Co1–xFexOy Oxygen Evolution Nanocatalysts: On the Way To Resolve (Electro)Chemically Triggered Surface-Bulk Discrepancy
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2023-12-15
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Journal Article
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Abstract
Unveiling relevant properties of the electrocatalyst’s active phase for the oxygen evolution reaction (OER) is crucial to rationally improve the efficiency of water electrolyzers. This is particularly challenging for materials with a nonuniform pristine phase, which further changes during the OER process. Here, combining surface- and bulk-sensitive analysis techniques unraveled the presence of a gradually changing surface-bulk discrepancy in flame-spray synthesized Co1-xFexOy nanoparticles as a function of the Fe-content. The bulk of the as-synthesized low Fe-content material (x = 0.01) consists of rock salt CoO and is covered on the surface by the thermodynamically more favorable Co3O4 phase. This surface Co3O4 limits the electrocatalytic performance and explains its highly reversible behavior in Co redox processes, as evidenced by cyclic voltammetry and soft X-ray absorption spectroscopy in total-electron-yield. In contrast, the high Fe-content material (x = 0.70), initially with a uniform CoFe2O4 spinel structure, undergoes irreversible surface modifications during OER, driven mainly by Co2+ oxidation in octahedral sites, boosting activity and stability. These insights demonstrate the necessity to resolve (electro)chemically triggered surface-bulk discrepancy on unsupported Co(−Fe)-based nanocatalysts for a better understanding of their electrochemical behavior and to further improve their electrocatalytic performance.
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published
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13 (24)
Pages / Article No.
15899 - 15909
Publisher
American Chemical Society
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Subject
alkalinewater splitting; cobalt iron oxide; eterogeneous (electro)catalysis; irreversible cobalt oxidation; L-edge; total-electron-yield; unsupported nanoparticles; X-ray absorption spectroscopy
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03910 - Schmidt, Thomas J. / Schmidt, Thomas J.