Simple and Scalable Synthetic Route for Tunable Compositions of Multimetallic Oxyfluorides as Oxygen Evolution Reaction Catalysts

This work suggests a simple and scalable synthetic route to prepare multimetallic oxyfluorides, without requiring high temperature, high pressure, and a specific atmosphere (F2, N2, Ar, vacuum, etc.). For that, tunable compositions of Ni2+–Co2+–Fe3+-based oxyfluorides Co(1–x)/2Nix/2Fe0.5O0.5F1.5 have been prepared by calcination at moderate temperature under ambient air of Co1–xNixFeF5(H2O)7 precursors, prepared beforehand through coprecipitation at room temperature, across the whole range of the solid solution (0 ≤ x ≤ 1). Structural and thermal analyses confirmed the successful substitution for both hydrated fluoride precursors and oxyfluorides. Finally, we evaluated the electrocatalytic performance of the different Ni2+–Co2+–Fe3+ oxyfluorides for oxygen evolution reaction. Among these, the trimetallic Co0.25Ni0.25Fe0.5O0.5F1.5 exhibits the lowest overpotential (290 and 370 mV respectively at 10 and 100 mA cm–2) and the highest specific activity (3.9 A m–2 at 1.53 V vs RHE). These results highlight the need for compositional tunability to maximize performance.