Zhao, J., Lian, J., Zhao, Z., Wang, X. and Zhang, J. 2022. A Review of In-Situ Techniques for Probing Active Sites and Mechanisms of Electrocatalytic Oxygen Reduction Reactions. Nano-Micro Letters. 15, (Dec. 2022), 19. DOI:https://doi.org/10.1007/s40820-022-00984-5.