Abstract
NiFe and CoFe (MFe) layered double hydroxides (LDHs) are among the most active electrocatalysts for the alkaline oxygen evolution reaction (OER). Herein, we combine electrochemical measurements, operando X-ray scattering and absorption spectroscopy, and density functional theory (DFT) calculations to elucidate the catalytically active phase, reaction center and the OER mechanism. We provide the first direct atomic-scale evidence that, under applied anodic potentials, MFe LDHs oxidize from as-prepared α-phases to activated γ-phases. The OER-active γ-phases are characterized by about 8% contraction of the lattice spacing and switching of the intercalated ions. DFT calculations reveal that the OER proceeds via a Mars van Krevelen mechanism. The flexible electronic structure of the surface Fe sites, and their synergy with nearest-neighbor M sites through formation of O-bridged Fe-M reaction centers, stabilize OER intermediates that are unfavorable on pure M-M centers and single Fe sites, fundamentally accounting for the high catalytic activity of MFe LDHs.
Highlights
NiFe and CoFe (MFe) layered double hydroxides (LDHs) are among the most active electrocatalysts for the alkaline oxygen evolution reaction (OER)
In spite of previous reports on the ex-situ crystal structure of the as-synthesized precursors of MFe LDH catalysts[23,24,25,26,27,28] and insitu local structure based on X-ray absorption spectroscopy (XAS) measurements[3,4,12,29,30,31,32], little is known about the long-range crystal structures of the catalytically active phase under OER
We studied the redox chemistry of NiFe LDH and CoFe LDH (M: Fe = ~3:1) using cyclic and linear sweep voltammetry (CV and LSV) and compared their OER performance with that of their Fefree hydroxide analogs, including β-Ni(OH)[2] and β-Co(OH)[2]
Summary
NiFe and CoFe (MFe) layered double hydroxides (LDHs) are among the most active electrocatalysts for the alkaline oxygen evolution reaction (OER). Studying the reactive structures of the MFe layered double hydroxides (LDHs) under in-situ conditions and the catalytic mechanism can provide a thorough understanding of the structure–property relationships of many related catalysts and potentially lead to the design of new catalysts with further improved performance. In spite of previous reports on the ex-situ crystal structure of the as-synthesized precursors of MFe LDH catalysts[23,24,25,26,27,28] and insitu local structure based on X-ray absorption spectroscopy (XAS) measurements[3,4,12,29,30,31,32], little is known about the long-range crystal structures of the catalytically active phase under OER conditions. A Fedoped β-CoOOH has been proposed as the active phase of CoFe LDH under OER conditions[11,12]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
