Four-electron oxygen reduction by brominated cobalt corrole.

The carbon-supported cobalt(III) complex of β-pyrrole-brominated 5,10,15-tris(pentafluorophenyl)corrole [Co(tpfc)Br(8)/C] is introduced as a nonplatinum alternative for electrocatalytic oxygen reduction in aqueous solutions. Through systematic work, the basic kinetic parameters of this reaction were studied, using rotating ring disk electrode electrochemical methods in the pH range of 0-11. Pronounced catalytic activity was detected in acid solutions along with shifts of the Co(II)/Co(III) and O(2) redox couples to more positive values (onset of 0.56 V at pH 0). A series of independent measurements have been used to prove that the dominant mechanism for oxygen reduction by Co(tpfc)Br(8)/C catalysis is the direct four-electron pathway to water.