Beyond the Active Site: Hydrophobic Microenvironment Engineering for Single‐Atom Catalysts

Single-atom catalysts (SACs) offer near-unity atomic utilization and uniform active sites, yet their aqueous-phase performance is constrained by competitive water adsorption, parasitic side reactions, and mass transfer limitations. This review systematically examines hydrophobic microenvironment engineering as a strategy to overcome these challenges, proposing a unified framework integrating wettability regulation with reaction-transport coupling. We comprehensively discuss construction strategies including surface modification, intrinsically hydrophobic supports, and biomimetic hierarchical structures, establishing a complete synthetic-to-wettability framework. Mechanistically, we elucidate how hydrophobic microenvironments optimize catalysis through mass transport regulation, active site protection, and electronic modulation, revealing multi-scale coupling from macroscopic contact angles to atomic dynamics. Drawing on advances in organic synthesis, energy conversion, and environmental catalysis, we outline core design principles such as moderate hydrophobicity and outline future directions, including stimuli-responsive catalysts. This framework guides the rational design and industrial translation of hydrophobic SACs.