Low-Dimensional Ionotronics.

Ionotronics encompasses a broad range of phenomena and devices based either on the electron-controlled manipulation of ions in electrolytic media or on the use of ionic behavior to control electronic functionality. Although the term itself is relatively recent, the scientific foundations of ionotronics span more than a century of research. Owing to their promising applications in areas ranging from energy storage and harvesting to robotic actuation, nanofiltration, water desalination, sensing, and neuromorphic computation, ionotronic systems have recently attracted rapidly growing attention, particularly in the context of low-dimensional electrodes. These advanced architectures can profoundly modify the electrode-electrolyte interface, where ion transport and interfacial phenomena play a central role. Such systems exhibit distinctive physics arising either from nanoscale confinement, which restricts the electrolyte to only a few layers of ions or solvent molecules, or from low-dimensional electronic effects imposed by confining materials such as graphene, carbon nanotubes, and MXenes. This Focus Review aims to provide a comprehensive yet accessible overview of the fundamental phenomena governing low-dimensional ionotronic systems, with particular emphasis on the underlying physics that determines their performance and enables emerging applications.