In a complementary thrust, in operando Raman spectroscopy was performed as this type of vibrational spectroscopy can help to elucidate changes in catalyst surface structure through the course of the reaction cycle (Fig. ). We focused on the spectral region of 100-900 cm -1 , where M-M and M-O vibrational modes are typically seen. While there is not an established literature base that can be used to unambiguously assign bands to the particular vibrational modes of Co0.5Fe0.5O0.5F1.5, we probe the changes in the spectra and reference vs. previous Raman observations of OER-active cobalt and iron-based catalysts. At open circuit, bands at 342, 513, 620, 687, 735 and 809 cm -1 were observed.