Scalable Fabrication of All-Biopolymer-Derived Conductive Hydrogels for Flexible Mechanosensors and Zinc-Ion Hybrid Supercapacitors

Traditional synthetic hydrogels for flexible electronic devices are mostly derived from nonsustainable polymers, resulting in environmental pollution. Herein, scalable, moldable, and stretchable ionic hydrogels are synthesized utilizing two model biopolymers, κ-carrageenan (κ-CG) and amylopectin (Amy). In such hydrogels, physically cross-linked κ-CG networks work as a relatively rigid component to maintain the shape of hydrogels, Amy networks cross-linked by borate/cis-diol dynamic covalent bonds help to improve the stretchability, and ZnSO4 is introduced as an ionic conductive component. The hydrogels, denoted as κ-CG/Amy/Zn2+ hydrogels, exhibit acceptable stretchability (>100%) because of the special cross-linking structure and ionic conductivity (2.9 S·m–1) due to the existence of various ions. Flexible mechanosensors (resistive strain sensors and capacitive pressure sensors) are demonstrated utilizing κ-CG/Amy/Zn2+ hydrogels, and high gauge factors (0.76 for strain sensors and 0.77 kPa–1 for pressure sensors) are achieved. Interestingly, κ-CG/Amy/Zn2+ hydrogels also work as quasi-solid-state electrolytes in zinc-ion hybrid supercapacitors, which exhibit an initial specific capacity of 47.4 mAh·g–1 at a current density of 3 A·g–1 and stable charge/discharge ability in more than 42,000 cycles. The sustainable biopolymer hydrogels may provide promising eco-friendly materials for future wearable devices and energy storage systems.