Partial breaking of the Coulombic ordering of ionic liquids confined in carbon nanopores

Ryusuke Futamura (1) , Taku Iiyama (1) , Yuma Takasaki (1) , Yury Gogotsi (1, 2) , Mark J. Biggs (3, 4) , Mathieu Salanne (5, 6) , Julie Segalini (7) , Patrice Simon (1, 5, 7) , Katsumi Kaneko (1)

1 Shinshu University [Nagano]
2 Drexel University
3 Loughborough University
4 University of Adelaide
5 RS2E - Réseau sur le stockage électrochimique de l'énergie
6 PHENIX - PHysicochimie des Electrolytes et Nanosystèmes InterfaciauX
7 CIRIMAT - Centre interuniversitaire de recherche et d'ingenierie des matériaux

Ionic liquids are composed of equal quantities of positive and negative ions. In the bulk, electrical neutrality occurs in these liquids due to Coulombic ordering, in which ion shells of alternating charge form around a central ion. Their structure under confinement is far less well understood. This hinders the widespread application of ionic liquids in technological applications. Here we use scattering experiments to resolve the structure of a widely used ionic liquid (EMI–TFSI) when it is confined inside nanoporous carbons. We show that Coulombic ordering reduces when the pores can accommodate only a single layer of ions. Instead, equally charged ion pairs are formed due to the induction of an electric potential of opposite sign in the carbon pore walls. This non-Coulombic ordering is further enhanced in the presence of an applied external electric potential. This finding opens the door for the design of better materials for electrochemical applications.

Domaines: Autre; Matériaux

Ryusuke Futamura, Taku Iiyama, Yuma Takasaki, Yury Gogotsi, Mark J. Biggs, et al.. Partial breaking of the Coulombic ordering of ionic liquids confined in carbon nanopores. Nature Materials, 2017, 16 (12), pp.1225-1232. ⟨10.1038/NMAT4974⟩. ⟨hal-02048141⟩