Following are some highlights of the publication:

The EQCM/PBD method has for the first time been applied to metal deposition/dissolution processes in deep eutectic solventsThe PBD responds to solution phase chemistry, while the E and QCM probes respond to interfacial processes onlyThe combination of electrochemical (E), gravimetric (QCM) and optical (PBD) responses provides diagnostic capabilityEQCM/PBD data reveal the influence of Ag/Cl− complex speciation in the high chloride concentration ionic liquidThe PBD response reveals the intrusion of solubility limitations into Sn anodic stripping

AbstractThe electrochemical quartz crystal microbalance (EQCM) and probe beam deflection (PBD) have been widely used to study interfacial processes in molecular solvent-based electrolytes. However, there has been limited use of the EQCM and none of PBD in room temperature ionic liquids, including deep eutectic solvents (DES). Here we explore the use of the combined EQCM/PBD technique to the study of Ag and Sn electrodeposition from a DES comprising a 1:2 mixture of choline chloride and ethylene glycol. While overcoming the effect of viscous loss in the acoustic wave (EQCM) part of the experiment is understood, the optical (PBD) technique fails to provide a meaningful response in slow scan rate voltammetric experiments; this contrasts sharply with the straightforward behavior seen in aqueous media. Solution transport considerations reveal this to be a consequence of long surface-to-beam transit times in the viscous DES. The problem can be overcome by operating at scan rates 1-2 orders of magnitude slower, permitting application of this powerful technique to novel media of technological interest. The PBD responses reveal unanticipated chemical effects: multiple complexes in the Ag system and solubility limitations in the Sn system, neither of which is evident from the electrochemical or QCM responses.

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