A soft chemistry method was chosen to generate Co0.5Fe0.5O0.5F1.5. A detailed description can be found in the supporting information. In brief, the catalyst was prepared in a controlled thermal decomposition of a hydrated fluoride precursor in mild conditions. The precursor CoFeF5(H2O)7 was precipitated by thermally assisted evaporation of a hydrofluoric acid (HF) solution containing metallic salts. The thermal decomposition of CoFeF5(H2O)7 was followed by combined thermogravimetric analysis (TGA) and thermodiffraction. Three thermal events appeared on the TGA curve and thermodiffractograms that correspond to the structural evolution of CoFeF5(H2O)7 across four domains (Fig. and): (i) stability of CoFeF5(H2O)7 (RT-100°C, green), (ii) dehydration of CoFeF5(H2O)7 (100-220°C, blue), (iii) formation of Co0.5Fe0.5O0.5F1.5 with the rutile structure type (220-280°C, purple) and (iv) formation of oxides, CoO and CoFe2O4 (T°C > 280°C, red). To sum up, CoFeF5(H2O)7 undergoes the following decompositions upon thermal treatment according to the reactions ( ), ( ) and ( ). The experimental weight loss values are in good agreement with theoretical values (theo wt%, exp wt%):