Multi-Layered Bipolar Ionic Diode Working in Broad Range Ion Concentration

Ion current rectification (ICR) is the ratio of ion current by forward bias to backward bias and is a critical indicator of diode performance. In previous studies, there have been many attempts to improve the performance of this ICR, but there is the intrinsic problem for geometric changes that induce ionic rectification due to fabrication problems. Additionally, the high ICR could be achieved in the narrow salt concentration range only. Here, we propose a multi-layered bipolar ionic diode based on an asymmetric nanochannel network membrane (NCNM), which is realized by soft lithography and self-assembly of homogenous-sized nanoparticles. Owing to the freely changeable geometry based on soft lithography, the ICR performance can be explored according to the variation of microchannel shape. The presented diode with multi-layered configuration shows strong ICR performance, and in a broad range of salt concentrations (0.1 mM similar to 100 mM), steady ICR performance. It is interesting to note that when each anion-selective (AS) and cation-selective (CS) NCNM volume was similar to each optimized volume in a single-layered device, the maximum ICR was obtained. Multi-physics simulation, which reveals greater ionic concentration at the bipolar diode junction under forward bias and less depletion under backward in comparison to the single-layer scenario, supports this tendency as well. Additionally, under different frequencies and salt concentrations, a large-area hysteresis loop emerges, which indicates fascinating potential for electroosmotic pumps, memristors, biosensors, etc.

Automated summary

In this study, a multi-layered bipolar ionic diode based on an asymmetric nanochannel network membrane (NCNM) was proposed, which showed strong and stable ICR performance. The freely changeable geometry based on soft lithography allowed for exploration of ICR performance. Multi-physics simulation confirmed the trend of higher ionic concentration and less depletion in the bipolar diode junction, compared to the single-layer scenario. The study also revealed the potential for applications such as electroosmotic pumps, memristors, and biosensors, with the emergence of large-area hysteresis loops under different frequencies and salt concentrations.