Separator-Inspired Redox-State-Selective Confinement for Reversible Retention in Anthraquinone-Based Aqueous Soft-Gel...

Aqueous anthraquinone-based organic redox batteries offer a promising route toward safe and sustainable energy storage, but their stability is often limited by redox-state-dependent active-material migration. In soft-gel electrodes, oxidized anthraquinone derivatives can remain confined within the original matrix, whereas reduction may alter charge distribution, protonation, polarity, ion association, and hydration affinity, promoting migration into water-rich regions and the bulk electrolyte. This review interprets this instability as a coupled phase-partitioning and transport problem rather than simply insufficient gel density. Inspired by functional separators, we discuss electrode-internal selective-confinement strategies, including physical confinement, reversible anchoring, electrostatic and solvation regulation, conductive interception, catalytic conversion, and structural stabilization. The key design target is reversible retention: reduced anthraquinone species should be delayed from escaping while remaining electronically connected and ionically accessible for subsequent oxidation. Future efforts should clarify reduced-state speciation, balance retention-transport-reversibility trade-offs, and establish standardized evaluation methods for soft-gel electrode systems.