Carbonate-based solvents have advantages over amines for capturing CO 2 from fossil fuel-fired power stations. However, due to slow reaction kinetics, boric acid has been proposed as rate promoter in carbonate-based solvents for reducing CO 2 emission. In this work, borate promotion mechanism has been validated and vapor liquid equilibrium for 35wt% carbonate solutions with 1wt%, 3wt% boric acid was investigated at 323K, 333K and 343K. Based on complexation reaction with mannitol, results show that the tetrahydroxy borate ion, B(OH) 4 − , is considered as a reactive specie toward carbon dioxide absorption. Effect of boric acid and temperature on equilibrium CO 2 partial pressures was discussed in the investigated CO 2 loading range.