Ion transport systems are critical to many societal challenges, particularly in applications involved in aqueous environments where traditional electronics may not be as well suited. The production and directed movement of photo-generated species to produce useful energy, the transportation of ions to generate clean water through desalination, and the implementation of devices capable of seamlessly interfacing with biological systems for sensing or therapeutic purposes are a few of the many examples that use ion transport that aim to improve our daily lives. In this work, three independent projects will be showcased that touch on ion transport systems with these applications in mind. Our first materials innovation is analogous to an electronic semiconductor pn-junction that entails doping water using mineral salts and freezing the liquid water to immobilize counterions, thus forming doped polycrystalline solid protonic semiconductors. In this regard, we fabricate pn-junction ice cube diodes that demonstrate excellent current rectification properties. A second materials design innovation is a novel electronic ratchet that utilizes alternating electronic polarization to drive net ionic current. The system is unique in its ability to rely solely on interfacial charging to drive sustained direct currents and continuous ion separation. Lastly, the exploration of a previously underutilized proton conducting protein as a suitable culture substrate for neural stem/progenitor cells will be showcased. Recent work regarding potential cellular binding mechanisms and surface patterning will be discussed that contribute to the protein’s ever-expanding use in the bioelectronics field.

Directed ion transport in liquid electrolyte solutions underlies many phenomena in Nature and industry. While Nature has devised structures that drive continuous ion flow without Faradaic redox reactions, artificial analogs do not exist. Here we report the first demonstration of an ion pump that drives aqueous ions against a force using a capacitive ratchet mechanism that does not require redox reactions. Modulation of an electric potential between gold thin films on either face of a nanoporous alumina wafer immersed in solution resulted in persistent voltages and ionic currents indicative of directional ion pumping. This occurs due to the non-linear capacitive nature of electric double layers, whose repeated charging and discharging sustains a continuous ion flux. The generated ionic power was used in conjunction with an additional shunt pathway to demonstrate electrolyte demixing. These ratchet-based ion pumps can potentially enable continuous desalination and selective ion separation using a modular, electrically powered device with no moving parts.