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2LiH + MgB 2 composite doped with TiO 2 (Li-RHC-Ti) is employed with a two-fold purpose: hydrogen purification under a H 2 –CO (0.1 mol%) mixture and CO methanation. Upon dynamic cycling under CO–H 2 mixture, hydrogen release curves display a quite stable amount of pure hydrogen of about 10 wt%, short release times of around 60 min, and minor degradation. Gas analysis by Fourier transform infrared spectroscopy (FTIR) after a thermal dehydrogenation process of MgH 2 and LiBH 4 under CO evidence the conversion of CO to CH 4. Li-RHC-Ti dehydrogenated under CO shows the simultaneous formation of CH 4 , CH 3 OH, and B(CH 3) 3 in the gas phase. X-ray powder diffraction (XRPD) and FTIR characterizations of the solid phases of Li-RHC-Ti after both H 2 –CO mixture and CO interactions demonstrate the formation of MgO, LiBO 2, and HCOO− species. Li-RHC-Ti acts as a hydrogen source and promoter for the CO conversion. Reaction pathways are proposed based on experimental results and equilibrium composition calculations. Image 1 • Li-RHC (2LiH + MgB 2 /2LiBH 4 + MgH 2) composite doped with TiO 2 (Li-RHC-Ti). • Dual ability of Li-RHC-Ti to purify CO–H 2 and to reduce this CO into CH 4. • Hydrides-CO systems for the preparation of gas mixtures based on CH 4. • Fast and stable dynamic cycling under a H 2 -CO mixture releasing 10 wt% H 2. • Formation of MgO, LiBO 2 and HCOO− after Li-RHC-Ti and CO interactions. [ABSTRACT FROM AUTHOR]

In this work, the mechanical milling of a FeTiMn alloy for hydrogen storage purposes was performed in an industrial milling device. The TiFe hydride is interesting from the technological standpoint because of the abundance and the low cost of its constituent elements Ti and Fe, as well as its high volumetric hydrogen capacity. However, TiFe is difficult to activate, usually requiring a thermal treatment above 400 °C. A TiFeMn alloy milled for just 10 min in a 100 L industrial milling device showed excellent hydrogen storage properties without any thermal treatment. The as-milled TiFeMn alloy did not need any activation procedure and showed fast kinetic behavior and good cycling stability. Microstructural and morphological characterization of the as-received and as-milled TiFeMn alloys revealed that the material presents reduced particle and crystallite sizes, even after such short time of milling. The refined microstructure of the as-milled TiFeMn is deemed to account for the improved hydrogen absorption-desorption properties. • First industrial-sized milling treatment procedure for TiFe alloys reported. • Milled alloy does not need thermal activation. • Milled alloy shows superior H 2 sorption behavior vs. thermally treated alloy. • Procedure is easily scalable to larger mills. [ABSTRACT FROM AUTHOR]

The hydrogen storage properties of 6Mg(NH 2) 2 9LiH- x (LiBH 4) (x = 0, 0.5, 1, 2) system and the role of LiBH 4 on the kinetic behaviour and the dehydrogenation/hydrogenation reaction mechanism were herein systematically investigated. Among the studied compositions, 6Mg(NH 2) 2 9LiH 2LiBH 4 showed the best hydrogen storage properties. The presence of 2 mol of LiBH 4 improved the thermal behaviour of the 6Mg(NH 2) 2 9LiH by lowering the dehydrogenation peak temperature nearly 25 °C and by reducing the apparent dehydrogenation activation energy of about 40 kJ/mol. Furthermore, this material exhibited fast dehydrogenation (10 min) and hydrogenation kinetics (3 min) and excellent cycling stability with a reversible hydrogen capacity of 3.5 wt % at isothermal 180 °C. Investigations on the reaction pathway indicated that the observed superior kinetic behaviour likely related to the formation of Li 4 (BH 4)(NH 2) 3. Studies on the rate-limiting steps hinted that the sluggish kinetic behaviour of the 6Mg(NH 2) 2 9LiH pristine material are attributed to an interface-controlled mechanism. On the contrary, LiBH 4 -containing samples show a diffusion-controlled mechanism. During the first dehydrogenation reaction, the possible formation of Li 4 (BH 4)(NH 2) 3 accelerates the reaction rates at the interface. Upon hydrogenation, this 'liquid like' of Li 4 (BH 4)(NH 2) 3 phase assists the diffusion of small ions into the interfaces of the amide-hydride matrix. • Reaction kinetics of 6Mg(NH 2) 2 -9LiH- x (LiBH 4) (x = 0, 0.5, 1, 2) system. • Reduction in the dehydrogenation apparent activation energies. • Excellent cycling properties over 20 cycle. • Rate-limiting processes and the role of Li 4 (BH 4)(NH 2) 3. [ABSTRACT FROM AUTHOR]

