Ion-transfer electrochemistry at arrays of nanoscale interfaces between two immiscible electrolyte solutions arranged in hexagonal format
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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 (rc) to radius (ra) ratios were prepared. Within these arrays, the diffusion-limited steady-state currents (iss) of tetrapropylammonium cation (TPrA+) ion transfer increased concomitantly with increasing rc/ra ratio, reaching a plateau at rc/ra ≥ 96, which is greater than that previously reported for square-patterned nanoITIES arrays (rc/ra ≥ 56). The diffusion regime and iss 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 rc/ra ratio, analogous to the experimental voltammograms. Overlay of simulated and experimental voltammograms for each rc/ra 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.
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