Redox switch of ionic transport in conductive polypyrrole-engineered unipolar nanofluidic diodes

Abstract

Controlling ion transport in nanoconfined spaces is a key task for the creation of smart nanofluidic devices. In this work, redox-active polypyrrole (PPy) polymers are introduced into anodic aluminum oxide (AAO) nanochannels to form smart unipolar nanofluidic diodes (UNDs) for the first time. The ionic transport behavior of the present polypyrrole-engineered UNDs can be controlled through the redox reactions of PPy. Under an applied oxidation potential, conductive PPy exhibits several redox states carrying different charges, following the formation of polarons and bipolarons with different oxidation states. Combined with the asymmetric distribution of PPy in the AAO nanochannels, the UNDs investigated here exhibit redox-switchable ion rectification and ion-gating properties. The influence of the charge asymmetry of the UNDs on their ionic transport behavior is assessed by precisely controlling the length of oxidized PPy segments in the AAO nanochannels and by carrying out theoretical simulations based on the Poisson and Nernst–Planck (PNP) equations.