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

Abstract

A small amount of catalyst, such as Ti, was found to greatly improve the kinetics of hydrogen reactions in the prototypical hydrogen storage compound NaAlH4. We propose a near-surface alloying mechanism for the rehydrogenation cycle based on detailed analysis of available experimental data as well as first-principles calculations. The calculated results indicate that the catalyst remains at subsurface sites near the Al surface, reducing the dissociation energy barrier of H2. The binding between Ti and Al modifies the surface charge distribution, which facilitates hydrogen adsorption and enhances hydrogen mobility on the surface.

Improvement of the hydrogen storage kinetics of NaAlH4 with nanocrystalline titanium dioxide loaded carbon spheres (Ti-CSs) by melt infiltration

“…8(c), while the Ti species are always detected from the EDS spectra of three samples (not shown here). So we believe that nanocrystalline TiO 2 and/or amorphous phase TieAl clusters, as the active species for NaAlH 4 , remain at the subsurface sites of the surface due to binding between Ti and Al near the Al surface, reducing the dissociation energy barrier of H 2 , which is agreement with the theory calculation results [33].…”

Thermodynamic stability of transition metals on the Mg-terminatedMgB2(0001) surface and their effects on hydrogen dissociation and diffusion

“…Many processes could impair the kinetic rates, such as nucleation, defect diffusion, and H 2 dissociation and diffusion at surfaces. Previous theoretical studies demonstrated that computational methods can be applied in the study of kinetic process for various hydrogen storage systems [26][27][28][29][30][31][32][33][34][35][36]), and some systems (such as AlH 3 and MgH 2 ) were reported to have undesired H 2 dissociation barriers which may hinder the reaction process [26][27][28][29][37][38][39]. Thus, as an initial stage to examine the kinetic process for MgB 2 hydrogenation and find out the possible rate limiting processes, we studied hydrogen dissociation and diffusion on MgB 2 surface in this work (and hydrogen diffusion in bulk MgB 2 in a separate paper [40]).…”

Alanates, a Comprehensive Review

“…Wang et al remind us, in favor of this role of subsurface Ti, that metallic aluminum does not absorb diatomic hydrogen from the gas phase by itself. Meanwhile, atomic hydrogen strongly reacts with aluminum surfaces to form alanes [142]. Thus, subsurface Ti would promote H 2 dissociation and enhance H mobility and adsorption [142].…”

“…Meanwhile, atomic hydrogen strongly reacts with aluminum surfaces to form alanes [142]. Thus, subsurface Ti would promote H 2 dissociation and enhance H mobility and adsorption [142]. These effects constitute essentially the “hydrogen pump” action mechanism that was proposed for Ti [134].…”