A Theoretical Understanding of both Activity and Stability Promotion of NiFe-Based OER Catalysts via 3d-2p-4f Orbital Hybridization.

The development of oxygen evolution reaction (OER) electrocatalysts is constrained between catalytic activity and structural stability. Herein, we develop an orbital hybridization strategy to simultaneously enhance both the activity and stability of catalysts. We study a samarium (Sm)-doped NiFe layered double hydroxide (NiFe-LDH) catalyst using density functional theory (DFT), where Sm is incorporated into the NiFe-LDH framework to form Transition Metals-Oxygen-Rare-Earth (TM-O-RE) structural units. This configuration facilitates hybridization among Sm 4f, O 2p, and metal (Ni/Fe) 3d orbitals, promoting charge delocalization and spin reconfiguration, which endows the catalyst with dual functionalities. First, by increasing the eg orbital occupancy at Ni sites, the adsorption energies of key OER intermediates are optimized, enhancing the adsorption affinity for the rate-determining intermediate *OH and reducing the theoretical overpotential from 1.01 to 0.52 V. Second, the introduced hybridization strengthens the covalency of the Fe-O bonds while mitigating electron depletion at Fe sites during the catalytic cycle. By buffering electron loss at Fe active centers and reinforcing Fe-O bond covalency, the energy barrier for Fe dissolution is increased by 0.74 eV, thereby thermodynamically stabilizing the structure. This work provides theoretical guidance for exploiting rare-earth f-electron chemistry as a bifunctional promoter in OER electrocatalysts.