Double layer effects at nanosized electrodes†

Bund, Andreas; Kubeil, Clemens

doi:10.1039/c3fd00050h

Cited by 3 publications

(3 citation statements)

References 30 publications

(44 reference statements)

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“…In a typical voltammetric measurement with excess supporting electrolyte (SE), λ D is typically ∼1 nm. Accordingly, ion migration effects resulting from the electric-field-driven ion transport are negligible at macroscopic electrodes, and diffusion is the dominant contribution to mass transport. − At low ionic strength, however, a significant depletion zone forms, accompanied by a sizable electric field, and if two electrodes are sufficiently close that their EDLs overlap, ion migration can contribute significantly to mass transport and thus to faradaic currents. ,,− As a result, currents can be enhanced or diminished depending on the charge of the redox-active species and whether the electrode reaction increases or decreases it. ,,, …”

mentioning

confidence: 99%

Ion Accumulation and Migration Effects on Redox Cycling in Nanopore Electrode Arrays at Low Ionic Strength

Wichert

et al. 2016

ACS Nano

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Ion permselectivity can lead to accumulation in zero-dimensional nanopores, producing a significant increase in ion concentration, an effect which may be combined with unscreened ion migration to improve sensitivity in electrochemical measurements, as demonstrated by the enormous current amplification (∼2000-fold) previously observed in nanopore electrode arrays (NEA) in the absence of supporting electrolyte. Ionic strength is a key experimental factor that governs the magnitude of the additional current amplification (AFad) beyond simple redox cycling through both ion accumulation and ion migration effects. Separate contributions from ion accumulation and ion migration to the overall AFad were identified by studying NEAs with varying geometries, with larger AFad values being achieved in NEAs with smaller pores. In addition, larger AFad values were observed for Ru(NH3)6(3/2+) than for ferrocenium/ferrocene (Fc(+)/Fc) in aqueous solution, indicating that coupling efficiency in redox cycling can significantly affect AFad. While charged species are required to observe migration effects or ion accumulation, poising the top electrode at an oxidizing potential converts neutral species to cations, which can then exhibit current amplification similar to starting with the cation. The electrical double layer effect was also demonstrated for Fc/Fc(+) in acetonitrile and 1,2-dichloroethane, producing AFad up to 100× at low ionic strength. The pronounced AFad effects demonstrate the advantage of coupling redox cycling with ion accumulation and migration effects for ultrasensitive electrochemical measurements.

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confidence: 99%

Ion Accumulation and Migration Effects on Redox Cycling in Nanopore Electrode Arrays at Low Ionic Strength

Wichert

et al. 2016

ACS Nano

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“…However, eq is valid for conditions where diffusion dominates, and electromigration contributes negligibly to mass transport, since the measurements are performed in the presence of a large concentration of supporting electrolyte (SE) . In contrast, at low ionic strength, ion migration can contribute significantly to mass transport. − This effect occurs because the Debye length, λ D , depends on ionic strength, so at low ionic strength the electric field extends from the electrode surface into the bulk of solution, which can either promote or impede the movement of ions to the electrode surface. − The enrichment of Ru(NH 3 ) 6 3+/2+ in the negatively charged nanopores to maintain electroneutrality, a phenomenon that has been widely observed in nanopores and nanofluidic channels at low ionic strength, could also contribute to the observed current amplification. − Enhanced currents have been observed at low ionic strength on a single microelectrode, producing a several-fold increase in I lim for the reduction of cationic species or oxidation of anionic species in the absence of SE. , In this study, we explore how migration effects, in combination with ion enrichment at nanopore-confined electrodes, might be further exploited to enhance mass transport in a dual electrode system exhibiting the RC effect, resulting in additional current amplification. Migration effects are expected to be larger in dual electrode systems, since the electric field established across the two electrodes can drive the movement of ions, at least in one direction, speeding up the redox cycling events.…”

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Redox Cycling on Recessed Ring-Disk Nanoelectrode Arrays in the Absence of Supporting Electrolyte

Contento

Bohn

2014

J. Am. Chem. Soc.

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In canonical electrochemical experiments, a high-concentration background electrolyte is used, carrying the vast majority of current between macroscopic electrodes, thus minimizing the contribution of electromigration transport of the redox-active species being studied. In contrast, here large current enhancements are achieved in the absence of supporting electrolyte during cyclic voltammetry at a recessed ring-disk nanoelectrode array (RRDE) by taking advantage of the redox cycling effect in combination with ion enrichment and an unshielded ion migration contribution to mass transport. Three distinct transport regimes are observed for the limiting current as a function of the concentration of redox species, Ru(NH3)6(2+/3+), revealed through the strong dependence of ion transport on ionic strength. Behavior at low analyte concentrations is especially interesting. In the absence of supporting electrolyte, ions accumulate in the nanopores, resulting in significantly increased current amplification compared to redox cycling in the presence of supporting electrolyte. Current enhancements as large as 100-fold arising from ion enrichment and ion migration effects add to the ~20-fold enhancement due to redox cycling, producing a total current amplification as large as 2000-fold compared to a single microelectrode of the same total area, making these RRDE arrays interesting for electrochemical processing and analysis.

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“…Furthermore, they showed that the size of nanoparticles could be determined with sub-angstrom resolution by detecting the current drop across the orice. 114 As the diameter of a nanopore decreases to a few nanometers, approaching the thickness of the electrical double layer, eld driven migration [119][120][121][122][123] and eldinduced accumulation or depletion [124][125][126][127][128] of charged entities in the nanopores become important. By controlling the surface charge of nanopore electrodes, the accumulation of oppositely charged ions leads to an enhancement in the ionic current through the nanopore.…”

Section: Nanopores Nanochannels and Nanopipettesmentioning

confidence: 99%

Emerging tools for studying single entity electrochemistry

2016

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Electrochemistry studies charge transfer and related processes at various microscopic structures (atomic steps, islands, pits and kinks on electrodes), and mesoscopic materials (nanoparticles, nanowires, viruses, vesicles and cells) made by nature and humans, involving ions and molecules. The traditional approach measures averaged electrochemical quantities of a large ensemble of these individual entities, including the microstructures, mesoscopic materials, ions and molecules. There is a need to develop tools to study single entities because a real system is usually heterogeneous, e.g., containing nanoparticles with different sizes and shapes. Even in the case of "homogeneous" molecules, they bind to different microscopic structures of an electrode, assume different conformations and fluctuate over time, leading to heterogeneous reactions. Here we highlight some emerging tools for studying single entity electrochemistry, discuss their strengths and weaknesses, and provide personal views on the need for tools with new capabilities for further advancing single entity electrochemistry.

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Double layer effects at nanosized electrodes†

Cited by 3 publications

References 30 publications

Ion Accumulation and Migration Effects on Redox Cycling in Nanopore Electrode Arrays at Low Ionic Strength

Ion Accumulation and Migration Effects on Redox Cycling in Nanopore Electrode Arrays at Low Ionic Strength

Redox Cycling on Recessed Ring-Disk Nanoelectrode Arrays in the Absence of Supporting Electrolyte

Emerging tools for studying single entity electrochemistry

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