Insight into the impact of calcination on the formation mechanism, microstructure, and OER performance of IrO2–Ta2O5 mixed metal oxide anodes

IrO2–Ta2O5 mixed metal oxide (MMO) coatings supported on metallic Ti are widely employed as anodes for the oxygen evolution reaction (OER) in acidic media. In this work, the effect of calcination process on the formation mechanism, microstructure, and electrochemical performance of IrO2–Ta2O5 coatings prepared by thermal decomposition of chloride precursors was systematically investigated. Thermo-gravimetric analysis coupled with Fourier transform infrared spectroscopy on evolved gas revealed the release of H2O and HCl during the thermal treatment, suggesting that hydrolysis-assisted reactions contribute to the MMO formation. Scanning electron microscopy coupled with energy-dispersive x-ray spectroscopy and x-ray powder diffraction analyses showed the formation of semicrystalline coatings consisting of rutile IrO2 crystalline particles dispersed in an amorphous Ta2O5 matrix. Increasing the calcination temperature promoted the IrO2 crystal growth and induced a progressive morphological transition from acicular structures to pseudo-cubical and elongated polyhedral systems. Electrochemical characterization demonstrated a trade-off between activity and durability, with lower calcination temperatures favoring a higher activity and higher calcination temperatures improving operational stability. These findings provide valuable guidelines for optimizing MMO anodes for acidic OER applications.