Nanosized Iron–Cobalt Oxyhydroxyfluorides with Rutile Structure as Oxygen Evolution Reaction Catalysts in Alkaline Media

To enhance the efficiency of the water splitting process, anodic electrocatalyst materials are engineered to improve kinetics. In this context, we report the first synthesis of nanosized Co- and Fe-based oxyhydroxyfluorinated materials Co 1– x Fe x –y 2+ Fe y 3+ O y (OH) z F 2– y – z (0 ≤ x ≤ 0.75) obtained by heat treatment under air of the series Co 1– x Fe x SiF 6 (H 2 O) 6 with fine control of the stoichiometric ratio. This synthesis method enables the control of the Co/Fe ratio and yields nanosized particles, as the rapid release of SiF 4 gas during the precursor decomposition induces structural fragmentation. Several characterization techniques were used to determine anionic (OH – and F – contents) and cationic compositions (Co/Fe ratio and oxidation state of iron), as well as crystalline structure, size, and morphology of the materials. Electrochemical measurements for OER in alkaline media showed that the best-performing catalyst is Co 0.50 2+ Fe 0.09 2+ Fe 0.41 3+ O 0.41 (OH) 0.20 F 1.39 with an overpotential of 328 mV at 10 mA·cm –2 and a low Tafel slope of 36 mV·dec –1 .