Double layer structure at the ionic liquid-electrode interface using sum frequency generation spectroscopy and electrochemistry

COLL 592

Steven Baldelli, sbaldelli@uh.edu, Selimar Rivera, and Cesar Aliaga. Department of Chemistry, University of Houston, Houston, TX 77204
The arrangement of ions at the platinum electrode in the room-temperature ionic liquid 1-butyl-3-methylimidazolium BF4-, PF6- , N(CN)2- and imide. Have been determined using sum frequency generation vibrational spectroscopy (SFG), electrochemical impedance spectroscopy (EIS), and the vibrational Stark effect. The results indicate that CO adsorbed on the Pt electrode has a Stark shift of 30-35 cm-1/V in the ionic liquid. The PZC of the ionic liquid-Pt system is approximately -500 mV (vs. Ag wire), with a capacitance of 0.10 F/m2. Further, polarization dependent SFG experiments suggest the ions re-organize at the surface depending on the electrode charge. Combining all these results indicate that the ions of a neat ionic liquid are organized in a Helmholtz layer at the electrified metal electrode interface.