| Abstract
| - We report the cyclic voltammetry, chronoamperometry, and scanning electrochemical microscopy of ferrocenedissolved in deep eutectic solvents (DES), consisting of choline chloride (ChCl) and either trifluoroacetamide(TFA) or malonic acid as the hydrogen-bond donor. Despite the use of ultramicroelectrodes, which wererequired due to the modest conductivities of the DES employed, linear diffusion behavior was observed incyclic voltammetric experiments. The high viscosity of 1:2 ChCl/TFA relative to non-aqueous electrochemicalsolvents leads to a low diffusion coefficient, 2.7 × 10-8 cm2 s-1 for ferrocene in this medium. Because of thedifficulties in achieving steady-state conditions, SECM approach curves were tip velocity dependent. Undercertain conditions, SECM approach curves to an insulating substrate displayed a positive-feedback response.Satisfactory simulation of this unexpected behavior was obtained by including convection terms into themass transport equations typically used for SECM theory. The observance of positive-feedback behavior atan insulating substrate can be described in terms of a dimensionless parameter, the Peclet number, which isthe ratio of the convective and diffusive timescales. Fitting insulator approach curves of ferrocene in 1:2ChCl/TFA shows an apparent increase in the diffusion coefficient with increasing tip velocity, which can beexplained by DES behaving as a shear thinning non-Newtonian fluid.
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