DFT Understanding of the Oxygen Reduction to Hydrogen Peroxide on Graphene Modified by Oxygen Functional Groups

Carbon-based materials modified with oxygen functional groups are efficient and inexpensive electrocatalysts for H2O2 production via the oxygen reduction reaction (ORR). However, how the ORR proceeds on the catalyst is not understood, hampering the targeted design of high-performance catalysts. Here, we investigate the kinetic process of the ORR through density functional theory calculations. The results reveal an important role of water in the ORR. During hydrogenation of OOH* to H2O2, the adsorbed hydrogen atom first transfers to a water molecule, and then another hydrogen atom from the water is donated to OOH*. In this mode, water behaves as a medium through which H* hydrogenates to a finitely distant adsorbed reactant. Such a model apparently reduces the coadsorption energy and hence reduces the energy barrier of the ORR. According to the proposed mechanism, −COOH has the highest activity among the active sites, with an ORR energy barrier of 0.55 eV.