First-principles study of Ti-doped sodium alanate surfaces

TL;DR

This study uses first-principles calculations to investigate how titanium dopes sodium alanate surfaces, revealing Ti's surface preference, its substitution behavior, and its role in forming H-rich compounds that enhance reaction kinetics.

Contribution

It provides new insights into Ti's surface behavior and its mechanism for improving sodium alanate's hydrogen storage properties.

Findings

Ti prefers to stay on the surface and substitutes for Na.

Ti attracts a large number of H atoms near its vicinity.

Formation of H-rich TiAl_n compounds on the surface enhances reaction kinetics.

Abstract

We have performed first-principles calculations of thick slabs of Ti-doped sodium alanate (NaAlH_4), which allows to study the system energetics as the dopant progresses from the surface to the bulk. Our calculations predict that Ti stays on the surface, substitutes for Na, and attracts a large number of H atoms to its vicinity. Molecular dynamics simulations suggest that the most likely product of the Ti-doping is the formation of H-rich TiAl_n (n>1) compounds on the surface, and hint at the mechanism by which Ti enhances the reaction kinetics of NaAlH_4.