This review article focuses on the synergistic electrocatalysis between single atoms and nanoparticles/cluster catalysts, highlighting recent advances and fundamental principles. The authors discuss the synthetic strategies, characterization methods, and synergistic mechanisms of these composite catalysts. Key findings include: 1. **Synthetic Strategies**: Various methods such as co-precipitation, solvothermal, impregnation, atomic layer deposition (ALD), and "coating-pyrolysis-etching" are used to integrate single atoms with clusters or nanoparticles. These methods ensure uniform dispersion and support the active sites. 2. **Characterization Methods**: Techniques like aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM), energy-dispersive X-ray spectroscopy (EDX), X-ray absorption spectroscopy (XAS), and density functional theory (DFT) calculations are employed to analyze the structure and electronic properties of the catalysts. 3. **Synergistic Mechanisms**: DFT calculations reveal the charge distribution, adsorption energies, and reaction mechanisms. The interaction between single atoms and clusters/nanoparticles can lead to changes in electronic structure, electron transfer, and reaction pathways, enhancing catalytic performance. 4. **Applications**: The review covers the application of these synergistic composite catalysts in various clean energy reactions, including oxygen reduction/evolution (ORR/OER), hydrogen evolution (HER), and carbon dioxide reduction (CO2RR). 5. **Challenges and Perspectives**: Despite the advancements, challenges such as catalyst stability, cost, and the complexity of multi-site interactions remain. The authors propose future directions for improving the design and performance of synergistic composite catalysts. The article emphasizes the importance of integrating single atoms with clusters or nanoparticles to enhance catalytic efficiency and stability, providing a comprehensive overview of the current state and future prospects in this field.This review article focuses on the synergistic electrocatalysis between single atoms and nanoparticles/cluster catalysts, highlighting recent advances and fundamental principles. The authors discuss the synthetic strategies, characterization methods, and synergistic mechanisms of these composite catalysts. Key findings include: 1. **Synthetic Strategies**: Various methods such as co-precipitation, solvothermal, impregnation, atomic layer deposition (ALD), and "coating-pyrolysis-etching" are used to integrate single atoms with clusters or nanoparticles. These methods ensure uniform dispersion and support the active sites. 2. **Characterization Methods**: Techniques like aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM), energy-dispersive X-ray spectroscopy (EDX), X-ray absorption spectroscopy (XAS), and density functional theory (DFT) calculations are employed to analyze the structure and electronic properties of the catalysts. 3. **Synergistic Mechanisms**: DFT calculations reveal the charge distribution, adsorption energies, and reaction mechanisms. The interaction between single atoms and clusters/nanoparticles can lead to changes in electronic structure, electron transfer, and reaction pathways, enhancing catalytic performance. 4. **Applications**: The review covers the application of these synergistic composite catalysts in various clean energy reactions, including oxygen reduction/evolution (ORR/OER), hydrogen evolution (HER), and carbon dioxide reduction (CO2RR). 5. **Challenges and Perspectives**: Despite the advancements, challenges such as catalyst stability, cost, and the complexity of multi-site interactions remain. The authors propose future directions for improving the design and performance of synergistic composite catalysts. The article emphasizes the importance of integrating single atoms with clusters or nanoparticles to enhance catalytic efficiency and stability, providing a comprehensive overview of the current state and future prospects in this field.