The activity origin of two-dimensional MN4-contained periodical macrocyclic structures towards electro-catalytic hydrogen evolution

The two-dimensional MN4-contained periodical macrocyclic structures (2D MN4/PMCs) have been extensively explored as single atom catalysts through both experimental and theoretical approaches. However, there still lacks deep understanding on the effect of the outer coordination environment in determining the catalytic activity of the inner MN4 center. Combining the density functional theory (DFT) calculations and machine learning (ML) algorithm, we computationally unraveled the origin of electro-catalytic activity of five kinds of 2D MN4/PMCs towards hydrogen evolution reaction (HER). With hydrogen adsorption free energy (ΔG_H*) as the indicator for HER catalytic activity, the IrPpor and RhPPpz are screened out as superior HER electrocatalysts based on the DFT calculations. Furthermore, ML studies generated the universal descriptor Φ that highly depends on charge assigned on the metal center (q) and the d-band center of central metal (ε_d), which is reversely proportional to ΔG_H*. The dependence of q and ε_d on the structural parameters of MN4/PMCs is further unraveled, demonstrating how the outer framework determines catalytic activity of 2D MN4/PMCs.