Diffusion regimes at nanoelectrode ensembles in different ionic liquids

Abstract

a b s t r a c tThe electrochemical and diffusion behaviour of different redox probes in different ionic liquids is studied at gold nanoelectrode ensembles (NEEs) in comparison with millimetre sized gold (Au-macro) and glassy carbon (GC) disk electrodes. The redox probes are neutral ferrocene (Fc), the ferrocenylmethyltrimetylammonium cation (FA + ) and the ferrocenylmonocarboxylate anion (FcCOO The CVs of the redox probes at the NEEs are peak shaped at low scan rate (v), while they are sigmoidally shaped at high v, but with some shift between forward and backward patterns. This is indicative of the occurrence of a total overlap (TO) diffusion condition when v is low which becomes a mixed diffusion layers (MDL) regime, with only a partial overlapping of individual diffusion layers, at high v values. In the most viscous IL, namely [P 14,666 ] [N(Tf) 2 ], at v higher than 0.8 V s −1 , a plateau current independent on the scan rate is achieved, indicating the tendency to reach the pure radial regime in this IL. The v values at which the transition between TO and MDL is observed scales directly with D and inversely with the IL viscosity. This behaviour is interpreted on the basis of the dependence of individual diffusion layers at each nanoelectrode on redox probe/IL interaction which fits with existing theoretical models very recently developed for nanoelectrode arrays.

Bioelectroanalysis with nanoelectrode ensembles and arrays

“…Transition from these conditions as a function of nanoelement distance has, nevertheless, been demonstrated experimentally by use of specially-made membranes [61]. It has recently been shown that, for NEE, transition from the total overlap to the pure radial diffusion can be observed on increasing electrolyte viscosity [67]. The voltammetric patterns recorded at NEEs in high-viscosity ionic liquids are, indeed, peak-shaped CV at low scan rates but become sigmoidally shaped at high scan rate (Fig.…”

Polycarbonate-based ordered arrays of electrochemical nanoelectrodes obtained by e-beam lithography

“…Depending on the distance between the nanoelectrode elements [17], the scan rate [17] and the viscosity of the electrolyte [18,19], different diffusion regimes can be observed. They are [1,2,20,21]: (A) total overlap regime, when radial diffusion boundary layers overlap totally; (B) pure radial, when the nanoelectrodes behave independently; (C) linear active, when the nanoelectrodes behave as isolated planar electrodes; (D) mixed diffusion regimes, that are regimes intermediate between cases (A) and (B).…”

Voltammetric behaviour of ferrocene in olive oils mixed with a phosphonium-based ionic liquid

“…This behaviour is conceivably due to the rather low diffusion coefficients of ferrocene (D Fc ) and ferrocenium ion (D Fc+ ) in this medium, which lead to mixed radialplanar diffusion conditions [9,[20][21][22][23]. In fact, in RTILs, diffusion coefficient values for both Fc and Fc + in the range of 5 Â 10 À7 -10 À8 cm 2 s À1 were in general reported [9,[20][21][22][23][24][25][26][27][28].…”