Ligand π‐Conjugation Area Modulates Hydrogen Evolution Performance in Metal–Organic Frameworks

ABSTRACT

Metal–organic frameworks (MOFs) combine permanent porosity, tunable compositions, ordered structures, and well‐defined coordination environments, making them versatile platforms for electrocatalyst design. Although ligand engineering has been widely explored for the hydrogen evolution reaction (HER), few studies have treated ligand π‐conjugation area as a defined molecular variable and systematically examined its relationship with HER performance. Here, we use a conjugated‐ligand engineering strategy to systematically vary ligand π‐conjugation area while maintaining comparable metal coordination environments. Pyromellitic dianhydride (PMDA), naphthalene‐1,4,5,8‐tetracarboxylic dianhydride (NTDA), and perylene‐3,4,9,10‐tetracarboxylic dianhydride (PTCDA), featuring benzene‐, naphthalene‐, and perylene‐based aromatic cores with 6, 10, and 20 π electrons, respectively, are used as precursors to the corresponding tetracarboxylate ligands to construct related Ni‐ and Co‐based MOFs with six‐coordinate metal centers. Across both metal series, increasing ligand π‐conjugation area consistently lowers overpotentials and Tafel slopes, decreases charge‐transfer resistance and mass‐transport‐related impedance, and increases electrochemically active surface area. This systematic ligand variation is accompanied by metal‐center binding‐energy shifts and bandgap narrowing. These results establish a clear structure–performance relationship between ligand π‐conjugation area and HER performance across the investigated MOF series, highlighting conjugated‐ligand engineering as an effective strategy for MOF electrocatalyst design.