Ion-transfer electrochemistry at arrays of nanoscale interfaces between two immiscible electrolyte solutions arranged in hexagonal format

Abstract

• Nanoscale interfaces between two immiscible electrolyte solutions were studied. • Arrays of pores were formed by focused ion beam milling. • Hexagonal array format was characterised by ion transfer voltammetry. • Comparison of experiment and numerical simulation was undertaken with good agreement. • nanoITIES arrays in hexagonal format reach independent diffusion at large separations. The electrochemical behaviour of hexagonally arranged nanopore arrays was studied by simple ion transfer across the interface between two immiscible electrolyte solutions (ITIES) formed between water and 1,2-dichloroethane. The hexagonal nanoITIES arrays were supported at nanopores fabricated by focused ion beam milling into 50 nm thick silicon nitride films. Six arrays with different pore centre-to-centre distance ( r c ) to radius ( r a ) ratios were prepared. Within these arrays, the diffusion-limited steady-state currents ( i ss ) of tetrapropylammonium cation (TPrA + ) ion transfer increased concomitantly with increasing r c / r a ratio, reaching a plateau at r c / r a ≥ 96, which is greater than that previously reported for square-patterned nanoITIES arrays ( r c / r a ≥ 56). The diffusion regime and i ss associated with simple ion transfer across a nanopore array was also examined using numerical simulations, via COMSOL Multiphysics software, incorporating a 3-dimensional geometry and employing finite element analysis. Simulated linear sweep voltammograms of TPrA + transfer demonstrated a unique diffusional behaviour dependent on hexagonal nanopore spacing and the r c / r a ratio, analogous to the experimental voltammograms. Overlay of simulated and experimental voltammograms for each r c / r a ratios showed good agreement. These results indicate that a new design criterion is required to achieve independent diffusion at hexagonal nanointerface arrays, in order to maximize nanodevice performance in electrochemical sensor technologies.