Prafulla K. Jha

SGO/SPES-Based Highly Conducting Polymer Electrolyte Membranes for Fuel Cell Application

Proton-exchange membranes (PEMs) consisting of sulfonated poly(ether sulfone) (SPES) with enhanced electrochemical properties have been successfully prepared by incorporating different amount of sulfonated graphene oxide (SGO). Composite membranes are tested for proton conductivity (30-90 °C) and methanol crossover resistance to expose their potential for direct methanol fuel cell (DMFC) application. Incorporation of SGO considerably increases the ion-exchange capacity (IEC), water retention and proton conductivity and reduces the methanol permeability. Membranes have been characterized by FTIR, XRD, DSC, SEM, TEM, and AFM techniques. Intermolecular interactions between the components in composite membranes are established by FTIR. The distribution of SGO throughout the membrane matrix has been examined using SEM and TEM and found to be uniform. The maximum proton conductivity has been found in 5% SGO composite with higher methanol crossover resistance.

Preparation of graphene oxide nano-composite ion-exchange membranes for desalination application

Nano-composite ion-exchange membranes (IEMs) consisting of graphene oxide (GO) (0.5, 1, 2, 5 and 10%) (w/w) and sulfonated polyethersulfone (SPES) of thickness 180 μm are prepared with enhanced electrochemical properties. In particular, the transport properties of SPES are favourably manipulated by the incorporation of GO. Intermolecular interactions between the components in composite membranes are established by FTIR. Membranes are characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) which showed the uniform distribution of GO sheets in SPES matrix. The maximum ionic conductivity has been found in 10% GO composite with higher methanol crossover resistance and selectivity. Water desalination performance of the nano-composite membranes have been evaluated by ionic flux, power consumption and current efficiency during salt removal. 10% GO nano-composite membrane shows 3.51 mol m−2 h−1 ionic flux, 4.3 kW h kg−1 power consumption and 97.4% current efficiency for salt removal. The values of ionic flux and current efficiency are 19% and 12% higher respectively while 20% lower power consumption is observed as compared to SPES membrane. The strong interfacial interactions due to the insertion of GO nanofillers into the SPES matrix improve the thermal and mechanical properties of the nanocomposite membranes. Nano-composite membrane shows the better performance and higher stability which may be used for the practical application such as DMFC and electrodialysis.

High pressure phase transition and elastic properties of cerium chalcogenides and pnictides

The structural properties of Cerium mono-chalcogenides and mono-pnictides have been investigated for the first time by using a modified interionic potential theory. The calculated transition pressures are in good agreement with the experimental results. The ionic bonding is found to be more pronounced in Ce-mono-chalcogenides than mono-pnictides. The calculated values of elastic constants are also predicted for the first time.

High pressure structural phase transition in alkaline earth chalcogenides

Abstract This paper reports on investigation of the pressure induced phase transition of BaSe, BaTe, SrSe and SrTe by using a three-body potential approach. The phase transition pressure and associated volume collapse obtained from this approach show a reasonably good agreement with experimental data. The variation of phase transition pressure and(−Δ v / v ol ), with Bulk modulus, and variation of phase transition pressure with ratio of cation to anion radius, follow a symmetric trend identical to that observed in other solids of this group. It is found that the present model has promise to predict the phase transition pressure for alkaline earth chalcogenides.

Electronic and phonon bandstructures of pristine few layer and metal doped graphene using first principles calculations

In the frame work of density functional theoretical calculations, the electronic and lattice dynamical properties of graphene (multilayers and supercell) have been systematically investigated and analyzed using the plane wave pseudopotentials within the generalized gradient approximation and local density approximation functional. We have also studied the functionalization of graphene by adsorption and absorption of transition metals like Al and Ag. We find that the electronic properties exhibit large sensitivity to the number of layers and doping. The Al and Ag doped graphene exhibits peak at Fermi level in the density of states arising from the flat bands near Fermi level. The bonding of metal atoms and graphene leads to a charge transfer between them and consequently shift Fermi level with respect to the conical point at K-point. The adsorption of Ag/Al atoms suggests an effective interaction between the adatoms and graphene layers without disturbing the original graphene structure of lower graphene la...

Structural Phase Transition and Elastic Properties of Thorium Pnictides at High Pressure

We have calculated the structural and elastic properties of thorium mono-pnictides at high pressure, for the first time, using a suitable interionic potential. This method has been found quite satisfactory in the case of uranium compounds, and describes the crystal properties in the framework of ionic model. The calculated equation of state, phase transition pressures for Bl to B2 transition and bulk modulus etc. in the case of all four ThX (X = N, P, As, Sb) compounds agree well with the experimental results. We have also reported the higher order elastic constants and discuss the dominance of various types of forces in them.

A lattice dynamical study of the role of pressure on Raman modes in high-Tc HgBa2CuO4

Abstract A lattice dynamical study has been carried out to investigate the Raman frequencies and the effect of pressure on the apical-oxygen (O A ) vibration (Raman Active) in the HgO A Cu bond in HgBa 2 CuO 4 high- T c superconductor by using an unscreened rigid ion model. The calculated Raman frequencies are, in general, in fair agreement with experimental values. The calculated values of the O A A 1g Raman mode agree reasonably well with the experimental Raman data up to 7.5 GPa and show that the O A A 1g vibrational mode increases linearly as the pressure is increased, suggesting phonons to play a dominant role in this system.

Phonon spectrum and lattice specific heat of the HgBa2CuO4 high-temperature superconductor

Abstract The phonon density of states and lattice specific heat have been calculated for the HgBa 2 CuO 4 high-temperature superconducting compound for the first time by using a simple lattice dynamical model theory, namely the rigid ion model. The obtained results show an overall consistent description of the lattice dynamics of this compound. However, we could not compare our results with experimentally measured values as they are not available so far. We emphasize that the neutron scattering and specific heat measurements justify our results. However, we expect that there will be not much difference as the present model has been quite successful in explaining the pressure dependence of the Raman active phonon modes for this compound [14,15].

Observation of torsional mode in CdS1−xSex nanoparticles in a borosilicate glass

Phonon modes found in low-frequency Raman scattering from CdS1−xSex nanocrystals embedded in a borosilicate glass arising from confined acoustic phonons are investigated. In addition to the breathing and quadrupolar modes, two additional modes are found in the spectra. In order to assign the new modes, confined acoustic phonon frequencies are calculated using the complex frequency model, the core-shell model, and the Lamb model. Based on the ratio of the frequencies of the new modes to those of the quadrupolar mode, the new modes are assigned to the first overtone of the quadrupolar mode (l=2, n=1) and to the l=1, n=0 torsional mode. To confirm the assignment of the torsional mode, the polarized Raman scattering measurements in parallel-polarized (VV) and perpendicular-polarized (VH) symmetries are performed. The torsional mode is present in both VV and VH symmetries. The appearance of the forbidden torsional mode is attributed to the near-spherical shape of the nanoparticle found from high-resolution tra...

Shape and Size Dependent Melting Point Temperature of Nanoparticles

The present paper reports a simple calculation of the size and shape dependent melting temperature of nanoparticles. The melting temperature of any nanoparticle basically depends on the ratio of surface atoms to the total atoms. Significant melting temperature suppression is observed when the particle size approaches the sub-20 nm range. The behavior of melting temperature is similar for the larger nanoparticles of all considered shapes but differs significantly for small nanoparticles. Different melting temperature is predicted for the nanoparticles of the same size in different shapes.