The probable growth mechanism is discussed in this
paper. Field emission scanning electron microscope (FESEM) and transmission electron
microscope (TEM) investigations revealed that the nanostructures were formed through
oriented attachment of primary nanocrystals. Fourier transform infrared spectroscopy
(FTIR) results showed the presence of Fe–O or Fe–O–Fe vibrational bands whereas
UV–vis–NIR optical absorbance spectra showed two prominent absorption bands around
540–560 and 670–680 nm. The room temperature magnetization measurement
revealed that the remanence and coercivity depend on the morphological attributes
of the nanocrystals. The magnetic hysteresis measurement also revealed that
α-Fe2O3
nanostructures displayed weak ferromagnetic behaviour at room temperature.
We report a facile method to design Co3O4-MnO2-NiO ternary hybrid 1D nanotube arrays for their application as active material for high-performance supercapacitor electrodes. This as-prepared novel supercapacitor electrode can store charge as high as ∼2020 C/g (equivalent specific capacitance ∼2525 F/g) for a potential window of 0.8 V and has long cycle stability (nearly 80% specific capacitance retains after successive 5700 charge/discharge cycles), significantly high Coulombic efficiency, and fast response time (∼0.17s). The remarkable electrochemical performance of this unique electrode material is the outcome of its enormous reaction platform provided by its special nanostructure morphology and conglomeration of the electrochemical properties of three highly redox active materials in a single unit.
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