Absorption　carbon　capture　is　currently　the　most　commercialized　technology　and　deemed　as　the　vital　solution　to　balance　continued　use　of　fossil　fuels　and　carbon　emission　reduction.　Nevertheless,　its　high　energy　cost　remains　the　major　concern　for　wide-scale　application.　Consequently,　it　is　of　great　significance　to　address　this　issue　by　analyzing　the　underlying　energy　conversion　mechanism,　answering　the　pivotal　question　＂What　characteristics　lead　to　a　superior　absorbent?＂,　and　developing　more　efficient　absorbent.　In　this　paper,　an　irreversible　decoupling　model　of　absorption　carbon　capture　system,　consisting　of　a　heat　engine　and　a　chemical　pump,　is　innovatively　established.　Accordingly,　key　performance　indicators　are　analytically　derived　and　the　optimal　operation　strategies　of　the　system　are　explicitly　determined.　Notably,　the　matching　of　two　subsystems　leads　to　a　novel　insight　into　the　heat　and　mass　transfer　interaction　of　absorbent,　according　to　which　the　simulated　results　and　the　question　concerning　the　best　absorbent　are　thermodynamically　interpreted　and　addressed,　respectively.　Additionally,　the　comparisons　between　the　calculated　optimal　energy　conversion　efficiencies　with　experimental　and　simulated　results　are　presented　and　discussed.　Our　findings　may　indicate　the　efficient　pathway　for　developing　advanced　absorbent　and　provide　instructing　information　for　the　design　and　operation　of　practical　carbon　capture　systems.