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Alfred Larsson. Portrait.

Alfred Larsson

Postdoctoral fellow

Alfred Larsson. Portrait.

Platinum surface oxides govern the cathodic overpotential of the oxygen reduction reaction

Author

  • Alfred Larsson
  • Andrea Grespi
  • Ozbej Vodeb
  • Karen van den Akker
  • Auden Ti
  • Claire Berschauer
  • Alexandra M. Imre
  • Philip Miguel Kofoed
  • Estephania Lira
  • Mahesh Ramakrishnan
  • Stuart Ansell
  • Justus Just
  • Henrik Grönbeck
  • Ulrike Diebold
  • Edvin Lundgren
  • Lindsay R. Merte
  • Dusan Strmcnik
  • Rik Mom
  • Marc T.M. Koper
Show all

Summary, in English

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.

Department/s

  • Lund Laser Centre, LLC
  • LTH Profile Area: Photon Science and Technology
  • LU Profile Area: Light and Materials
  • LTH Profile Area: Nanoscience and Semiconductor Technology
  • Synchrotron Radiation Research
  • NanoLund: Centre for Nanoscience
  • MAX IV Laboratory

Publishing year

2026

Language

English

Publication/Series

EES Catalysis

Document type

Journal article

Publisher

Royal Society of Chemistry

Topic

  • Physical Chemistry (including Surface- and Colloid Chemistry)

Status

Epub

ISBN/ISSN/Other

  • ISSN: 2753-801X