Detection of Spontaneous FeOOH Formation at the Hematite/Ni(Fe)OOH Interface during Photoelectrochemical Water Splitting by Operando X-ray Absorption Spectroscopy
Ismail, Ahmed S.M.; Garcia-Torregrosa, Ivan; Vollenbroek, Jeroen C.; Folkertsma, Laura; Bomer, Johan G.; Haarman, Ties; Ghiasi, Mahnaz; Schellhorn, Meike; Nachtegaal, Maarten; Odijk, Mathieu; van den Berg, Albert; Weckhuysen, Bert M.; de Groot, Frank M.F.
(2021) ACS Catalysis, volume 11, issue 19, pp. 12324 - 12335
(Article)
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
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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.
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Keywords: catalysts, hematite, interface, iron oxyhydroxide, nickel iron oxyhydroxide, operando X-ray spectroscopy, water splitting, Taverne, Catalysis, General Chemistry
ISSN: 2155-5435
Publisher: American Chemical Society
Note: Funding Information: This work was supported by the Netherlands Center for Multiscale Catalytic Energy Conversion (MCEC), an NWO Gravitation programme funded by the Ministry of Education, Culture, and Science of the Government of the Netherlands. This project has also received partial funding from the EU-H2020 Research and Innovation Programme under Grant Agreement No. 654360, having benefitted from the access provided by the Paul Scherrer Institute, Villigen, Switzerland, to the SuperXAS beamline at the SLS within the framework of the NFFA-Europe Transnational Access Activity. Publisher Copyright: © 2021 American Chemical Society
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