Structure–Activity Relationships in Phloroglucinol‐Bridged Binuclear Versus Mononuclear Iron/Cobalt Phthalocyanine Electrocatalysts for the Oxygen Reduction Reaction: A Combined Experimental and Computational Investigation

ABSTRACT

Iron and cobalt phthalocyanines (FePc and CoPc) rank among the most promising non‐precious metal electrocatalysts for the oxygen reduction reaction (ORR), yet a systematic structure–activity comparison combining experimental and computational approaches remains lacking. This study examines how peripheral nitro substitution combined with a phloroglucinol bridging ligand modulates ORR activity in FeTNPc and CoTNPc in 0.1 M KOH. Rotating disk electrode (RDE) measurements showed that heteronuclear Fe–Co bridge coordination shifted the ORR pathway of FePc toward the ideal 4‐electron process ( n = 3.79, versus a more mixed‐pathway response for the monomers, particularly CoTNPc), while anodically shifting the onset potential by up to 40 mV relative to monomeric FeTNPc and CoTNPc. X‐ray photoelectron spectroscopy (XPS) and UV–Vis spectroscopy corroborated the predicted redistribution of electron density at the metal centers. Critically, density functional theory (DFT) calculations of O ₂ adsorption free energy correlated quadratically with experimental half‐wave potentials ( R ² = 0.997), and the Fe dz ² orbital energy emerged as a reliable electronic descriptor of activity, with nitro‐substituted bimetallic FeCoPc exhibiting a narrow HOMO–LUMO gap (∼1.05 eV). These findings establish an orbital‐energy‐guided design rule for tailoring phthalocyanine electrocatalysts, offering a route to reduce PEMFC reliance on platinum‐group metals.