Iontronic components: From liquid- to solid-states

In modern electronics, the ionic charges have not occupied the same role as the electrons mainly because of their relatively low mobilities. However, these “slow” charge carriers contribute to brain computing with high efficiency and extremely low power consumption. Inspired by the “ionic” life, iontronic components have recently attracted considerable attention. In this review, we first introduce the progress of iontronic devices operating with the involvement of water, specifically, two types of systems—nanofluidic and hydrogels. Next, the issues and challenges within these liquid-state ionic devices are summarized. To avoid the negative impact of water, we also propose two solid-state materials—ionogels and charged metal nanoparticles—to construct several basic ionic devices such as diodes and transistors. Finally, we summarize this review and outlook the promising directions for the further developments of iontronic devices.