Five different ionic liquids containing the tetracyanoborate anion were synthesized and evaluated for CO₂ separation performance. Measured CO₂ solubility values were exceptionally high compared to analogous ionic liquids with different anions and ranged from 0.128 mol L⁻¹ atm⁻¹ to 0.148 mol L⁻¹ atm⁻¹. In addition, CO₂ permeability and CO₂/N₂ selectivity values were measured using a supported ionic liquid membrane architecture and the separations performance of the ionic liquid membranes exceeded the Robeson upper bound. These results establish the distinct potential of ionic liquids with the tetracyanoborate, [B(CN)₄], anion for the separation of CO₂.