High-strength multifunctional cellulose-based hydrogels: Simultaneous achievement of supercapacitive energy storage and photothermal conversion.

In this study, we successfully prepared a multifunctional composite hydrogel that can rapidly gelize in a short period of time, possesses excellent mechanical properties, conductive properties, and photothermal conversion properties. This article prepared a hydrogel that rapidly polymerizes within a short time using Two-dimensional transition metal carbides/nitrides (MXene), water-soluble cellulose (WSCA), ZnCl2, and acrylic acid (AA) as raw materials. During the formation of the hydrogel, Zn2+ formed dynamic coordination bonds with the carboxyl groups of polyacrylic acid (PAA), and the hydroxyl groups of WSCA formed hydrogen bonds with the carboxyl groups of PAA and the surface groups of MXene, constructing a network-spanning hydrogen bond system. The construction of these coordination bonds and hydrogen bond systems provided a supporting template for the AA polymerization. When the Zn2+ and ammonium persulfate (APS) composition of the redox initiator reduced the initiation reaction temperature, it promoted the decomposition of APS to generate sulfate radical free radicals, initiating the rapid polymerization of AA monomers into PAA long chains, and forming a covalent cross-linked framework through inter-chain radical bonding. The MXene nanosheets were anchored by hydrogen bonds in the network and provided conductive properties and photothermal conversion functions. In addition, the hydrogel can initiate reactions at room temperature, has an ionic conductivity of 31.59 mS/cm at room temperature, a tensile strength and elongation at break of 1.538 MPa and 736.85%, respectively, and the supercapacitor based on this hydrogel maintains a capacitance retention of 83% and a coulombic efficiency of 90% after 10,000 charge-discharge cycles. Under sunlight irradiation of 0.3 W cm-2, the surface temperature of the hydrogel can reach 100 °C. The preparation of this hydrogel provides a new strategy and approach for developing energy storage devices with good mechanical properties and no irritation, as well as hydrogen bond-coordination bond-based dual-network hydrogels with good photothermal conversion performance.