Hierarchical High-Throughput Screening of the Ligand Effect of Electrocatalytic Oxygen Reduction on Dual-Metal Atomic Catalysts (M₁M₂N₆-R): A First-Principles Study

The design of low-cost and high-activity oxygen reduction catalysts on the cathode is important to improve the conversion efficiency in proton exchange membrane fuel cells. A series of nonprecious 3d-TM-combined M1M2N6/C candidates are constructed within high-throughput screening to find out high-efficient oxygen reduction reaction (ORR) catalysts through axially coordinating with 13 kinds of potentially accompanied ligands by first-principles calculation. Among the fabricated 55 pristine M1M2N6 structures, some pre-3d metals (d(e) <= 5) of Sc-, Ti-, and V-contained M1M2N6/C are excluded due to poor ORR activities with too low negative limiting potentials (U-L) values (U-L < -1.0 V). The screening results of three common ligands (R = -OH, -F, and -NH2) coordination indicate that axial ligand modification could significantly enlarge the U-L of M1M2N6-R. A volcano relationship between U-L and Delta G of OH* intermediate is helpful to select four excellent ORR candidates of NiNi-, CoNi-, FeCo-, and CoCo-combinations to further perform 10 kinds of axial ligand engineering. More applicable ligands of -CO, -COH, -NH, -NO, -Cl, and -CH2 are identified to enhance ORR activity for certain pristine M1M2N6 catalysts. Totally, 16 different candidates exhibit good ORR activity with U-L > 0.80 V of Pt(111) by ligand modification screening. The increased moderate positive charge on central metals is ascribed to the weakened interaction between catalysts and OH* in *OH-intermediates. Our work provides valuable insights into understanding ligand engineering on dual-metal catalysts, which is helpful for designing highly efficient, nonprecious single-atom catalysts by tuning the metal bonding environment.