MnFe₂O₄ Nanoparticles as an Efficient Electrode for Energy Storage Applications

In this study, solvothermal method was used for the synthesis of MnFe₂O₄ nanoparticles at different processing period of 7, 14, and 21 h. X-ray diffraction (XRD) pattern study confirms that MnFe₂O₄ nanoparticles correspond to the face-centered cubic spinel structure and belong to the Fd3m [227] space group. From Raman spectra analysis, two major peaks were observed at 476 and 616 cm^-1, which correspond to the vibration modes of MnFe₂O₄ nanoparticles; especially, the broad peak at 620 cm^-1 (A1g) corresponds to the symmetric stretching vibration of oxygen atoms at tetrahedral site. Infrared spectra (FTIR) analysis at 490 and 572 cm^-1 can be attributed to the stretching vibration of tetrahedral groups of FeO₄, and the vibration of octahedral groups of FeO₆ belongs to the intrinsic vibrations of manganese ferrites. The uniformly distributed MnFe₂O₄ nanospheres (RT2) can be affirmed by field emission scanning electron microscopy images and confirmed by the high-resolution transmission electron microscopic studies. The electrochemical properties of synthesized MnFe₂O₄ nanoparticles investigated by cyclic voltammetry, impedance spectroscopy and galvanstatic charging and discharging (GCD) studies clearly predict the reversible faradaic reactions of MnFe₂O₄ nanospheres. Further, the MnFe₂O₄ nanospheres (RT2) exhibit high specific capacitance of 697 F g^-1 at 0.5 A g^-1 current density in galvanostatic charging and discharging profile and after 1000 cycles exhibits 79% retain ability of initial specific capacitance and hence can be considered as the efficient electrode for supercapacitor applications.

Low Surface Energy and pH Effect on SnO₂ Nanoparticles Formation for Supercapacitor Applications

The SnO₂ nanoparticles formation by hydrothermal method at different experimental conditions such as temperature, pH, reaction time, and capping agent (cetyltrimethylammonium bromide), was studied. X-ray diffraction results confirmed regular rutile crystal structure of SnO₂. The characteristic Raman peak observed at 635 cm^-1 corresponded to A_1g modes of Sn-O vibrations. The study of optical property using photoluminescence confirmed the emissive spectra of SnO₂. The infrared peak observed at 618 cm^-1 corresponded to E_u modes of Sn-O vibrations of TO phonon because of E_⊥ to c-axis. Scanning electron microscope images clearly revealed the formation of complete SnO₂ nanoparticles. The unique SnO₂ nanoparticles stacked together to form microspheres at pH-5 showed high specific capacitance of 274.8 F/g at a current density of 0.5 A/g. The observed results confirmed the feasibility of SnO₂ nanoparticles being used as appropriate positive electrode candidate for supercapacitor applications.

Structural, Optical and Magnetic Properties of NiO Nanopowders

Nickel oxide (NiO) nanopowders were synthesized without using surfactant by chemical reduction technique. NaBH4 influence on structural, optical and magnetic properties of NiO product was investigated. XRD results revealed the formation of dominant single phase, cubic face centered nickel oxide. Raman peaks depicts the characteristic first-order transverse optical (TO) phonon, two phonon excitation (TO + LO), excitation (2LO) Raman mode vibrations of face centered cubic NiO. PL studies revealed the presence of strong emission band which is in good agreement with the intrinsic NiO product. FTIR studies explored metal oxygen vibrations of the obtained product. TEM results revealed the nanoscale product with spherical shape structures. VSM studies explored weak ferromagnetic behavior of the obtained product. High concentration of NaBH4 increases magnetization value and exhibits the typical weak ferromagnetic curve. Reducing agent played a vital role in the structural, optical and magnetic properties of the obtained NiO product.

Hexamine Role on Pseudocapacitive Behaviour of Cobalt Oxide (Co₃O₄) Nanopowders

Influence of hexamine surfactant concentration on crystallite size, structure, morphology, vibrational and optical properties of cobalt oxide nanopowders were explored. The cobalt oxide nanopowders were synthesized by employing a simple chemical reduction method using cobalt (II) nitrate hexahydrate (Co(NO3)2 ·6H2O) as precursor and sodium borohydride (NaBH4) as reducing agent along with hexamine as surfactant. XRD studies revealed the formation of face-centered cubic (Fd3m) crystalline structure of Co3O4 with an average crystallite size of 8-18 nm. The observed prominent characteristic Raman active modes of A1g, Eg, and F2g revealed the formation of Co3O4 nanopowders. The optical properties of Co3O4 nanopowders are examined by photoluminescence spectra. The obtained IR results confirmed the formation of Co3O4 nanopowders. The band observed 569 cm-1 is the characteristic of the Co3+ ions in the octahedral hole vibration and the 665 cm-1 band is attributable to the Co2+ ions in the tetrahedral hole vibration in the cubic lattice. The estimated specific capacitance of the obtained Co3O4 nanopowders was 291 F/g at 10 mV/s which could be a potential candidate for pseudo capacitive nature of the active materials.

Single crystalline TiO2 nanorods as effective fillers for lithium ion conducting PVdF-HFP based composite polymer electrolytes

PVdF-HFP based composite electrolytes were prepared with single crystalline TiO₂ nanorods (PT) and commercial TiO₂ submicrons (PTC) as fillers. The effect of size/shape of the fillers on the properties of polymer electrolytes were investigated.

Laser Raman and ac impedance spectroscopic studies of PVA: NH4NO3 polymer electrolyte

Ion conducting polymer electrolyte PVA:NH(4)NO(3) has been prepared by solution casting technique and characterized using XRD, Raman and ac impedance spectroscopic analyses. The amorphous nature of the polymer films has been confirmed by XRD and Raman spectroscopy. An insight into the deconvoluted Raman peaks of upsilon(1) vibration of NO(3)(-) anion for the polymer electrolyte reveals the dominancy of ion aggregates at higher NH(4)NO(3) concentration. From the ac impedance studies, the highest ion conductivity at 303 K has been found to be 7.5x10(-3)Scm(-1) for 80PVA:20NH(4)NO(3). The conductivity of the polymer electrolytes has been found to depend on the degree of dissociation of the salt in the host polymer matrix. The combination of the above-mentioned analyses has proven worth while and in fact necessary in order to achieve better understanding of these complex systems.