Effects of proton management substituents on asymmetrical iron porphyrin-based electrocatalyst for oxygen reduction reactions

Two asymmetric porphyrins, FePor-Th and FePor-ThCA , were synthesized to investigate the effect of proton management on electrocatalytic oxygen reduction reaction (ORR) performance. Introducing a carboxylic acid group in FePor-ThCA does not alter the energy band gap (2.78 eV) as compared to FePor-Th , confirmed by the density functional theory (DFT) calculations. Carbon nanotubes were used as the support materials to construct composites, and both electrocatalysts demonstrated a preference for the four-electron route under alkali conditions, as revealed by a series of electrochemical evaluations. FePor-ThCA/CNT exhibited an onset potential of 0.86 V vs. RHE, a half-wave potential of 0.68 V vs.RHE, and a current density of 5.22 mA cm –2 , surpassing its counterpart. It is proposed that the carboxylic acid group may facilitate proton transfer, along with electron transfer, at the FePor-ThCA/CNT interface, thereby reducing the charge transfer resistance and enhancing ORR activity.