Enhanced photocatalytic and electrocatalytic properties of IrO₂ nanoparticles via Cr and Co ion doping: Insights into surface oxygen defect structures

The growing global energy demand underscores the urgent need for cost-effective visible light-activated photocatalysts capable of efficiently converting diverse molecules into energy-relevant compounds. In parallel, advancements in catalyst synthesis methodologies have intensified research efforts aimed at developing multifunctional catalysts that synergistically integrate photocatalytic and electrocatalytic functionalities. A prevailing strategy to enhance catalytic efficiency in nanoparticles (NPs) focuses on increasing the concentration of active sites, particularly oxygen vacancies, which are critical for improving both photocatalytic and electrocatalytic performance. To address this challenge, IrO₂ nanoparticles were employed as electrocatalysts and doped with transition metal ions, specifically Cr and Co, to systematically investigate their dual photocatalytic and electrocatalytic properties. Structural and electronic characterizations confirmed that the doping process effectively induced the formation of oxygen vacancies. Among the doped systems, Cr-doped IrO₂ (Cr@IrO₂) NPs exhibited superior photocatalytic activity, which was attributed to significant improvements in visible light absorption compared to both undoped IrO₂ and Co-doped IrO₂ NPs. This enhancement is primarily ascribed to the incorporation of Cr ions on the IrO₂ surface, which introduced a higher density of oxygen vacancies due to charge mismatch phenomena, thereby amplifying visible light absorption intensity and catalytic efficiency.