Diode stretches capabilities of ionotronics

Whereas electronics manipulate electrons, ionotronic devices manipulate ions. This commonality with living organisms means soft, deformable ionotronics may find use in human-machine interfaces, soft robotics, and bionic prosthetics.

An important building block in the development of ionotronics for these applications is a high-performance ionic junction consisting of two types of ionic conductors, equivalent to a p- and n-type junction in electronics. Lee et al. developed this type of diode, which will allow precise control of ion flow. Their liquid-free, stretchable diode performed well, demonstrating excellent non-Faradaic ionic current rectification.

Most ionotronics of today are made with liquids, but the authors built their diode with ionoelastomers, which are liquid-free ionic conductors. Ionoelastomers have excellent mechanical robustness and result in less leakage, volatility, and degradation.

Rigid electrodes typically limit the stretchability of an ionotronic device, but the potential applications of ionotronics need soft, stretchable, deformable devices. The authors used 2-hydroxyethyl acrylate in the two types of ionoelastomers to enhance the stretchability and promote synchronous deformation with a liquid metal electrode, which made their diode significantly more stretchable than previous devices.

“Developing an all-intrinsically-stretchable ionoelastomer diode with a metal electrode brings us one step closer to emerging ionotronics with high environmental and mechanical stability that facilitate the human-machine interface,” said author Seung Won Lee.

They used their stretchable diode to generate a stretchable ionic OR logic gate. Their logic gate exhibited four binary input logic states and two output states, even when deformed with a stretch ratio of up to four.

Next, the authors plan to investigate the mechanisms underlying the non-Faradaic ionic current rectification in this diode.

Source: “Intrinsically stretchable ionoelastomer junction logic gate synchronously deformable with liquid metal,” by Seung Won Lee, Jihye Jang, Yeonji Kim, Seokyeong Lee, Kyuho Lee, Hyowon Han, Hyeokjung Lee, Jin Woo Oh, Hoyeon Kim, Taebin Kim, Michael D. Dickey, and Cheolmin Park, Applied Physics Reviews (2022). The article can be accessed at https://doi.org/10.1063/5.0104765 .