Mediation at High Potentials for the Reduction of Oxygen to Water by Cobalt Porphyrin–Quinone Systems in Porous Aerogel Carbon Electrodes

Reduced p-, m-, and o-benzoquinones: hydroquinone (HQ), resorcinol (Res), and catechol (Cat), undergo irreversible monolayer adsorption in aerogel carbon (AEC) electrodes with rates of , , and for HQ, Res, and Cat, respectively. The adsorbed species showed electrochemical quasi-reversible behavior in 1 M with half-wave potentials of , , and vs Ag/AgCl/KCl (saturated) for AEC/HQ, AEC/Res, and AEC/Cat, respectively. Upon adsorption of Co(III) tetra(p-sulfonatophenyl)porphyrin in these electrodes, a single reduction wave was observed and its was independent of the nature of the adsorbed reduced quinone. This was attributed to a metalloporphyrin/quinone complex, which formed and stabilized at the electrode surface. This species, after being reduced, reacted with oxygen with a rate of . Mediation of oxygen reduction by these systems occurred at a relatively high potential almost completely via a four-electron-transfer process.