Opalka Susanne M, Løvvik Ole M, Brinks Hendrik W, Saxe Paul W, Hauback Bjørn C
United Technologies Research Center, East Hartford, Connecticut 06108, Centre for Materials Science and Nanotechnology, University of Oslo, N-0318 Oslo, Norway.
Inorg Chem. 2007 Feb 19;46(4):1401-9. doi: 10.1021/ic062032e.
First-principles modeling, experimental, and thermodynamic methodologies were integrated to facilitate a fundamentally guided investigation of quaternary complex hydride compounds within the bialkali Na-Li-Al-H hydrogen storage system. The integrated approach has broad utility for the discovery, understanding, and optimization of solid-state chemical systems. Density functional theory ground-state minimizations, low-temperature powder neutron diffraction, and low-temperature synchrotron X-ray diffraction were coupled to refine the crystallographic structures for various low-temperature distorted Na2LiAlH6 allotropes. Direct method lattice dynamics were used to identify a stable Na2LiAlH6 allotrope for thermodynamic property predictions. The results were interpreted to propose transformation pathways between this allotrope and the less stable cubic allotrope observed at room temperature. The calculated bialkali dissociation pressure relationships were compared with those determined from pressure-composition-isotherm experiments to validate the predicted thermodynamic properties. These predictions enabled computational thermodynamic modeling of Na2LiAlH6 and competing lower order phases within the Na-Li-Al-H system over a wide of temperature and pressure conditions. The predictions were substantiated by experimental observations of varying Na2LiAlH6 dehydrogenation behavior with temperature. The modeling was used to identify the most favorable reaction pathways and equilibrium products for H discharge/recharge in the Na-Li-Al-H system, and to design conditions that maximize the theoretical hydrogen reversibility within the Na-Li-Al-H system.
第一性原理建模、实验和热力学方法相结合，以便对双碱金属Na-Li-Al-H储氢体系中的四元复合氢化物进行基于基本原理的研究。这种综合方法在固态化学体系的发现、理解和优化方面具有广泛的应用价值。密度泛函理论基态最小化、低温粉末中子衍射和低温同步辐射X射线衍射相结合，以优化各种低温畸变的Na2LiAlH6同素异形体的晶体结构。直接方法晶格动力学用于确定一种稳定的Na2LiAlH6同素异形体，以进行热力学性质预测。对结果进行解释，以提出该同素异形体与室温下观察到的较不稳定立方同素异形体之间的转变途径。将计算得到的双碱金属离解压力关系与压力-组成-等温线实验确定的关系进行比较，以验证预测的热力学性质。这些预测使得能够在广泛的温度和压力条件下对Na2LiAlH6以及Na-Li-Al-H体系中竞争性的低阶相进行计算热力学建模。Na2LiAlH6脱氢行为随温度变化的实验观察证实了这些预测。该建模用于确定Na-Li-Al-H体系中H释放/再充注最有利的反应途径和平衡产物，并设计出使Na-Li-Al-H体系内理论氢可逆性最大化的条件。
