This study explores the use of nanocurvature-induced electric field modulation to control the activity of single-atom electrocatalysts (SACs). By hosting M-N4 active sites on spherical carbon supports with varying degrees of nanocurvature, the researchers demonstrate that larger nanocurvature induces a stronger electric field. This effect is confirmed through in-situ Raman spectroscopy using a Stark shift reporter. The strategy is effective across a broad range of SAC systems and electrocatalytic reactions, such as CO2 reduction, alkaline oxygen reduction, hydrogen evolution, and oxygen evolution. For instance, Ni SACs with optimized nanocurvature achieved a high CO partial current density of ~400 mA cm-2 at >99% Faradaic efficiency for CO2 reduction in acidic media. The findings highlight the potential of nanocurvature-induced electric field modulation as a powerful tool for controlling the activity and selectivity of SACs in various electrocatalytic reactions.This study explores the use of nanocurvature-induced electric field modulation to control the activity of single-atom electrocatalysts (SACs). By hosting M-N4 active sites on spherical carbon supports with varying degrees of nanocurvature, the researchers demonstrate that larger nanocurvature induces a stronger electric field. This effect is confirmed through in-situ Raman spectroscopy using a Stark shift reporter. The strategy is effective across a broad range of SAC systems and electrocatalytic reactions, such as CO2 reduction, alkaline oxygen reduction, hydrogen evolution, and oxygen evolution. For instance, Ni SACs with optimized nanocurvature achieved a high CO partial current density of ~400 mA cm-2 at >99% Faradaic efficiency for CO2 reduction in acidic media. The findings highlight the potential of nanocurvature-induced electric field modulation as a powerful tool for controlling the activity and selectivity of SACs in various electrocatalytic reactions.