Investigation of the Modified Adams Fusion Method for Enhanced Oxygen Evolution Reaction Activity of Iridium Oxide Catalysts

Abstract

As technological and industrial scales continue to expand, carbon emissions have increased, leading to environmental pollution and climate change. Hydrogen has gained attention as a clean energy for the transition toward sustainable energy systems. Green hydrogen produced via water electrolysis emits no CO₂ during use and is regarded as a next-generation clean energy source. Among various water electrolysis technologies, proton exchange membrane water electrolysis (PEMWE) has been actively studied due to its advantages of operating at high efficiency, rapid response, and device miniaturization. However, the oxygen evolution reaction (OER) in PEMWE proceeds under harsh conditions, including strong acidity and high current density, requiring the use of precious-metal catalysts, which significantly increases system costs. Therefore, reducing iridium usage while maintaining high catalytic activity is a crucial challenge for large-scale deployment. Improving OER activity of catalyst is directly linked to reducing precious-metal consumption. Iridium, a representative OER catalyst, is generally used in its oxide form. The Adams fusion method is widely used for synthesizing iridium oxide due to its simplicity, and numerous studies have attempted to modify this method to enhance catalytic activity and stability. In this study, a modified Adams fusion method was developed to improve the activity of IrOx catalysts through control of catalyst morphology and iridium oxidation-state distribution. The modified Adams fusion method was established through systematic experiments on additives, calcination temperatures, and acid-treatment, and successfully synthesized modified Adams fusion method-IrOx (MA-IrOx) with a higher proportion of Ir(III) species than the rutile-IrO2 synthesized by the conventional Adams fusion method. The MA-IrOx exhibited an overpotential of 292 mV at 10 mA cm⁻² and a mass activity of 73.63 A g Ir⁻¹ at 1.55 VRHE. In addition, a membrane electrode assembly was fabricated using ultrasonic spray coating. The superior catalytic performance was demonstrated by achieving a cell voltage of 1.744 V at a current density of 2 A cm⁻² with a low iridium loading of 0.2 mg cm⁻², indicating the strong potential of MA-IrOx as an efficient OER catalyst for PEMWE applications.