The embodiments of the present disclosure relate to a carbon dioxide absorbent containing an ionic material containing a spiro ammonium cation and a hydroxide anion. The carbon dioxide absorbent according to an embodiment contains a hydroxide anion having a small molecular weight and high basicity, such that absorption performance per unit volume of the absorbent may be effectively improved. Further, the carbon dioxide absorbent according to an embodiment is soluble in water and thus may not cause layer separation problems.

A redox flow acid-gas capture system includes an electrochemical cell including a cathode configured to contact a stream including an electroactive species in an inactive state and provide a reduced stream including the electroactive species in an active state, and an anode configured to contact an adduct stream including an adduct of an electroactive species and an acid-gas and provide an oxidized stream including the electroactive species in the inactive state and the acid-gas; an absorber configured to contact the reduced stream and the acid-gas and form the adduct stream including the adduct of the electroactive species and the acid-gas; and at least one of an oxygen stripper unit, or a degasser unit configured to provide a degassed stream including the electroactive species in an inactive state, and an acid-gas stream.