Figure 5: XANES profiles of Co3O4 under electrochemical conditions.
Fluorescence-detected quasi-in situ XANES spectra of Co3O4 films in various catalyst states. For increasingly positive potentials, the Co K-edge absorption edge shifted reversibly to higher energies suggesting oxidation of 10–15% of the cobalt ions under stationary oxygen evolution conditions. Under OER conditions, the XANES profile exhibited an almost linear increase because of significantly weaker shoulders marked with A and B. The intensity at the principal edge-maximum at (C) was clearly reduced only in the oxygen evolving active state (at +1.62 V). Samples were freeze-quenched under potential control using liquid N2 after 15 min at the given potential in 0.1 M KPi and stored in liquid N2 until XAS measurements were conducted.
