Chronoamperometric response at nanoscale liquid–liquid interface arrays

Abstract

In this work, potential step chronoamperometry (PSCA) was used to study the behaviour of arrays of nanoscale interfaces between two immiscible electrolyte solutions (nanoITIES). The nanoITIES arrays were formed at nanoporous silicon nitride membranes containing 400 nanopores in a hexagonal close-packed arrangement. Three membrane designs, with nanopore radii of 75, 50 and 17 nm, were studied by ion-transfer of tetrapropylammonium cations across the nanopore array-supported water1,6-dichlorohexane interface. The cell time constants and charging times were determined prior to experimental PSCA. The three membrane designs studied exhibited charging times in the range of 0.08 s to 0.46 s, with the smallest pore configuration (17 nm radius) exhibiting the longest charging time. The experimental steady-state currents were 30-50 % lower than of the calculated inlaid disc model currents, due to diffusion zone overlap at adjacent interfaces. The three 1 ISE member 2 nano-interface arrays studied also showed response times of 6  1 s, being the time required to reach 95 % of the steady-state current.

Electrochemical Characterisation of Nanoscale Liquid|Liquid Interfaces Located at Focused Ion Beam‐Milled Silicon Nitride Membranes

“…This is, again, in agreement with previous studies 5c. d, 22c This lower current is attributed to the overlap of diffusion zones at adjacent nanointerfaces within the array, so that there is not independent diffusion to each individual nanointerface. The extent of this overlap depends on the relative separation of nanointerfaces (the ratio ${{{r_{\rm{c}} } \mathord{\left/ {\vphantom {{r_{\rm{c}} } {r_{\rm{a}} }}} \right.…”

“…It is also notable in Figures 3 a and 3 b that the capacitance of the system is significant. Previous studies have reported similar charging effects for membrane designs prepared through EBL 5a,d. In such cases, the SiN membrane can be considered as an insulator sandwiched between two conductors (the electrolyte solutions), establishing an electrical capacitor, which contributes a capacitance additional to that of the ITIES,5d which is reflected in the recorded CV curves.…”

“…As no true limiting current plateau is achieved in the diffusion‐limited region, the experimentally limiting current was determined at a potential approximately 200 mV positive of the foot of the ion‐transfer wave,5c, d which was at approximately 0.45–0.50 V (Figure 3). It was observed that the ion‐transfer wave foot progressively shifted to a more negative applied potential with increasing analyte concentration.…”

“…22c The underlying principle of the observed behaviour at nanoelectrode arrays of a few micrometres in size may be explained that such an array of nanoelectrodes can be treated as a single microelectrode of the same interfacial area, with the equivalent properties and associated spherical diffusion zone 5a. c, d, 22c…”

Effects of Unequal Diffusion Coefficients and Coupled Chemical Equilibria on Square Wave Voltammetry at Disc and Hemispherical Microelectrodes

“…Moreover, the theory reported in this paper can be applied to the study of ion transfer processes at liquid|liquid macrointerfases [13,14] and, as a first approach, at microinterfaces supported at micropores and microholes [15,16]. Note that notable differences between the diffusion coefficients of the target ion in each phase are frequently observed, especially when one of them is a liquid membrane [17] or room temperature ionic liquids [18][19][20][21] such that the results here reported are of interest in this field.…”