Flexible phase change composites based on hierarchically porous polypyrrole scaffold for broad-band solar absorption and efficient solar-thermal-electric energy conversion

Phase change materials (PCMs) with thermal energy storage property are vital in solar-thermal energy conversion and utilization systems. However, low thermal conductivity, low light absorption, and severe brittleness are major application-hindering factors. In this work, paraffin wax (PW) was vacuum impregnated into poly (dimethylsiloxane) (PDMS)/boron nitride (BN)/polypyrrole (PPy) foam to create flexible phase change composites (PCCs) with excellent thermal conductivity and solar-thermal energy conversion efficiency. The PDMS/ BN/PPy foams were successfully prepared via the sugar template and chemical vapor deposition methods. The PDMS/BN/PPy/PW PCCs exhibited excellent phase change latent heat of 172 J g-1 and dimensional retention ratio of 98.91%. The continuous BN network imparted the PCCs with enhanced thermal conductivity of 0.43 W m-1 K-1. Meanwhile, the flexible PCCs were capable of being elastically deformed and closely adhered to the rough surface, thus further improving the heat transfer efficiency. More importantly, the wrinkled PPy and the hierarchical porous structure improved light absorption by extending the optical path for multiple reflections, maintaining an outstanding solar-thermal energy conversion efficiency of 91.9%. A solar-thermal-electric energy conversion (STEEC) system was constructed to display the potential of PCCs to generate clean energy. PCCs could output a current of 84.7 mA and support the rotation of a fan for 243 s, even without light irradiation. This study provides a facile approach to preparing multi-functional PCCs, showing the advantages in the rapid collection and storage of solar energy.