Single-Atom Saturation:A Fundamental Principle forSingle-Atom-Site Catalyst Design

Single-atom alloys (SAAs), with twin advantages of alloys and single-atom catalysts, have emerged as an innovative class of electrocatalysts. This uniqueness is expected to achieve unattainable catalytic performance but simultaneously gives rise to the absence of guidelines for designing desired SAAs. Herein, we proposed a fundamental principle, single-atom saturation (<i>S</i>_SA), to quantify the binding strength of different intermediates on SAAs, enabling the rapid and qualitative evaluation of the catalytic activity across various reactions. <i>S</i>_SA is rationalized by combining the variation of electronic structure (<i>d</i> electron occupancy saturation) and geometrical structure (coordination saturation) of the single guest atom as well as the effect of the host atom type and the intermediate adsorption configuration. Based on the insights given by <i>S</i>_SA, Pd₁Cu(111), Ru₁Cu(111), Ir₁Ag(111), Pt₁Ag(111), and Pt₁Cu(111) are predicted to possess excellent activity for CO₂ reduction, N₂ reduction, O₂ evolution, O₂ reduction, and H₂ evolution reactions, respectively, most of which are supported by reported experiments. Moreover, <i>S</i>_SA is also applicable to nitrogen-doped graphene-supported single-atom catalysts (SACs) with ultrahigh accuracy. In general, single-atom saturation is a concise, interpretable, and universal descriptor that deciphers the structure–activity relation of SAAs across various reactions, where the insights revealed also offer a simple and fundamental principle for the design of excellent single-atom-site catalysts.