Highly Durable Platinum based Cathode Electrocatalysts for PEMFC Application using Oxygen and Nitrogen Functional Groups Attached Nanocarbon Supports

The combined effect of oxygen and nitrogen functional groups on highly crystalline carbon supports like multiwalled carbon nanotubes (MWCNT) and MWCNT‐few layer graphene hybrid structures (MWCNT+FLG) have been investigated towards oxygen reduction reaction (ORR) performance and carbon corrosion durability in polymer electrolyte membrane fuel cell (PEMFC) applications. The pristine carbon supports were modified with oxygen and nitrogen functionalities by treating with concentrated mineral acids and subsequent nitrogen plasma treatment assisted with R.F. magnetron sputtering. Pt nanoparticles were dispersed over these chemically modified carbon supports by polyol reduction method. The physicochemical properties of as synthesized electrocatalysts were studied by different techniques such as XRD, TEM, FTIR, Raman and XPS. Electrochemical properties were investigated by cyclic voltammetry and linear sweep voltammetry in 0.1M HClO₄ medium. Compared to commercial Pt/C catalysts, durability show ∼30 % enhancement for the as prepared electrocatalysts due to the presence of large amount of pyrrolic nitrogen and highly oriented graphitic nature of the catalyst supports. The ORR performance were comparable with Pt/C (TEC10E30E) in terms of MSA, 259, 270, 252 A g⁻¹ for Pt/C, Pt/N‐f‐MWCNT, Pt/N‐f‐(MWCNT+FLG) respectively.     

Network Selection Based on Weight Estimation of QoS Parameters in Heterogeneous Wireless Multimedia Networks

Network selection in a heterogeneous wireless environment is a major challenge to ensue seamless mobility across different radio air interfaces. To provide the desired quality of service for a given application in a multimedia environment, different parameters, including delay, bandwidth, packet loss and cost per byte, play an important role in network selection. In this paper, we present a novel algorithm for optimal network selection. A heterogeneous environment consisting of four networks, UMTS, WLAN, GPRS and WiMAX has been considered. We propose a network selection algorithm in which weight estimation for the representative set of the network attributes is computed using entropy and technique for order preference by similarity to ideal solution approach. The numerical results show that the proposed model can be effectively implemented to select the desired network in a heterogeneous environment employing triple-play services.     

Molybdenum ion: a structural probe in lithium–antimony–germanate glass system by means of dielectric and spectroscopic studies

In this study, we have synthesized multi-component 10Li₂O–(30 ? x)Sb₂O₃–40GeO₂–20PbO:x MoO₃ (with five values of x ranging from 1.0 to 9.0) and investigated dielectric properties over a frequency range of 10²–10⁶ Hz and in the temperature range 30–300 °C of these samples. The evaluated dielectric parameters include dielectric constant, ε′(ω); ac conductivity, σ _ac; and electric modulus, M(ω). The results were interpreted with the aid of the experimental data on optical absorption, IR, Raman, and ESR spectroscopy. The analysis of the results of spectroscopic studies have indicated that a considerable proportion of molybdenum ions reduce to Mo⁵⁺ state, form molybdenyl complexes, occupy octahedral positions, act as modifiers, and create dangling bonds in the glass network. The concentration of such molybdenyl complexes seemed to be increasing with increase in the concentration of MoO₃. The temperature dispersion of real part of dielectric constant, ε′(ω), has been analyzed using space charge polarization model. The frequency and temperature dependence of the dielectric loss parameters have exhibited relaxation character. The relaxation effects have been attributed to molybdenyl complexes and to the divalent lead ions. Electrical conductivity exhibited an increasing trend and the activation energy showed a decreasing trend with increase in the concentration of MoO₃. The increase of conductivity is attributed to (i) the increasing concentration of polaron Mo⁵⁺–Mo⁶⁺ pairs and (ii) increase in the concentration of dangling bonds in the glass network that causes the substantial decrement in jump distance for Li⁺ ions, which contribute to ionic conductivity.     

