Hydrogen adsorption and subsurface absorption on (Formula presented) : Atomic-scale insights toward efficient and stable HER catalysts

The adsorption and diffusion of hydrogen on Ni(001) surfaces were studied using density functional theory (DFT). Three adsorption sites were considered: top, bridge, and hollow. Hollow sites are the most stable for atomic hydrogen (with an adsorption energy of (Formula presented), when van der Waals interactions are considered), followed by bridge sites (with (Formula presented) ), while top sites are unfavorable (with (Formula presented) ). For molecular hydrogen, perpendicular orientations lead to desorption, whereas parallel orientations promote dissociation into hollow sites. Nudged Elastic Band (NEB) calculations yield a low diffusion barrier ((Formula presented) ), indicating efficient hydrogen mobility on the surface. At high coverages, simultaneous occupation of hollow and bridge sites pushes hydrogen inward, suggesting the onset of subsurface absorption. These results clarify the atomistic mechanisms of hydrogen interaction with (Formula presented) and provide insight into the catalytic behavior and stability of nickel-based electrodes for the hydrogen evolution reaction.