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A promising NiFe(OH)x catalyst for oxygen evolution reaction (OER) has been successfully fabricated and studied in detail using in situ X-ray absorption near-edge structure (XANES) spectroscopy. The chemical nature of elements (Ni, Fe) in electrocatalysts has been elucidated from Fe and Ni K- and L-edge XANES. The increase of oxidation states of Ni from Ni(III) to Ni(3.6) together with a highly covalent Fe(IV)–O bond under OER process is observed. Charge transfer between Ni and Fe through a “Ni–O–Fe” bond is proposed, accounting for the high catalytic activities of NiFe(OH)x.
Wang et al. (Wed,) studied this question.