Chemistry

Sorting Storage Options

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Science  23 Mar 2007:
Vol. 315, Issue 5819, pp. 1638-1639
DOI: 10.1126/science.315.5819.1638d

In the search for a practical mode of hydrogen storage for vehicle applications, light metal hydride compounds such as LiBH4 are appealing because of their high weight percentage of hydrogen. However, many such compounds are thermodynamically quite stable, and so require excessive heating to liberate H2. One means of addressing this problem is to mix together two or more hydride compounds which, on releasing hydrogen, can form a stable co-product that drives the reaction—MgH2, for example, reacts with LiBH4 to yield MgB2. Alapati et al. have used plane wave density functional theory in an effort to narrow the dauntingly large range of potential compound combinations worth exploring in this vein. Specifically, they performed a rough energy calculation of 152 known light metal solids and used the results to screen more than 300 unreported possible reactions among them. Thirteen reactions that fell within a promising range of enthalpies (including a lower as well as upper bound, so as to ensure feasible rehydrogenation of the material) were then subjected to more computationally intensive phonon density-of-states calculations. The authors note that their approach is limited by the assumption of reaction to a known morphology and also leaves open the question of favorable kinetics. Nonetheless, computed enthalpies of known reactions proved sufficiently accurate (within 10 kJ/mol of experiment) to offer a promising preliminary sifting mechanism for guiding future experiments. — JSY

Phys. Chem. Chem. Phys. 9, 10.1039/b617927d (2007).

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