In order to probe the reaction mechanism and understand the roles of Co and Fe atoms for Co0.5Fe0.5O0.5F1.5, we first performed density functional theory (DFT) computations. Here, we chose (110) facet because of its lowest surface energy and thus the most stable surface in rutile structures. Two reaction pathways are considered here, adopting different O-O bond formation strategies, which are the water nucleophilic attack (WNA) and the interaction of two metal-oxo units (I2M) (Fig. ).