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

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.

Nanocrystalline Iron Pyrophosphate-Regulated Amorphous Phosphate Overlayer for Enhancing Solar Water Oxidation

“…Additionally, the pre-edge peak of FePi is located at 7,134 eV, while the peak of FePy@FePi is located at 7,138 eV. This result fits well with the result showed in Fe 2 p XPS spectra [ 44 – 46 ]. Because FePi amorphous layer contains Fe(II) spices, the Fe valance in FePi is a little bit lower than FePy@FePi.…”

Experimental correlation of Mn3+cation defects and electrocatalytic activity of α-MnO2– an X-ray photoelectron spectroscopy study

“…212–219 However, herein we employed 0.0709 mF cm −2 for C s corresponding to the areal capacitance of the bare GC disk electrode, that is, the substrate electrode for the preparation of α-MnO 2 -AB thin-film WEs. 17 On the other hand, according to McCrory et al , 157 for metal oxide catalysts in NaOH and KOH solutions C s values ranging from 0.022 mF cm −2 to 0.130 mF cm −2 are reported, 220–232 thus the C s value based on the bare GC disc electrode, that was used in our work, is well within this range. However, since original (untreated) data to all double-layer capacitance measurements is provided in the ESI† to this manuscript, it will be straightforward for other groups to convert to ECSAs based on other C s values, or the specific capacitance of an atomically flat α-MnO 2 surface, which will possibly be determined in a future study, respectively.…”

“…[212][213][214][215][216][217][218][219] However, herein we employed 0.0709 mF cm À2 for C s corresponding to the areal capacitance of the bare GC disk electrode, that is, the substrate electrode for the preparation of a-MnO 2 -AB thin-lm WEs. 17 On the other hand, according to McCrory et al, 157 for metal oxide catalysts in NaOH and KOH solutions C s values ranging from 0.022 mF cm À2 to 0.130 mF cm À2 are reported, [220][221][222][223][224][225][226][227][228][229][230][231][232] thus the C s value based on the bare GC disc electrode, that was used in our work, is well within this range. However, since original (untreated) data to all This journal is © The Royal Society of Chemistry 2022…”

In Situ Exploring of the Origin of the Enhanced Oxygen Evolution Reaction Efficiency of Metal(Co/Fe)–Organic Framework Catalysts Via Postprocessing

“…Among them, CF-PBA-400 exhibits the smallest overpotential of 254 mV (vs reversible hydrogen electrode, RHE), for a current density of 10 mA cm –2 , which well surpasses the benchmarked IrO 2 and most Co/Fe-based catalysts reported to date. At present, the operando characterization techniques, especially operando X-ray absorption spectroscopy (XAS) − and operando Raman spectra, are widely used to track the in situ structural transformation of the catalysts and the mechanism of the OER. The local electronic structural evolution of the active Co and Fe ions in CF-PBA-400 during OER processes was studied via ex situ and in situ X-ray absorption spectroscopy (XAS), and the results revealed the occurrence of site exchange between Co and Fe during the pyrolysis process, which directly affected the catalytic activity.…”