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 O 2 activation remains elusive. Here, we synthesize cobalt azaphthalocyanine (CoAzPc) electrocatalysts with tunable energy levels via substituent engineering. The electron-donating CoAzPc-CH 3 exhibits superior ORR activity with a half-wave potential of 0.82 V (versus RHE) and only 12 mV decay after 5000 cycles. Mechanistic studies reveal that the -CH 3 substituent elevates the HOMO level, narrows the energy gap, and optimizes the Co-centered electronic environment. The strengthened dz 2 (Co)-π*(O 2 ) orbital interaction facilitates electron transfer, accelerates O 2 activation and weakens the O-O bond.