▎ 摘　　要

NOVELTY - A composite material comprises three-branched triazobenzene/graphene (I). USE - Composite material is used for solar thermal storage. ADVANTAGE - The composite material has energy density of 150-250 Wh/kg and excellent durability. DETAILED DESCRIPTION - A composite material comprises three-branched triazobenzene/graphene of formula (I). An INDEPENDENT CLAIM is included for preparation of composite material, which involves adjusting pH of 10-30 parts mass aqueous solution of graphene oxide to 8-10 with sodium carbonate, dissolving mixture in solution of sodium borohydride, maintaining mixture at 85 degrees C for 2 hours, centrifuging, filtering and washing mixture with distilled water to obtain redox graphene, re-dispersing redox graphene in water by ultrasonically dispersing mixture, preparing triazobenzene/graphene composite by dissolving triazobenzene and sodium nitrate in deionized water at room temperature, dripping hydrochloric acid to mixture to form diazonium salt, adding diazonium salt to redox graphene, washing product with water, ethanol and dimethylformamide and drying mixture in oven at 70 degrees C.