Optical switching properties of RCo2-type alloy thin films by electrochemical hydrogenation

The switchable optical properties of Pd-protected RCo₂-type Ho_0.6Mm_0.4Co₂ alloy thin films have been investigated in a KOH electrolyte. The reversible optical switching has been carried out simultaneously by measuring transmitted light through the thin film during electrochemical charging–discharging of hydrogen. The dependence of switching speed and cyclic durability of the film on the charging and discharging current density as well as concentration of KOH electrolyte has been studied. In addition, cyclic voltammetric measurements have been performed to examine the hydride formation and decomposition reactions.     

Graphite nanoplatelets/multiwalled carbon nanotubes hybrid nanostructure for electrochemical capacitor

Recently, the focus on carbon based nanostructures for various applications has been due to their novel properties such as high electrical conductivity, high mechanical strength and high surface area. In the present work, we have investigated the charge storage capacity of modified graphite nanoplatelets and hybrid structure of graphite nanoplatelets-multiwalled carbon nanotubes (MWNTs). These MWNTs can be used as spacers to reduce the possibility of restacking of graphite nanoplatelets and hence increases the surface area of the hybrid carbon nanostructure thereby high degree of metal oxide decoration is achieved over the hybrid structure. MWNTs were prepared by catalytic chemical vapor deposition technique and further purified with air oxidation and acid treatment. Graphite was treated with conc. nitric acid and sulphuric acid in the volumetric ratio of 1:3 for 3 days and these modified graphite nanoplatelets were further stirred with MWNTs in equal weight ratio to form hybrid nanostructure. Further, ruthenium oxide (RuO2) nanoparticles were decorated on this hybrid structure using chemical route followed by calcination. RuO2 decorated hybrid carbon nanostructure was characterized by using X-ray diffraction, Electron microscopy and Raman spectroscopy. The performance of the hybrid structure based nanocomposite as electrochemical capacitor electrodes was analyzed by studing its capacitive and charge-discharge behaviours using cyclic voltammetry and chronopotentiometry techniques and the results have been discussed.     

Development of non-perfluorinated hybrid materials for single-cell proton exchange membrane fuel cells

Development of low temperature fuel cells that operate under 100 °C are needed to reduce the costs, to design a class of hybrid membranes and to construct various structures of membrane-electrode-assembles (MEAs) for proton exchange membrane fuel cells (PEMFC). In this work, PVA/PMA/SiO₂ hybrid composite membranes were synthesized and their conductivities were determined by impedance measurements. We found a maximum conductivity value of 4.2 × 10⁻³ S/cm at 80 °C and 100% relative humidity (RH). A fuel cell test evaluation for various MEAs was conducted by the potentiodynamic analysis and the current density values were determined from the current–voltage (I–V) curves. A maximum current density of 635 mA/cm² was obtained at 80 °C and 100% RH. To the best of our knowledge, this is the first time that a high current density of PVA-based electrolytes for PEMFCs operating at low temperature is reported. The structural characters were examined using of XRD and FTIR methods, and thermal properties were studied using DSC and TGA techniques and the results were discussed (cf. supplementation). The present study revealed that the single cell performance depends mainly on the temperature, relative humidity and chemical compositions of the membranes.     

Carbon nanostructure grown using bi-metal oxide as electrocatalyst support for proton exchange membrane fuel cell

A novel carbon nanostructure grown by catalytic chemical vapour deposition technique has been applied as an electrocatalyst support for oxygen reduction reaction in proton exchange membrane fuel cell. The growth of carbon nanostructure (CNS) is carried over a low cost bi-metal oxide catalyst (Fe–Sn–O) synthesized by sol–gel technique. Platinum nanoparticle decoration on Fe–Sn–O incorporated CNS (CNS-FSO) is performed by ethylene glycol reduction method. The structural as well as morphological analysis confirms the formation of CNS-FSO and platinum decoration on CNS-FSO. The electrochemically active surface area (ECSA) of platinum decorated CNS-FSO (Pt/CNS-FSO) is 68 m² g⁻¹, as revealed from cyclic voltammetry. Polarization studies are carried out at different temperatures (40 °C, 50 °C and 60 °C) to exploit the oxygen reduction reaction activity of Pt/CNS-FSO. A maximum power density of 449 mW cm⁻² (without back pressure) at 60 °C shows the potential of this novel CNS-FSO as an electrocatalyst support in proton exchange membrane fuel cell.     

