Electrochemical Behavior of Nanoelectrode Ensembles in the Ionic Liquid [BMIm][BF₄]

Abstract

The electrochemical behavior of nanoelectrode ensembles (NEEs), prepared by electroless plating of Au using microporous polycarbonate membranes as template, is tested in the ionic liquid [BMIm] [BF 4 ]. The accessible potential window is significantly wider in [BMIm] [BF 4 ] than in water, extending approximately, for 3.4 V vs. 1 V, respectively. The voltammetric behavior at NEEs of two redox probes, namely butyl viologen (BV 2þ ) and (ferrocenylmethyl) trimethylammonium (FA þ ) are examined at different scan rates. In both cases, at scan rates higher than 200 mV/s sigmoidally shaped voltammograms typical of a pure radial diffusion regime are observed. At lower scan rates the voltammograms are peak shaped, as expected for total overlap diffusion conditions. This is the first time that the pure radial regime is obtained with NEEs made using commercially available polycarbonate templates, since in water solution only the total overlap regime is typically observed. This is explained as a consequence of the high viscosity of [BMIm] [BF 4 ] which reflects in lowering of diffusion coefficients and smaller thickness of diffusion layers, for the same time scale, with respect to water solutions, but also the fact that the nanoelectrodes are slightly recessed helps in observing the pure radial regime. In order to make operative the pure radial condition it is indeed required that the thickness of diffusion layer at individual nanoelectrodes be smaller than the hemi-distance between neighboring nanoelectrodes. Examining the analytical performances achievable with NEEs in [BMIm] [BF 4 ], it is shown that a limit is given by the decreased diffusion coefficients. Detection limits at NEEs in the ionic liquid are indeed higher than those obtained in water solutions. This notwithstanding, detections limits at NEEs in [BMIm] [BF 4 ] are always improved with respect to those at conventional electrodes.

Irreversible Redox Reactions of Ferrocene/Ferrocenium on Self-Assembled Monolayer Modified Gold Electrode in Ionic Liquid BMIMBF[sub 4]

“…As shown in Fig. 4b, the peak current is proportional to the square root of the scan rate, indicating that both the oxidation and the reduction reactions are diffusion controlled processes, that has also been reported in the [35][36][37][38][39] The D value of Fc was estimated by the slope of the anodic straight line in Fig. 4b, assuming the redox reaction is reversible.…”

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).…”

Nanoimprinted arrays of glassy carbon nanoelectrodes for improved electrochemistry of enzymatic redox-mediators

“…Notwithstanding the biocompability and chemical inertness of gold as electrode material, the use of nanogold suffers from some limits related to the relatively narrow potential window accessible which, on the cathodic side is limited by facilitated hydrogen evolution and, on the anodic side, by facilitated gold oxides formation [4,17]. For the case of NEEs, the spatial distribution of the nanoelectrodes is random arranged, consequently the diffusion regime is not always fully controllable, possibly changing from total overlap to pure radial or to mixed [4,[18][19][20] by changing the scan rate or the viscosity of the matrix in the electrochemical cell [21,22]. These limits prompted to the development of ordered nanoelectrode arrays (NEAs).…”