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

Larsson, Alfred LU orcid ; Grespi, Andrea LU orcid ; Vodeb, Ozbej ; van den Akker, Karen ; Ti, Auden LU orcid ; Berschauer, Claire LU orcid ; Imre, Alexandra M. ; Kofoed, Philip Miguel LU ; Lira, Estephania LU and Ramakrishnan, Mahesh LU , et al. (2026) In EES Catalysis
Abstract

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... (More)

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.

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publication status
epub
subject
in
EES Catalysis
publisher
Royal Society of Chemistry
external identifiers
  • scopus:105033130500
  • pmid:41858921
ISSN
2753-801X
DOI
10.1039/d6ey00014b
language
English
LU publication?
yes
additional info
Publisher Copyright: This journal is © The Royal Society of Chemistry, 2026
id
7a7750a1-32e5-41a1-b5f3-8ea3b2e69c6d
date added to LUP
2026-04-29 13:40:06
date last changed
2026-05-05 08:08:43
@article{7a7750a1-32e5-41a1-b5f3-8ea3b2e69c6d,
  abstract     = {{<p>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 V<sub>RHE</sub> in 0.1 M HClO<sub>4</sub> and demonstrate that platinum spontaneously oxidizes at the open-circuit potential (OCP) under O<sub>2</sub> 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.</p>}},
  author       = {{Larsson, Alfred and Grespi, Andrea and Vodeb, Ozbej and van den Akker, Karen and Ti, Auden and Berschauer, Claire and Imre, Alexandra M. and Kofoed, Philip Miguel and Lira, Estephania and Ramakrishnan, Mahesh and Ansell, Stuart and Just, Justus and Grönbeck, Henrik and Diebold, Ulrike and Lundgren, Edvin and Merte, Lindsay R. and Strmcnik, Dusan and Mom, Rik and Koper, Marc T.M.}},
  issn         = {{2753-801X}},
  language     = {{eng}},
  publisher    = {{Royal Society of Chemistry}},
  series       = {{EES Catalysis}},
  title        = {{Platinum surface oxides govern the cathodic overpotential of the oxygen reduction reaction}},
  url          = {{http://dx.doi.org/10.1039/d6ey00014b}},
  doi          = {{10.1039/d6ey00014b}},
  year         = {{2026}},
}