Biomass modified boron nitride/polyimide hybrid aerogel supported phase change composites with superior energy storage capacity and improved flame retardancy for solar-thermal energy storage

Solar energy, as a renewable and environmentally friendly energy source, is a viable alternative heat source for thermal storage. However, due to leakage, low photothermal conversion efficiency, poor thermal conductivity, and flammability, phase change materials (PCMs) are not effective at absorbing and utilizing solar energy. Here, we have prepared a form-stable, enhanced thermal conductivity and improved flame retardant phase change composite (PEG-LBN@PI) consisting of lignin-modified boron nitride (LBN)/polyimide (PI) hybrid aerogel and polyethylene glycol (PEG). Benefiting from the cooperation of LBN, the PCM loading rate of PEG-LBN@PI-1 reaches 96.20% and the relative enthalpy efficiency (η) reaches 99.79%. Even after 200 thermal cycles, the η of PEG-LBN@PI-1 value reduces by as low as 0.12%. Meanwhile, PEG-LBN@PI composites show excellent solar-thermal conversion behavior to increase solar energy utilization. Furthermore, due to the flame retardant performance of PI matrix, PEG-LBN@PI composites exhibit an improved flame retardancy, in which the peak heat release rate (pHRR) and total heat release (THR) rate of PEG-LBN@PI-3 are 23.3% and 17.3% lower than that of pure PEG. This work proposes the form-stable and flame retardant PEG-LBN@PI composites with superior energy storage capacity and photothermal conversion capability.