Adsorption of 2,2′-bipyridine at an Au(111)|ionic liquid electrified interface

The adsorption of added 2,2′-bipyridine (2,2′-BP) from 1-ethyl-2,3-dimethyl imidazolium bis(trifluoromethanesulfonyl)imide (EMMImNTf2) at an Au(111) electrode has been investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Addition of 2,2′-BP to the ionic liquid clearly modifies the interfacial region as a result of the competition between 2,2′-BP and EMMImNTf2 to occupy the electrode surface. Within the region of ideal polarizability, the 2,2′-BP adlayer undergoes structural changes, shown by the presence of peaks in the CV curves. Between −0.2 V and + 0.9 V, the capacitance-potential curves obtained from EIS data present a capacity maximum depending strongly on the ac frequency, which is typical pseudo-capacitive behavior indicative of a reorganization of the interfacial layer. At more positive potentials a true capacity value close to 10 μF.cm− 2 and invariant with the potential suggests that the 2,2′-BP molecules adopt a perpendicular orientation with the nitrogen atoms facing the electrode surface, similar to their adsorption on gold from aqueous solutions.