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Zusammenfassung:
Herein, we report the synthesis and electro-chemical oxygen evolution experiments for a graphene-supported Ni3MnO4 catalyst. The changes that occur at the Ni active sites during the electrocatalyic oxygen evolution reaction (OER) were elucidated by a combination of operando Ni L-edge X-ray absorption spectroscopy (XAS) and Ni 2p3d resonant inelastic X-ray scattering (RIXS). These data are compared to reference measurements on NiO, beta-Ni(OH)(2), beta-NiOOH, and gamma-NiOOH. Through this comparative analysis, we are able to show that under alkaline conditions (0.1 M KOH), the oxides of the Ni3MnO4 catalyst are converted to hydroxides. At the onset of catalysis (1.47 V), the beta-Ni(OH)(2)-like phase is oxidized and converted to a dominantly gamma-NiOOH phase. The present study thus challenges the notion that the beta-NiOOH phase is the active phase in OER and provides further evidence that the gamma-NiOOH phase is catalytically active. The ability to use Ni L-edge XAS and 2p3d RIXS to provide a rational basis for structure-activity correlations is highlighted.
