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The influence of additives on the reaction kinetics and for microstructure refinement in LiBH 4-MgH 2 composites is investigated in detail. Indications on the rate limiting processes during the reactions are obtained by comparison of the measured reaction kinetics to simulations with one specific rate limiting process. The kinetics of the sorption reactions are derived from volumetric measurements as well as from in-situ Xray diffraction (XRD) measurements. During desorption, the hydrogen is released at a constant rate, which possibly is correlated to the one-dimensional growth of MgB 2 platelets. In contrast, the kinetic curves of the absorption reactions exhibit the typical shape of contracting-volume controlled kinetics. The microscopical interpretation of kinetic measurements are supported by transmission electron microscopy (TEM) images confirming the formation of additive-nanostructures in the grain boundaries upon cycling. The present investigations underline the importance of the additives as nucleation substrates and the influence of the microstructure on the reaction kinetics.

A breakthrough in hydrogen storage technology was achieved by preparing nanocrystalline hydrides using high‐energy ball milling and the use of suitable catalysts/additives. These new materials show fast or in case of Mg‐based hydrides very fast absorption and desorption kinetics within minutes, thus qualifying lightweight Mg‐ or Al‐based hydrides for storage applications. This article summarizes our current understanding of the kinetics of Mg‐based light metal hydrides, describes an approach for a cost‐effective processing technology and highlights some promising new developments in lightweight metal hydride research.

NaAlH(4) is the archetypical complex hydride for hydrogen storage. The extraordinary effect of dopants on the sorption kinetics triggered the investigation of this empirical finding. In this paper, a short review of the state of the art is given. To gain further understanding of the mechanisms involved we label the interacting species during the sorption process. This was experimentally realized by hydrogen-deuterium exchange measurements during the decomposition of NaAlH(4) followed by thermogravimetry, Raman spectroscopy and mass spectrometry. By these experiments we are able to obtain specific information on the diffusing species and formation of intermediates. The activation energy of tracer diffusion in NaAlH(4) is found to be 0.28 eV. The results are evidence for a vacancy-mediated desorption process of NaAlH(4).

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