Multi-phonon scattering and Ti-induced hydrogen dynamics in sodium alanate

TL;DR

This study combines ab initio calculations and neutron scattering to explore how Ti doping affects hydrogen dynamics in sodium alanate, revealing Ti's role in bond breaking and potential for improved hydrogen storage.

Contribution

It demonstrates that substitutional Ti doping is energetically feasible and influences hydrogen bond dynamics, offering new insights into enhancing alanate-based hydrogen storage.

Findings

Ti prefers to substitute for Na in NaAlH_4.

Neutron scattering shows strong two-phonon features.

Ti acts as a hydrogen attractor facilitating bond breaking.

Abstract

We use ab initio methods and neutron inelastic scattering (NIS) to study the structure, energetics, and dynamics of pure and Ti-doped sodium alanate (NaAlH_4), focusing on the possibility of substitutional Ti doping. The NIS spectrum is found to exhibit surprisingly strong and sharp two-phonon features. The calculations reveal that substitutional Ti doping is energetically possible. Ti prefers to substitute for Na and is a powerful hydrogen attractor that facilitates multiple Al--H bond breaking. Our results hint at new ways of improving the hydrogen dynamics and storage capacity of the alanates.