Insight into the impact of calcination on the formation mechanism, microstructure, and OER performance of IrO ₂ –Ta ₂ O ₅ mixed metal oxide anodes

Abstract IrO 2 –Ta 2 O 5 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 IrO 2 –Ta 2 O 5 coatings prepared by thermal decomposition of chloride precursors was systematically investigated. TGA coupled with FTIR spectroscopy on evolved gas revealed the release of H 2 O and HCl during the thermal treatment, suggesting that hydrolysis-assisted reactions contribute to the MMO formation. SEM-EDS and XRPD analyses showed the formation of semicrystalline coatings consisting of rutile IrO 2 crystalline particles dispersed in an amorphous Ta 2 O 5 matrix. Increasing the calcination temperature promoted the IrO 2 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 temperatures favoring a higher activity and higher temperatures improving operational stability. These findings provide valuable guidelines for optimizing MMO anodes for acidic OER applications.