Ionic Diodes: Pioneering the Future of Ionotronics in Electronics and Beyond

The exploration in ionotronics has driven the advancement in several emerging fields, including energy storage, bioelectronics, flexible electronics, and human-machine interactions. Among these, ionic diode devices that use ions as charge carriers have been extensively explored, exhibiting significant potential for integrating biology and electronics. Unlike traditional diodes, ionic diodes not only perform rectification but also enable novel functions and properties (sensing, energy harvesting, and biological detection). This account comprehensively summarizes the recent advancements and challenges associated with ionic diodes. It begins with an overview of various ionic diode designs, categorized into rigid and flexible types, to give a clearer understanding of this evolving field. The rigid ionic diodes manifest a notably high rectification ratio of 1600, exhibiting an exceptional rectification performance, while their flexible counterparts achieve a ratio of approximately 200, realizing a trade-off between flexibility and electronic performance. Typically, gel ionic diodes, which exemplify a promising blend of bionics and flexible electronics, are highlighted. Next, the applications of ionic diodes in sensors, energy harvesting, ionic logic gates, and environmental and biological detection are thoroughly discussed. Lastly, strategies to enhance the performance of ionic diodes are explored along with insights into their future development. This review delves into the mechanisms, designs, and applications of ionic diodes, offering insights to researchers and paving the way for innovative advancements in the field.