High enthalpy efficiency lignin-polyimide porous hybrid aerogel composite phase change material with flame retardancy for superior solar-to-thermal energy conversion and storage

Liquid-solid organic phase change materials (PCMs) exist shortcomings of leakage, poor solar-to-thermal conversion efficiency, and flammability , which restrict the application scope of solar-thermal energy storage. To meet these problems, PCMs (ZrP-PI@PEG) with excellent thermal energy storage, solar-to-thermal conversion, and flame retardancy were fabricated in this study. The polyimide (PI)/sodium lignosulfonate-zirconium phosphate (SL-ZrP) hybrid-aerogels (ZrP-PI) were prepared by freeze-drying and thermal imidization. ZrP-PI aerogels composited with polyethylene glycol (PEG) via vacuum impregnation to fabricate the composite PCMs (CPCMs, ZrP-PI@PEG). The in-situ biochar generated from SL-ZrP increases both solar-to-thermal conversion and flame retardant of CPCMs. The final result demonstrates that ZrP-PI@PEG exhibits a superior adsorption ratio (95.5%) and outstanding latent heat (157.67 J/g), as well as about 13% flame retardant index decrease in heat release rate (HRR) and total heat release rate (THR). Furthermore, ZrP-PI@PEG shows great thermal stability and reliability after conducting a leakage experiment and thermal cycling test. These superior resultants indicate that ZrP-PI@PEG has a good potential for widespread and long-term use in solar thermal energy storage.