Defective carbons have recently been considered as one of the most promising alternatives to precious metal electrocatalysts. However, atomic structural tailoring of carbon defects poses challenges, especially in regulating defect density to maximize the active sites. Herein, we report an interfacial self-corrosion strategy to control the removal and reconstruction of carbon atoms via a series of thermal redox reactions of ZnO quantum dots and formed CO2 gas in confined carbon cavity. The ultra-dense carbon defects (HDPC) (2.46 × 1013 cm−2) in the derived porous carbon served as efficient active sites for oxygen reduction, resulting in an excellent catalyst in both base and acid (half-wave potentials of 0.90 or 0.75 V in 0.1 M KOH or HClO4). The normalized specific activity and density functional theory calculation reveal a gradient “proximity effect” between carbon defects with different spatial distance, indicating that the quantitative control of carbon defect density is the key to enhancing electrocatalytic activity.