Revealing Significant Electronic Effects on the Oxygen Reduction Reaction with Iron Porphyrins

Understanding electronic effects on catalysis from a mechanism point of view is of fundamental significance but is also challenging. We herein report on electronic effects on the oxygen reduction reaction (ORR) with Fe porphyrins. By using FeIII tetraphenylporphyrin (TPP‐Fe) and FeIII tetra(pentafluorophenyl)porphyrin (TPFP‐Fe), we showed their different electrochemical and chemical behaviors for ORR. Mechanism studies revealed that the FeIII‐superoxo species of TPP‐Fe can undergo smooth protonation with trifluoroacetic acid (TFA) but the electron‐deficient FeIII‐superoxo species of TPFP‐Fe cannot be protonated with TFA. The FeIII‐superoxo reactivity difference between TPP‐Fe and TPFP‐Fe is the origin of their different catalytic ORR behaviors.