Anisotropic hemp-stem-derived biochar supported phase change materials with efficient solar-thermal energy conversion and storage

As cheap and renewable sources,the exploitation of biomass resources was of great value in phase change energy storage.In this study,hemp stems were converted into biochars with three-dimensional multi-level anisotropic pores through a temperature-controlled charring process,which were used as supports for polyethylene glycol(PEG6000)to form shape-stable composite phase change materials(ss-CPCMs).It is shown that the ss-CPCMs using anisotropic hemp-stem-derived biochar obtained at a carbonization temperature of 900℃as a support has high PEG6000 loading rate(88.62wt%),large latent heat(170.44 J/g)and favorable thermal stability owning to its high surface area and hierarchical pores.The biochar-based ss-CPCM also has good light absorption ability with a maximum solar-thermal conversion efficiency of 97.70%.In addition,the different thermal conductivities in the transverse and longitudinal directions of ss-CPCMs reflect the unique anisotropic structure.This work can not only improve the high-value utilization of biochars,but also provide the ss-CPCMs with excellent performance for solar-thermal conversion and storage systems.