Synergistic Interactions Between Single Atoms and Clusters/Nanoparticles on Nitrogen-Doped Carbon Supports for Electrocatalysis: A Critical Review

Since the discovery of single-atom catalysts (SACs) in 2011, research has primarily focused on achieving atomic dispersion, which can lead to their remarkable catalytic activity, selectivity, and atom utilization. In parallel, nanoparticles (NPs)-based catalysts have a long-standing history and a proven track record in electrocatalysis. Integration of single atoms (SAs) and NPs within a single catalytic framework has recently emerged as a promising strategy to enhance electrocatalytic performance beyond what each component can achieve on its own. Therefore, understanding these synergistic interactions is crucial for improving the activity, selectivity, and long-term stability of hybrid catalysts. Despite this potential, systematic investigations on these hybrid catalyst systems are relatively limited and present significant challenges. This review provides a comprehensive overview of the structural classifications, mechanistic insights, and recent advances in electrocatalytic applications of SA-NP hybrid systems. We further highlight synthetic strategies for nitrogen-doped carbon materials as supports that co-stabilize SAs and NPs, and critically discuss key challenges and future perspectives for the rational design and application of these advanced electrocatalysts are critically discussed.