O₂ reduction by iron porphyrins with electron withdrawing groups: to scale or not to scale

Iron porphyrins are synthesized by systematically introducing electron withdrawing groups (EWGs) on pyrroles to evaluate the relationship between rate (k) and overpotential (η). The results indicate that while EWGs lead to a rise in the thermodynamic FeIII/II reduction potential (E0), the potential of the O2 reduction reaction (ORR) does not scale with E0. More importantly, the iron porphyrins with higher E0 show an order of magnitude higher...