Platinum surface oxides govern the cathodic overpotential of the oxygen reduction reaction
Journal article, 2026
The oxygen reduction reaction (ORR) on platinum is limited by a substantial overpotential, which hampers the efficiency of fuel cell technologies. While adsorbate binding energies have been widely used to explain ORR kinetics, we here illustrate a more complex role of platinum surface oxides, which are often ambiguously defined in the literature. We use operando total reflection X-ray absorption fine structure spectroscopy (RefleXAFS), supported by X-ray photoelectron spectroscopy, density functional theory, and microkinetic modeling, to resolve the surface oxides on polycrystalline platinum and their impact on ORR. We identify the formation of a surface oxide as early as 1 VRHE in 0.1 M HClO4 and demonstrate that platinum spontaneously oxidizes at the open-circuit potential (OCP) under O2 saturation. Furthermore, we show that the oxide coverage increases with upper vertex potential, slower scan rates, and extended hold times at OCP, illustrating how oxides inhibit ORR during fuel cell start-up. Crucially, we demonstrate that the ORR onset is delayed until these oxides are reduced, establishing a direct, negative relationship between oxide coverage and ORR activity. This reveals a revised mechanism in which the potential-determining step is the reduction of surface oxides, and the slow kinetics of this restructuring ultimately determine when surface sites become catalytically available.
Author
Alfred Larsson
Lund University
Leiden University
Andrea Grespi
Lund University
Ozbej Vodeb
Jozef Stefan Int Postgrad Sch
Leiden University
National Institute of Chemistry
Karen van den Akker
Leiden University
Auden Ti
Lund University
Claire Berschauer
Lund University
Alexandra M. Imre
Vienna University of Technology
Philip Miguel Kofoed
Malmö university
Estephania Lira
Lund University
Mahesh Ramakrishnan
Lund University
Stuart Ansell
Lund University
Justus Just
Lund University
Henrik Grönbeck
Chalmers, Physics, Chemical Physics
Ulrike Diebold
Vienna University of Technology
Edvin Lundgren
Lund University
Lindsay R. Merte
Malmö university
Dusan Strmcnik
National Institute of Chemistry
Rik Mom
Leiden University
Marc T. M. Koper
Leiden University
EES CATALYSIS
2753-801X (eISSN)
Vol. In PressSubject Categories (SSIF 2025)
Materials Chemistry
Inorganic Chemistry
Physical Chemistry
DOI
10.1039/d6ey00014b
PubMed
41858921