Abstract: The hydrogen sorption behavior of the Mg2FeH6–MgH2 hydride system is investigated via in-situ synchrotron and laboratory powder X-ray diffraction (SR-PXD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), particle size distribution (PSD) and volumetric techniques. The Mg2FeH6–MgH2 hydride system is obtained by mechanical milling in argon atmosphere followed by sintering at high temperature and hydrogen pressure. In-situ SR-PXD results show that upon hydriding MgH2 is a precursor for Mg2FeH6 formation and remained as hydrided phase in the obtained material. Diffusion constraints preclude the further formation of Mg2FeH6. Upon dehydriding, our results suggest that MgH2 and Mg2FeH6 decompose independently in a narrow temperature range between 275 and 300 °C. Moreover, the decomposition behavior of both hydrides in the Mg2FeH6–MgH2 hydride mixture is influenced by each other via dual synergetic-destabilizing effects. The final hydriding/dehydriding products and therefore the kinetic behavior of the Mg2FeH6–MgH2 hydride system exhibits a strong dependence on the temperature and pressure conditions. [Copyright &y& Elsevier]

We report a systematic investigation of the effect that selected metal-based additives have on the dehydrogenation properties of the reactive hydride composite (RHC) model system 2NaBH 4 +MgH 2. Compared to the pristine system, the material doped with 3TiCl 3 ·AlCl 3 exhibits superior dehydrogenation kinetics. The addition of 3TiCl 3 ·AlCl 3 alters the controlling mechanism of the second dehydrogenation step making it change from a two-dimensional interface controlled process to a two-dimensional nucleation and growth controlled process. The microstructural investigation of the dehydrogenated 2NaBH 4 +MgH 2 via high-resolution transmission electron microscopy (HRTEM) shows significant differences in the MgB 2 morphology formed in the doped and undoped systems. The MgB 2 has a needle-like structure in the sample doped with 3TiCl 3 ·AlCl 3 , which is different from the plate-like MgB 2 structure in the undoped sample. Moreover, nanostructured metal-based phases, such as TiB 2 /AlB 2 particles, acting as heterogeneous nucleation sites for MgB 2 are also identified for the sample doped with 3TiCl 3 ·AlCl 3. • Ti and Al-based additives strongly enhances the material dehydrogenation properties. • The formed Ti and Al borides stronghly influence the microstructural features of MgB 2. • Crystallographic-chemical theory of nucleation and growth is a potential tool to identify new additives. [ABSTRACT FROM AUTHOR]

