Synthesis of new protic ionic liquids for proton-exchange membranes: What else is out there?
Eduardo MAURINA MORAIS1, Anna MARTINELLI1
1Chalmers University of Technology, Gothenburg, Sweden
One of the main selling points of ionic liquids is their versatility since different physicochemical properties can be achieved by simply combining different pairs of ions. However, what happens when the common combinations don’t achieve the desired properties? One answer to this problem is to develop new precursor compounds. Practically, in the case of protic ionic liquids that are made from neutralization reactions between acids and bases, this means making new protic ionic liquids by exploring new acids and bases. Considering that the development of new strong acids can be quite challenging, we opted for developing new organic bases.
The objective of our work is to synthesize well-characterized, high purity, gram-scale organic bases that can be later used to synthesize protic ionic liquids using methods developed in our previous work, in which triazolium based protic ionic liquids were synthesized and compared to imidazolium based compounds. These protic ionic liquids are meant to be later used as proton conducting species in high temperature proton exchange membrane fuel cells, by supporting them in a polymeric material, such as polybenzimidazole (PBI).
Our most recent work focused on two classes of protic ionic liquids, biobased and imidazolium based. The biobased protic ionic liquids were made using a furfural based amine synthesized by improving the method proposed by Socha et al. The imidazolium based protic ionic liquids were designed to be highly acidic, by using electron-withdrawing groups (nitro and cyano), similar to my previous work.
There are many specific challenges with the design, synthesis, analysis, and application of new protic ionic liquids, and we hope that the work and results that we will present can be of help to anyone exploring this field.
 Morais, E.M.; Abdurrokhman, I; Martinelli; A. Solvent-free synthesis of protic ionic liquids. Synthesis, characterization and computational studies of triazolium based ionic liquids. J. Mol. Liq. 2022, 360, 119358. DOI: 10.1016/j.molliq.2022.119358
 Socha, A. M.; Parthasarathi, R.; Shi, J.; Pattathil, S.; Whyte, D.; Bergeron, M.; George, A.; Tran, K.; Stavila, V.; Venkatachalam, S.; et al. Efficient biomass pretreatment using ionic liquids derived from lignin and hemicellulose. PNAS. 2014, 111 (35), E3587-E3595. DOI: 10.1073/pnas.140568511
 Morais, E. M.; Grillo, I. B.; Stassen, H. K.; Seferin, M.; Scholten, J. D. The effect of an electron-withdrawing group in the imidazolium cation: the case of nitro-functionalized imidazolium salts as acidic catalysts for the acetylation of glycerol. New J. Chem., 2018, 42, 10774-10783. DOI: 10.1039/C8NJ02520G