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Mordenite-incorporated PVA–PSSA membranes as electrolytes for DMFCs
No full textComposite membranes with mordenite (MOR) incorporated in poly vinyl alcohol (PVA)–polystyrene
sulfonic acid (PSSA) blend tailored with varying degree of sulfonation are reported. Such a membrane
comprises a dispersed phase of mordenite and a continuous phase of the polymer that help tuning the
flow of methanol and water across it. The membranes on prolonged testing in a direct methanol fuel
cell (DMFC) exhibit mitigated methanol cross-over from anode to the cathode. The membranes have
been tested for their sorption behaviour, ion-exchange capacity, electrochemical selectivity and mechanical
strength as also characterized by Fourier transform infrared spectroscopy and thermogravimetric
analysis. Water release kinetics has been measured by magnetic resonance imaging (NMR imaging)
and is found to be in agreement with the sorption data. Similarly, methanol release kinetics studied
by volume-localized NMR spectroscopy (point resolved spectroscopy, PRESS) clearly demonstrates that
the dispersion of mordenite in PVA–PSSA retards the methanol release kinetics considerably. A peak
power-density of 74mW/cm2 is achieved for the DMFC using a PVA–PSSA membrane electrolyte with
50% degree of sulfonation and 10 wt.% dispersed mordenite phase. A methanol cross-over current as low
as 7.5mA/cm2 with 2M methanol feed at the DMFC anode is observed while using the optimized composite
membrane as electrolyte in the DMFC, which is about 60% and 46% lower than Nafion-117 and
PVA–PSSA membranes, respectively, when tested under identical conditions
Electrochemical synthesic and characterization of BaB6 from molten melt
No full textBarium hexaboride (BaB6) crystals were electrochemically synthesized using molten salt
technique. Barium carbonate (BaCO3) and boron trioxide (B2O3) was used as reactants. Lithium
fluoride (LiF) was used as the supporting electrolyte. The molten electrolyte consisted of 50 wt %
BaCO3 and B2O3 with different stiochiometric ratios of Ba and B and 50 wt % lithium fluoride.
DTA/TGA studies were made to determine the eutectic point of the melt and it was found to be around
821oC. The electrolytic cell had a high purity graphite crucible, which served as the electrolyte
holding vessel and also as the anode for the electrolysis. An electro-polished molybdenum rod was
employed as the cathode. The electrolysis was performed at 870ºC under argon atmosphere, at
current densities ranging from 0.2-0.5 A/cm2. The electrodeposited crystals were examined for the
phase identification using X-ray diffraction technique. The AAS and the chemical analysis were made
for the determination of chemical composition of the synthesized crystals. The purity of the crystals
was also assessed using ICP-MS, XRF and EDX, which reveal that the crystals were associated with
trace amount of impurities like oxygen, carbon and iron. The compound is found to be more than 99
% pure. The morphology of the crystals was examined using Scanning Electron Microscopy (SEM).
From the above studies, it is concluded that the molten salt process is a simple preparative procedure
for the synthesis of sub-micron size barium hexaboride crystals
Density Functional Investigation of Relativistic Effects on the Structure and Reactivity of Tetrahedral Gold Clusters
No full textThe influence of relativistic effects on the structure, vibrational modes, and reactivity of recently discovered
tertrahedral gold clusters (Au19 and Au20) are investigated using density functional methods. The intramolecular
reactivity of the clusters was analyzed using density functional-based reactivity descriptors. The work shows
that whereas the structural properties and vibrational modes are considerably affected by the relativistic effects,
the reactivity trends based on Fukui function calculation on various atoms within this cluster remain unaffected
by the absence or presence of relativistic effects. The reactivity descriptors reveal that the vertex atoms are
the most reactive ones in Au20 toward a nucleophilic attack. On the other hand, atoms connecting the missing
vertex edge with the pyramid base along with the vertex atom are the most reactive for a nucleophilic attack
in Au19. The atoms lying at the center of each face are favorable for an electrophilic attack in both cases.
