• • Single-atom catalysts achieve nearly 100% atom utilization efficiency, a theoretical maximum that directly translates to reduced precious metal loading and cost in industrial catalysis.
• • The review identifies five core atomic-level challenges: disordered active site distribution, restricted electronic structure, atom agglomeration, difficulty in increasing loading density, and coordination environment control, which collectively limit performance.
• • Mechanistic analysis reveals that these challenges are interconnected, forming a systemic problem that requires multi-strategy synergy (support engineering, coordination regulation, spatial confinement, dynamic synthesis) for breakthroughs.
• • Future progress hinges on developing in-situ characterization with high spatial and temporal resolution, exploring multi-site synergistic mechanisms, and building standardized databases for rational design, which are essential for scaling up SACs from lab to industrial applications.