Enrichment is a prerequisite for CO2 reduction from air and demands mild conditions for energy saving. Electrochemically generated OH- and H+ can be employed for atmosphere CO2 enrichment (capture and recovery) under ambient condition. This study demonstrated the importance of the coexisting ambient O-2 in the electrochemical OH-/H+ generation. Our system showed that CO2 in air could be captured simultaneously with the OH-/H+ generation. Meanwhile, O-2 in air served to start up such generation from a cell voltage of 1.3 V, significantly lower than 2.2 V without O-2. Simple modeling and experiments of OH-/H+ generation evidenced that ambient O-2 elevated the effectiveness of OH-/H+ generation by lifting the energy efficiency in a galvanostatic mode, and accelerating the generation rate in a potentiostatic mode. Meanwhile, the effectiveness elevation was attributed to an improvement of the intrinsic properties of electrode reactions for OH-/H+ generation. Rather, beyond the cell voltage of 4.9 V, no difference was observed in the effectiveness regardless of the presence of ambient O-2. This study would be helpful for designing an effective electrochemical process of atmospheric CO2 enrichment by utilizing ambient O-2 that undergoes an electrode process without consumption.