The Key Role of Competition between Orbital and Electrostatic Interactions in the Adsorption on Transition Metal Single‐Atom Catalysts Anchored by N‐doped Graphene

Rational design of single‐atom catalyst (SAC) presents a promising route to precise heterogeneous catalysis, yet it requires us to understand the catalytic activity that often can be correlated with the adsorption energies. Here, we investigate the hydrogen adsorption on a series of 3d transition metal (TM) SACs anchored on the N4‐coordination site of N‐doped graphene (MN4/C), and find that the adsorption energies present a volcano curve that violates the d‐band theory. By decomposing the adsorption energies into two distinctive contributions, i. e., the orbital interaction (ΔEorbit ) and electrostatic interaction (ΔEelstat ), we find that it is the competition between the two that results in the volcano curve. We further identify that the trend of ΔEorbit is dictated by the TM 4 s orbital that is governed by bonding with the substrate, while ΔEelstat is regulated by the charge transfer from TM single‐atom to the N4/C substrate, which originates mainly from the bonding between the TM 3dxy orbital and the substrate. Furthermore, we establish the intrinsic dipole moment of active site as a quantitative descriptor for both ΔEorbit and ΔEelstat in the adsorption on MN4/C, and apply it to understanding the trends of adsorption energies on 4d and 5d TM‐based MN4/C SACs. Our findings provide deep insights into understanding the adsorption and thus the catalytic activity on TM‐based SACs. Adsorption on single‐atom catalyst: The adsorption energies of the hydrogen atom on the MN4/C single‐atom catalysts present a volcano curve that violates the d‐band theory, and it arises from the competition between the orbital (ΔEorbit ) and electrostatic (ΔEelstat ) interactions. The intrinsic dipole moment of active site is found to be a quantitative descriptor of the competition and thus the adsorption trend.