Morphological and Elemental Investigations on Co–Fe–B–O Thin Films Deposited by Pulsed Laser Deposition for Alkaline Water Oxidation: Charge Exchange Efficiency as the Prevailing Factor in Comparison with the Adsorption Process

Catalysis Letters - Mixed transition-metals oxide electrocatalysts have shown huge potential for electrochemical water oxidation due to their earth abundance, low cost and excellent...     

Structural evolution of Pd-capped Mg thin films under H2 absorption and desorption cycles

In this paper we present a study on the relation between the evolution, upon successive H₂ cycling, of the crystalline order and the H₂ sorption properties of Pd-capped textured Mg thin films grown on Si and glass substrates.     

Deuterium thermal desorption from Ni-rich deuterated Mg thin films

Mg–Ni multilayers and Ni-rich Mg thin films were deposited by electron gun and pulsed laser deposition, respectively. Samples were submitted to thermal treatment in deuterium or hydrogen atmosphere at 423 K and 10⁵ Pa pressure to promote the metal to hydride phase transition.The H chemical bonding in the multilayer samples, after annealing in H₂ atmosphere, was examined by Fourier transform infrared spectroscopy: the obtained spectra suggest that the samples with the Mg:Ni=2:1 atomic ratio contain the Mg₂NiH₄ phase while the samples with lower Ni concentration contain both the MgH₂ and the Mg₂NiH₄ phases.The effect of the Ni additive on the stability of the deuteride phase was studied by thermal desorption spectroscopy (TDS). The TDS spectra of the single-phase Mg₂NiD₄ samples show a TDS peak at 400 K. The TDS spectra of the two-phase samples show both the D₂ desorption peak at 400 K and a second peak at higher temperature that we attributed to the dissociation of the MgD₂ phase. The high-temperature peak shifts to lower temperatures by increasing the Ni content.It is suggested that in the two-phase samples, the lattice volumes having the Mg₂Ni structure resulting from the dissociation of the Mg₂NiD₄ phase reduce the thermodynamic stability of the MgD₂ phase.     

Physically and chemically synthesized TiO2 composite thin films for hydrogen production by photocatalytic water splitting

TiO₂ thin films have been synthesized by radio-frequency magnetron sputtering and sol–gel method to study the hydrogen generation by photocatalytic water splitting under visible light irradiation. Photoelectrochemical cell with chemical bias, involving photo-anode in form of TiO₂ film deposited on conducting indium tin oxide (ITO) film and Pt as cathode, is developed. The effect of conducting ITO layer on photo-voltage is studied by varying the thickness of ITO films. Constant H₂ generation rate is obtained for long period of time by both the TiO₂ films because of the separated evolution of H₂ and O₂ gas, thus eliminating the back-reaction effect. Sputter-deposited film as compared to sol–gel-synthesized film showed better H₂ generation rate, mainly explained in terms of the higher visible light absorption achieved by oxygen vacancies created in the TiO₂ film by the energetic target ions during deposition in pure Ar gas pressure.     

Co–B nanoparticles supported on carbon film synthesized by pulsed laser deposition for hydrolysis of ammonia borane

Thin films of Carbon-supported Co–B nanoparticles were synthesized by using Pulsed Laser Deposition (PLD) and used as catalysts in the hydrolysis of Ammonia Borane (AB) to produce molecular hydrogen. Amorphous Co–B-based catalyst powders, produced by chemical reduction of cobalt salts, were used as target material for nanoparticles-assembled Co–B film catalysts preparation through PLD. Various Ar pressures (10–50 Pa) were used during deposition of carbon films to obtain extremely irregular and porous carbon support with high surface area prior to Co–B film deposition. Surface morphology of the catalyst films was studied using Scanning Electron Microscopy, while structural characterization was carried out using X-Ray diffraction. The hydrogen generation rate attained by carbon-supported Co–B catalyst film is significantly higher as compared to unsupported Co–B film and conventional Co–B powder. Almost complete conversion (95%) of AB was obtained at room temperature by using present film catalyst. Morphological analysis showed that the Co–B nanoparticles produced after the laser ablation process act as active catalytic centers for hydrolysis while the carbon support provides high initial surface area for the Co–B nanoparticles with better dispersion and tolerance against aggregation. The efficient nature of our carbon-supported Co–B film is well supported by the obtained very low activation energy (∼29 kJ (mol)⁻¹) and exceptionally high H₂ generation rate (13.5 L H₂ min⁻¹ (g of Co)⁻¹) by the hydrolysis of AB.     

Growth of Pb-nanowires in one single process by co-sputtering of Al–Pb targets

We show that Pb nanowires may grow by co-sputtering of Al–Pb target. During sputter deposition, stress is generated inside the deposited film. Because Pb is immiscible in Al, stress relaxation occurs through Pb segregation along the aluminum grain boundary. Extrusion of Pb is inhibited if a few layers of Al oxide are formed on the surface of the film. However, if the surface oxide is broken by external perturbations, for example air-operated corrosion or electron beam, then segregated Pb extrudes in form of nanowires.     

Hydrogen permeation through a slab sample in the case of high hydrogen concentration

Hydrogen trapping sites have a great influence on the hydrogen permeation through a slab sample. The diffusion of the hydrogen in a crystal is generally governed by a parabolic partial differential equation: a numerical simulation code, realized for the study of the permeation of hydrogen in presence of trapping sites, has been utilized for the analysis of the influence of reversible and irreversible traps on the diffusion of hydrogen in a metal for the case of high (not negligible) hydrogen concentration with boundary conditions which cannot be treated analytically.     

Study of Nitrogen Implanted in Aluminum at Various Doses

Experimental and theoretical studies are carried out to understand transport of nitrogen in aluminum during implantation process. 60 keV and 120 keV N₂⁺ ion are implanted in pure Al substrates at doses ranging from l×l0¹⁷ to 9×l0¹⁷ N-atoms per cm². RBS and Glancing angle XRD studies are carried out. RBS studies show that the depth profiles are gaussian in nature at low doses and gradually become rectangular in shape as the dose increases. XRD analysis reveals that AlN is formed even at low doses. Theoretical simulations of depth profiles at low dose, include displacement mixing and radiation enhanced diffusion, which are modelled to be described by a diffusion like process. Effective diffusion coefficient in radiation environment is found to be equal to 8×l0^-16 cm².sec^-1. At high doses, when new N-atoms are added during implantation their transport gets linked with the already formed AlN. This leads to a rectangular shape of depth profiles observed at high doses.