Alapati Sudhakar V, Johnson J Karl, Sholl David S
Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
J Phys Chem B. 2006 May 4;110(17):8769-76. doi: 10.1021/jp060482m.
Hydrides of period 2 and 3 elements are promising candidates for hydrogen storage but typically have heats of reaction that are too high to be of use for fuel cell vehicles. Recent experimental work has focused on destabilizing metal hydrides through alloying with other elements. A very large number of possible destabilized metal hydride reaction schemes exist. The thermodynamic data required to assess the enthalpies of these reactions, however, are not available in many cases. We have used first principles density functional theory calculations to predict the reaction enthalpies for more than 100 destabilization reactions that have not previously been reported. Many of these reactions are predicted not be useful for reversible hydrogen storage, having calculated reaction enthalpies that are either too high or too low. More importantly, our calculations identify five promising reaction schemes that merit experimental study: 3LiNH(2) + 2LiH + Si --> Li(5)N(3)Si + 4H(2), 4LiBH(4) + MgH(2) --> 4LiH + MgB(4) + 7H(2), 7LiBH(4) + MgH(2) --> 7LiH + MgB(7) + 11.5H(2), CaH(2) + 6LiBH(4) --> CaB(6) + 6LiH + 10H(2), and LiNH(2) + MgH(2) --> LiMgN + 2H(2).
第2周期和第3周期元素的氢化物是很有前景的储氢候选物，但它们的反应热通常过高，无法用于燃料电池汽车。最近的实验工作集中在通过与其他元素合金化来使金属氢化物失稳。存在大量可能的失稳金属氢化物反应方案。然而，在许多情况下，评估这些反应焓所需的热力学数据并不存在。我们使用第一性原理密度泛函理论计算来预测100多个以前未报道的失稳反应的反应焓。预测这些反应中的许多对可逆储氢无用，计算出的反应焓要么过高要么过低。更重要的是，我们的计算确定了五个值得进行实验研究的有前景的反应方案：3LiNH₂ + 2LiH + Si → Li₅N₃Si + 4H₂、4LiBH₄ + MgH₂ → 4LiH + MgB₄ + 7H₂、7LiBH₄ + MgH₂ → 7LiH + MgB₇ + 11.5H₂、CaH₂ + 6LiBH₄ → CaB₆ + 6LiH + 10H₂以及LiNH₂ + MgH₂ → LiMgN + 2H₂。
