Ionic rectification via electrical double layer modulation at hydrogel interfaces

Abstract

Hydrogel-based iontronics have emerged as key enablers for sustainable energy harvesting and bio-inspired sensing, with applications spanning human-machine interfaces, brain-computer interfaces, and neuromorphic computing. Central to their operation is precise modulation of the electrical double layer (EDL) at hydrogel interfaces, which governs ionic rectification, a critical function for efficient iontronic performance. This review systematically examines EDL modulation strategies for achieving ionic rectification in hydrogel systems, classifying them into four fundamental mechanisms: (1) EDL formation on charged polymer chains in polyelectrolyte hydrogels; (2) nanopore-confined EDL enhanced by hydrogel modification; (3) EDL at hydrogel-based p-n junctions; and (4) asymmetric EDL at hydrogel/electrode interfaces. Representative studies highlighting breakthrough applications of these mechanisms are discussed, alongside an outlook on the future of EDL engineering in hydrogel-based iontronics, emphasizing both opportunities and challenges in optimizing performance.