Detection of Spontaneous FeOOH Formation at the Hematite/Ni(Fe)OOH Interface during Photoelectrochemical Water Splitting by Operando X-ray Absorption Spectroscopy

Ahmed S.M. Ismail*, Ivan Garcia-Torregrosa, Jeroen C. Vollenbroek, Laura Folkertsma, Johan G. Bomer, Ties Haarman, Mahnaz Ghiasi, Meike Schellhorn, Maarten Nachtegaal, Mathieu Odijk, Albert Van Den Berg, Bert M. Weckhuysen, Frank M.F. De Groot*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

The role that the α-Fe2O3/NiFeOOH interface plays in dictating the oxygen evolution reaction (OER) mechanism on hematite has been a source of intense debate for decades, but the chemical characteristics of this interface and its function are still ambiguous and subject to speculation. In this study, we employed operando X-ray absorption spectroscopy to investigate the interfacial dynamics at the α-Fe2O3/NiFeOOH interface. We uncovered the spontaneous formation of a FeOOH interfacial layer under (photo)electrochemical conditions. This FeOOH interfacial layer plays a role in the surface passivation of hematite and in accumulating the (photo)generated holes upon external potential application. This hole-accumulation process leads to the extraction of more (photo)generated holes from hematite before releasing them to NiFeOOH to carry out the water-splitting reaction, and it also explains the reason for the delay in the nickel oxidation process. Based on these observations, we propose a model where NiFeOOH acts mainly as an OER catalyst and a facilitator of holes extraction from hematite, while the interfacial FeOOH layer acts as a surface passivation and hole-accumulation overlayer.

Original languageEnglish
Pages (from-to)12324-12335
Number of pages12
JournalACS catalysis
Volume11
Issue number19
Early online date20 Sep 2021
DOIs
Publication statusPublished - 1 Oct 2021

Keywords

  • catalysts
  • hematite
  • interface
  • iron oxyhydroxide
  • nickel iron oxyhydroxide
  • operando X-ray spectroscopy
  • water splitting

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