Effect of Electron Availability on Selectivity of O2 Reduction by Synthetic Monometallic Fe Porphyrins

Herein we report that biomimetic analogues of cytochrome c oxidase (CcO) couple reduction of O2 to oxidation of a single-electron carrier, Ru(NH3)6^2+, under steady-state catalytic turnover. Higher Ru^II concentrations favor the 4-electron vs 2-electron O2 reduction pathway. Our data indicate that the capacity of electrode-adsorbed Fe-only porphyrins to catalyze reduction of O2 to H2O is due to high availability of electrons and is eliminated under the biologically relevant slow electron delivery.