1. Introduction to single-atom catalysts2. Synthesis techniques for single-atom catalysts3. Characterization techniques for single-atom catalysts4. Single-atom catalysts for electrocatalytic oxygen reduction5. Single-atom catalysts for electrocatalytic oxygen evolution reaction6. Single atom catalysts for electrocatalytic hydrogen evolution reaction7. Single-atom catalysts for electrocatalytic carbon dioxide reduction8. In situ/operando X-ray absorption spectroscopy in small molecule-based electrocatalysis9. Single-atom catalyst for Li-S batteries10. Conclusion and outlooks