Hydrogen Dissociation and Diffusion on Transition Metal(=Ti,Zr,V,Fe,Ru,Co,Rh,Ni,Pd,Cu,Ag)-doped Mg(0001) Surfaces

TL;DR

This study uses ab-initio density functional theory to analyze how different transition metal dopants on Mg(0001) surfaces affect hydrogen dissociation and diffusion, identifying Ni as the optimal dopant for fast hydrogen absorption.

Contribution

It systematically evaluates the effects of various transition metal dopants on Mg surfaces, revealing the dopants that optimize hydrogen dissociation and diffusion processes.

Findings

Doping with early transition metals eliminates H$_2$ dissociation barriers but hinders diffusion.

Late transition metals do not significantly reduce dissociation barriers.

Ni doping offers the best combination of low barriers for both dissociation and diffusion.

Abstract

The kinetics of hydrogen absorption by magnesium bulk is affected by two main activated processes: the dissociation of the H$_2$ molecule and the diffusion of atomic H into the bulk. In order to have fast absorption kinetics both activated processed need to have a low barrier. Here we report a systematic ab-initio density functional theory investigation of H$_2$ dissociation and subsequent atomic H diffusion on TM(=Ti,V,Zr,Fe,Ru,Co,Rh,Ni,Pd,Cu,Ag)-doped Mg(0001) surfaces. The calculations show that doping the surface with TM's on the left of the periodic table eliminates the barrier for the dissociation of the molecule, but the H atoms bind very strongly to the TM, therefore hindering diffusion. Conversely, TM's on the right of the periodic table don't bind H, however, they do not reduce the barrier to dissociate H$_2$ significantly. Our results show that Fe, Ni and Rh, and to some extent Co and Pd, are all exceptions, combining low activation barriers for both processes, with Ni being the best possible choice.