Atomic-Level Insight into Oxygen Adsorption on (hkl) Platinum Surfaces and Implications for the Reactivity in the Oxygen Reduction Reaction

Understanding of the oxygen reduction reaction (ORR) on nanometal catalysts and specific rate predictions remain a major challenge. We quantified adsorption of molecular oxygen on Pt (100), (111), and (110) surfaces in common electrolytes and for a range of applied potentials in several times higher accuracy than feasible before using molecular dynamics simulations, and explore the following colvalent bond formation using density functional theory calculations. A direct correlation between the oxygen affinity to Pt (hkl) surfaces and the experimentally measured ORR activity in the order Pt(100) < Pt(111) < Pt(110) in HClO₄ solution and Pt(111) < Pt(100) < Pt(110) in H₂SO₄ and H₃PO₄ solutions is discovered. The adsorption energies are in a range to explain specific rate differences. Experimental data for the time scale of events support that the ORR activity is driven by O₂ adsorption and initial chemisorption. The methods can be potentially applied to metal and alloy surfaces of any regularity, shape, and composition to provide quantitative insights into metal-electrolyte-gas interfaces, and promote the rational design of more effective catalysts for ORR, OER, and other electrode reactions to the large nanometer scale.