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

A small amount of catalyst, such as Ti, was found to greatly improve the kinetics of hydrogen reactions in the prototypical hydrogen storage compound sodium alanate (NaAlH₄). We propose a near-surface alloying mechanism for the rehydrogenation cycle based on a 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.