In recent years, many solid-state hydride-based materials have been considered as hydrogen storage systems for mobile and stationary applications. Due to a gravimetric hydrogen capacity of 5.6 wt% and a dehydrogenation enthalpy of 38.9 kJ/mol H 2 , Mg(NH 2 ) 2 + 2LiH is considered a potential hydrogen storage material for solid-state storage systems to be coupled with PEM fuel cell devices. One of the main challenges is the reduction of dehydrogenation temperature since this system requires high dehydrogenation temperatures (~ 200 °C). The addition of KH to this system significantly decreases the dehydrogenation onset temperature to 130 °C. On the one hand, the addition of KH stabilizes the hydrogen storage capacity. On the other hand, the capacity is reduced by 50% (from 4.1 to 2%) after the first 25 cycles. In this work, the particle sizes of the overall hydride matrix and the potassium-containing species are investigated during hydrogen cycling. Relation between particle size evolution of the additive and hydrogen storage kinetics is described by using an advanced synchrotron-based technique: Anomalous small-angle X-ray scattering, which was applied for the first time at the potassium K-edge for amide-hydride hydrogen storage systems. The outcomes from this investigation show that, the nanometric potassium-containing phases might be located at the reaction interfaces, limiting the particle coarsening. Average diameters of potassium-containing nanoparticles double after 25 cycles (from 10 to 20 nm). Therefore, reaction kinetics at subsequent cycles degrade. The deterioration of the reaction kinetics can be minimized by selecting lower absorption temperatures, which mitigates the particle size growth, resulting in two times faster reaction kinetics.

The morphology and structural changes of confined matter are still far from being understood. This report deals with the development of a novel in situ method based on the combination of anomalous small-angle X-ray scattering (ASAXS) and X-ray absorption near edge structure (XANES) spectroscopy to directly probe the evolution of the xenon adsorbate phase in mesoporous silicon during gas adsorption at 165 K. The interface area and size evolution of the confined xenon phase were determined via ASAXS demonstrating that filling and emptying the pores follow two distinct mechanisms. The mass density of the confined xenon was found to decrease prior to pore emptying. XANES analyses showed that Xe exists in two different states when confined in mesopores. This combination of methods provides a smart new tool for the study of nanoconfined matter for catalysis, gas, and energy storage applications.

In this study two hybrid organic-inorganic ureasilicate monomers with different length of polymer segments were chosen for preparation of sol-gel material that includes two moieties blended on the molecular scale. The first monomer was obtained by crosslinking a double terminated polyoxyalkyleneamine with an isocyanate modified silicone ethoxide and the second one - by crosslinking between the isocyanate modified silicone ethoxide with an amino modified silicone ethoxide. Sol-gel route was applied for transformation of the liquid monomer blends in transparent materials with varying degree of rigidity. The prepared samples were characterized by small-angle X-ray scattering, Fourier-transform infrared spectroscopy, positron annihilation lifetime spectroscopy, and swelling experiments. The results demonstrate that the structure of the obtained materials could be tuned by a simple variation of molar fraction ratio between these two monomers. This makes it possible to obtain nanostructured materials with predictable properties.

The nanostructure of hydrogenated amorphous silicon (a-Si∶H) is studied by a combination of small-angle x-ray scattering (SAXS) and small-angle neutron scattering (SANS) with a spatial resolution of 0.8 nm. The a-Si∶H materials were deposited using a range of widely varied conditions and are representative for this class of materials. We identify two different phases that are embedded in the a-Si∶H matrix and quantified both according to their scattering cross sections. First, 1.2 nm sized voids (multivacancies with more than 10 missing atoms) which form a superlattice with 1.6 nm void-to-void distance are detected. The voids are found in concentrations as high as 6×10^{19}  cm^{-3} in a-Si∶H material that is deposited at a high rate. Second, dense ordered domains (DOD) that are depleted of hydrogen with 1 nm average diameter are found. The DOD tend to form 10-15 nm sized aggregates and are largely found in all a-Si∶H materials considered here. These quantitative findings make it possible to understand the complex correlation between structure and electronic properties of a-Si∶H and directly link them to the light-induced formation of defects. Finally, a structural model is derived, which verifies theoretical predictions about the nanostructure of a-Si∶H.

Precipitation hardening involves solutionising, quenching and annealing steps, the latter often at various temperatures. The phenomena observed in Al-Mg-Si alloys are very complicated and partially not well understood. During and after quenching, solute atoms diffuse through the lattice assisted by vacancies and form atom clusters that gradually grow. These act back onto vacancies, which complicates the situation. We apply positron annihilation techniques in addition to traditional hardness, resistivity and thermal measurements to clarify what happens in various stages of thermal treatment: The quenching process can be divided into a stage of vacancy loss and of precipitation. Very short artificial ageing treatments after heating at different rates show that there is a competition between vacancy losses and cluster formation as the temperature increases. The difference between natural ageing and artificial ageing can be defined based on the importance of excess vacancies. Based on such results the behaviour of “invisible” objects such as vacancies and small clusters can be better understood but some open question remain such as the kinetics of secondary ageing or the details of the negative effect of natural ageing on artificial ageing.

