Elucidation the relationship between electrode potentials and heterogeneous electrocatalytic reactions has attracted widespread attention. Herein we construct the well-defined Mn single-atom (MnSA) catalyst with four N-coordination through a simple thermal pyrolysis preparation method to investigate the electrode potential micro-environments effect on carbon dioxide reduction reactions (CO₂RR) and oxygen reduction reactions (ORR). MnSA catalysts generate higher CO production Faradaic efficiency of exceeding 90% at −0.9 V for CO₂RR and higher H₂O₂ yield from 0.1 to 0.6 V with excellent ORR activity. Density functional theory (DFT) calculations based on constant potential models were performed to study the mechanism of MnSA on CO₂RR. The thermodynamic energy barrier of CO₂RR is lowest at −0.9 V vs. reversible hydrogen electrode (RHE). Similar DFT calculations on the H₂O₂ yield of ORR showed that the H₂O₂ yield at 0.2 V was higher. This study provides a reasonable explanation for the role of electrode potential micro-environments.