RESUMO
The morphology of a nanoparticle strongly controls the path of electronic interaction, which directly correlates with the physicochemical properties and also the electrochemical comportment. Combining it with a two-dimensional (2D) material for a layer-by-layer approach will increase its possibilities in applications such as energy conversion and storage. Here, two different morphologies of MnFe2O4, nanoparticles and nanoneedles, are developed by a facile hydrothermal approach and sandwiched with reduced graphene oxide for constructing a 2D/3D sandwiched architecture. The rGO planar structure with abundant hierarchical short pores facilitates the thorough utilization of the utmost surface area to permeate the electrolyte within the structure to minimize the accumulation of rGO nanosheets laterally. The ferrite composited with rGO manifests high specific capacitance as the EDLC behaviour surpasses the faradaic pseudocapacitance boosting electrical conductivity compared to the as-synthesized MnFe2O4 structures. Benefiting from a 3D structure and the synergetic contribution of the MnFe2O4 nanoneedles and electrically conductive rGO layer, the MnFe2O4 nanoneedles@rGO electrode exhibits a high areal capacitance of 890 mF cm-2 and a remarkable specific capacitance of 1327 F g-1 at a current density of 5 mA cm-2. 93.36% of the initial capacitance was retained after 5000 cycles in 1 mol L-1 Na2SO4 indicating its high cycling stability. The synthesis route proves to be beneficial for a comprehensive yield of MnFe2O4@rGO nanosheets of different morphologies for use in the sophisticated design of energy-storing devices. This research strongly suggests that nanoparticle geometry, in addition to two-dimensional carbon-based materials, is a critical factor in a supercapacitor design.
RESUMO
Herein we report the development of novel multiferroic nanocomposites for their enhanced magnetic and electrical properties by employing a simple cost-effective chemical process at low temperatures. Novel perovskite-mixed spinel nanocomposites of (1 - x)BiFeO3/xMnFe2O4 where x = 0.1-0.5 have been prepared by a sol-gel auto-combustion technique. The calcination temperature was optimized and the phase formation of BiFeO3/MnFe2O4 nanocomposites was confirmed from the X-ray diffraction patterns for the samples calcined at 500 °C for 2 h. The grain sizes have been found to vary from 60 to 90 nm. The vibrational modes of the prepared nanocomposites were studied using Raman spectroscopy and FESEM and EDX were used to carry out the microstructural and composition analysis respectively. The magnetic properties seemed to have a strong dependence on the concentration of the spinel ferrite in the composite system. Saturation magnetization and coercivity exhibit an increase with increase in the MnFe2O4 content. The electrical properties from solid state impedance analysis confirm the non-Debye characteristics and the maximum activation energy is 0.931 eV for the 0.5BiFeO3/0.5MnFe2O4 nanocomposite. Dispersion in the dielectric constant and dielectric loss in the low frequency range has also been determined, which decreases with increase in temperature at lower ac frequencies.