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First-Principles Study of the Li-Na-Ca-N-H System: Compound Structures and Hydrogen-Storage Properties


With the goal of finding new materials as a resource for alternative energy, various classes of hydrogen storage materials have been developed. One of the possible candidates is solid-state metal amide/imide. These chemically bounded solid-state materials will release hydrogen when heated and rehydrogenate upon an increase in pressure. Therefore, this practical requirement limits the operating temperature to between -40 to 80 °C and the pressure to between 1 to a few hundred bars. The main goal is to find new metal amide/imide materials within these specified thermodynamics ranges. Note that normally not only the thermodynamics but kinetics properties are also crucial. While a kinetics study would tell how fast hydrogen can be released and absorbed, this research focuses on the thermodynamics part only.

First-principle calculations are useful tools for predicting new materials structures and exploring hydrogen-released reactions. Since density functional theory (DFT) can provide the accuracy as small as quantum-mechanical level, it is used to calculate properties of these amide/imide materials. Other tools used in this research include: prediction of ground-state structures of some amide/imide materials has been explored by electrostatics-based calculation (PEGS), Grand Canonical Linear Programming Method (GCLP) is used to calculate allowed hydrogen-released reactions under the specified thermodynamics range, and zero-point vibrational energy is calculated by phonons calculations.

Here, all known and predicted crystal structures of materials in the Li-Na-Ca-N-H system are investigated in order to find the allowed hydrogen-released reactions.

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