Fig. 1. Schematics of fabrication for reconstructed Alg hydrogel and mechanically robust aqueous supercapacitor.

a Fabrication steps of the reconstruction method: anisotropic drying/shrinkage of Ca–Alg pre-gel and crosslinking/rehydration in Ca²⁺ solution. To futher enhance the hydrogel mechanical performance, an ion-exchange step from Ca²⁺ to Xⁿ⁺ (Ba²⁺, Al³⁺, or Fe³⁺) is additionally introduced. b, c Photographs showing a reconstructed hydrogel with a large area and a thick bulky hydrogel by lamination, respectively. d Schematic illustration of a mechanically robust aqueous supercapacitor composed of activated carbon (AC) electrodes and three-layered hydrogel electrolyte.