Proton Adsorption on Single-Atom Catalysts: Insights from Electrostatic Interaction Decomposition

Transition metal-anchored nitrogen-doped graphene single-atom catalysts have emerged as a versatile class of catalysts that combine the advantages of homogeneous and heterogeneous catalysis. The adsorption of a reactant on the single-atom catalyst is critical for predicting the catalytic performance across different reactions. In this work, we focus on the most fundamental adsorbate, the proton (H+), to understand the intrinsic adsorption properties of single-atom catalysts. Using (periodic) density functional theory, we have analyzed the trend in bonding interactions between H+ and period 4 transition metal-anchored nitrogen-doped graphene single-atom catalysts (TM = Ti, V, Cr, Mn, Fe, and Co). We find that the bond progressively weakens from Ti to Mn and then systematically strengthens again further along period 4, from Mn to Co. To elucidate these trends, we introduce a new electrostatic interaction decomposition scheme that distinguishes between contributions arising from the intrinsic electronic properties of the interacting fragments and those induced by geometric deformations along the adsorption process. These contributions are further decomposed into attractive (i.e., nucleus–electron attraction) and repulsive (i.e., nucleus–nucleus and electron–electron repulsion) components to establish the origin of trends in electrostatic interactions. The introduction of this scheme, together with the elucidated bonding trends, offers valuable insights for the rational design of next-generation single-atom catalysts.