Search

• Determination of a reaction kinetic model of the de- / hydrogenation of recycled Mg based waste material. • Scaled-up hydrogenation experiments with in-house build autoclave at different temperature conditions. • Development of a validated simulation model that provides perfectly consistent results with experimental data. With the increased use of renewable energy sources, the need to store large amounts of energy will become increasingly important in the near future. A cost efficient possibility is to use the reaction of recycled Mg waste with hydrogen as thermo-chemical energy storage. Owing to the high reaction enthalpy, the moderate pressure and appropriate temperature conditions, the broad abundance and the recyclability, the Mg/Al alloy is perfectly suitable for this purpose. As further development of a previous work, in which the performance of recycled Mg/Al waste was presented, a kinetic model for hydro- and dehydrogenation is derived in this study. Temperature and pressure dependencies are determined, as well as the rate limiting step of the reaction. First experiments are carried out in an autoclave with a scaled-up powder mass, which is also used to validate the model by simulating the geometry with the scaled-up experiments at different conditions. [ABSTRACT FROM AUTHOR]

The Ca(BH4)2–Mg2NiH4 system presented here is, to the best of our knowledge, the first described Ca(BH4)2-based hydride composite that reversibly transfers boron from the Ca-based compound(s) to the reaction partner. The ternary boride MgNi2.5B2 is formed upon dehydrogenation and the formation of Ca(BH4)2 upon rehydrogenation is confirmed. [ABSTRACT FROM AUTHOR]

Lithium reactive hydride composite 2LiBH 4 + MgH 2 (Li-RHC) has been lately investigated owing to its potential as hydrogen storage medium for mobile applications. However, the main problem associated with this material is its sluggish kinetic behavior. Thus, aiming to improve the kinetic properties, in the present work the effect of the addition of Fe to Li-RHC is investigated. The addition of Fe lowers the starting decomposition temperature of Li-RHC about 30 °C and leads to a considerably faster isothermal dehydrogenation rate during the first hydrogen sorption cycle. Upon hydrogenation, MgH 2 and LiBH 4 are formed whereas Fe appears not to take part in any reaction. Upon the first dehydrogenation, the formation of nanocrystalline, well distributed FeB reduces the overall hydrogen storage capacity of the system. Throughout cycling, the agglomeration of FeB particles causes a kinetic deterioration. An analysis of the hydrogen kinetic mechanism during cycling shows that the hydrogenation and dehydrogenation behavior is influenced by the activity of FeB as heterogeneous nucleation center for MgB 2 and its non-homogenous distribution in the Li-RHC matrix. [ABSTRACT FROM AUTHOR]

Abstract: The hydrogenation behavior of 3CaH2+4MgB2+CaF2 composite was studied by manometric measurements, powder X-ray diffraction, differential scanning calorimetry and attenuated total reflection infrared spectroscopy. The maximum observed quantity of hydrogen loaded in the composite was 7.0wt%. X-ray diffraction showed the formation of Ca(BH4)2 and MgH2 after hydrogenation. The activation energy for the dehydrogenation reaction was evaluated by DSC measurements and turns out to be 162±15kJmol−1 H2. This value decreases due to cycling to 116±5kJmol−1 H2 for the third dehydrogenation step. A decrease of ca. 25–50°C in dehydrogenation temperature was observed with cycling. Due to its high capacity and reversibility, this composite is a promising candidate as a potential hydrogen storage material. [Copyright &y& Elsevier]

Abstract: The kinetics of the reversible reaction of hydrogen gas with magnesium forming MgH2 is enhanced significantly by the addition of transition metals oxide catalysts and by using nanostructured powders. Hydrogen absorption and desorption properties of such systems were studied by differential scanning calorimetry (DSC) under hydrogen atmosphere, from which the heat of hydride formation and decomposition is determined. Apart from Mg and stoichiometric MgH2, we find an additional, slightly destabilized phase, which is formed prior to MgH2 upon hydrogenation. The amount of this phase depends on the degree of nanostructuring and the used additive. X-ray diffraction measurements confirm the compared to MgH2 slightly different lattice parameters of the intermediate phase. The results correspond to recent neutron diffraction measurements, by which a new MgH2−δ phase was found. We propose that this destabilized phase acts as a gateway for de-hydrogenation of MgH2. [Copyright &y& Elsevier]

Abstract: Nanocrystalline Mg powder without and with 2mol% Nb2O5 catalyst was studied in a 6M KOH electrolyte as electrode material for electrochemical hydrogen charging processes. Since the hydrogen overpotential of Mg, which is a measure of the hydrogen evolution at the electrode surface, was observed to be reduced by the addition of Nb2O5, it is assumed that the catalyst influences the electrode reactions. Considering this assumption hydrogenation was studied at different current densities. The storage capacity as well as the kinetic of Mg/Nb2O5 electrodes increased significantly up to 1wt.% H2 at a charging time of 30min with decreasing current density. The storage capacity of nanocrystalline Mg powder showed only minor changes to lower hydrogen contents with decreasing current density. [Copyright &y& Elsevier]

Abstract: Nanocrystalline Mg powder without and with 2mol% Nb2O5 catalyst was studied as an electrode material for electrochemical hydrogen charging in a 6M KOH electrolyte. A strong influence of the compaction parameters, the current density and the catalyst on the hydrogenation behavior was observed. The addition of graphite and PTFE to the Mg/Nb2O5 electrodes improves the charging kinetics as well as the hydrogen content. The hydrogen contents achieved in Mg with Nb2O5, however, show a broad scatter. It was concluded that the catalyst distribution influences the upper limit of the storage capacity as well as the oxidation process at the surface during preparation. Since the addition of Nb2O5 was observed to reduce the hydrogen overpotential of Mg depending on the catalyst distribution, it is assumed that the catalyst influences the electrode reactions. Therefore, hydrogenation was investigated for different Nb2O5 distributions at different current densities in detail. [Copyright &y& Elsevier]