Ozolins V, Majzoub E H, Wolverton C
Department of Materials Science and Engineering, University of California, Los Angeles, California 90095-1595, USA.
J Am Chem Soc. 2009 Jan 14;131(1):230-7. doi: 10.1021/ja8066429.
Introduction of economically viable hydrogen cars is hindered by the need to store large amounts of hydrogen. Metal borohydrides [LiBH(4), Mg(BH(4))(2), Ca(BH(4))(2)] are attractive candidates for onboard storage because they contain high densities of hydrogen by weight and by volume. Using a set of recently developed theoretical first-principles methods, we predict currently unknown crystal structures and hydrogen storage reactions in the Li-Mg-Ca-B-H system. Hydrogen release from LiBH(4) and Mg(BH(4))(2) is predicted to proceed via intermediate Li(2)B(12)H(12) and MgB(12)H(12) phases, while for Ca borohydride two competing reaction pathways (into CaB(6) and CaH(2), and into CaB(12)H(12) and CaH(2)) are found to have nearly equal free energies. We predict two new hydrogen storage reactions that are some of the most attractive among the presently known ones. They combine high gravimetric densities (8.4 and 7.7 wt % H(2)) with low enthalpies [approximately 25 kJ/(mol H(2))] and are thermodynamically reversible at low pressures due to low vibrational entropies of the product phases containing the B(12)H(12) anion.
经济上可行的氢动力汽车的推广受到大量氢气储存需求的阻碍。金属硼氢化物（LiBH₄、Mg(BH₄)₂、Ca(BH₄)₂）是车载储存的有吸引力的候选材料，因为它们按重量和体积计算都含有高密度的氢。使用一组最近开发的理论第一性原理方法，我们预测了Li-Mg-Ca-B-H系统中目前未知的晶体结构和储氢反应。预计LiBH₄和Mg(BH₄)₂释放氢是通过中间相Li₂B₁₂H₁₂和MgB₁₂H₁₂进行的，而对于硼氢化钙，发现两条相互竞争的反应途径（生成CaB₆和CaH₂，以及生成CaB₁₂H₁₂和CaH₂）具有几乎相等的自由能。我们预测了两个新的储氢反应，它们是目前已知反应中最具吸引力的一些反应。它们结合了高重量密度（8.4和7.7 wt% H₂）和低焓[约25 kJ/(mol H₂)]，并且由于含有[B₁₂H₁₂]²⁻阴离子的产物相的低振动熵，在低压下是热力学可逆的。
