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.