Improving Electrocatalytic Oxygen Reduction Activity and Selectivity with a Cobalt Corrole Appended with Multiple Positively Charged Proton Relay Sites

The electrocatalytic four-electron (4e(-)) oxygen reduction reaction (ORR) is important in new energy conversion technologies. Improving the activity and 4e(-) selectivity of the ORR is required for the practical applications of these technologies. We herein report the Co corrole 1 with an appended N,N-di(2-picolyl)ethylenediamine (DPEN) unit and its electrocatalytic 4e(-) ORR in different pH aqueous solutions. The appended DPEN of Co corrole 1 has two pyridyl groups and one tertiary amine unit, which are expected to be partially protonated in aqueous solutions of pH <= 7. This will convert DPEN to an intramolecular group functioning as multiple positively charged and proton relay sites. Importantly, 1 is more active and selective than Co tris(pentafluorophenyl)corrole 2, the DPEN-free analogue of 1, for the electrocatalytic 4e(-) ORR in pH <= 7 aqueous solutions, whereas 1 and 2 display similar activities and selectivities for the ORR in basic solutions. These results confirmed our catalyst design strategy by using protonated multiple pyridyl and amine groups as positively charged proton relay sites to improve the activity and 4e(-) selectivity of the ORR. Therefore, this work is significant because it shows the benefit of using molecular catalysts for studying structure-function relationships and to underline the potential applications of molecular electrocatalysis.