Interestingly, the atoms with a missing cap in Au19 are highly favorable for electrophilic attack, and Au20 has
more sites for a favorable nucleophilic attack
Preparation of Lanthanum Ferrite Substituted with Mg and Ca
No full textand environmental monitoring systems. In this work, lanthanum ferrite and substituted compounds have been prepared by combustion synthesis
process using lanthanum nitrate, ferric nitrate, and urea. The parent compound has been substituted with alkaline earth metals like Mg and Ca. The
synthesized compounds are characterized using thermal analysis, X-ray diffraction (XRD), UV-visible, Fourier transform infrared spectroscopy,
scanning electron microscopy (SEM). From thermal analysis, it is seen that Mg2+ and Ca2+ ions have pronounced effect on the phase formation
process. From XRD spectrum, it is seen that the crystalline lanthanum ferrite possesses an orthorhombic disorder perovskite structure with space
group Pbnm with four formula units per unit cell, where La ion is tetragonally coordinated. The UV-visible reflectance spectra of lanthanum ferrite
and substituted compounds shows two prominent absorption bands, which are shifted towards the lower wavelength side on substitution. The FTIR
spectra of the parent substituted compounds recorded between 400 to 4000cm−1. The existence of the prominent bands shows the formation of
the single-phase crystalline lanthanum ferrite. From the SEM figure, if we compare the morphological features of the electrodes before and after
substitution, it could be seen that the surface of the materials are disintegrated on oxygen evolution and weaken the intergrain spots
Recovery of Nickel (I) Ions from Electroplating Rinse Water Using Hectorite Clay
No full textThis paper describes the recovery of Ni (II) from electroplating rinse water using the Hectorite clay. Batch mode adsorption experiments were carried out and the effect of contact time, adsorbent dosage, pH, initial metal ion
concentration and temperature were studied. Different isotherms were obtained using nickel electroplating rinse waters of various concentrations. The ion exchange process follows second order kinetics and langmuir isotherm. The paper discusses thermodynamic parameters, including changes in Gibbs free energy, entropy and enthalpy for the
ion-exchange of Ni (II) from electroplating rinse water on Hectorite clay, revealed that the ion-exchange process was
spontaneous and exothermic under different temperatures. The maximum adsorption capacity obtained was 62.24 mg/g
at pH 7-8, the optimum adsorbent dosage and contact time was found to be 2 g/l within 5hours
Stacking faults and microstructural parameters in non-mulberry silk fibres
No full textWe have analysed the broadening of X-ray reflections observed in nonmulberry
silk fibres in terms of stacking faults and microstructural parameters using a
single-order method and have, with these parameters, developed, for the first time, a procedure
to compute the whole pattern of these silk fibres. The essential deviations in the
values of microstructural parameters obtained from line profile and whole pattern fitting
procedures are discussed in this paper
Combustion synthesis of nanocrystalline cerium hexaboride using citric acid as a fuel
No full textCerium hexaboride (CeB6) is being used as a neutron absorber in nuclear industry, in high-temperature
applications, in electronic devices for nuclear applications, as decorative coatings, etc. In this work,
nanocrystalline cerium hexaboride has been synthesized by combustion in “cerium nitrate–lithium tetraborate–
citric acid” mixtures using the latter as a fuel. The synthesized materials have been characterized by XRD,
chemical analysis, and SEM
Cathodic behaviour of stainless steel in coastal Indian seawater: Calcareous deposits overwhelm biofilms
No full textType-316 stainless steel (SS) was investigated as the cathode in galvanic couples in full-strength seawater from the
Gulf of Mannar on the southeast coast of India. Tests were devised to examine the impact of SS cathodes on anode
materials with or without the accrual of marine biofilms. Biofilmed SS cathodes significantly enhanced the rate of
corrosion of nickel, causing noble shifts in the couple potentials. With mild steel and zinc as the anodes, calcareous
deposits developed quite rapidly on the SS cathodes and led to a significant reduction of bacterial numbers. The
calcareous deposits also caused substantial reduction of galvanic corrosion rates for mild steel, whereas there was no
difference for zinc. The deposits were identified by XRD as essentially carbonates, oxides and hydroxides of calcium
and magnesium. Potentiodynamic polarization performed on the actual couples after disconnection and equilibration
provided reasonable interpretations of the galvanic corrosion trends. Data from this work suggest that a potential of
about 70.70 V vs. saturated calomel electrode (SCE) should provide optimum protection of SS in warmer, fullstrength
seawater that supports the precipitation of calcareous deposits. The criterion commonly recommended for
temperate conditions of lower water temperature and estuarine waters of lower alkalinity is 71.0 V (SCE)
Photoelectrochemical behaviour of pulse plated CdS films
No full textCadmium sulphide (CdS) films were deposited
by the pulse plating technique at room temperature and at
different duty cycles in the range of 6–50% using AR grade
0.25 M cadmium sulphate and 0.30 M sodium thiosulphate
at a deposition potential of -0.75 V (SCE). The total
deposition time was kept constant at 1 h. The thickness of
the films were around 2.0 lm. X-ray diffraction (XRD)
studies indicate the formation of polycrystalline films with
the cubic structure. The crystallite size increased from 23.0
to 27.5 nm as the duty cycle increased from 10 to 50%.
Optical absorption studies indicated a direct band gap in
the range of 2.40–2.80 eV as the duty cycle is decreased.
XPS studies indicated the formation of CdS. Photoelectrochemical
(PEC) cell measurements made with the
photoelectrodes deposited at 50% duty cycle have exhibited
higher conversion efficiency compared to earlier
reports
Exploration of unalloyed bimetallic Au–Pt/C nanoparticles for oxygen reduction reaction
No full textThe synthesis of carbon-supported unalloyed Au–Pt bimetallic nanoparticles using polyol method at a
temperature as low as 85 ◦C is reported. Various compositions of Au–Pt/C bimetallic nanoparticles are
characterized using transmission electron microscopy (TEM), X-ray florescence (XRF), X-ray diffraction
and cyclic voltammetry. Electron microscopy shows that the particles have a near-narrowsize distribution
that peaks at an average size of ∼5 to 6 nm. The electrocatalytic activity of Au–Pt/C nanoparticles towards
the oxygen reduction reaction (ORR) is studied by linear sweep polarization measurements obtained using
a rotating disc electrode (RDE). The results reveal that a four-electron transfer pathway is mainly operative
for ORR and the half-wave potential for ORR on bimetallic Au–Pt/C (20%:20%) is ∼100mV less negative
when compared with that of Pt/C (home-made and E-Tek). Studies of the methanol oxidation reaction
(MOR) on these catalysts show that the MOR activity is significantly lowered with increasing content of
Au in Au–Pt/C