Oxygen Reduction Reaction on Cobalt–(6)Pyrrole Cluster: Density Functional Theory Study

Abstract

We investigate the potential energy surface profile for various water formation reaction schemes on an unsupported cobalt–(6)pyrrole [Co–(6)Ppy] cluster in the vacuum state by density functional theory (DFT) calculations. We find that in the Co–(6)Ppy cluster, the formation of H 2 O 2 is energetically not favorable. Instead of forming H 2 O 2ad , the HO 2ad + H reaction forms 2OH ad or O ad + H 2 O immediately. The adsorption of H 2 O 2 on the Co–(6)Ppy cluster is possible only if the H 2 O 2 molecule comes from or forms outside of the cluster. The formation of two OH molecules instead of H 2 O 2 on the Co–(6)Ppy cluster suggests that the oxygen reduction reaction (ORR) mechanism on the unsupported Co–(6)Ppy cluster in the vacuum state prefers the direct four-electron reduction to water.