Electrochemical Reactions at Ionic Liquid/Gold Interface Probed By Electrochemical Surface Plasmon Resonance

Ionic liquids (ILs) are promising materials for electrochemical devices.  To maximize the performance of such devices, studies on the interfacial structure, its dynamics, and the kinetics of electrochemical reactions at electrochemical IL interfaces are of crucial importance.  Previously we studied the dynamics of the structure at IL|Au interface by using electrochemical surface plasmon resonance (ESPR) [1].  The transient curves of the SPR angle, which reflects the change in the structure in the electrical double layer, showed extraordinarily slow relaxation on the order of minutes during multi-potential steps, and revealed asymmetry of the relaxation time to the potential step direction [1].  In the present study, electrochemical reactions at the IL|Au interface have been studied using ESPR. 

We have found that redox reactions at the IL|Au interface can also be sensitively probed using ESPR when we add redox species such as ferrocene and its derivatives in ILs.  Sigmoid curves of the SPR angle are observed during electrode potential scan.  We have analyzed the sigmoid curves by simultaneously using a theory and a digital simulation, and have revealed specific interaction between redox species and IL ions depending on their charges.

[1] N. Nishi, Y. Hirano, T. Motokawa, T. Kakiuchi, Phys. Chem. Chem. Phys. 15 (2013) 11615.