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Abstract

In a sustainable development objective, it is necessary to consider both the performance and the preciousness of metals for the development of new catalysts. In this way, this work aims to reduce the amount of cobalt in the mixed Co–Fe oxyfluoride Co0.5Fe0.5O0.5F1.5, obtained from the thermal degradation of the hydrated fluoride precursor CoFeF5(H2O)7, while maintaining its electrocatalytic performance as an electrocatalyst for the Oxygen Evolution Reaction (OER) in alkaline media. To achieve this, the proposed strategy consists in substituting the Co2+ ions by Fe2+ ions in CoFeF5(H2O)7, chosen for its earth abundance, leading to the solid solution (Co1–xFex)2+Fe3+F5(H2O)7 obtained by co-precipitation. This series of hydrated precursors was then subjected to a thermal treatment in ambient air in order to obtain the corresponding solid solution of the oxyfluorides Co(1–x)/2Fe(1+x)/2O(1+x)/2F(3–x)/2. Structural and thermal analyses confirm a Co2+/Fe2+ substitution in hydrated fluoride precursors, while those of calcined samples indicate a complex thermal decomposition leading to Co–Fe oxyfluorides. The OER electrocatalytic performance of these oxyfluorinated materials shows that it is possible to reduce the amount of cobalt by up to 20% without affecting the overall OER activity, namely an overpotential of 320 mV at 10 mA·cm–2 and a mass activity of 112 A·g–1 at 1.55 V vs. RHE, with high stability.

Keywords

• Oxyfluoride
• Solid solution
• Coprecipitation
• Thermal treatment
• Electrocatalysis
• OER