Effect of Calcination Temperature on the Morphological and Electrochemical Characteristics of Supported Iridium Hydroxyoxide Electrocatalysts for the PEM Electrolyzer Anode

The iridium hydroxyoxide, IrOx(OH)y, supported on antimony tin oxide was synthesized using a polyol method for oxygen evolution reaction. The effects of heat-treatment (calcination) on the chemical, physical and electrochemical characteristics of the electrocatalyst are studied. Changes in the physical and chemical structure of the electrocatalyst due to heat-treatment were investigated using X-ray diffraction, scanning electron microscopy/energy dispersive X-ray spectroscopy, transmission electron microscopy, nitrogen physisorption, and X-ray photoelectron spectroscopy. The electrocatalysts were also electrochemically characterized using cyclic and linear sweep voltammetry measurements. The results showed that the IrOx(OH)y electrocatalyst synthesized with the polyol method had an amorphous structure with a particle size distribution of 1–5 nm. Calcination at temperatures higher that 500°C increased the particle size of the iridium species to approximately 30 nm, decreased the surface area by 50%, and altered the structure of iridium based materials from amorphous iridium-hydroxyoxide (IrOx(OH)y) to crystalline iridium oxide (IrO2). Furthermore, the oxidation charge measured from the cyclic voltammograms decreased by roughly 80% and the Tafel slope increased by 25%. The amorphous IrOx(OH)y electrocatalyst had higher activity and better performance (more than 90%) compared to the crystalline IrO2.