First-Principles Study of Ti-Catalyzed Hydrogen Chemisorption on an Al Surface:  A Critical First Step for Reversible Hydrogen Storage in NaAlH₄

Abstract

Complex metal hydrides are perhaps the most promising hydrogen storage materials for a gradual transformation to a hydrogen-based economy. We have used a computational approach to aid the ongoing experimental effort to understand the reversible hydrogen storage in Ti-doped NaAlH(4) and propose a plausible first step in the rehydrogenation mechanism. The study provides insight into the catalytic role played by the Ti atoms on an Al surface in the chemisorption of molecular hydrogen and identifies the local arrangement of the Ti atoms responsible for the process. Our results can potentially lead to ways of making other similar metal hydrides reversible.

Vacancy mediated desorption of hydrogen from a sodium alanate surface: An ab initio spin-polarized study

“…The role of Ti dopant in the latter case has been recently identified as catalytic role on Al surface in the chemisorption of molecular hydrogen. 40 Here we have demonstrated that two Al-H bond lengths will become elongated and weakened due to the presence of a Na vacancy on the NaAlH 4 ͑001͒ surface. Spontaneous recombination from the surface to form molecular hydrogen is observed in the spin-polarized ab initio molecular dynamics simulation.…”

Catalytic effect of near-surface alloying on hydrogen interaction on the aluminum surface

“…13,17 TiAl 3 has two possible structures: cubic L1 2 and tetragonal D0 22 . 19 We will examine Ti positions following both arrangements near an Al(001) surface.…”

“…We do not find any favorable active Ti sites on the surface as considered in previous studies. 13,22,23 The result is understandable since the Al surface has a lower surface energy than the Ti surface, so exposing Ti atoms raises the energy. A surface reconstruction induced by the presence of Ti in the topmost surface layer was proposed in Ref.…”

From the computer to the laboratory: materials discovery and design using first-principles calculations

“…In two papers [168,169], Chaudhuri and Chopra et al demonstrated that aluminum doped with very small amounts of Ti can activate molecular H 2 at temperatures as low as 90 K. In the earlier work, Chaudhuri et al showed using first-principles techniques that a particular local arrangement of Ti atoms is responsible for catalyzing the chemisorption of molecular hydrogen on TiAl surfaces. The subsequent work by Chopra et al published 6 years later extended the earlier first-principles calculations.…”