Ion current rectification (ICR) has been widely explored in single conical nanopores and recently observed in anodized aluminum oxide (AAO) membranes. The symmetry-breaking property is associated with transport selectivity and concentration polarization, thus has significant implications in separation, desalination, energy storage, harvesting and conversion, sensing, and other applications. Herein, the time-dependence in the electrokinetic transport through AAO membranes or nanopore arrays is studied experimentally in 1:1 electrolyte solution with voltammetry and other electroanalytical methods. The hysteresis or memory effect in ICR, firstly discovered by our group in single conical nanopores, are observed in AAO membranes with barrier layers. While a single current-potential branch displays ICR signature, i.e. the current is higher at one potential polarity over the opposite, multiple pinched current-potential hysteresis loops are resolved when the potential is scanned cyclically. The ICR and hysteresis loops are found to depend on the potential scan rates, fabrication conditions and other parameters. The time- or history-dependent electrokinetic ion transport behaviors are interpreted by the compositions of the available mobile charge carriers, electrostatic effects at the transport-limiting region, with the aids from finite element simulations.

Hysteresis in the rectified ion transport through anodized aluminum oxide nanopore arrays

ACS Fall 2021

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