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In situ observation of reactive oxygen species forming on oxygen-evolving iridium surfaces

DOI: 10.1039/C6SC04622C DOI Help

Authors: Verena Pfeifer (Fritz-Haber-Institut der Max-Planck-Gesellschaft; Elektronenspeicherring BESSY II) , Travis E. Jones (Fritz-Haber-Institut der Max-Planck-Gesellschaft) , Juan J. Velasco Vélez (Fritz-Haber-Institut der Max-Planck-Gesellschaft; Max-Planck-Institut für Chemische Energiekonversion) , Rosa Arrigo (Diamond Light Source) , Simone Piccinin (Consiglio Nazionale delle Ricerche – Istituto Officina dei Materiali) , Michael Hävecker (Fritz-Haber-Institut der Max-Planck-Gesellschaft; Max-Planck-Institut für Chemische Energiekonversion) , Axel Knop-gericke (Fritz-Haber-Institut der Max-Planck-Gesellschaft) , Robert Schlögl (Fritz-Haber-Institut der Max-Planck-Gesellschaft; Max-Planck-Institut für Chemische Energiekonversion)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Chem. Sci.

State: Published (Approved)
Published: December 2016

Open Access Open Access

Abstract: Water splitting performed in acidic media relies on the exceptional performance of iridium-based materials to catalyze the oxygen evolution reaction (OER). In the present work, we use in situ X-ray photoemission and absorption spectroscopy to resolve the long-standing debate about surface species present in iridium-based catalysts during the OER. We find that the surface of an initially metallic iridium model electrode converts into a mixed-valent, conductive iridium oxide matrix during the OER, which contains OII− and electrophilic OI− species. We observe a positive correlation between the OI− concentration and the evolved oxygen, suggesting that these electrophilic oxygen sites may be involved in catalyzing the OER. We can understand this observation by analogy with photosystem II; their electrophilicity renders the OI− species active in O–O bond formation, i.e. the likely potential- and rate-determining step of the OER. The ability of amorphous iridium oxyhydroxides to easily host such reactive, electrophilic species can explain their superior performance when compared to plain iridium metal or crystalline rutile-type IrO2.

Subject Areas: Chemistry

Facility: BESSY II


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