Generally, amine group captures CO2 according to 2:1 or 1:1 stoichiometry. Here, we report a kind of improved carbon capture using amino‐functionalized ionic liquids (ILs) through 1:2 stoichiometry. A serial of amino‐functionalized ILs various with basicity and steric hindrance of anion were designed, prepared, and applied in CO2 capture. Through a combination of absorption experiment, quantum chemical calculation, spectroscopic investigation and calorimetric method, the results indicated that one amine group could bind two CO2 through proton transfer (PT) process and intramolecular hydrogen bond formation, which leading to enhanced capacity that breaks through equimolar. The basicity and steric hindrance of anion play a significant role in promoting amine group to capture two CO2. P666142Asp with dual anion was further designed and synthesized to promote PT process, which showed high capacity of 1.96 mol/mol IL at 30°C and 1 atm as well as excellent reversibility. © 2018 American Institute of Chemical Engineers AIChE J, 65: 230–238, 2019