Natural cellulose-based kapok fiber composite aerogel phase change materials with flame retardancy, fire warning, thermal energy storage and thermoelectric conversion

As a promising candidate to mitigate the intermittence of solar energy, multifunctional phase change materials (PCMs) with flame retardancy and fire warning are urgently desirable. Herein, we design a cellulose-based multifunctional aerogel PCMs with leak-proof, thermal energy storage, thermoelectric conversion, flame retardancy, and fire warning. As a natural plant fiber, the hollow structure of Kapok fiber (KF) endows the composite PCMs a high loading ratio and thermal energy storage density. Additionally, the polyhydroxyl KF can rapidly carbonize via synergistic catalysis of phytic acid and MXene, enhancing flame retardancy and achieving rapid fire alarm. Specifically, KSM@PEG-PA PCMs exhibit 98 % encapsulation efficiency and a high heat storage density of 173.1 J/g, as well as exceptional solar-thermal conversion efficiency (97.1 %). KSM@PEG-PA10 further converts the harvested thermal energy into electrical energy, generating 587 mV of voltage, 78.7 mA of current at 500 mw/cm 2 . The peak heat release rate (pHRR) and total heat release (THR) of KSM@PEG-PA is significantly decreased by 52.6 % and 32.8 %, respectively. Furthermore, the KSM@PEG-PA10 achieves an ultra-fast fire alarm response time of 2.0 s. This work offers valuable insights on the design of composite PCMs, expanding the application prospects in solar energy and fire safety.