Frontier orbital tailoring promotes electron transfer for accelerated oxygen activation in cobalt azaphthalocyanine

Abstract

Molecular catalysts with well-defined coordination structures hold great promise for the oxygen reduction reaction (ORR), yet the role of orbital-level electronic regulation during O₂ activation remains elusive. Here, we synthesize cobalt azaphthalocyanine (CoAzPc) electrocatalysts with tunable energy levels VIA substituent engineering. The electron-donating CoAzPc–CH₃ exhibits superior ORR activity with a half-wave potential of 0.82 V vs. RHE (RHE: Reversible Hydrogen Electrode) and only 12 mV decay after 5000 cycles. Mechanistic studies reveal that the –CH₃ substituent elevates the HOMO level, narrows the energy gap, and optimizes the Co-centered electronic environment. The strengthened dz²(Co)–π*(O₂) orbital interaction facilitates electron transfer, accelerates O₂ activation and weakens the O–O bond.