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Pd-capped nanocrystalline Mg films were prepared by electron beam evaporation and hydrogenated under isothermal conditions to investigate the hydrogen absorption process via ion beam techniques and in situ optical methods. Films were characterized by different techniques such as X-ray diffraction (XRD) and scanning electron microscopy (SEM). Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA) provided a detailed compositional depth profile of the films during hydrogenation. Gas-solid reaction kinetics theory applied to ERDA data revealed a H absorption mechanism controlled by H diffusion. This rate-limiting step was also confirmed by XRD measurements. The diffusion coefficient (D) was also determined via RBS and ERDA, with a value of (1.1±0.1)·10−13 cm2/s at 140 ∘C. Results confirm the validity of IBA to monitor the hydrogenation process and to extract the control mechanism of the process. The H kinetic information given by optical methods is strongly influenced by the optical absorption of the magnesium layer, revealing that thinner films are needed to extract further and reliable information from that technique.

This manuscript investigates the thermal desorption behaviour of MgH2/Mg(OH)2composites by means of thermal desorption spectroscopy. Besides the H2O and H2desorption events due to Mg(OH)2dehydration and MgH2decomposition reactions, respectively, two additional H2desorption peaks arise at lower temperatures. These peaks are related to solid-state reactions between magnesium hydride and magnesium hydroxide through different channels. The low temperature H2peak (∼150 °C) is related to reaction between a H atom diffusing from MgH2and a surface OH group, whereas the intermediate temperature H2peak (∼350 °C) is due to an interface reaction between the hydride and the hydroxide. The present work supports the theory that the onset of the H2desorption coming from MgH2decomposition is controlled by an incubation process, consisting in the formation of catalytically active vacancies at the MgO/Mg(OH)2surface by dehydration. Possible ways to improve the H2desorption kinetics from MgH2are discussed in the light of the results obtained. [ABSTRACT FROM AUTHOR]

X-ray photoelectron spectroscopy (XPS) is a widely used and easy accessible characterisation technique for investigating the chemical composition of materials. However, investigating the composition of van der Waals (vdW) flakes by XPS is challenging due to the typical spot size of XPS setups compared to the dimensions of the flakes, which are usually one thousand times smaller than the spot size. In this work, we demonstrate the feasibility of quantitative elemental analysis of vdW materials by using high-throughput mechanical exfoliations, which favour the coverage of arbitrary substrates with flakes of areas of the order of the cm 2 using minimal quantities of materials (about 10 μg). We have analysed the chemical composition of MoS 2 , graphite, WSe 2 and FePS 3 . The high-resolution measurement of their main core levels through XPS demonstrates the absence of significant contamination during the transfer method. In the case of air-sensitive FePS 3 , the glove box fabrication and its degradation in air are discussed. Overall, this research opens the possibility of evaluating the purity of commercial or lab-synthesized flakes and paves the way towards a more systematic comparison between the composition of vdW materials produced and used among different laboratories.

Titanium trisulfide (TiS 3 ) nanoribbons, when coated with titanium dioxide (TiO 2 ), can be used for water splitting in the KOH electrolyte. TiO 2 shells can be prepared through thermal annealing to regulate the response of TiS 3 /TiO 2 heterostructures by controlling the oxidation time and growth atmosphere. The thickness and structure of the TiO 2 layers significantly influence the photoelectrocatalytic properties of the TiS 3 /TiO 2 photoanodes, with amorphous layers showing better performance than crystalline ones. The oxide layers should be thin enough to transfer photogenerated charge through the electrode-electrolyte interface while protecting TiS 3 from KOH corrosion. Finally, the performance of TiS 3 /TiO 2 heterostructures has been improved by coating them with various electrocatalysts, NiS x being the most effective. This research presents new opportunities to create efficient semiconductor heterostructures to be used as photoanodes in corrosive alkaline aqueous solutions.

Tuning the electrocatalytic properties of MoS 2 layers can be achieved through different paths, such as reducing their thickness, creating edges in the MoS 2 flakes, and introducing S-vacancies. We combine these three approaches by growing MoS 2 electrodes by using a special salt-assisted chemical vapor deposition (CVD) method. This procedure allows the growth of ultrathin MoS 2 nanocrystals (1-3 layers thick and a few nanometers wide), as evidenced by atomic force microscopy and scanning tunneling microscopy. This morphology of the MoS 2 layers at the nanoscale induces some specific features in the Raman and photoluminescence spectra compared to exfoliated or microcrystalline MoS 2 layers. Moreover, the S-vacancy content in the layers can be tuned during CVD growth by using Ar/H 2 mixtures as a carrier gas. Detailed optical microtransmittance and microreflectance spectroscopies, micro-Raman, and X-ray photoelectron spectroscopy measurements with sub-millimeter spatial resolution show that the obtained samples present an excellent homogeneity over areas in the cm 2 range. The electrochemical and photoelectrochemical properties of these MoS 2 layers were investigated using electrodes with relatively large areas (0.8 cm 2 ). The prepared MoS 2 cathodes show outstanding Faradaic efficiencies as well as long-term stability in acidic solutions. In addition, we demonstrate that there is an optimal number of S-vacancies to improve the electrochemical and photoelectrochemical performances of MoS 2 .

