Four-electron transfer pathway mixed with

Recently, Kadish et al. synthesized three series of Co corroles (shown in Figure 4.11(D)) and investigated their catalytic activity toward the O2 reduction reaction.The mixed valent Co(II)/ Co(III) complexes, (PCY)Co2, and the biscorrole complexes, (BCY)Co2, both contain two Co(III) ions in their air-stable forms. It was foimd that all these complexes could catalyze the direct four-electron pathway for O2 reduction to H2O in aqueous acidic electrolyte. The most efficient catalysis process was observed when the complex had an anthracene spacer. The four-electron transfer pathway was further confirmed by RRDE measurement, in which only a relatively small amount of hydrogen peroxide was detected at the ring electrode in the vicinity of E1/2 0.47 V vs SCE for (PCA)Co2 and 0.39 V for (BCA)Co2. The cobalt(III) mono-corrole, (Me4Ph5Cor)Co, could also catalyze ORR at En2 = 0.38 V, with the final products being an approximate 50% mixture of H2O2 and H2O. 

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