Electrochemical Stability of the Reconstructed Fe₃O₄(001) Surface

Abstract

Establishing the atomic‐scale structure of metal‐oxide surfaces during electrochemical reactions is a key step to modeling this important class of electrocatalysts. Here, we demonstrate that the characteristic (√2×√2)R45° surface reconstruction formed on (001)‐oriented magnetite single crystals is maintained after immersion in 0.1 M NaOH at 0.20 V vs. Ag/AgCl and we investigate its dependence on the electrode potential. We follow the evolution of the surface using in situ and operando surface X‐ray diffraction from the onset of hydrogen evolution, to potentials deep in the oxygen evolution reaction (OER) regime. The reconstruction remains stable for hours between −0.20 and 0.60 V and, surprisingly, is still present at anodic current densities of up to 10 mA cm−2 and strongly affects the OER kinetics. We attribute this to a stabilization of the Fe3O4 bulk by the reconstructed surface. At more negative potentials, a gradual and largely irreversible lifting of the reconstruction is observed due to the onset of oxide reduction.

OperandoIdentification of the Reversible Skin Layer on Co3O4as a Three-Dimensional Reaction Zone for Oxygen Evolution

“…Further support for this scenario comes from recent SXRD observations for UHV-prepared Fe 3 O 4 (100) single crystals in NaOH solution. 65 For this oxide, the presence of a reconstructed surface layer, which extends over three cationic planes and exclusively contains Fe 3+ ions, was found to be sufficient to stabilize the structure of Fe 3 O 4 bulk and no skin was observed including in the OER regime. 65 …”

“… 65 For this oxide, the presence of a reconstructed surface layer, which extends over three cationic planes and exclusively contains Fe 3+ ions, was found to be sufficient to stabilize the structure of Fe 3 O 4 bulk and no skin was observed including in the OER regime. 65 …”

Correlating Orbital Composition and Activity of LaMnxNi1–xO3 Nanostructures toward Oxygen Electrocatalysis

“…However, we cannot exclude that subtle reconstruction processes at the first atomic layer may take place upon polarization at the solid/electrolyte interface. 21 …”

“…However, this strategy fails to recognize the complexities associated with electrochemical interfaces and the fact that the electronic structure/property of the material can be significantly altered by the electrode potential (Fermi level) under operational conditions. 19 − 21 This aspect has been elegantly illustrated by the recent report on correlative operando microscopy of Co(OH) 2 platelets. 22 At a fundamental level, electron transfer kinetics is determined by the overlap in the energy scale of the density of states of redox molecules in solution and the solid-state material, as elegantly described by the Gerischer model for interfacial electron transfer.…”

Electrocatalytic Site Activity Enhancement via Orbital Overlap in A2MnRuO7 (A = Dy3+, Ho3+, and Er3+) Pyrochlore Nanostructures

“…The voltametric responses are stable upon consecutive cycling up to potentials close to 1.7 V vs RHE, suggesting that the surface composition remains unaffected over a wide potential range. However, it should also be acknowledged that surface reconstructions can take place at oxide surfaces which cannot be unambiguously assigned to voltametric features, as recently shown by Gurmelli et al 30 At constant loading, Ho2RuMnO7 displays the largest current while the peaks in Dy2RuMnO7 are rather broad spreading up to approximately 1.2 V. The two pseudo-capacitive peaks are qualitatively similar to the highly active LaMnO3 although Ru sites are also expected to contribute in this potential range. [31][32] As summarized in Table S5, integration of the pseudo-capacitive responses provides information on the number density of active redox surface sites (Γsites) normalized by the oxide loading and specific surface area.…”