Oxygen-containing intermediates formed in oxygen reduction reaction (ORR) are widely believed to act as site-blockers. Recent experiments showing positive effects of O-containing intermediates throw doubt upon this prevailing understanding[1]. This situation calls for an overhaul of current understanding of mechanisms of the ORR. The theoretical challenge is how to consistently treat the formation of O-containing intermediates, surface charge on metal surface, ion and potential distribution in the solution, field-dependent behaviors of surficial water molecules, and thermodynamic relations and kinetics of the ORR. In the present article, a self-consistent framework bridging first-principles approaches and mean-field approaches, nanoscale and microscale, interface and bulk, is developed to address the above challenge. Model, parametrized with density functional theory results and rotating disk electrode data, sheds light on the potential-dependent Tafel slope and volcano shape of the activity versus binding energy of intermediate curve, focusing on the effects of surface charge and O-containing intermediates. Chemisorption of O-containing intermediates decreases surface charge density on metal surface, increases proton affinity at the interface, and brings positive effects to the ORR activity other than the negative effects of site-blocking.[2]

Reference:

[1] Gómez-Marín, A.M.; Rizo, R.; Feliu, J.M. Oxygen Reduction Reaction at Pt Single Crystals: A Critical Overview. Catal. Sci. Technol. 2014, 4, 1685-1698.

[2] Huang, J.; Malek, A.; Zhang, J.; Eikerling, M.H. Non-Monotonic Surface Charging Behavior Of Platinum: A Paradigm Change. J. Phys. Chem. C 2016, 120, 13587–13595.