Y. K. Vijay

Hydrogen storage in thin film metal hydride—a review

Abstract During the last decade hydrogen has attracted world wide interest as a secondary energy carrier resulting in a lot of research work on its production, storage and use. The incorporation of hydrogen into thin film form discussed in this article is a relatively new field of research. The main advantages of thin film metal hydrides are that these provide large surface area with fast charging discharging rate for hydrogen, pulverization is slower, both critical pressure and critical temperature are significantly lower, better heat transfer arrangements, protective surface coating could be done to stop poisoning by oxygen and activation of thin film hydrides is possible by coating with a layer of catalytic material.

Enhancement of hydrogen gas permeability in electrically aligned MWCNT-PMMA composite membranes.

The multi-walled carbon nanotube (MWCNT) dispersed polymethylmethacrylate (PMMA) composite membranes have been prepared for hydrogen gas permeation application. Composite membranes are characterized by Raman spectroscopy, optical microscopy, X-ray diffraction, electrical measurements and gas permeability measurements. The effect of electric field alignment of MWCNT in PMMA matrix on gas permeation has been studied for hydrogen gas. The permeability measurements indicated that the electrically aligned MWCNT in PMMA has shown almost 2 times higher permeability for hydrogen gas as compare to randomly dispersed MWCNT in PMMA. The enhancement in permeability is explained on the basis of well aligned easy channel provided by MWCNT in electrically aligned sample. The effect of thickness of membrane on the gas permeability also studied and thickness of about 30microm found to be optimum thickness for fast hydrogen gas permeates.

Effect of Solvent and Subsequent Thermal Annealing on the Performance of Phenylenevinylene Copolymer:PCBM Solar Cells

The morphology of the photoactive layer used in the bulk heterojunction photovoltaic devices is crucial for efficient charge generation and their collection at the electrodes. We investigated the solvent vapor annealing and thermal annealing effect of an alternating phenylenevinylene copolymer P:PCBM blend on its morphology and optical properties. The UV-visible absorption spectroscopy shows that both solvent and thermal annealing can result in self-assembling of copolymer P to form an ordered structure, leading to enhanced absorption in the red region and hole transport enhancement. By combining the solvent and thermal annealing of the devices, the power conversion efficiency is improved. This feature was attributed to the fact that the PCBM molecules begin to diffuse into aggregates and together with the ordered copolymer P phase form bicontinuous pathways in the entire layer for efficient charge separation and transport. Furthermore, the measured photocurrent also suggests that the space charges no longer limit the values of the short circuit current (J(sc)) and fill factor (FF) for solvent-treated and thermally annealed devices. These results indicate that the higher J(sc) and PCE for the solvent-treated and thermally annealed devices can be attributed to the phase separation of active layers, which leads to a balanced carrier mobility. The overall PCE of the device based on the combination of solvent annealing and thermal annealing is about 3.7 %.

The titanium-coated polymeric membranes for hydrogen recovery

Abstract The polymeric membranes are commercially used for gas separation. The important parameters for their commercial application are good permeabilities and permselectivities. These parameters have a strong dependence on the free volume properties of the material. The membranes alone are generally not suitable when high product purity and recovery is desired. However, the titanium-coated polymeric membranes can solve the problem. Hydrogen molecules when diffuse through metals like titanium and palladium, break into atomic form and recombine after recovery. The binding of metallic clusters on the polymeric material is improved partially by heat treatment, however, good results are obtained by dissolving the coated membranes and recasting them. The permeability of hydrogen in comparison to air has been found to increase 2–5 times.

Microstructure change in poly(ethersulfone) films by swift heavy ions

PES membrane of thickness 25 microm was irradiated by Cl(9+) ions of energy 100 MeV at IUAC, New Delhi. Microstructure changes due to exposure to high-energy ions were investigated by Fourier transform infrared (FTIR) and ultraviolet/visible (UV/vis) absorption spectroscopies, X-ray diffraction technique and by dynamic mechanical analysis (DMA). A significant loss of crystallinity is observed by the XRD data. Particle size or grain size calculated using Scherrer formula indicates measurable change in particle size of irradiated samples. The polymer chain scissions and structure degradations are expected to occur for irradiated samples. Optical properties of the films were changed due to irradiation that could be clearly seen in the absorption spectra. FTIR does not show the remarkable change in the irradiated samples, but there is some change in the surface roughness observed by AFM.

