Noble-metal-free catalysts, such as metal-nitrogen-carbon (M-N-C) materials, have attracted significant attention owing to their excellent electrocatalytic activity toward the oxygen reduction reaction (ORR). Among them, FeN4 single-atom catalysts embedded in graphene have been extensively investigated as promising ORR catalysts. However, the reaction mechanism still remains controversial, and the predicted potential deviates from experimental observations. In this work, we employed DFT calculations to elucidate the ORR mechanism taking the solvation effect into consideration. The results reveal that the central Fe atom is covered by *O2, which acts as a modifying ligand to optimize the adsorption of reaction intermediates, yielding a theoretical limiting potential of 0.61 V. When solvation is included, the limiting potential increases to 0.78 V (implicit solvent) and 0.71 V (explicit solvent), in good agreement with experimental values. The enhanced catalytic activity originated from solvent stabilization of the adsorbed ORR intermediates via hydrogen bonding, which facilitates the overall reaction process. The solvent effect is particularly pronounced for the *OH species, whose adsorption is significantly stabilized by explicit water molecules, thereby hindering further reduction of *OH/*OH and rendering the O2-mediated mechanism is more favorable for FeN4 in explicit solvent surroundings. Finally, by incorporating the applied potential through a constant-potential model, the limiting potential reaches approximately 0.8 V, consistent with the experimental findings. This work demonstrates the necessity of assessing the effect of solvent and would help design better ORR electrocatalysts.
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