Synthesis of Sr0.9K0.1FeO3−δ electrocatalysts by mechanical activation

Potassium-substituted SrFeO3−δ for possible application as oxygen evolution electrode in alkaline or molten salt media was prepared by mechanical activation and characterized by X-ray diffraction, dilatometric and thermogravimetric analysis, Mössbauer spectroscopy, and electrical conductivity measurements. Room temperature mechanical activation of a mixture of oxide precursors with subsequent thermal treatments at 700–900 °C results in the formation of Sr0.9K0.1FeO3−δ with tetragonal perovskite-like structure. Such allows to decrease the synthesis temperature, if compared to the conventional solid-state route, and to prevent possible volatilization of potassium. The results of Mössbauer spectroscopy studies indicate that the oxygen nonstoichiometry in the samples annealed in air at 900–1100 °C with subsequent rapid cooling vary in the range δ=0.30–0.32. The electrical conductivity in air exhibits a metal-like behaviour at temperatures above 400 °C and semiconductor behaviour in the low-temperature range, reaching 13–30 S/cm under prospective operation conditions for alkaline electrolyzers (≤90 °C).

graphical abstractXRD patterns of Sr0.9K0.1FeO3−δ powders, as-prepared and after annealing at different temperatures.Log(σ·T) vs. 1000/T plot of the electrical conductivity of Sr0.9K0.1FeO3−δ. The inset shows the thermal variation of σ. Ceramics used were prepared by mechanical activation followed by a two-step sintering process at 900 °C for 1 h and 1000 °C for 5 h (82% densification).Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Sr0.9K0.1FeO3−δ was successfully obtained by mechanical activation of oxide precursors. ► Synthesis temperature is significantly lower when compared to a conventional solid-state route. ► Oxygen nonstoichiometry of annealed samples at 900–1100 °C vary in the range δ=0.30–0.32. ► Sr0.9K0.1FeO3−δ shows metal and semiconductor behaviour above and below 400 °C, respectively.