Single-Atom Iridium-Based Catalysts: Synthesis Strategies and Electro(Photo)-Catalytic Applications for Renewable Energy Conversion and Storage

Developing renewable energy-related technologies, which are strongly dependent on various catalytic processes, has recently attracted enormous attention to overcome the ever-increasing energy consumption and fossil fuel-based environmental issues. The scarcity and high cost of Pt-group metal-based catalysts, however, are challenges for their future particular applications. Hitherto, single-atom catalysts (SACs) are being considered new advanced materials for different catalytic reactions due to their outperforming performance and 100% active atom utilization. We herein comprehensively recapitulate breakthroughs in synthetic strategies, properties, and applications of Ir-based SACs, being considered as an up-and-coming candidate for electro(photo)-catalytic reactions in sustainable energy-related technologies. Recent synthetic strategies of Ir-based SACs focusing on interaction and coordination environments of isolated Ir single atoms on distinct substrates are introduced; then, various advanced characterization tools (ex-situ and in-situ) for determining the existence of Ir single atoms are presented. Noteworthy applications of Ir-based SACs in electrocatalysis and photocatalysis are described and discussed to further provide an in-depth understanding of their outperforming efficiency. Finally, challenges and prospects of Ir-based SACs for real applications are briefly highlighted, which can provide an overview for designing high-performance and cost-effective iridium-group metal-based catalysts for various catalytic processes.