The molecular cobalt complex, Co-(salophen), and para-hydroquinone (H(2)Q) serve as effective cocatalysts for the electrochemical reduction of O-2 to water. Mechanistic studies reveal redox cooperativity between Co(salophen) and H(2)Q H(2)Q serves as an electron-proton transfer mediator (EPTM) that enables electrochemical O-2 reduction at higher potentials and with faster rates than is observed with Co(salophen) alone. Replacement of H(2)Q with the higher-potential EPTM, 2-chloro-H(2)Q allows for faster O-2 reduction rates at higher applied potential. These results demonstrate a unique strategy to achieve improved performance with molecular electrocatalyst systems.