Gold-etching redox reactions at the gold interface of an ionic liquid monitored using electrochemical surface plasmon resonance

I²/I⁻ redox reaction on the gold interface of an ionic liquid, 1-octyl-3-methylimidazolium bis(nonafluorobutanesulfonyl)amide, has been studied using electrochemical surface plasmon resonance (SPR) to investigate how SPR can sense the dissolution/deposition of gold film accompanied with the two-step processes of the I²/I⁻ redox reaction. The SPR response measured simultaneously with cyclic voltammetry (CV) has clearly shown that SPR can sense the change in the gold film thickness due to the gold dissolution/deposition. The classical least squares method has successfully separated the two contributions to the SPR response: one from the gold thickness and the other from the surface concentration of dissolved redox species. Model simulations for CV and light reflectivity have reproduced the two SPR contributions well. Furthermore, a systematic deviation of the experimental data from the simulation results observed at positive potentials has suggested that the gold dissolution/deposition processes induce the surface roughness change of the gold film on the Angstrom level.