Spin states and glassy magnetism in LaCo1−xNixO3 (0 ≤ x ≤ 0.5)

We investigated the effect of Ni substitution on electronic structure and magnetic properties of perovskite LaCoO₃ in the substitution range 0 ≤ x ≤ 0.5. A homovalent +3 state and spin state transition of Co⁺³ has been observed upon Ni substitution in x-ray absorption measurements at the Co and the Ni K-edges. Thermally driven spin state transition has been found to disappear with Ni substitution. A change in nature of magnetic interactions from antiferromagnetic to ferromagnetic and spin glass behavior with substitution is observed in dc and ac magnetization measurements. Ni substitution has been found to lower the average effective magnetic moment which has been ascribed to the decrease in Co/Ni ratio. Changes in fine structure and magnetic properties due to Ni substitution have been explained through the stabilization of intermediate spin state of Co⁺³ by the lattice expansion induced changes in crystal field. The Jahn-Teller distortion is assumed to be suppressed in the expanded lattice and possibility of antiferro-orbital ordering has been proposed for the ferromagnetic super-exchange interactions Co⁺³(IS)–O–Co⁺³(IS). The present work provides possible explanation for the ambiguity in the origin of FM in Co and Ni based perovskite cobaltites as well as supports the idea of lattice expansion induced ferromagnetism.     

Influence of samarium doping on structural and dielectric properties of strontium bismuth tantalate ceramics derived by molten salt synthesis route

Layered Sr(Bi_1?xSm_x)₂Ta₂O₉ ceramics with x ranging from 0 to 0.10 (10 mol%) were fabricated by the low temperature molten salt synthesis route. X-ray powder diffraction studies revealed that the single phase orthorhombic layered perovskite structure is retained in all these compositions. Scanning electron microscopic studies on these ceramics confirmed the presence of well packed equiaxed plate shaped grains. The dielectric and electrical conductivity properties were studied in the 100 Hz–1 MHz frequency range at 300 K. Interestingly, the 10 mol% samarium doped SrBi₂Ta₂O₉ ceramics exhibited high dielectric constant (ε_r = 155) and low dielectric loss (0.00298) compared to those of other compositions. The electrical conductivity of undoped and samarium doped ceramics increased linearly with increase in frequency.     

Sonochemical assisted synthesis and spectroscopic characterization of Fe3+ doped ZnO diluted magnetic semiconductor

Fe³⁺ doped ZnO nanopowder has been synthesized by sonochemical assistance and characterized by different spectroscopic techniques. The structure, surface morphologies and optical properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence spectrometer (PL) and ultraviolet–visible spectrophotometer. XRD reveals that Fe³⁺ ions enter into ZnO lattices without any secondary phases. SEM micrographs of prepared sample show that surface is rough and stone like structure with different sizes. PL studies of Fe³⁺ doped ZnO nanopowder exhibits ultraviolet and blue emission bands. Magnetometric measurements (vibrating sample magnetometer) indicate ferromagnetic behavior at room temperature. This observation is further confirmed by the EPR spectrum of Fe³⁺ doped ZnO at room temperature.     

Bayes estimators of exponential parameters utilizing a guessed guarantee with specified confidence

This paper proposes a procedure to modify the conjugate prior for the parameters of an exponential distribution in the light of an available guessed guarantee μ₀ with specified confidence c (0<c<1). The Bayes estimators under modified priors have been obtained. The proposed estimators have been compared with Bayes estimators under conjugate prior, shrinkage estimators and maximum likelihood estimators on the basis of a simulation study.     

A Facile Aqueous Sol–Gel Process for the Synthesis of Alumina–Lanthanum Phosphate Nanocomposite

A facile aqueous sol–gel process is being reported for the first time for the synthesis of alumina–lanthanum phosphate (Al₂O₃–LaPO₄) nanocomposite. X-ray diffraction (XRD) analysis confirms the absence of any reactive phase even after heating to 1600°C. Microstructural analysis reveals a mutually controlled grain growth and the XRD analysis shows that the crystallite size of LaPO₄ is in the range of 5–7 nm, indicating the exceptional inhibition of grain growth as well as the nanostructure of the sintered composite.