Physical and electrochemical properties of 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium iodide,and 1-butyl-3-methylimidazolium tetrafluoroborate

The density, viscosity, refractive index, heat capacity, heat of dilution, ionic conductivity, and electrochemical stability of 1-butyl-3-methylimidazolium bromide (bmim]Br]), 1-butyl-3-methylimidazolium iodide (bmim]I]), and 1-butyl-3-methylimidazolium tetrafluoroborate (bmim]BF₄]) were measured at room temperature or over a temperature range of 293.2 to 323.2 K. The density and refractive index values of bmim]I] appeared to be the highest among three ionic liquids (ILs). However, the experimental viscosity values of bmim]Br] were higher than those of bmim]BF₄], while the heat capacities and heats of dilution of bmim]BF₄] were higher than those of bmim]Br]. The cyclic voltammogram of bmim]br] and bmim]BF₄] indicated electrochemical windows in the stability range from 2.7 V of bmim]Br] to 4.7 V of bmim]BF₄].