A synergistic effect of the hydrogen bond on the cycloaddition of CO2 and epoxides to form cyclic carbonates was investigated through experimental study and characterization. A highly effective homogeneous system of hydroxyl-functionalized quaternary ammonium ionic liquids with a different number of the hydroxyl group in the cation was developed for the fixation of CO2 to form cyclic carbonates. A mechanism via the hydrogen bond activation for the cycloaddition was proposed based on both experimental data and modeling. This research enhances the understanding of the promotion of reaction via hydrogen bonding and forms the basis for the rational design of catalytic systems for the fixation of CO2 into organic compounds. (C) 2015 Elsevier Ltd. All rights reserved.