Electronic Structure and Orbital Filling in 2D YCl Electride Single-Atom Catalysts: A Combined First-Principles and Machine-Learning Study

Two-dimensional (2D) electrides host excess electrons in interstitial spaces, referred to as interstitial anionic electrons (IAEs). This unique electronic structure provides opportunities to tailor the properties of single-atom catalysts (SACs), in which electron configuration plays a critical role. However, the influence of the IAE layer in 2D electrides on SACs remains largely unexplored. Here, we employ first-principles density functional theory and machine-learning study to investigate single atoms adsorbed on a 2D YCl electride, a representative 2D electride with van der Waals–stacked layers. Transition metals adsorbed on YCl exhibit significant charge transfer with the IAEs. The relationship between the valence electron numbers of the adsorbed metal ( V M ) and the adsorbed intermediates ( V A ) can be partially rationalized by the ten-electron count rule, with O- and N-based adsorbates closely following this rule, whereas C and H exhibit noticeable deviations. Adsorption of different transition metals on YCl effectively modulates the spatial distribution of IAEs, thereby tuning the catalytic behavior of the resulting SACs. Several single-atom dopants on YCl create favorable hydrogen adsorption sites, indicating their potential for the hydrogen evolution reaction.