[Display omitted] • Market relevance of aboveground hydrogen storage is investigated. • Aboveground storage will likely play a much smaller role than underground storage. • Storage costs are the most decisive factor for market relevance. • Efficiency and systemic suitability can improve aboveground storage competitiveness. • Based on current projections, aboveground storage will only gain small market shares. Hydrogen storage is expected to play a crucial role in the comprehensive defossilization of energy systems. In this context, the focus is typically on underground hydrogen storage (e.g., in salt caverns). However, aboveground storage, which is independent of geological conditions and might offer other technical advantages, could provide systemic benefits and, thereby, gain shares in the hydrogen storage market. Against this background, this paper examines the market relevance of aboveground compared to underground hydrogen storage. Using the open-source energy system model and optimization framework of Europe, PyPSA-Eur, the influence of geological independence, storage cost relations, and technical storage characteristics (i.e., efficiencies) on mentioned market relevance of aboveground hydrogen storage are investigated. Further, the expectable market relevance based on current cost projections for the future is assessed. The studies show that in terms of hydrogen capacities, aboveground hydrogen storage plays a considerably smaller role compared to underground hydrogen storage. Even when assuming comparatively low aboveground storage cost, it will not exceed 1.7% (1.9 TWh H2,LHV) of total hydrogen storage capacities in a cost-optimal European energy system. Regarding the amounts of annually stored hydrogen, aboveground storage could play a larger role, reaching a maximum share of 32.5% (168 TWh H2,LHV a-1) of total stored hydrogen throughout Europe. However, these shares are only achievable for low cost storage in particularly suited energy system supply configurations. For higher aboveground storage costs or lower efficiencies, shares drop below 10% sharply. The analysis identifies some especially influential factors for achieving higher market relevance. Besides storage costs, the demand-orientation of a particular aboveground storage system (e.g., hydrogen storage at demand pressure levels) plays an essential role in market relevance. Further, overall efficiency can be a beneficial factor. Still, current projections of future techno-economic characteristics show that aboveground hydrogen storage is too expensive or too inefficient compared to underground storage. Therefore, to achieve notable market relevance, rather drastic cost reductions beyond current expectations would be needed for all assessed aboveground hydrogen storage technologies. [ABSTRACT FROM AUTHOR]

NaAlH 4 was melt infiltrated within a CO 2 activated carbon aerogel, which had been preloaded with TiCl 3 . Nanoconfinement was verified by Small Angle X-Ray Scattering (SAXS) and the nature of the Ti was investigated with Anomalous SAXS (ASAXS) and X-Ray Absorption Near Edge Structure (XANES) to determine its size and chemical state. The Ti is found to be in a similar state to that found in the bulk Ti-doped NaAlH 4 system where it exists as Al 1− x Ti x nanoalloys. Crystalline phases exist within the carbon aerogel pores, which are analysed by in-situ Powder X-Ray Diffraction (PXD) during hydrogen cycling. The in-situ data reveals that the hydrogen release from NaAlH 4 and its hydrogen uptake occurs through the Na 3 AlH 6 intermediate when confined at this size scale. The hydrogen capacity from the nanoconfined NaAlH 4 is found to initially be much higher in this CO 2 activated aerogel compared with previous studies into unactivated aerogels. [ABSTRACT FROM AUTHOR]

Highlights: [•] Nanoconfined 2LiBH4–MgH2–0.13TiCl4 was simply prepared by solution impregnation and melt infiltration. [•] Up to two times faster desorption kinetics as compared with nanoconfined 2LiBH4–MgH2. [•] Significant low onset dehydrogenation temperature (T= 140°C). [•] New reactive phase formations during de/rehydrogenation. [ABSTRACT FROM AUTHOR]

Abstract: Nanoconfinement of 2LiBH4–MgH2–TiCl3 in resorcinol–formaldehyde carbon aerogel scaffold (RF–CAS) for reversible hydrogen storage applications is proposed. RF–CAS is encapsulated with approximately 1.6 wt. % TiCl3 by solution impregnation technique, and it is further nanoconfined with bulk 2LiBH4–MgH2 via melt infiltration. Faster dehydrogenation kinetics is obtained after TiCl3 impregnation, for example, nanoconfined 2LiBH4–MgH2–TiCl3 requires ∼1 and 4.5 h, respectively, to release 95% of the total hydrogen content during the 1st and 2nd cycles, while nanoconfined 2LiBH4–MgH2 (∼2.5 and 7 h, respectively) and bulk material (∼23 and 22 h, respectively) take considerably longer. Moreover, 95–98.6% of the theoretical H2 storage capacity (3.6–3.75 wt. % H2) is reproduced after four hydrogen release and uptake cycles of the nanoconfined 2LiBH4–MgH2–TiCl3. The reversibility of this hydrogen storage material is confirmed by the formation of LiBH4 and MgH2 after rehydrogenation using FTIR and SR-PXD techniques, respectively. [Copyright &y& Elsevier]