Partial breaking of the Coulombic ordering of ionic liquids confined in carbon nanopores
journal contributionposted on 15.09.2017, 09:07 authored by Ryusuke Futamura, Taku Iiyama, Yuma Takasaki, Yury Gogotsi, Mark Biggs, Mathieu Salanne, Julie Segalini, Patrice Simon, Katsumi Kaneko
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 the widely used ionic liquid (EMI-TFSI) when it is confined inside nanoporous carbons. We show that Coulombic ordering reduces when the pores can only accommodate 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.
R.F. is supported by Kotobuki Co. Fund. This research was supported by Grant-in-Aid for Young Scientists (B) (No. 26870240), Young Scientists (A) (No. 17H04953), Scientific Research (A) (No. 24241038), Scientific Research (B) (No. 17H03039), CREST (JPMJCR1324) and Center of Innovation Program from Japan Science and Technology Agency. The synchrotron radiation experiments were performed at the BL02B2 of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal No. 2012B1438, No. 2013B1243, No.2014A1167 and No. 2014B1196) and at the BL5S2 of Aichi Synchrotron Radiation Center, Aichi Science & Technology Foundation, Aichi, Japan (Approval No. 2016D4005 and No. 201606124). P.S. acknowledges the support from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement n.102539 (Advanced Grant, Ionaces project). M.J.B. acknowledges the support of the Australian Research Council Discovery Program (DP110101293). Y.G. work on CDC was supported by the Fluid Interface Reactions, Structures & Transport, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.