Upon the application of oxidizing potentials, the band at 513 redshifted to 501 cm -1 , new band components arose at 590 and 580 cm -1 , and a band at 687 cm -1 rose and fell. A band that progressively shifted from 609 to 580 cm -1 with positive potentials has previously been observed for CoOx thin films as Co underwent Co(II/III) and Co(III/IV) redox transitions 39 . A reasonable assignment would also be such changes in our spectra to Co-O species that are oxidized at 1.1V and 1.4 V. The emergence of a band at 503 cm -1 may also match that of CoOOH . The potentials at which these changes occurred matched that of the Co(II/III) and the Co(III/IV) oxidations and onset of OER catalysis. In addition, the spectral features observed for Co0.5Fe0.5O0.5F1.5 did not particularly match any spectra for iron oxide phases . With above data in mind, we were able to construct a plausible mechanism for the OER on Co0.5Fe0.5O0.5F1.5 surfaces (Fig. ). First, a 2e -, 3H + process occurs at 1.1 VRHE to generate Co(III) and deprotonate adsorbed water groups to *OH. Next, the Co(III)-OH becomes further oxidized at 1.4VRHE