Unraveling the\nOrigin of the Repulsive Interaction\nbetween Hydrogen Adsorbates on Platinum Single-Crystal Electrodes

Hydrogen adsorption on platinum (Pt) single-crystal electrodes\nhas been studied intensively in both experiments and computations.\nYet, the precise origin and nature of the repulsive interactions observed\nbetween hydrogen adsorbates (H<sub>ads</sub>) have remained elusive.\nHere, we use first-principles density functional theory calculations\nto investigate in detail the interactions between H<sub>ads</sub> on\nPt(111), Pt(100), and Pt(110) surfaces. The repulsive interaction\nbetween H<sub>ads</sub> on Pt(111) is deconvoluted into three different\nphysical contributions, namely, (i) electrostatic interactions, (ii)\nsurface distortion effect, and (iii) surface coordination effect.\nThe long-range electrostatic interaction, which is generally considered\nthe most important source of repulsive interactions in surface adsorption,\nwas found to contribute less than 30% of the overall repulsive interaction.\nThe remaining >70% arises from the other two contributions, underscoring\nthe critical influence of surface-mediated interactions on the adsorption\nprocess. Surface distortion and coordination effects are found to\nstrongly depend on the coverage and adsorption geometry: the effect\nof surface distortion dominates when adsorbates reside two or more\nPt atoms apart; the effect of surface coordination dominates if hydrogen\nis adsorbed on neighboring adsorption sites. The above effects are\nconsiderably less pronounced on Pt(100) and Pt(110), therefore resulting\nin weaker interactions between H<sub>ads</sub> on these two surfaces.\nOverall, the study highlights the relevance of surface-mediated effects\non adsorbate–adsorbate interactions, such as the often-overlooked\nsurface distortion. The effect of these interactions on the hotly\ndebated adsorption site for the adsorbed hydrogen intermediate in\nthe hydrogen evolution reaction is also discussed.