Single Metal Atom Catalysts and ORR: H-Bonding, Solvation, and the Elusive Hydroperoxyl Intermediate

Abstract

The widely investigated oxygen reduction reaction (ORR) is well-known to proceed via two competing routes, involving two or four electrons, and yielding different reaction products, respectively. Both pathways are believed to share a common, elusive intermediate, namely, the hydroperoxyl radical. By exploiting a cobalt single-atom biomimetic model catalyst, based on a self-assembled monolayer of Co-porphyrins grown on an almost free-standing graphene sheet, we identify, in situ at room temperature in O2+H2O atmosphere, a hydroperoxyl-water cluster that is stabilized at the Co singlemetal atom catalytic site. We show that the interplay between charge transfer, dipole and Hbonding, and water solvation behavior actually determines the hydroperoxyl-water complex stability, the Co-OOH bonding geometry, and, prospectively, opens to the engineered control of the selectivity of ORR pathways.