Dopamine-Decorated Ti3C2Tx MXene/Cellulose Nanofiber Aerogels Supported Form-Stable Phase Change Composites with Superior Solar-Thermal Conversion Efficiency and Extremely High Thermal Storage Density.

The exploitation of from-stable phase change materials (PCMs) with superior energy storage capacity and excellent solar-thermal conversion performance is crucial for the efficient exploitation of solar energy. Herein, 2D-layered polymerized dopamine-decorated Ti3C2Tx MXene nanosheets (P-MXene) with superior photothermal effects and excellent oxidation stability were synthesized from Ti3AlC2 particles by the selective etching and self-polymerization of dopamine. Then, novel biomass-derived PCM composites, eMPCMs, were fabricated by impregnating erythritol into P-MXene/cellulose nanofiber (CNF) hybrid aerogels. The porous and interconnected 3D aerogels adequately support erythritol and resist liquid leakage during thermal storage. Differential scanning calorimetry (DSC) results showed that the eMPCMs based on P-MXene/CNF aerogels exhibited an extremely high thermal storage density (325.4-330.6 J/g) and excellent PCM loading capacity (up to 1929%). The introduction of P-MXene nanosheets into eMPCMs significantly increased the solar-thermal conversion and storage efficiency, solar-thermal-electricity conversion capacity, and thermal conductivity of the synthesized PCM composites. Moreover, the P-MXene/CNF hybrid aerogel-based PCM composites possessed excellent long-term thermal reliability and thermostability. Hence, the synthesized eMPCMs reveal tremendous potential for efficient solar-thermal storage fields.

Recyclable, Self-Healing, and Flame-Retardant Solid-Solid Phase Change Materials Based on Thermally Reversible Cross-Links for Sustainable Thermal Energy Storage.

Conventional polymeric phase change materials (PCMs) exhibit good shape stability, large energy storage density, and satisfactory chemical stability, but they cannot be recycled and self-healed due to their permanent cross-linking structure. Additionally, the high flammability of organic PCMs seriously restricts their applications for thermal energy storage (TES). Therefore, it is urgently required to explore PCM composites exhibiting superior recyclability, good self-healing capability, and excellent flame retardancy simultaneously. Herein, tri-maleimide end-capped cyclotriphosphazene flame retardant (TMCTP) was synthesized via the nucleophilic substitution between 1,3,5,2,4,6-triazatriphosphorine-2,2,4,4,6,6-hexachloride and N-(2-hydroxyethyl)maleimide. Then, novel dynamically cross-linked PCM composites (FPCMs) with superior recyclability, good self-healing capability, and excellent flame retardancy were fabricated by bonding PEG and TMCTP to polymeric skeleton via reversible furan/maleimide Diels-Alder (DA) reaction. TMCTP, which covalently and dynamically binding in the polymeric FPCMs, acted not only as an efficient flame retardant for reducing the flammability of PCM composites but also as dynamic cross-linking skeletons for thermally induced self-healing and recycling. Differential scanning calorimetry (DSC) analysis confirmed the reversible energy storage and release ability of FPCMs. Due to its reversible DA covalent bonds, the introduction of TMCTP endowed the FPCMs with considerably increased self-healing efficiency (up to 93.1%) and recyclability efficiency (94.6%). Moreover, with the introduction of TMCTP into FPCMs, the heat release rate (HRR) and total heat release (THR) significantly decreased, while the char residue and limiting oxygen index (LOI) value increased, confirming that the flame retardancy of FPCMs greatly improved. Hence, the synthesized FPCMs show enormous potential in TES applications.