Probing the Dynamics Process of High-Entropy Alloy Catalysts: Fundamentals, Synthesis, and In Situ TEM Insights.

Catalysts play a crucial role in advancing green and clean energy technologies for a sustainable future. Among the various catalysts reported, high-entropy alloys (HEAs) stand out due to their superior stability and synergistic effects during catalytic processes, which arise from their complex composition and dynamic behavior. However, despite their promising potential, the incorporation of multiple elements (often more than four) with differing properties in HEA-based catalysts complicates their growth and challenges their synthesis. Recent development of delicate synthetic strategies and theoretical understanding promotes the effective construction of HEAs. Advances of visible characterization techniques contribute to the cognition for the formation and evolution mechanisms of HEAs and further facilitate the accurate design. This review aims to provide a comprehensive overview of current synthesis strategies for HEA-based catalysts while exploring their growth and evolution under real reaction conditions using in situ transmission electron microscopy (in situ TEM). First, the fundamental parameters, properties, and rational design principles of HEAs are examined to establish a detailed foundational understanding. Next, synthesis strategies for HEA-based catalysts, highlighting the most frequently employed methods. The third section focuses on the application of in situ TEM in elucidating the atomic-level mechanisms governing HEA formation. Finally, future opportunities are highlighted for designing next-generation HEA catalysts.