Electrochemical concentration gradients in deep eutectic solvents

Concentration gradients present in the solution during the redox chemistry of selected metals and conducting polymer (poly(3,4ethylenedioxythiophene) (PEDOT)) films redox cycled in Deep Eutectic Solvents (DES) were observed for the first time through the application of the Probe Beam Deflection (PBD) technique combined with the Electrochemical Quartz Crystal Microbalance (EQCM). Suitability of choline chloride (ChCl) based DES for applications as electrolytes in PEDOT based charge storage devices has also been investigated using EQCM. The combination of carefully optimized experimental parameters (temporally extended chronoamperometry and slow scan rate voltammetry) with modified design of the instrument (reduced probe’s distance of approach) allowed for in-situ observations of electrochemically induced concentration gradients in DES based systems. During the studies of electroactive polymer films, complete determination of mobile species transfers in PEDOT/Ethaline and PEDOT/Propaline systems has been achieved. The application of PBD-EQCM technique in studies of metal electrodeposition from DES allowed for monitoring metal speciation in dynamic and quantitative fashion. EQCM study of ChCl based DES indicated Ethaline as the most promising potential electrolyte for PEDOT based charge storage devices. Additionally, an unusual mass exchange process has been detected in PEDOT/Propaline and PEDOT/Acetaline processes. This work has shown a novel, affordable and non-invasive route for observation of electrode/electrolyte interface processes in DES. The experimental protocol developed can potentially be implemented in further studies of DES as well as Ionic Liquids.