Synthesis of a Low-Band-Gap Small Molecule Based on Acenaphthoquinoxaline for Efficient Bulk Heterojunction Solar Cells

A novel small molecule (SM) with a low-band-gap based on acenaphthoquinoxaline was synthesized and characterized. It was soluble in polar solvents such as N,N-dimethylformamide and dimethylacetamide. SM showed broad absorption curves in both solution and thin films with a long-wavelength maximum at 642 nm. The thin film absorption onset was located at 783 nm, which corresponds to an optical band gap of 1.59 eV. SM was blended with PCBM to study the donor-acceptor interactions in the blended film morphology and the photovoltaic response of the bulk heterojunction (BHJ) devices. The cyclic voltammetry measurements of the materials revealed that the HOMO and LUMO levels of SM are well aligned with those of PCBM, allowing efficient photoinduced charge transfer and suitable open circuit voltage, leading to overall power conversion efficiencies (PCEs) of approximately 2.21 and 3.23% for devices with the as-cast and thermally annealed blended layer, respectively. The increase in the PCE with the thermally annealed blend is mainly attributed to the improvement in incident photon to current efficiency (IPCE) and short circuit photocurrent (J(sc)). Thermal annealing leads to an increase in both the crystallinity of the blend and hole mobility, which improves the PCE.

Crystallization kinetics and optical band gap studies of Se96In4 glass before and after slow neutron irradiation

Abstract Results of differential scanning calorimetry (DSC) under non-isothermal condition on Se 96 In 4 semiconducting chalcogenide glass before and after slow neutron irradiation, for different exposure times, have been reported and discussed. Some of Sn atoms have been injected into the glass by nuclear transmutation processes and the binary glass is converted into a ternary. This is accompanied by an increase in the activation energy of crystallization, E c , and in the glass transition temperature, T g and a decrease in the glass transition activation energy, E t , in the onset crystallization temperature, T c and in the peak temperature of crystallization T p . Optical band gap measurements have also been carried out, before and after irradiation, on identical thin pellets of Se 96 In 4 glass. The energy band gap, E g , is found to decrease upon irradiation. These effects have been attributed to a structural change upon doping and to irradiation induced defects.

Nanofilter for hydrogen purification

Abstract The application of polymeric membranes in combination with metallic films can be used for gas purification, in particular hydrogen (Int J Hydrogen Energy 27(2) (2002) 905), whose molecules are very small. The affinity of hydrogen to certain metals supports its flow, but restricts the permeation of other gases. However, the flow rate is very small in dense membranes. Attempts have been made to etch nuclear tracks created in polymeric foils, from both sides in a very controlled way such that conical etched pits meet at their vertices. This has been characterized by gas permeation measurements. The low density of 10 6 – 10 8 tracks / cm 2 is generated by a 60 MeV carbon ion beam at the NSC Pelletron, New Delhi. The primary ion fluence of 10 10 / cm 2 was reduced by means of a gold absorber foil. The gas flow rate has shown a considerable improvement along with the selectivity of hydrogen over the carbon dioxide where the molecular sizes of 0.21 and 0.4 nm , respectively, are separable.

Hydrogen in FeTi thin films by ERDA with Ag107 ions

Abstract Hydrogen content in hydride at various depths is very important. In the present work hydrogen content in hydrogenated FeTi thin films has been investigated by ERDA (Elastic Recoil Detection Analysis) using 160 MeV, Ag 107 ions. ERDA investigations have shown that FeTi thin films without exposing hydrogen have about 50 atm% of hydrogen content and after hydrogenation these films acquire 5–10 atm% of additional hydrogen. It was observed that the hydrogenation of irradiated films did not increase the hydrogen concentration further. It implies than a beam did not cause track formation in the sample at this energy.

Kinetics of hydrogen absorption in obliquely deposited FeTi thin films

Abstract FeTi thin films of thickness about 1000 A were obliquely deposited at 5 × 10 −5 Torr by thermal evaporation onto the glass substrate at room temperature. The resistance of the films deposited at different angles increases with the absorption of hydrogen and decreases with desorption. The resistance of the samples also increases with the angle of deposition. The change in resistance value is taken as a measure of amount of hydrogen absorbed in the samples. It is observed that the amount of hydrogen absorbed increases with the deposition angle which is due to an increase in the porosity of thin films.