Redox-Couple Mediation: A promising strategy to enhance the electrocatalytic performance of Surface-Active ionic liquid interfaces

The unique characteristics of the aqueous interfacial and micellar aggregates of surface-active ionic liquids (SAILs) endow them with excellent electrocatalytic properties, selectivity and efficiency toward electrochemical transformations. However, the low electron-tunnelling probability on account of the significant spatial separation between the electrode and the bulky SAIL-bound electroactive analytes is expected to render the SAILs with an apparent electrocatalytic performance that is significantly lower than their true potential. The availability of appropriate redox-mediators in the vicinity of SAIL-bound electroactive analytes is a possible strategy to bridge this undesired mismatch between the apparent and the expected electrocatalytic performance from the aqueous micellar solutions of SAILs. In anticipation of this presumption, the current work was designed to explore the potential utility of a well-known redox mediator, K4[Fe(CN)6], to enhance the electrocatalytic performance of aqueous micellar solutions of SAILs. The impact of K4[Fe(CN)6] over the surface activity, self-aggregation characteristics and electrocatalytic performance of 1-Dodecyl-3-methylimidazolium chloride ([DDMIM]Cl) was investigated using conductometry, voltammetry and scanning electrochemical microscopy (SECM). The carriedout investigations suggest that the ion-pairing of the negatively charged redox mediator with the imidazolium head groups at the electrode/electrolyte and micelle/water interface-localized SAIL units significantly enhances the electrocatalytic performance of aqueous micellar solutions of [DDMIM]Cl toward electro-dehalogenation of halocarbons, oxygen reduction reaction (ORR) and electrochemical sensing of nitrite ion. We demonstrate that the redox couple mediation in SAIL micellar solutions ensures electrocatalytic reduction of water-insoluble toxic halocarbons, 4-electron ORR and electrocatalytic oxidation of toxic nitrite ions over non-catalytic electrode surfaces. Importantly, the K4[Fe(CN)6] mediation in aqueous micellar solutions of [DDMIM]Cl is demonstrated to ensure selective and sensitive electrochemical sensing of nitrite ions with a sensitivity as high as 0.52 mu A nM- 1 and limit of detection as low as 0.2 nM (the best to be reported till date). The presented work, the first of its kind we believe, presents an innovative strategy to improve the electrocatalytic performance of aqueous micellar solutions of SAILs that shall have far-reaching implications over their use as green sustainable electrocatalytic solvent systems for large-scale practical applications.