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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]

Various nanocrystalline and nano-amorphous Mg–Ni–RE (RE=rare earth or Y) alloys with attractive hydrogen storage properties were prepared by direct quenching of the melt and by crystallization of amorphous precursors. Varying the quenching rate, different microstructures could be obtained by melt-spinning. Having a knowledge of the mechanism and kinetics of the crystallization process, the devitrification of the amorphous samples could be carried out in a controlled way leading to nanocrystalline material.The hydrogenation kinetics and the H-storage capacity of amorphous, partially and completely nanocrystalline alloys were investigated and it was found that they are dependent on the microstructure and on the phase composition of the alloys. Therefore, the crystallization of the amorphous or nano-amorphous alloys was thoroughly studied, applying different experimental methods and approaches. The sequence of the crystal phases formation and the development of the alloys microstructure were investigated. Crystallization kinetics and mechanisms were determined as well. [Copyright &y& Elsevier]

Abstract: Nanocrystalline Mg powders of different particle size were obtained by inert gas evaporation and studied during electrochemical and gas-phase hydrogen cycling processes. The samples were compared to dehydrided samples obtained by mechanical milling of MgH2 with and without 2mol% Nb2O5 as catalyst. The hydrogen overpotential of the pure Mg, which is a measure of the hydrogen evolution at the electrode surface, was observed to be reduced with smaller particle sizes reaching values comparable to samples with Nb2O5 additive. On the other hand gas-phase charging experiments showed the capacity loss with smaller particle sizes due to oxidation effects. These oxidation effects are different depending on the synthesis method used and showed a major influence on the hydrogen sorption kinetics. [Copyright &y& Elsevier]