Electrochemical Oxidation of Hydrogen on Basal Plane Platinum Electrodes in Imidazoliurn Ionic Liquids

In this paper, the electrochemical oxidation of hydrogen at the interface between single-crystal platinum electrodes and imidazolium-type room-temperature ionic liquids (RTILs) is studied. This is the first report about the electrochemical properties of single-crystal platinum electrodes in contact with ionic liquids. It was found that the imidazolium cation can be reduced to 1-alkyl-3-methylimidazol-2-ylidene species on the basal plane platinum electrodes and that the presence of hydrogen increases the reversibility of this process, suggesting that it is a proton-coupled electron-transfer reaction. On the other hand, it was found that the oxidation of H(2) is a surface structure-sensitive process on RTIL/Pt interfaces. The activity toward H(2) oxidation was found to increase in the order of Pt(100) < Pt(110) < Pt(111) in [C(4)mim][OTf], [C(2)mim][EtSO(4)], and [C(4)mim] [BF(4)]. However, in [C(2)mim] [NTf(2)], Pt(100) is the best electrocatalytic electrode for this reaction. Finally, a complex kinetic behavior was observed upon potential cycling of [C(4)mim][OTf] saturated with H(2) in contact with Pt(110) as a working electrode. This is the first experimental example of an electrochemical oscillator in RTILs. The competitive adsorption of H(2) and carbenes and the electrode reconstruction, modulated by the adsorbates, can be at the origin of this electrochemical oscillatory behavior. The results presented here are expected to be useful for clarifying the complex nature of the platinum electrode/RTIL interface and to be of practical use for its possible applications in the electrosynthesis of carbenes, electrochemical sensors, and fuel cells.