In this work, we study the electronic and atomic structural modifications occurring in TiO2 anatase nanoparticles as anode materials in Na-ion batteries upon sodiation and desodiation. The structural investigation is performed over both long- and short-range order by combining a comprehensive extended X-ray absorption fine structure (EXAFS) characterization with X-ray diffraction (XRD). The evolution of the electronic structure upon cycling is qualitatively investigated by X-ray absorption near-edge structure (XANES) analysis. The goal of this work is to correlate the outstanding electrochemical performance of carbon-coated TiO2 anatase nanoparticles in sodium batteries with the electronic and structural modifications induced during the sodiation and desodiation processes upon cycling. This work also demonstrates for the first time a coherent explanation of the structural changes observed, where an electrochemically induced short-range ordering is revealed upon cycling.

Heterogeneous Cu catalysts are widely used in photocatalytic hydrogen generation. The typical working mode includes the transfer of photo-induced charges from a semi-conductor to CuO which itself is reduced to Cu2O to initiate the catalytic cycle. In this contribution a photosensitizer (dye), excited by visible light absorption, was used to transfer an electron to the CuO which after reduction catalyzes the water reduction to hydrogen. Several copper(II)-catalysts on high surface silica were prepared by impregnation or precipitation and applied in photocatalytic water reduction. The best catalyst CuO(Cl0.1)/SiO2, synthesized via incipient wetness impregnation of CuCl2 in MCM-41 and a following precipitation with NaOH, achieved a 6 times higher activity (1702 mmol h(-1) g(-1)) compared to a previously investigated copper system (280 mmol h(-1) g(-1) for CuI) under the same reaction conditions. All materials were fully characterized by XRD, TEM and N-2 sorption and further by magnetic resonance and X-ray methods EPR, ASAXS and XAS. In situ measurements evidenced a reduction of the initial Cu(II)-species, which confirms the (proposed) photocatalytic mechanism. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Solid-state hydride compounds are a promising option for efficient and safe hydrogen-storage systems. Lithium reactive hydride composite system 2LiBH(4) + MgH2/2LiH + MgB2 (Li-RHC) has been widely investigated owing to its high theoretical hydrogen-storage capacity and low calculated reaction enthalpy (11.5 wt % H-2 and 45.9 kJ/mol H-2). In this paper, a thorough investigation into the effect of the formation of nano-TiAl alloys on the hydrogen-storage properties of Li-RHC is presented. The additive 3TiCl(3)center dot AlCl3 is used as the nanoparticle precursor. For the investigated temperatures and hydrogen pressures, the addition of similar to 5 wt % 3TiCl(3)center dot AlCl3 leads to hydrogenation/dehydrogenation times of only 30 min and a reversible hydrogen-storage capacity of 9.5 wt %. The material containing 3TiCl(3)center dot AlCl3 possesses superior hydrogen-storage properties in terms of rates and a stable hydrogen capacity during several hydrogenation/dehydrogenation cycles. These enhancements are attributed to an in situ nanostructure and a hexagonal AlTi3 phase observed by high-resolution transmission electron microscopy. This phase acts in a 2-fold manner, first promoting the nucleation of MgB2 upon dehydrogenation and second suppressing the formation of Li2B12H12 upon hydrogenation/dehydrogenation cycling.

Polymer electrolyte fuel cells (PEFCs) offer an efficient way of chemical-to-electrical energy conversion that could drastically reduce the environmental footprint of the mobility and stationary energy supply sectors, respectively. However, PEFCs can suffer from severe degradation during start/ stop events, when the cathode catalyst is transiently exposed to very high potentials. In an attempt to mitigate corrosion of conventional carbon support materials for Pt catalyst nanoparticles under these conditions, conductive metal oxides like antimony-doped tin oxide (ATO) are considered alternative support materials with improved corrosion resistance. A combined in situ anomalous small-angle X-ray scattering and post mortem transmission electron microscopy study reveals PEFC-relevant degradation properties of ATO-supported Pt in comparison to carbon-supported Pt catalysts. Against expectation, the superior stability of ATO-supported Pt nanoparticles cannot be merely explained by improved support corrosion resistance. Instead, the dominant loss mechanism of electrochemical Ostwald ripening is strongly suppressed on ATO support, which can be explained with a potential-dependent switching of support oxide surface conductivity. This electrochemical transistor effect represents an important design principle for the development of optimized metal oxide support materials that protect supported Pt nanoparticles at high potentials, where careful consideration of the metal oxide hatband potential is required in order to maintain high catalyst performance at normal PEFC cathode operation conditions at the same time.