The work put forth in this study highlights the utility of exploring hetero-anionic composition in the discovery of efficient catalytic materials. A mixed anion compound, Co0.5Fe0.5O0.5F1.5, was fabricated through a controlled thermal conversion route and, the resultant material exhibited exceptionally high activity for the OER. A set of mechanistic investigations were carried out to elucidate key steps in the reaction mechanism and through this process, we found the OER proceeding through a super-Nernstian pH-dependent process. In all, the research illustrated here is envisioned to open pathways in electrocatalyst design through the exploration of multi-metallic oxyfluoride materials that in key cases can surpass the activity of the state-of-the-art oxides. Mechanistically, exciting questions have yet to be answered, such as the elucidation of electronic structure changes and the precise interplay of Co, Fe, F, and O components in the lattice, for which both theoretical modelling and X-ray absorption spectroscopy can potentially be instrumental. In the context of the OER, while Co0.5Fe0.5O0.5F1.5 surpasses the performance of most known Co-based catalysts, there is no reason that it has to be the most active oxyfluoride. Thus, many promising avenues in nanostructuration, structural and compositional modulation may yield an even more active nextgeneration material. Table : Atomic coordinates and equivalent isotropic displacement parameters in triclinic system. ) Co( ) Fe( ) Fe( ) F( ) O( ) F( ) O( ) ) Fe( ) Fe( ) F( ) O( ) F( ) F( ) F( ) O( ) F( ) F( ) O( ) O( ) O( ) O( ) O( ) O( Table . Selected inter-atomic distances (Å) and bond valence calculations of CoFeF5(H2O)7 in triclinic system.