Enrichment effects of ionic liquid mixtures at polarized electrode interfaces monitored by potential screening

The behavior of ionic liquids (ILs) at charged interfaces is pivotal for their application in supercapacitors and electrochemical cells. Recently, we demonstrated for neat ILs that the potential screening at polarized electrode interfaces shows a characteristic voltage dependence, as determined in situ by X-ray Photoelectron Spectroscopy. Herein, we use this fingerprint-type behavior to characterize the nature of the IL/electrode interfaces for IL mixtures of [C8C1Im][Tf2N] and [C8C1Im]Cl on Au and Pt electrodes. For Au, the IL/electrode interfaces are dominated by the Cl− anions even down to 0.1 mol % [C8C1Im]Cl content. In contrast, [Tf2N]− anions enrich at the IL / Pt electrode interfaces down to 10 mol % [C8C1Im][Tf2N]; only at lower concentrations, a transition to a Cl− enrichment occurs. These mixture studies demonstrate that even small concentrations of another ILs or contaminations, e.g. remaining from synthesis, can strongly influence the situation at charged IL interfaces