This review focuses on porous supported single-site catalyst systems (PS-SSCs) for efficient water electrocatalysis. It highlights how porous structures enable high-density metal sites, enhance mass transfer, modulate interfacial effects, and create synergistic sites. Recent progress of PS-SSCs using various porous supports is summarized. Future challenges include mechanistic understanding, scalable synthesis, durability, and integrated electrode design for advanced electrolyzers.

Single-site catalysts (SSCs) have attracted increasing attention due to their ultrahigh atomic utilization and intrinsic catalytic activity in water electrolysis. However, the low volumetric density of SSCs on bulk supports limits the overall activity. Coupling porous supports with SSCs (PS-SSCs) can synergistically achieve exponential performance improvements. Nevertheless, the critical role of porous supports in modulating the electronic and structural properties of SSCs remains not fully understood. This review comprehensively discusses the multifunctional effects of porous supports in enhancing single-metal-site density, mass transfer, interface stress/electric field, and synergistic catalytic activity. Subsequently, recent advances in PS-SSCs for water electrolysis, emphasizing the function of different PS-SSCs in practical water electrolyzers, are summarized. Finally, the main challenges in advancing PS-SSCs are outlined, encompassing theoretical design principles, operational durability, scalable synthesis, and pore structure architecture.