P. Muhammed Shafi

Impact of crystalline defects and size on X-ray line broadening: A phenomenological approach for tetragonal SnO2 nanocrystals

Nanocrystalline tin oxide (SnO2) powders with different grain size were prepared by chemical precipitation method. The reaction was carried out by varying the period of hydrolysis and the as-prepared samples were annealed at different temperatures. The samples were characterized using X-ray powder diffractometer and transmission electron microscopy. The microstrain and crystallite size were calculated for all the samples by using Williamson-Hall (W-H) models namely, isotropic strain model (ISM), anisotropic strain model (ASM) and uniform deformation energy density model (UDEDM). The morphology and particle size were determined using TEM micrographs. The directional dependant young’s modulus was modified as an equation relating elastic compliances (sij) and Miller indices of the lattice plane (hkl) for tetragonal crystal system and also the equation for elastic compliance in terms of stiffness constants was derived. The changes in crystallite size and microstrain due to lattice defects were observed while ...

Metallic 1T-MoS2 with defect induced additional active edges for high performance supercapacitor application

Molybdenum disulphide (MoS2) is widely explored in the area of electrochemical energy storage devices as an alternative to graphene. Here we introduce a 1T-MoS2 electrode with defect induced active edges for high performance supercapacitors. The metallic phase (1T) facilitates enhanced electrical conductivity and defect rich morphology that results in a high specific capacitance value. The structural characterisation confirms the formation of 1T phase and defect concentration in the material. Transmission electron microscopy imaging further confirms the presence of defects in high defect density MoS2 (HDD-MoS2) and low defect density MoS2 (LDD-MoS2). The electrochemical studies show that the prepared high defect density MoS2 electrode exhibits a maximum specific capacitance of 379 F g−1 and 68.9 F g−1 at 1 A g−1 current density in three and two electrode systems, respectively. The symmetric HDD-MoS2 supercapacitor exhibits an outstanding cell performance with an energy density of 21.3 W h kg−1, at a power density of 750 W kg−1 and a capacitance retention of 92% after 3000 cycles. These findings suggest that 1T MoS2 with high defect density can be a potential candidate for high performance supercapacitor electrode application.

Synthesis and investigation on electrochemical property of ε-MnO2 nanoparticle

The e-MnO2 Nanoparticle was synthesized through wet chemical method. The phase formation and crystalline structure were well understood by powder X-ray diffraction (XRD). Presents of further impurities or functional group studies were carried out by Fourier transform infrared spectroscopy (FTIR). Further the formation of MnO2 particles is confirmed by Raman spectroscopy. The weight loss as well as the heat flow associated with the thermal decomposition was studied by thermogravimetric analysis (TGA) along with differential thermal analysis (DTA). The electrochemical behavior of the prepared MnO2 nanoparticles were investigated by cyclic voltammetry (CV), Galvenostatic charge-discharge techniques and electrochemical impedance spectroscopy (EIS).

Graphene oxide-MnO2 nanocomposite for supercapacitor application

Increased depletion of fossil fuels along with global warming and climate change made the society to think about alternate green and sustainable energy sources and better energy storage devices. Extensive research has been performed on the development of solar cells, fuel cells, Lithium- ion battery and supercapacitors to combat the green house effect and its consequences, and to meet the increased energy crisis. Supercapacitors, also known as electrochemical capacitors are gained a great attention because of their pulse power supply, long cycle life (>100,000), simple principle and high dynamic of charge propagation. Its greater power density than lithium- ion battery and much larger energy density than conventional capacitors brought super capacitors to a promising energy storage device to meet the increased energy demands. Here we demonstrate supercapacitor electrode materials with graphene oxide (electric double layer capacitor) and α-MnO2 nanomaterial (pseudo-capacitor), as well as composite of these materials, which means that the bulk of the material undergoes a fast redox reaction to provide the capacitive response and they exhibit superior specific energies in addition to the carbon-based supercapacitors (double-layer capacitors). A simple soft chemical route is utilized to synthesize graphene oxide, α-MnO2 and graphene oxide-MnO2 composite. The phase and the structure of the synthesized materials are studied using X-ray diffractometry (XRD). The functional group and the presence of impurities are understood from Fourier transform infrared (FTIR) spectra. The capacitive properties of the graphene oxide, graphene oxide - MnO2 nanocomposite and α-MnO2 are tested with the help of cyclic voltammetry (CV) and galvanostatic charge – discharge techniques using 1 M Na2SO4 in aqueous solution as electrolyte. It was found that graphene oxide - MnO2 nanocomposite shows better electrochemical behaviour compared to individual graphene oxide and α-MnO2 nanomaterial.

Structural evolution of tetragonal MnO2 and its electrochemical behavior

MnO2 nanoparticles were synthesized by simple chemical precipitation method and were subjected to different heat treatment process. The structural evolution of as-prepared MnO2 nanoparticles at different annealing temperature was confirmed by XRD analysis. The weight loss as well as the heat flow associated with the thermal decomposition was studied by thermogravimetric analysis (TGA) along with differential thermal analysis (DTA). The functional group and phase formation were confirmed by Fourier transform infrared spectroscopy (FTIR). Finally electrochemical properties were evaluated using cyclic voltammetry (CV) and galvanostatic charge-discharge techniques. The cyclic voltammogram and charge-discharge curve of 450 ˚C annealed MnO2 nanoparticles exhibited relatively good capacitive behavior.

Synthesis and characterization of α-MnO2 electrode for supercapacitor application

The α-MnO2 nanoparticles were synthesized for supercapacitor electrode application by controlled co-precipitation method. The as-prepared sample was annealed at different temperature to enhance the crystallinity and it is confirmed with XRD analysis. The electro chemical behavior and conductivity of the material were investigated by cyclic voltammetry with charge-discharge techniques and AC Impedance analyzer.