Meso‐Substituent Engineering Tunes Co‐OOH Binding in Cobalt Porphyrins for Selective H ₂ O ₂ Electrosynthesis

ABSTRACT

Cobalt porphyrins are prototypical molecular catalysts for two‐electron oxygen reduction to H ₂ O ₂ because of their well‐defined CoN ₄ active sites and synthetically tunable ligand frameworks. However, conventional phenyl‐substituted cobalt porphyrins generally exhibit limited H ₂ O ₂ selectivity due to excessively strong Co‐OOH chemisorption, which can favor O─O bond activation and the competing four‐electron oxygen reduction pathway. Herein, we establish a meso‐substituent engineering strategy to regulate Co‐OOH interaction in cobalt porphyrins without altering the primary CoN ₄ coordination motif. By progressively replacing meso‐phenyl groups with thienyl and bithienyl substituents, the optimized CoT ₂ TP catalyst achieves a H ₂ O ₂ Faradaic efficiency of 98.4% together with a H ₂ O ₂ production rate of 74.96 mg cm ⁻² h ⁻¹ at 120 mA cm ⁻² . In situ attenuated total reflection surface‐enhanced infrared absorption spectroscopy (ATR‐SEIRAS) reveals a continuous blue shift of the O─O stretching vibration of adsorbed *OOH with increasing thiophene incorporation, indicating weakened Co‐OOH chemisorption and facilitated Co─OOH bond cleavage. Density functional theory calculations further show that bithienyl substitution shifts the Co d‐band center away from the Fermi level and optimizes the *OOH adsorption strength. This work establishes remote meso‐substituent regulation of Co‐OOH binding as a molecular design strategy for selective H ₂ O ₂ electrosynthesis.