Hierarchical hollow P-doped ZIF-8/MXene aerogel composites for phase change materials integrating shape stability, thermal energy storage, solar-thermal conversion and flame retardancy

Organic phase change materials (PCMs) suffer from liquid-phase leakage, insufficient solar-thermal conversion capability, inherent flammability, which severely hinders their utilization. Herein, we design a three-dimensional hierarchically porous aerogel composite PCMs that integrates hollow phosphorus-doped ZIF-8 microshells (P-ZIF-8) with chitosan (CS) and MXene nanosheets for multifunctional synergy. Specifically, the hierarchically porous aerogel exhibits exceptional mechanical strength (withstanding >5000 times its own weight), endowing the composite PCMs with superior shape stability. This hierarchical framework, comprising aerogel network and hollow P-ZIF-8 microshells, provides a dual encapsulation effect and achieves outstanding encapsulation capability (97.6 %) and latent heat storage density (190.0 J/g), maintaining thermal durability and stability over 200 heating-cooling cycles. The MXene and P-ZIF-8 microshells synergistically enhance solar-thermal harvesting and energy conversion in composite PCMs, achieving a solar-thermal conversion efficiency of 98.3 % and outputting 442.1 mV and 69.1 mA in a solar-thermal-electric generator under 500 mW/cm 2 . The P-ZIF-8 microshells and MXene both provide physical barriers and catalytic charring effect, markedly enhancing the flame retardancy of the composite PCMs with peak heat release rate (pHRR) and total heat release (THR) significantly reduced by 31.1 % and 17.1 %, respectively. This work offers a versatile pathway for multifunctional PCMs that simultaneously meet the needs of thermal energy storage, solar harvesting and fire safety.