Direct air capture (DAC) is important for achieving net-zero greenhouse gas emissions by 2050. However, the ultradilute atmospheric CO 2 concentration (~400 parts per million) poses a formidable hurdle for high CO 2 capture capacities using sorption-desorption processes. Here, we present a Lewis acid-base interaction–derived hybrid sorbent with polyamine-Cu(II) complex enabling over 5.0 mol of CO 2 capture/kg sorbent, nearly two to three times greater capacity than most of the DAC sorbents reported to date. The hybrid sorbent, such as other amine-based sorbents, is amenable to thermal desorption at less than 90°C. In addition, seawater was validated as a viable regenerant, and the desorbed CO 2 is simultaneously sequestered as innocuous, chemically stable alkalinity (NaHCO 3 ). The dual-mode regeneration offers unique flexibility and facilitates using oceans as decarbonizing sinks to widen DAC application opportunities.