Preparation of double cross-linked starch/CaCl₂/PVA conductive hydrogel for flexible solid-state supercapacitor

The double cross-linked hydrogels with good mechanical strength and ionic conductivity were prepared using starch as the matrix, combined with the double crosslinking strategy of calcium chloride (CaCl₂) and poly (vinyl alcohol) (PVA). The tensile strength and compressive stress of the starch hydrogel were enhanced with increasing PVA content. The moisture retention rate and swelling property of the hydrogel sample decreased over time. Elevated PVA content contributed to increased freezing points and enthalpy values of the starch hydrogel. A The hydrogel samples exhibited good hydrophilicity and optical translucency. The cyclic voltammetry (CV) curves of starch hydrogel samples maintained the near rectangular shape with center symmetry, retaining this characteristic even under mechanical pressure or bending conditions. The starch hydrogels with high CaCl₂ content exhibited lower internal resistance. Galvanostatic charge-discharge (GCD) curves demonstrated the near-triangular curve profiles with charging voltages reaching 1.5 V, accompanied by favorable energy density and power density performance. Through the integration of bio-based material composites and double-crosslinking structural design, the mechanical properties, environmental adaptability, and electrochemical performance of starch-based hydrogels have been synergistically enhanced. These findings provide theoretical guidance for the development of conductive hydrogels tailored for flexible solid-state supercapacitors.