Room temperature hydrogen gas sensing properties of mono dispersed platinum nanoparticles on graphene-like carbon-wrapped carbon nanotubes

We present platinum nanoparticles dispersed wrinkled graphene-like carbon-wrapped carbon nanotubes (Pt/GCNTs) as a room temperature chemiresistive hydrogen gas sensor. Pt nanoparticles are decorated over GCNTs surface using poly (sodium 4-styrene sulfonate) (PSS) functionalization, followed by ethylene glycol reduction method. The highly defective wrinkled graphene-like surface of GCNTs provides large surface area and PSS functionalization provides stable immobilization of mono dispersed Pt nanoparticles on the carbon surface. A simple and inexpensive drop cast technique is used to fabricate the thick film sensor of the material. Hydrogen resistive gas sensing properties of Pt/GCNTs are studied at different gas concentrations, temperatures and Pt wt. % loadings. Pt/GCNTs sensor shows optimal sensitivity at room temperature with stable and reproducible response towards hydrogen. The sensor with 2 wt. % of Pt showed maximum sensitivity that is three fold higher than Pt decorated carbon nanotubes (Pt/CNTs) with the same Pt wt. % loading. The present study shows potential to explore novel H2 sensors^.     

Palladium dispersed multiwalled carbon nanotube based hydrogen sensor for fuel cell applications

Palladium nanocatalysts supported on surface-oxidized multiwalled carbon nanotubes (MWNT) were prepared by the aqueous solution reduction of _PdCl2${\mathrm{PdCl}}_2$. MWNT have been synthesized by catalytic chemical vapor deposition (CCVD) technique. Pyrolysis of acetylene using a fixed-bed catalytic reactor over rare earth (RE) based _AB2${\mathrm{AB}}_2$ alloy hydride catalyst, obtained through hydrogen decrepitation technique, has been performed to synthesize MWNT. Structural, morphological and vibrational characterizations have been carried out using XRD, SEM, TEM and Raman spectroscopy, respectively. In situ electrical resistance measurements for thin films of MWNT obtained by spin coating samples were carried out by two-probe technique in a chamber with provision to introduce known concentration of hydrogen in constant air flow. Investigations of hydrogen sensing properties of Pd–MWNT ensembles have been carried out. The stability of Pd–MWNT thin films after several cycles of adsorption and desorption was studied. The change in electrical resistance due to hydrogen adsorption is reversible, with increase to saturation on exposure to hydrogen gas. The results demonstrate that chemically treated MWNT functionalized with nanostructured Pd show good _H2${\mathrm{H}}_2$ sensing response at room temperature.     

Surface modification of CP-Ti to improve the fretting-corrosion resistance: Thermal oxidation vs. anodizing

Fretting corrosion is one of the important reasons for the failure of prosthesis made of titanium and titanium alloys under in vivo condition. The fretting-corrosion behaviour of untreated, anodized and thermally oxidized commercially pure titanium (CP-Ti) in Ringer's solution was evaluated based on the change in free corrosion potential (FCP) measured as a function of time. A comparison of the performance of untreated, anodized and thermally oxidized CP-Ti under fretting-corrosion conditions is reported for the first time in this paper. The study reveals that surface modification of CP-Ti by both anodizing and thermal oxidation improved the fretting-corrosion resistance of CP-Ti and among them the performance of thermally oxidized CP-Ti is superior to that of the anodized one. Adhesive galling is the predominant wear mechanism for untreated CP-Ti, adhesive wear and delamination are found to be operative for anodized CP-Ti whereas an abrasive wear mechanism is operative for thermally oxidized CP-Ti when they are fretted against an alumina ball.     

Magnetic and transport properties of Laves phase Dy1−xMmxCo2 (x = 0–0.5) alloys

The influence of Mm substitution (Mm = mischmetal) on structural, transport and magnetic properties of (Dy_1?xMm_x)Co₂ (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) alloys has been investigated by means of X-ray diffraction (XRD), temperature dependent electrical resistivity (ρ(T)), ac susceptibility (χ(T)) and thermopower (S(T)). XRD patterns show the formation of solid solutions crystallizing with cubic Laves (C15) type structure at room temperature. The pronounced discontinuities in the resistivity and thermopower at Curie temperature (T_C) are explained based on the suppression of the spin-fluctuation contribution. The gradual decrease in T_C and sharpness of discontinuities in ρ(T) and S(T) with increasing Mm substitution has been discussed.     

Parametric sensitivity of fracture behaviour of concrete

The fictitious crack method (FCM) is applied to determine the load-deflection diagrams of notched plain concrete beams under three-point bending using various forms of strain softening in the stress-deformation relationship. The results indicate that there is a need to determine a more realistic relationship.