Progress in the study of ionicity of protic ionic liquids

Protic ionic liquids (PILs) are formed by proton transfer from Bronsted acid and Bronsted base. The balance of proton transfer reaction leads to the presence of molecular components in addition to the ionic components in most PILs. The proportion of ionic components in PILs is ionicity. This paper reviews the qualitative and quantitative methods for studying the ionicity of PILs. In addition, a thermodynamic research method based on the quantitative measurement of ionicity is introduced.