Xiaomin Zhang

Polyvinyl alcohol (PVA)‐based hydrogel electrolytes are widely employed in flexible solid‐state supercapacitors owing to their biodegradability, nontoxicity, and low cost. However, the further application of pure PVA hydrogel is limited by its low mechanical properties, narrow electrochemical working window, and insufficient frost resistance. In this study, a cellulose solution dissolved in sulfuric acid was directly incorporated into the PVA hydrogel, and the PVA/cellulose composite hydrogel was prepared via a freeze–thaw cycling method. The resulting composite exhibited excellent mechanical properties, with a tensile strength of up to 0.66 MPa and an elongation at break of 896%, as well as remarkable self‐healing capability. After soaking in LiCl electrolyte, the obtained composite hydrogel electrolyte was used to assemble a supercapacitor, which delivered a specific capacitance of 248 mF cm ⁻² at a current density of 2 mA cm ⁻² and remained electrochemically operational at −25 °C. Even after 180° bending, the specific capacitance retention rate of the capacitor is as high as 98.4%, and the hydrogel still has 95% specific capacitance retention after fracture self‐healing. These results indicate that the PVA/cellulose composite hydrogel electrolyte has broad application prospects in flexible wearable energy storage devices.

Cellulose‐based hydrogels have gained prominence in hydrogel electrolyte substrate research due to their remarkable flexibility and renewable raw materials. However, cellulose hydrogels produced by traditional bottom‐up synthesis strategies generally suffer from insufficient mechanical properties and low areal‐specific capacitance in constructed capacitors. This study employs a top‐down strategy, utilizing the natural cellulose framework of delignified wood as a structural substrate. Through the synergistic effects of in situ sodium alginate filling and gradient zinc perchlorate cross‐linking, a zinc‐ion–cross‐linked wood‐based hydrogel electrolyte (ZWH) was constructed. When the Zn ²⁺ concentration in the hydrogel electrolyte was 2 mol·L ⁻¹ , the resulting ZWH‐2 material demonstrated breakthrough performance enhancements: achieving a mechanical strength of 9.47 MPa and exhibiting an ionic conductivity as high as 68.97 mS·cm ⁻¹ . Energy storage systems utilizing this electrolyte exhibited exceptional electrochemical performance. The activated carbon symmetric supercapacitor and zinc‐activated carbon asymmetric supercapacitor achieved areal‐specific capacitances of 165 and 361 mF·cm ⁻² at a current density of 2 mA·cm ⁻² . In this study, zinc ions serve dual roles as both cross‐linkers for the hydrogel and electrolyte components, facilitating a multifunctional electrolyte system with bend resistance. This study offers innovative perspectives for creating sustainable, adaptable energy storage devices suitable for a broad temperature spectrum.

Chitin is a cost‐effective and abundant resource, enriched with nitrogen and oxygen elements, making it an ideal precursor for carbon‐based materials. However, traditional methods for preparing activated carbon from chitin often require substantial amounts of activators and complex carbonization processes, leading to suboptimal energy storage efficiency. This study presents a partial dissolution system achieved by modulating the mass ratio of chitin to activators (KOH and urea) and optimizing freeze‐thaw cycles. When chitin/KOH/urea is mixed at a 1:1:1.5 mass ratio and subjected to three freeze‐thaw cycles, the resulting porous carbon demonstrates a high specific surface area of 1783 m ² g ⁻¹ with significant N (4.75%) and O (11.16%) doping. The electrode achieves a specific capacitance of 309.1 F g ⁻¹ at 0.5 A g ⁻¹ in a three‐electrode system with 6 m KOH as the electrolyte. After 5000 charge–discharge cycles at 5 A g ⁻¹ , the capacitance retention rate remains at 91.08%, indicating excellent cycling stability. When assembled into a symmetrical supercapacitor, it exhibits an energy density of 5.69 Wh kg ⁻¹ at a power density of 4996.1 W kg ⁻¹ , demonstrating remarkable energy storage performance. This work introduces a novel method for preparing chitin‐derived porous carbon materials.

The photo‐induced cis‐trans isomerization of azobenzene molecules, known for their significant color changes, is extensively utilized in the functional modification of polymeric materials. However, the research on the functionalization of biomass‐based polyesters with azobenzene is limited. A key raw material for biomass‐based coatings possess reactive double bonds and excellent film‐forming capabilities, offering significant advantages for azobenzene functionalization in biomass‐based polyester applications. In this study, AESO served as the polyester matrix and acrylate azobenzene derivatives as the functional molecules. Under ultraviolet radiation, AESO underwent a carbon–carbon crosslinking reaction with the azobenzene derivatives to synthesize a novel resin. The coating of this resin on a PET substrate exhibited excellent pencil hardness (3B), adhesion (5B), and solvent resistance. By alternating exposure to ultraviolet and blue light, the coating displayed reversible switching between cis and trans isomers, enabling reversible writing and erasing of patterns. Even after 20 cycles of writing and erasing, high‐resolution patterns could still be observed (clearly visible under a 12x microscope). Furthermore, the image could be retained for up to 2 h under sunlight irradiation. This study presents a new method for functionalizing biobased polyesters.

The PVA-based hydrogel electrolyte, characterized by its high ionic conductivity and degradability, holds significant promise for applications in flexible supercapacitors. However, pure PVA hydrogel electrolytes have suffered from deficiencies in flexibility, self-healing properties, and anti-freezing performance. In this study, a novel approach was employed by in situ blending polyvinyl alcohol (PVA) with zinc chloride (ZnCl₂) dissolved cellulose. When the mass ratio of PVA to cellulose was 2 : 1, the resulting PVA/cellulose composite hydrogel electrolyte exhibited a commendable tensile strength (198 kPa) and remarkably high elongation at break (2415%); the assembled zinc/carbon asymmetric supercapacitor demonstrated an area-specific capacitance of 636 mF cm⁻² (2 mA cm⁻²). Moreover, at −30 °C, the capacitance retention exceeded 94%, indicating excellent anti-freezing properties. Subsequent electrical performance tests on the self-healed hydrogel electrolyte capacitors yielded a capacitance retention rate exceeding 94%, demonstrating outstanding self-healing properties. This novel class of hydrogel electrolytes provides a viable research perspective for addressing the aforementioned issues. Additionally, this study also involved straightforward treatment of used hydrogels, allowing for the recovery of high-value zinc salts such as zinc carbonate and zinc chloride, with a recycling efficiency as high as 55%. The entirety of the experiment exhibited an environmentally friendly and sustainable engineering process.