Ligand Regulated the Coordination Environment of Cobalt-Group-MOF for Efficient Electrocatalytic Oxygen Reduction/Evolution Catalysis

In recent years, the TMN₄ moieties have demonstrated significant catalytic activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in graphene, CxNy, and other carbon-based two-dimensional (2D) support materials. Modifying the coordination number and species of N atoms in the TMN₄ moieties has proven to be an effective approach to regulate their catalytic activity. In this research, by incorporating different triphenylene ligands, we have successfully constructed TMA₂B₂ (TM = Co, Rh, Ir; A/B = N, O, S, Se) moieties with varying coordination environments within 2D metal organic frameworks (MOFs), which are linked by TM and triphenylene. These moieties serve as an effective model to elucidate the structure-property relationship of two-dimensional 2D-MOFs in OER and ORR. Our findings confirm that alterations in the coordination environment can finely tune the <i>d</i>-band electron distribution of the TM within the TMA₂B₂ unit, particularly activating the <i>d</i>_<i>yz</i> and <i>d</i>_z² orbitals of O₂, thereby influencing the interactions between TM and key intermediates. We discovered that the regulatory effect of the coordination environment is closely linked to the electronegativity of the coordinating atoms, which led us to establish reliable descriptors such as φ₁ and φ₂ to elucidate the impact of coordination environments on the performance of OER/ORR. This criterion can be applied to numerous other 2D-MOFs and provides an in-depth understanding of the structure-activity relationship facilitates the development of highly efficient bifunctional electrocatalysts for OER and ORR applications.