Location-dependent effect of nickel on hydrogen dissociation and diffusion on Mg (0001) surface: Insights into hydrogen storage material design

Density functional theory (DFT) calculations have been performed to investigate the hydrogen dissociation and diffusion on Mg (0001) surface with Ni incorporating at various locations. The results show that Ni atom is preferentially located inside Mg matrix rather than in/over the topmost surface. Further calculations reveal that Ni atom locating in/over the topmost Mg (0001) surface exhibits excellent catalytic effect on hydrogen dissociation with an energy barrier of less than 0.05 eV. In these cases, the rate-limiting step has been converted from hydrogen dissociation to surface diffusion. In contrast, Ni doping inside Mg bulk not only does little help to hydrogen dissociation but also exhibits detrimental effect on hydrogen diffusion. Therefore, it is crucial to stabilize the Ni atom on the surface or in the topmost layer of Mg (0001) surface to maintain its catalytic effect. For all the case of Ni-incorporated Mg (0001) surfaces, the hydrogen atom prefers firstly immigrate along the surface and then penetrate into the bulk. It is expected that the theoretical findings in the present study could offer fundamental guidance to future designing on efficient Mg-based hydrogen storage materials. (c) 2021 Chongqing University. Publishing services provided by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ) Peer review under responsibility of Chongqing University

Automated summary

This study performed Density Functional Theory (DFT) calculations to investigate the hydrogen dissociation and diffusion on the Mg (0001) surface with Ni incorporation at different locations. The results revealed that the Ni atom prefers to locate inside the Mg matrix rather than on or over the topmost surface. Further calculations showed that the Ni atom located on or over the topmost Mg (0001) surface exhibits an excellent catalytic effect on hydrogen dissociation with a low energy barrier. However, Ni doping inside the Mg bulk not only has little effect on hydrogen dissociation but also hinders hydrogen diffusion. Therefore, stabilizing the Ni atom on the surface or in the topmost layer of the Mg (0001) surface is crucial to maintain its catalytic effect. For all the cases of Ni-incorporated Mg (0001) surfaces, the hydrogen atom prefers to migrate along the surface before penetrating into the bulk. It is expected that the theoretical findings in this study can provide fundamental guidance for the future design of efficient Mg-based hydrogen storage materials.