Heterostructures formed by ultrathin borocarbonitride (BCN) layers grown on TiO 2 nanoribbons were investigated as photoanodes for photoelectrochemical water splitting. TiO 2 nanoribbons were obtained by thermal oxidation of TiS 3 samples. Then, BCN layers were successfully grown by plasma enhanced chemical vapour deposition. The structure and the chemical composition of the starting TiS 3 , the TiO 2 nanoribbons and the TiO 2 -BCN heterostructures were investigated by Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Diffuse reflectance measurements showed a change in the gap from 0.94 eV (TiS 3 ) to 3.3 eV (TiO 2 ) after the thermal annealing of the starting material. Morphological characterizations, such as scanning electron microscopy and optical microscopy, show that the morphology of the samples was not affected by the change in the structure and composition. The obtained TiO 2 -BCN heterostructures were measured in a photoelectrochemical cell, showing an enhanced density of current under dark conditions and higher photocurrents when compared with TiO 2 . Finally, using electrochemical impedance spectroscopy, the flat band potential was determined to be equal in both TiO 2 and TiO 2 -BCN samples, whereas the product of the dielectric constant and the density of donors was higher for TiO 2 -BCN.

In the last decades, a broad family of hydrides have attracted attention as prospective hydrogen storage materials of very high gravimetric and volumetric capacity, fast H 2 -sorption kinetics, environmental friendliness and economical affordability. However, constraints due to their high activation energies of the different H 2 -sorption steps and the Gibbs energy of their reaction with H 2 has led to the need of high thermal energy to drive H 2 uptake and release. High heat leads to significant degradation effects (recrystallization, phase segregation, nanoparticles agglomeration…) of the hydrides. In this context, this short review aims to summarize alternative non-thermal methods and non-straightforward thermally driven methods to overcome the previous constraints. The phenomenology lying behind these methods, i. e. tribological activation, sonication, and electromagnetic radiation, and the effect of these processes on hydrogen sorption properties of hydrides are described. These non-usual approaches could boost the capability of the next generation of solid-hydride materials for hydrogen conversion in energy sector, in mobile devices and as hydrogen reservoirs., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Both numerical simulation and hardness measurements were used to determine the mechanical and microstructural behavior of AZ31 bulk samples when submitted to the Equal Channel Angular Pressing (ECAP) technique. Billets of this representative of Mg-rich alloys were submitted to different numbers of passes for various ECAP modes (anisotropic A, isotropic B C ). The strain distribution, the grain size refinement, and the micro-hardness were used as indicators to quantify the effectiveness of the different processing routes. Structural characterizations at different scales were achieved using Scanning Electron Microscopy (SEM), micro-analysis, metallography, Small Angle Neutron Scattering SANS, X-Ray Diffraction (XRD), and texture determination. The grain and crystallite size distribution and orientation as well as defect impacts were determined. Anelastic Spectroscopy (AS) on mechanically deformed samples have shown that the temperature of ECAP differentiate the fragile to ductile regime. MgH₂ consolidated powders were checked for using AS to detect potential hydrogen motions and interaction with host metal atoms. After further optimization, the different mechanically-treated samples were submitted to hydrogenation/dehydrogenation (H/D) cycles, which shows that, for a few passes, the B C mode is better than the A one, as supported by theoretical and experimental microstructure analyses. Accordingly, the hydrogen uptake and (H/D) reactions were correlated with the optimized microstructure peculiarities and interpreted in terms of Johnson-Avrami- Mehl-Kolmogorov (JAMK) and Jander models, successively.

This work investigates the growth of B-C-N layers by chemical vapor deposition using methylamine borane (MeAB) as the single-source precursor. MeAB has been synthesized and characterized, paying particular attention to the analysis of its thermolysis products, which are the gaseous precursors for B-C-N growth. Samples have been grown on Cu foils and transferred onto different substrates for their morphological, structural, chemical, electronic and optical characterizations. The results of these characterizations indicate a segregation of h-BN and graphene-like (Gr) domains. However, there is an important presence of B and N interactions with C at the Gr borders, and of C interacting at the h-BN-edges, respectively, in the obtained nano-layers. In particular, there is a significant presence of C-N bonds, at Gr/h-BN borders and in the form of N doping of Gr domains. The overall B:C:N contents in the layers is close to 1:3:1.5. A careful analysis of the optical bandgap determination of the obtained B-C-N layers is presented, discussed and compared with previous seminal works with samples of similar composition.

High-temperature (1000 °C) thermolytic decomposition of ethane 1,2-diamineborane (BH3NH2CH2CH2NH2BH3) deposited onto a Cu foil has been performed in an ultra-high-vacuum environment. A combined thermolytic, structural (x-ray diffraction), microscopic (scanning electron microscopy) and spectroscopic (Raman, x-ray photoemission spectroscopy) analysis, has identified a ternary borocarbonitride (BCN) compound as a result of the process. The obtained BCN compound is nanocrystalline, surrounded by crystallites of ammonium hydroxide borate hydrate. The ternary compound presents a 0.2:0.6:0.2 B:C:N composition in the bulk and 0.11:0.76:0.13 stoichiometry at the very surface, richer in C-C networks with respect to the bulk. Furthermore, the resulting BCN compound does not show oxidation at the surface due to the in-vacuum thermolysis of the single precursor.

The electrical van der Pauw's method has recently been extended to measure the thermal conductivity of different elements and compounds. This technique provides an easy way to determine the sample in-plane thermal conductivity by avoiding the influence of the thermal contact resistances. However, the reported calculated error values appear to be underestimated when dealing with the materials with low thermal conductivity (<5 W/Km) at room temperature. The causes of this underestimation are investigated in this communication and it has been found that they are due to the drastic influence of conduction heat losses through the thermo-resistance wires as well as the resulting modification of the sample temperature map. Both phenomena lead to experimental values of the sample thermal conductivity, which are systematically higher than the tabulated ones. The magnitude of this systematic error is ∼100% dealing with the samples of macroscopic dimensions, and low thermal conductivity indicated that the obtained accurate measurements can be quite challenging.

Ethane 1,2-diamineborane (EDAB) is an alkyl-containing amine-borane adduct with improved hydrogen desorption properties as compared to ammonia borane. In this work, it is reported the high temperature thermolytic decomposition of EDAB. Thermolysis of EDAB has been investigated by concomitant thermogravimetry-differential thermal analysis-mass spectrometry experiments. EDAB shows up to four H₂ desorption events below 1000 °C. Small fractions of CH₄, C₂H₄ and CO/CO₂ are also observed at moderate-high temperatures. The solid-state thermolysis product has been characterized by means of different structural and chemical methods, such as X-ray diffraction, Raman spectroscopy, Scanning electron microscopy, Elemental analysis, and X-ray photoelectron spectroscopy (XPS). The obtained results indicate the formation of a ternary borocarbonitride compound with a poorly-crystalline graphitic-like structure. By contrast, XPS measurements show that the surface is rich in carbon and nitrogen oxides, which is quite different to the bulk of the material.

This manuscript investigates the thermal desorption behaviour of MgH(2)/Mg(OH)(2) composites by means of thermal desorption spectroscopy. Besides the H(2)O and H(2) desorption events due to Mg(OH)(2) dehydration and MgH(2) decomposition reactions, respectively, two additional H(2) desorption peaks arise at lower temperatures. These peaks are related to solid-state reactions between magnesium hydride and magnesium hydroxide through different channels. The low temperature H(2) peak ( approximately 150 degrees C) is related to reaction between a H atom diffusing from MgH(2) and a surface OH group, whereas the intermediate temperature H(2) peak ( approximately 350 degrees C) is due to an interface reaction between the hydride and the hydroxide. The present work supports the theory that the onset of the H(2) desorption coming from MgH(2) decomposition is controlled by an incubation process, consisting in the formation of catalytically active vacancies at the MgO/Mg(OH)(2) surface by dehydration. Possible ways to improve the H(2) desorption kinetics from MgH(2) are discussed in the light of the results obtained.

Effects of ultrasonic irradiation on magnesium hydride (MgH(2)) suspended in decane were investigated with the purpose of improving its hydrogen desorption process. Firstly, we have found that the presence of MgH(2) improves the sonolysis of decane enhancing the amount of hydrogen evolved during the sonication process. The sonicated-MgH(2) maintains its microstructural properties practically unaltered but a drastic reduction of the particle size of MgH(2) (down to approximately 20mum) as well as a high pressure MgH(2) phase are observed. However, no substantial modifications of H-kinetic properties of hydride occur as is determined by thermal desorption measurements. This could be attributed to decomposition of decane during sonication which leads to the formation of carbon compounds that hinder the thermal decomposition of MgH(2).